Analytical Chemistry of Nuclear Materials Held in Vienna, 17-21 September 1962

TECHNICAL REPORTS SERIES No. 18

» Analytical Chemistry

Nuclear Materials

REPORT OF THE PANEL ON ANALYTICAL CHEMISTRY OF NUCLEAR MATERIALS HELD IN VIENNA, 17-21 SEPTEMBER 1962

INTERNATIONAL ATOMIC ENERGY AGENCY - VIENNA, 1963

ANALYTICAL CHEMISTRY OF NUCLEAR MATERIALS The following States are Members of the International Atomic Energy Agency:

AFGHANISTAN ITALY ALBANIA JAPAN ARGENTINA REPUBLIC OF KOREA AUSTRALIA LEBANON AUSTRIA LIBERIA BELGIUM LUXEMBOURG BOLIVIA MALI BRAZIL MEXICO BULGARIA MONACO BURMA MOROCCO BYELORUSSIAN SOVIET SOCIALIST NETHERLANDS REPUBLIC NEW ZEALAND CAMBODIA NICARAGUA CANADA NORWAY CEYLON PAKISTAN CHILE PARAGUAY CHINA PERU COLOMBIA PHILIPPINES CONGO (LÉOPOLDVILLE) POLAND CUBA PORTUGAL CZECHOSLOVAK SOCIALIST REPUBLIC ROMANIA DENMARK SAUDI ARABIA DOMINICAN REPUBLIC SENEGAL ECUADOR SOUTH AFRICA EL SALVADOR SPAIN ETHIOPIA SUDAN FINLAND SWEDEN FRANCE SWITZERLAND FEDERAL REPUBLIC OF GERMANY SYRIAN ARAB REPUBLIC GHANA THAILAND GREECE TUNISIA GUATEMALA TURKEY HAITI UKRAINIAN SOVIET SOCIALIST REPUBLIC HOLY SEE UNION OF SOVIET SOCIALIST REPUBLICS HONDURAS UNITED ARAB REPUBLIC HUNGARY UNITED KINGDOM OF GREAT BRITAIN AND ICELAND NORTHERN IRELAND INDIA UNITED STATES OF AMERICA INDONESIA URUGUAY IRAN VENEZUELA IRAQ VIET- NAM ISRAEL YUGOSLAVIA

The Agency's Statute was approved on 23 October 1956 by the Conference on the Statute of the IAEA held at United Nations Headquarters, New York; it entered into force on 29Julyl957. The Headquarters of the Agency are situated in Vienna, Its principal objective is "to accelerate and enlarge'the contribution of atomic energy to peace, health and prosperity throughout the world".

Printed by the IAEA in Austria August 1963 TECHNICAL REPORTS SERIES No. 18

ANALYTICAL CHEMISTRY OF NUCLEAR MATERIALS

REPORT OF THE PANEL ON ANALYTICAL CHEMISTRY OF NUCLEAR MATERIALS HELD IN VIENNA 17-21 SEPTEMBER 1962

INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1963 ANALYTICAL CHEMISTRY OF NUCLEAR MATERIALS IAEA, VIENNA, 1963 STl/DOC/lO/18 FOREWORD

The last two decades have witnessed an enormous development in chemical analysis. The rapid progress of nuclear energy, of solid-state physics and of other fields of modern industry has extended the concept of purity to limits previously unthought of, and to reach the new dimensions of these extreme demands, entirely new techniques have been invented and applied and old ones have been refined. Many determinations at the trace impurity level which 20 years ago were largely of academic interest only are today regularly present in the daily routine of the analytical laboratory. At the same time, a higher accuracy of macro-determinations is required from the chemists because of the high value of many of the materials handled. The importance of the control of the composition of the materials used in nuclear energy projects is obvious. The first step in such a programme consists almost invariably in geological prospecting and the exploitation of the natural resources of the country, and the correct analysis of ores and semi-elaborated materials is essential to its success. In a more advanced stage, the knowledge of the composition and purity of fuels, moderators, coolants and structural materials used in reactors is also of primary significance. Finally, the operation of reactors and the reprocessing of partially spent nuclear fuels depend also on the continuous control of chemical composition and sometimes pose real challenges to the analytical chemists as a consequence of the special conditions under which the analyses have to be performed. With about 200 reactors presently operating in the world and more projected, in development or under construction, the importance of these subjects increases every day. Recognizing these facts, the International Atomic Energy Agency convened a Panel on Analytical Chemistry of Nuclear Materials to discuss the general problems facing the analytical chemist engaged in nuclear energy development, particularly in newly developing centres and countries, to analyse the present situation and to advise as to the directions in which research and development appear to be most necessary. The Panel also discussed the analytical programme of the Agency's laboratory at Seibersdorf, where the Agency has already started a programme of international comparison of analytical methods which may lead to the establishment of international standards for many materials of interest. It was particularly fitting that this first panel on the analytical chemistry of nuclear materials should have been chaired by Professor Hans Malissa, President of the Analytical Section of the International Union of Pure and Applied Chemistry, which effectively ensured that the panel's work could proceed without fear of duplicating that of other international bodies. The papers presented to the Panel and a summary of its discussions and recommendations are included in this Technical Report, which it is hoped will be found useful by all chemists concerned with nuclear energy development.

CONTENTS

PART I. ANALYSIS OF URANIUM AND THORIUM 9

A. Report to the Panel by Dr. С. J. Rodden 9 B. Summary of Discussion 25

PART II. TRACE IMPURITY ANALYSIS IN NUCLEAR MATERIALS 33

A. Report to the Panel by Professor Dr. J. Minczewski 33 B. Comments by Professor Dr. I. P. Alimarin 43 C. Comments on Analyses of Nuclear Materials in Japan by Professor Dr. T. Somiya 48 D. Summary of Discussion 55

PART III. ANALYTICAL CHEMISTRY OF IRRADIATED NUCLEAR FUEL PROCESSING 61

A. Report to the Panel by Dr. F.J. Woodman 61 B. Summary of Discussion 74

PART IV. RECOMMENDATIONS OF THE PANEL 79

List of participants 81

PART I

ANALYSIS OF URANIUM AND THORIUM

A. REPORT TO THE PANEL BY DR. C. J. RODDEN

INTRODUCTION

Of the three nuclear fuels, uranium, thorium and plutonium, that are presently considered for use in nuclear reactors the one most commonly used is uranium. Of these three elements uranium is more readily determined by chemical analysis since it has valence states such that a change of two valence states can be readily utilized. Plutonium in general has only one valence-state change while thorium exists only in the tetravalent state and cannot be determined by oxidimetric-titration methods. The analysis of uranium and thorium is such an inclusive subject that it is felt a more restrictive discussion as applied to materials which are now being or may soon be exchanged on an international basis would be appropriate. With this in mind the present discussion considers concentrates, alloys, ceramics and compounds of uranium and thorium. There have been several review articles and books on the determination of uranium 11, 2, 3, 4, 5, 6] , which give certain methods of separation and determination which may be applicable for high uranium-containing materials.

URANIUM

The types of materials analysed will to a large degree indicate the method or methods that will be used. In the case of uranium fuels either in the form of alloys, ceramics or cermets the method should be as precise and accurate as possible, especially if one is analysing uranium with a high uranium-235 content, since the monetary value of the fuel is high. Inva- riably the knowledge of uranium-235 content is generally desirable and the chemist in many cases has this problem to answer. Since the international exchange of materials of high uranium content is increasing it is highly desirable that methods which are acceptable to all concerned be used. Although uranium in some instances may be determined without prior separation of interfering elements, in general some kind of separation is necessary.

Uranium concentrates

The uranium concentrates encountered in the uranium industry are generally of high grade, ranging from 60 to 90% U3O8, although an occasional low-grade concentrate may be obtained. A few randomly selected analyses of various types of concentrates are given in Table I.

9 t

TABLE III (cont.)

REPRESENTATIVE ANALYSIS OF URANIUM CONCENTRATES

Origin V2O5 P2Os Na SO, Mo Fe Cu As в H20 C02 NHj u,o,

1 United States 0.07 0.03 2.19 0.31 <0.05 0.15 <0.10 <0.005 6.81 0.68 77.86

3 United States 2.42 0.22 1.81 1.75 0.09 1.84 <0.10 <0.005 0.36 - 87.46

16 United States <0.20 0.59 0.03 2.35 0.29 2.22 0.59 4.88 0.14 - 74.77

21 United States 0.25 0.61 1.71 4.62 0.13 0.34 - <0.10 <0.005 1.09 0.02 85 81

23 Canada <0.02 0.08 3.28 1.74 0.003 0.42 <0.01 <0. 01 0.006 - <0.08 79 39

26 Canada <0.02 0.08 <0.03 2.37 0.001 0.40 <0.01 <0.01 0.009 <0.08 77.83

28 South

Africa <0.02 <0.08 <0.02 6.28 <0.001 0.61 - 0.06 0.004 0.12 <0.08 0.023 88.12

29 Australia 0.75 0.944 0.863 3.98 0.56 0.10 68.45

30 Belgian

Congo 0.03 0.45 1.92 0.49 0.003 2.49 0.01 <0.01 0.03 0.35 74.07

" 31 South

Africa 0.026 1.91 0.0007 0.40 92.00 As one can see certain elements that would interfere with a volumetric or gravimetric determination of uranium must be removed. In the concentrates analysed these interferences are mainly vanadium and iron and no serious problem of removing these impurities presents itself. One problem connected with certain types of uranium concentrates is the preservation of the samples. Many of these materials are adversely affected by changes in humidity and it has been found that the only way to preserve these samples in their original composition is to have them put in glass containers with vacuum sealed tops somewhat similar to those used for canning fruits and vegetables. By having the warm material placed in these containers, and then cooling, a vacuum tight seal is made. Many attempts at drying the materials under controlled humidity conditions were unsuccessful. The present practice is to weigh the sample as soon as the container is opened and then not to use the material in this container again for the uranium determination. The results obtained by six different laboratories using materials sealed as described above are given in Table II. The standard deviation between laboratories for many analyses varied from 0.05 to 0.12%. The above values were selected at random and are indicative of the precision of analysis obtained by several laboratories using two different methods of analysis. The methods used are outlined as follows.

TABLE II

U308 (%) IN CONCENTRATES

Laboratories Producer Average

1 2 3 4 5 6

A 89. Ы 89. 03 88.98 89.18 89.01 89.03 89.04

В 84.58 84.77 84.75 84.74 84. 56 84.66 84.68

С 80.40 80.49 80.52 80.73 80.58 80.60 80.55

D 84.37 84.46 85.54 85.43 85.42 85.50 85.45

Cupferron-dicbromate procedure — method used by Laboratories 1, 3, 4, 5 and 6 ¡5J

The samples are decomposed by treatment with sulphuric and nitric acid; interfering elements are removed by a sulphide precipitation, using either hydrogen sulphide or thioacetamide, followed by a cupferron- chloroform extraction in an acid medium. Nitric-acid and organic matter are removed by fuming with perchloric and sulphuric acids. The uranium

11 solution is reduced in a Jones reductor, aerated to oxidize any trivalent uranium to the tetravalent state, and titrated with potassium dichromate which has been standardized with standard U3O8.

Phosphate-ceric sulphate procedure — method used by Laboratory 2 [4]

The samples are decomposed by treatment with sulphuric and nitric acid. Interfering elements are removed by precipitation of uranyl ammonium phosphate in the presence of ethylenediaminetetraacetic acid at a pH of 1.7 followed by dissolving the phosphate precipitate in sulphuric acid and making a cupferron-chloroform extraction. After destroying the organic matter and removing the nitric acid by fuming with perchloric and sulphuric acid, the solution is passed through a Jones reductor. After aerating to oxidize the trivalent uranium to tetravalent uranium the uranium is titrated with eerie sulphate solution standardized with standard U3O8. The results given in Table II are indicative of what is usually obtained when analyses are made on a routine basis. Certain precautions are desirable, suchas correctingthe volume of the burrette for changes in temperature (using a titration volume of such magnitude — usually 50 to 100 ml — that reading errors are minimized) and standardizing against U3O8 of about the same weight that is being titrated. WhenUaOs is titrated with dichromate, with diphenylamine as the indicator, it has been found that the titer of gU/g dichromate changes with the amount of uranium being titrated. This is tied up with the indicator but is not a strict indicator titration error. In another type of concentrate a different procedure was used by the producer. The results of two laboratories are given in Table III. The standard deviation between laboratories for many samples was 0.1%. The methods used follow.

TABLE Ш

U308 (%) IN CONCENTRATES

Laboratories

Lot Average 1 2

222 91.45 91.45 91.45

191 89.32 89.29 89.30

151 92.37 92.26 92.32

680 94.59 94.65 94.62

23 92.01 92.14 92.08

20 91.37 91.65 91.51

12 Cellulose column procedure — method used by Laboratory 1

The sample is dissolved in a small amount of nitric acid and is transferred, after absorbing the sample on cellulose, to a cellulose column containing a layer of activated aluminia at the top. The column is prepared with an ether-nitric acid mixture (50 HNO3- 950 diethyl ether) and the sample, is transferred quantitatively with the ether-nitric acid mixture. The uranium is eluted with this mixture and the effluent, in a platinum or silica dish, is evaporated to dryness on a water bath after adding some water. The dish is then transferred to a cold muffle furnace and the temperature is raised to a final ignition at 900° С for 1 h. The method used by Laboratory 2 is the same as that employed in the cupferron-dichromate procedure. The results given in Table III were selected at random. In general the agreement is like that given in the first five lots, although an occasional variation such as is found in Lot 20 may be*obtained. The agreement with this type of concentrate, the analyses of which were done in two countries far removed from each other with no access to the analytical values, is quite gratifying. Considering concentrates in general the fact that good agreement is obtained with three different methods would be an indication that the accuracy of the analyses is satisfactory. Unlike precision, however, which can be readily calculated, the accuracy of an analysis is a matter of opinion. In- sofar as a material for the standardization of a titrating solution is concerned I am in favour of a high-purity uranium metal. Uranium oxide has two disadvantages: it is difficult to prepare so that the stoichiometry is correct and the temperature gradient (850 to 950°C, sea level) in which the compound U3O8 can be obtained is small. Variations in altitude may also affect the temperature in which U3O8 is stable.

Alloys, ceramics and cermets

In the analysis of alloys, ceramics and cermets containing uranium we have many more problems than in the analysis of concentrates. First, the question of sampling is a big problem; second, we have the question of solution and separation from interfering elements; and third, since in many instances the materials analysed contain enriched uranium, the question of accuracy is important. Table IV gives some representative types of alloys, ceramics and cermets. The sampling problem is all-important and in many instances the analyst has no control over this operation. In certain cases, for example, in the recovery of enriched uranium scrap, it may be necessary to dissolve the entire lot of alloy, etc. before taking a sample. Many of the alloy-type materials are notorious insofar as segregation is concerned. On the other hand certain fuel elements cannot be sampled and non- destructive testing may be used, such as gamma-ray counting, X-ray trans-

13 TABLE IV

. TYPES OF URANIUM FUEL ELEMENTS

Alloys Ceramics Cermets

U - Al U02 - Th02 U02 - Stainless steel

U - Be U02- Pu02 U02 - Zr

U - Сг U02 - AljOj U02- Al

U - Mo UO2- BeO U02- Nb

U - Nb UO2 - SÍO2

U - Si U02- Zr02

U - Zr mission, X-ray densitometry, or mass densitometry measurements. Usually these methods do not give a high order of precision or accuracy but are satisfactory for plant control. These types of materials cause the chemist to use all his chemical knowledge and ingenuity to solve problems of solution and separation prior to the determination of uranium. When one looks at the array of elements that are put in these experimental fuels it would appear that the nuclear fuel designer went out of his way to prepare mixtures that would give the analytical chemist all kinds of problems. No attempt will be made to describe methods for all these types of material. They are considered in detail in a forthcoming book, The Analysis of Essential Atomic Reactor Materials [4]. Examples of some of the methods used in more commonly analysed alloys, ceramics and cermets follow.

Uranium-aluminium alloy

The sample is dissolved in aqua regia and any insoluble residue is filtered off, ignited and treated with hydrofluoric acid after which the residue is dissolved in nitric acid. After fuming with sulphuric acid the solution is analysed by the cupferron-dichromate procedure.

Uranium-molybdenum alloys — zirconium clad

The sample is dissolved in sulphuric acid and nitric acid with the cautious addition of hydrofluoric acid. The solution is fumed with sulphuric acid and the solution treated as in the cupferron-dichromate procedure.

UO2 in stainless steel (cermet)

The sample is dissolved in aqua regia and perchloric acid. After solution any residue is treated with hydrofluoric acid and then fused with sodium pyrosulphate. The solution is transferred to a mercury cathode

14 electrolysis apparatus (Dynacath) to remove the iron, chromium and nickel and then the uranium is precipitated with ammonium hydroxide. The precipitate is dissolved in sulphuric acid and then analysed according to the cupferron-dichromate procedure.

U0z-Th02 (5% иОг-95% ТЬОг)

The sample is fused with NaHSCMnot KHSO4 ) and dissolved in water. After adding hydrochloric acid the sample is precipitated with NH4OH. The residue is dissolved in hydrochloric acid and the uranium is extracted with a 1-1 mixture of tributyl phosphate and methylisobutylketone. The organic layer is stripped of uranium with hot water. The aqueous strippings are evaporated to fumes with sulphuric acid and the determination is finished as under the cupferron-dichromate procedure.

иОг-ВеО

The sample is treated with nitric and hydrofluoric acid and the solution is evaporated to a gel and treated with sulphuric acid. After fuming with sulphuric acid the uranium is determined as in the cupferron-dichromate procedure.

Uranium-zirconium alloy

This alloy has been reserved for the last as it is the only one for which we have comparative results by different methods and by different laboratories. In order to avoid the question of segregation the samples were dissolved by one laboratory and the solutions, in sealed containers, were shipped to the different laboratories. The samples were dissolved in hydrochloric acid with the addition of hydrogen peroxide and sulphuric acid. After the solution was made to a certain volume, aliquots were sent in sealed containers to the various laboratories. The methods used by these laboratories were as follows.

Cupferron-dichromate method used by Laboratories 1 and 4 [5]

Owing to the high zirconium content of these alloys the usual extraction procedure using a cupferron solution was not satisfactory. Instead of using a 6% cupferron solution to precipitate the zirconium prior to extraction 15 g of solid cupferron is added and the bulk of the zirconium extracted with chloroform. The small amount of zirconium left is removed by using the 6% aqueous cupferron solution. The uranium is determined as with the cupferron-dichromate procedure.

Ion-exchange procedure — method used by Laboratory 3 [7]

In this method an aliquot of the solution is evaporated to dryness, taken up in concentrated hydrochloric acid and passed through an ion-exchange column containing a resin of the Dowex-1 type. The uranium and iron are

15 absorbed on the column while the zirconium passes through. The uranium and iron are eluted from the column with dilute hydrochloric acid (0.7 N) and the effluent is evaporated to dryness. The residue is dissolved inhydro- chloric acid and the iron removed by an ammonium carbonate precipitation. The solution containing the uranium is fumed with sulphuric acid and after adding hydrochloric acid the solution is reduced in a lead reductor and titrated with eerie sulphate.

Ammonium carbonate-ceric sulphate method used by Laboratory 5

In this procedure the uranium is separated from interferences by a double ammonium carbonate precipitation followed by the conversion of the carbonate to sulphate. The uranium in the sulphate solution is precipitated with ammonia, taken up in sulphuric acid and reduced in a Jones reductor. After aeration, the uranium (IV) is titrated with eerie sulphate.

Ferric sulphate method used by Laboratory 2 [4]

In this method no separations are made. The sample is fumed with sulphuric and perchlorate acids, reduced with chromous sulphate and the hot solution is titrated with ferric sulphate solution first to the uranium (IV) state and then to the uranium (VI) state using potentiometric end points. The results obtained by five different laboratories are shown in Table V. I might say that when this programme was first started synthetic solutions approximately the concentration of a uranium-zircaloy alloy were distributed to several laboratories. The agreement was far from satisfactory. The methods were then changed or modified with the results shown in Table V. To obtain an estimate of the accuracy of the cupferron-dichromate method, weighed amounts of uranium were dissolved in solutions approximating the composition of the alloys and the cermet shown in Table VI. The recovery is also shown in this Table.

Compounds of uranium

The compounds of uranium that are exchanged in commerce are mainly UO2, UO3, UF4 and UF6 as well as uranium metal. These materials may be of either normal or enriched isotopic concentrations. Fortunately, they are all of such purity that in most instances chemical separation of impurities are unnecessary. Routine analyses are generally made by the gravimetric method of ignition to U3O8 and correcting the final weight of oxide for the impurities that are determined by a spectrographic procedure. Occasionally, for highly precise work the uranium is determined by a method using a weighed amount of standard potassium dichromate as the oxidizing agent after reduction of the uranium. The methods used for the various materials are outlined below.

16 TABLE V URANIUM IN SOLUTION OF URANIUM-ZIRCALOY

Laboratories (gU/g solution) Standard deviation Sample ' Average amongst laboratories 1 2 3 4 5

1 0 008297 0 008276 0. 008285 0 008298 0 008315 0. 008294. 0.000015

2 0 004718 0 004683 0.004682 0 004718 0 004713 0.004703 0.000019

3 0 003287 0 003288 0.003285 0 003297 0 003290 0.003289 0. 000005

All results were done in quintuplet by each laboratory and the above are averages of the results reported. TABLE VI

RECOVERY OF URANIUM FROM ALLOYS

Recovery Alloy (%

U - Al 100.0

U - Mo 99.9

. U - Stainless steel 99.8

U - Zr 99.8

Uranium in UO2 or UO3

A sample of 5 to 10 g is ignited in a platinum boat to U3Og in air at 850- 900° С for 1 h. Impurities are determined, if necessary, by a spectrograph^ analysis and the results corrected accordingly. Table VII indicates the results obtained in four laboratories on UO3. The results are those selected at random for four independent laboratories. The standard deviation between laboratories over a year ranges from 0.01 to 0.05%. Like the uranium concentrates UO3 is hygroscopic and is weighed immediately after opening the sample bottle. The procedures used by all laboratories were essentially the same.

TABLE VII

DETERMINATION OF URANIUM (%) IN UO3

Laboratories

Sample No. Average

1 2 3 4

3 81.36 81.38 81.36 81.28 81.34

4 81.56 81.58 81.57 81.56 81.57

1 82.46 82.47 82.39 82.46 82.44

Uranium in UF4

The usual method employed for the determination of uranium in UF4 is to pyrohydrolyse 1 to 10 g of the sample in a current of steam at a

18 TABLE VIII

URANIUM (%) IN UF4

Laboratories

Sample No. Average

1 2 3 4

3 74.22 74.24 74.40 74. 26 74.28

2 74.00 73.97 74.20 73.96 74.03

1 74.09 74.02 74.12 73. 88 74.03

4 74.13 74.22 74. 22 74.14 74.18 temperature of 750 to 900° С followed by ignition of the sample. Corrections are made for impurities if necessary. These are determined spectrographically. The results obtained by several laboratories are given in Table VIII. The standard deviation between laboratories over a year ranges from 0.02 to 0.13%. The precision is not as good as with UO3. To obtain an estimate of the accuracy of this determination, a sample of UF4 was analysed by the above pyrohydrolysis method, and also by a precise method whereby a 5- to 10-g sample — after solution in sulphuric acid and nitric acid and removal of the nitric acid by fuming the solution — was run through a Jones reductor, aerated to the uranium (IV) end point using a potentiometric end point, and a weighed amount of standard potassium dichromate in slight excess was added. The excess dichromate was titrated with 0.01 N ferric sulphate using a potentiometric end point. The results obtained are shown in Table IX. The U3O8 found from the pyrohydrolysis was also analysed with the results given in the same Table.

Uranium metal

Uranium metal is rarely analysed for its uranium content. Usually spectrographic and chemical methods are used to determine the impurity content and thus to determine the quality of the metal.

Uranium in UFg .

A representative sample of the UF6 is taken by melting the UF6 and allowing it to flow into a fluorothene tube which is cooled in liquid nitrogen. The tube is sealed and allowed to come to room temperature. After drying in a desiccator for 1 h the tube is weighed. The sample is again frozen in liquid nitrogen and the plug, gasket and nut are removed. The tube with the plug, etc. is placed in a platinum dish with 150 ml of cold water. After hydrolysis has been completed the tube and plug, etc. are washed, removed, dried and weighed. The solution is evaporated to dryness and then pyro-

19 TABLE IV

URANIUM CONTENT OF UF4

Pyrohydrolysis method (750°C, 2h), Total uranium ignition (900"C, lh) New Brunswick Laboratory precision method

2-g sample 5- to 10-g sample {%)

75.88 75.877

75.86 75.878

75.87 75.866

75.86

75.88

75.87

75.88

75.85

75.86

75.87

Average 75.868 75.874

UjOg residue from pyrohydrolysis analysed by a precision method

Uranium in Uj08 U,08 (%>

84.797 99.995

84.804 100.003

84.784 99.979

Average 84.795 99.992 hydrolysed at 850° С. It is then ignited at 900° С and, if necessary, the impurities are spectrographically analysed and the results corrected accordingly. The results of two samples picked at random are given inTabléX. The standard deviation in one laboratory during routine use for many years was about 0.3%.

20 TABLE IV

URANIUM CONTENT (%) OF UFfi

Laboratories

Sample Average 1 2 3

1 67.59 67.59 ' 67.57 67.58

2 67.57 67.61 67.58 67.59

The above discussion on the determination of uranium in various types of materials does not cover all or necessarily the best methods. They re- present-the result of cumulative experience over a period of years. It would be desirable if a programme for exchange of materials could be arranged on an international basis so that all countries would be analysing the same sample. The international agency would appear to be the best qualified to undertake and evaluate the results of such a programme.

THORIUM

The interest in thorium has varied considerably during the years and the amount of information on the comparison of analyses is not as great as in the case of uranium. Thorium has but one valence and consequently cannot be determined by oxidation-reduction reactions. Although several methods have been suggested for the determination of thorium by volumetric means, such as titration with ethylenediaminetetraacetic acid, molybdate, iodate, oxalate and m-nitrophenylaronic acid, the most commonly employed method for transfer of thorium materials is the gravimetric procedure. In most instances the precipitate is ignited to the oxide. Methods for thorium have been compiled in several instances 14, 8, 9]. Materials containing relatively high amounts of thorium that are exchanged are chiefly concentrates and thorium nitrate. Results are considered below.

Thorium sludge

Several types of concentrates, tagged with the rather inglorious title of sludge, have been exchanged both nationally and internationally. These materials are relatively impure and require separations in most cases. One such type of material had 42.0% Th02, 3.5% l%Og, 17.4% rare earths and about 3% phosphate. Others have higher or lower thorium oxide content with variations in other impurities. The thorium content of the nitric acid- soluble portion of the sludge is determined. The insoluble in the nitric acid is discarded.

21 TABLE XIV

THORIUM OXIDE CONTENT (%) OF THORIUM NITRATE

Laboratories

Sample Average 1 2

1 53.24 53 51 53.38

2 55.62 55 94 55.78

3 55.06 55 74 55.40

4 56,05 55 85 55. 95

The results obtained with one type of sludge are given in Table XI. The standard deviation between laboratories was 0.34%. The methods used by the two laboratories follow.

Jodate-oxalate procedure — method used by Laboratory 1

The dried sample is treated with nitric acid and the insoluble residue is filtered off and washed. Two iodate precipitations are made to separate the thorium. The iodate is dissolved in hydrochloric acid with the aid of bi- sulphite and the thorium is precipitated with ammonium hydroxide. After dissolving the hydroxide precipitate in hydrochloric acid the thorium is precipitated with oxalic acid from a solution with final hydrochloric acid concentration of 2%. The oxalate is ignited at 1000°C.

Oxalate-meta nitrobenzoic acid procedure — method used by Laboratory 2

The nitric acid solution is precipitated with potassium hydroxide. The precipitate is dissolved in hydrochloric acid and the solution is diluted until it is 0.3 N in hydrochloric acid. The thorium in the solution is then precipitated with oxalic acid (final HCL concentration about 0.15 N). The oxa- lates are treated with potassium hydroxide and the thorium hydroxide is dissolved in nitric acid. The thorium is precipitated with meta-nitrobenzoic acid after removing all of the excess nitric acid by evaporation. The precipitate is ignited at 1000° С. With another sludge of similar composition but of different origin, results using identical procedures were obtained by two laboratories. The procedure was the iodate-oxalate one described above. The results are shown in Table XII. The standard deviation between laboratories over a large number of lots was 0.22%. As can be seen the agreement between laboratories with thorium concentrates is not as satisfactory as those obtained with uranium concentrates.

22 TABLE XIV

THORIUM OXIDE CONTENT (%) OF THORIUM NITRATE

Laboratories

Lot. No

1 2

2 45.75 45.97

4 46.28 46.58

6 44.76 45.05

8 46.24 46.46

10 46.66 46.70

12 45.55 45.21

Thorium nitrate

The only other article of commerce in which comparative results from various laboratories are available is thorium nitrate. This material contains only minor impurities. One type of this material which was analysed in different countries is given in Table XIII. The standard deviation between laboratories for many lots was 0.28%. In spite of efforts to resolve the difference no satisfactory reason for the variation in results was obtained. The procedures used by the two laboratories follow.

TABLE XIII

THORIUM OXIDE CONTENT (%) OF THORIUM NITRATE

Laboratories Lot. No

1 2

1 46.8 47.1

2 47.2 46.9

3 46.8 46.9

4 47.8 47.2

5 47.4 46.7

6 47.0 46.4

23 TABLE XIV

THORIUM OXIDE CONTENT (%) OF THORIUM NITRATE

Laboratories 1 2

48. 47 48. 38

48.47 48.44

48. 52 48.49

48.41

Average 48.49 48.43

Ammonium hydroxide-oxalate procedure — method used by Laboratories 1 and 2

The thorium in a nitric acid solution is precipitated with ammonium hydroxide. This precipitate is dissolved in hydrochloric acid and the solution is evaporated to dryness. Saturated oxalic acid solution is added to the residue. The oxalate is ignited at 1000°C. In an exchange of thorium nitrate standard sample candidate the results of two laboratories using essentially the above method are shown in Table XIV. The standard deviation between laboratories was 0.04%. Thorium metal is rarely analysed for its thorium content. The quality is judged by the analysis for impurities, many of which are done by spectrographs procedures. The agreement on the determination of thorium in material for which we have considerable data shows that there is room for improvement. In certain instances sampling may be at fault but in the materials cited it is difficult to believe that this is the main reason. As can bè seen the agreement between laboratories with thorium concentrates is not as satisfactory as those obtained with uranium concentrates.

REFERENCES

[1] STEELE, T. W. and TAVERNER, L., Proc. 2nd. UN Int. Conf. PUAE 3 (1958) 510-26. [2] RODDEN, C.J. and TREGONING, J.J., Manual of Analytical Methods for the Determination of Uranium and Thorium in their Ores, Supt. of Doc. , Gov. Printing Off. , Wash., D. C. (April 1955). [3] RODDEN, C.J. and WARF, J. C., The Analytical Chemistry of the Manhattan Project (RODDEN, C.J., Ed. ) McGraw-Hill Book Co. , Inc., New York (1950). [4] The Analysis of Essential Atomic Reactor Materials (RODDEN, C.J. , Ed.) in preparation. [5] Selected Measurement Methods for Plutonium and Uranium in the Nuclear Fuel Cycle (JONES, R., Ed. ) in preparation. [6] deSESA, M. A. , in: Uranium Ore Processing (CLEGG, J. W. and FOLEY, D. D., Eds. ) Addison-Wesley Publ. Co. , Inc., Reading, Mass. (1958). [7] MILNER, G. W.C. and NUNN, J. H. , Analyt. chim. Acta 17 (1957) 494. [8] BANKS, C.V., USAECRep. TID-7555 (Nov. 1957). [9] BANKS, C.V., "Analysis of thorium", Progress in Nuclear Energy, Series IX _I: Analytical Chemistry, PergamonPress, London (1959) 33-56 and in: Proc. 2nd. UN Int. Conf. PUAE 28 (1958) 517-31.

24 В. SUMMARY OF DISCUSSION

(Chairman: Professor Dr. H. Malissa)

1. URANIUM ANALYSIS

1 (a) Comments on methods

(i) General

The precision attainable at the present time in uranium determinations by the most widespread techniques is satisfactory. Dr. C.J. Rodden, howr ever, mentioned that the same cannot be said of accuracy. To know the accuracy of the particular method one is using is particularly important in balances of uranium, especially when costly enriched uranium is involved. For instance, uranium in scrap may be determined by a method based on cupferron separation, or a similar one at the beginning of a recovery process and by ignition at its end, as what comes out is nearly a pure oxide. Both methods may have a different built-in bias and the difference in balance becomes quite serious after some time of operation without the analysts involved being aware of it. Dr. R.F. Cellini pointed out the importance of determining, for production purposes, not only total uranium but also the different valency states in which it can be present in a sample, and suggested that some consideration to this problem be given in future in the intercomparison and standardization programme of the International Atomic Energy Agency's (IAEA) laboratory. He also suggested in connection with this last subject, that future intercomparison work by the IAEA be oriented to materials of direct practical interest and not to pure solutions or systems. Professor Dr. I. P. Alimarin recommended, as a source of information on the analytical aspects of uranium chemistry, the book by Markov, Vinogradov et al.* Dr. Rodden mentioned the new book on analysis of nuclear materials which is in preparation in the United States of America under his direction (see Ref. [4], Part I, this report). This book covers uranium analysis, although its scope is wider.

(ii) Concentrates, rich ores, pure compounds and metal

The most widespread technique for this type of determination is oxidative titrimetry of the uranous ion by permanganate or eerie ions with an end point reading by a potentiometry or a visual indicator. It was felt that the technique is satisfactory as currently used and that it can be applied to samples containing from 0.05% up to pure compounds and metal without difficulties, though its more normal range of application is from a few per cent to pure metal. A discussion was held on the reduction step prior to the titration. Dr. G.A. Welch reported the use of a bar of spectrographicallypure alu-

* MARKOV, VINOGRADOV et al.. Uranium and Methods for its Determination, Glavatom, Moscow (i960); printed in Russian only.

25 minium for the analysis of pure uranium samples, in the presence of traces of cadmium as a catalyst, to effect the reduction. He considered that this technique gives better and quicker results than the use of a Jones reductor when used by unskilled personnel. Some phosphoric acid is added and no aeration is made, as no reduction below the U4+ state takes place. Dr.Rodden reported that aluminium had been tried as a reductor many years ago in his laboratory but without using cadmium as a catalyst, and that good results were not obtained. Dr. Cellini reported that in Spain reduction was usually made with an electrolytic cadmium sponge; with it, no U3+ is formed and no re-oxidation by air is necessary. In a column 8 cm long, at one drop per second, the reduction is quantitative. In this connection, Dr. Rodden mentioned that they had also tried cadmium as reductor years ago, but were discouraged from using it because of its health hazard. In France, titanium chloride was introduced as a reducing agent in solution for the determination of uranium in radioactive solutions, because maintenance problems were found when using the Jones reductor inside alpha-gamma enclosures. The reducer acts effectively in a nitric acid medium if sulphamic acid is also present. It is currently used at the Marcoule factory, reported Dr. M. Corpel, and Dr. J. Huré pointed out that it has also been adopted to determine uranium in the feed to refining plants when the ore concentration plants deliver nitric acid uranium solutions, as some French plants do. Previously it was necessary to change to a sulphuric acid medium for the analysis; this step has been avoided by the use of the soluble reductant.

Professor Alimarin and Dr. T. Somiya mentioned that some photo- oxidation may take place before the titration, especially when sunlight strikes the sample directly. This effect has not been observed by Dr. Rodden who claimed that in any case it has no significance if the sample is titrated within the hour. He had observed some oxidation by air if traces of copper or molybdenum were present, but no photo-oxidation. However, he mentioned that his laboratory benches do not get direct sunlight. Dr. Somiya mentioned that when the acidic solution of the sample containing dissolved oxygen is reduced by shaking with liquid amalgam, hydrogen peroxide is formed and interferes with the titration. In this connection. Dr. Rodden reported that a similar effect has been said to occur in Jones reductors but that in experiments made in the United States of America it was always found that the reductor destroyed the peroxide. No effect was ever detected when the reductor was kept covered with liquid all the time so that air bubbles could not get inside. In connection with the analysis of uranium concentrates, Dr. Rodden reported that serious difficulties are found in drying them reproducibly, and he considers now that, for purposes of comparison, better agreement is reached if the different samples taken from the same lot are packed, her- metically sealed, and analysed immediately after opening the container, without any prior drying. Dr. Cellini reported that in Spain they have also had serious difficulties in the matter and that agreement with other countries was only reached when a common method was used. He pointed out that an agreement to 0.10% must be considered satisfactory for concentrates.

26 This would affect the second decimal figure and can be considered as the limit of the method for practical purposes.

(iii) Intermediate and low concentrations, common ortes, and traces

Most of the ores exploited today are of low content, from 0.05 to 1%. Dr. Cellini considered that probably more than 90% of those currently worked are in this region of concentration and reported that in Spain the limit of exploitation has been fixed at 0.12%. Dr. Huré reported that in France the limit was set at 0.05% (500 ppm); over that amount, the ore is considered economically exploitable and below that limit, not. Dr. Cellini reported that in Spain they have normalized methods through comparison between the laboratories concerned with prospection, mining and plants, and the central analytical laboratory, which has all responsibility as to methods used. In the case of ores, good agreement could not be reached until the same standard methods were used. Spectrophotometric techniques withdibenzoyl methane, sodium 1, 2-dihydroxybenzene disulphonate and ferrocyanide, and polarography with Na2CC>3lM as supporting electrolyte are used for uranium solutions of concentrations of about 0.02 - 0.05% to 1 - 2 g/1. For each method the range of optimal applicability has been determined. For lower amounts of uranium, between 0.0002 and 0.09%, as found normally in ashes, natural waters and leaching residues, fluorimetry is used. In the case of natural waters this technique is applied by passing the water through a small exchange column which fixes the uranium and by sending the resin samples to the central laboratory, where they are eluted and the uranium determined. Soils are fused with sodium carbonate and the fluorimetric analysis is carried out on the spot in mobile analytical units. Frequent use is also made on the spot of colorimetry on paper using ferrocyanide. Prospection is made by fluorimetry; for control of mine operation and mill work, spectrophotometry with dibenzoyl methane, which has been fixed by the laboratories concerned as the standard method,, is applied. Dr. L. Kosta reported that in Yugoslavia colorimetry is made mainly with ammonium thioglycolate from 0.1% to a few per cent. Low-grade ores are currently determined by fluorimetry, with the aid of a small portable transistorized fluorimeter developed by the Yugoslavs themselves. Professor Alimarin favoured the use of fluorimetry, counting and spectrography for the determination of uranium in low-grade ores. The work of the Russian scientists Rusanov and Vinogradov were mentioned in connection with the determination of uranium by spectrography. Professor Dr. J. Minczewski reported that also in Poland spectrography is widely used in the laboratory to determine uranium in very low-grade ores already sorted out on the basis of fluorimetric results and in leach residues, and that the technique gives a precision of 15 to 20%, comparable with fluorimetry, at levels as low as 0.001%. Earlier they tried spectrophotometry, but it was found that the methods were too cumbersome and uncertain for this application because of the previous separation necessary and the low levels of concentration involved. The practice in France is to use fluorimetry in the field, by means of a small battery-operated fluorimeter which weighs approximately 2 kg; the

27 uranium is first separated by paper chromatography. Counting is also used for this purpose. Natural waters are checked by essentially the same procedure as the one already mentioned by Dr. Cellini, that is by fixing the uranium as a sulphate complex on a few milliliters of anion exchanger and sending the resin samples to a central laboratory where they are eluted and analysed by flúorimetry. For ores over 500 ppm, spectrophotometry is used. He felt that spectrography would not be accurate enough for this purpose. Some special methods were also briefly discussed at the suggestion of Professor Dr. F. Hecht. Dr. Cellini reported that X-ray fluorescence with strontium as an internal standard was used in Spain to determine uranium in complex residues of a uranium content of 0.1 to 0. 5%, with a limit of detection of 0.01 and a standard deviation of 5%. This is particularly useful in this case because of the low interference inherent to the method. Dr. M.T. Kelley mentioned that absorption of X-rays using the absorption edge phenomenon, is applied routinely at an Oak Ridge laboratory to determine uranium in scrap. Discussing coulometric methods. Dr. Rodden considered that 0.1% was about the maximum reproducibility attainable, but Dr. Kelley pointed out that with large samples it was possible to reach0.05%. However, Dr. Corpel reported that they had applied the technique for quantities of approximately 1 mg of plutonium and could not get better precision than 2 to 3%. Results improved with larger samples but were still considerably below the sensitivity reported by Dr. Kelley.

(iv) Comments on special subjects

(a) Uranium cermets

Dr. Rodden reported that stainless steel cermets and alloys are analysed by separating the bulk impurities on a mercury cathode and then treat- ing the solution as a normal impure uranium one by the methods available. Dr. Welch said, in answer to a question by Professor Dr. H. Malissa, the Chairman, that the content of uranium in cermets is of the order of 20 to 40%.

(b) Uranium carbides

In France, total combustion in O2 is used to give the U/С ratio, reported Dr. Huré. The fraction of carbon present as carbide is determined by acid attack and gas chromatography of the gaseous hydrocarbons formed, but the method is not considered absolutely sure for every application.

Dr. Welch commented that the isotope dilution method of uranium analysis using U233 as a tracer is not such a luxury as it may appear at first sight, especially when it is used on enriched uranium. In this case mass spectrometry analysis has to be used anyhow and the inclusion ofthe'tracer gives the total uranium content in addition to the mass spectrum.

28 Considering isotopic analysis as such, Dr. F.J. Woodman reported that mass spectrometry is to be preferred to spectral shift methods for accountancy purposes, though the latter are more useful if highly enriched uranium residues are handled. With regard to spectral shift methods Dr. Welch, answering a question of Dr. Rodden, said that the presence of U23t> in irradiated uranium does not introduce any trouble with the high resolution spectrographs presently available.

1 (b) Standards

(i) Uranium

It was pointed out that no agreed international standard of uranium for analytical purposes exists and that the present meeting provided an oppor- tunity to discuss the subject. The convenience of the existence of auranium standard was stressed unanimously by the participants. The ideal conditions that such a stándard should meet were discussed in relation to purity, homogeneity and reproducible stoichiometry. It was pointed out that it should be a solid material; solutions which will in principle present no homogeneity problems, do not keep well for a long time. Dr. Rodden pointed out that at New Brunswick they have used three different reference materials: standard potassium dichromate from the National Bureau of Standards, triuranium octoxide of the same origin and uranium metal. Of these, only the first one is an agreed primary standard, and is not a standard of uranium. The oxide assayed only 99.94% U3O8. Themetal was much better, as it was very pure (99.98 or 99.99%), homogeneous and, of course, independent of stoichiometry complications. It could be used with only some pickling to remove the oxide and gave very good results. How- ever, it is not prepared in the United States of America any more, as it was found later that the presence of certain impurities was necessary to improve the metallurgical properties. Dr. Huré reported that a very pure uranium metal with total impurities < 100 ppm, probably suitable for the purpose, was currently produced by electrolytic refining in France, but only in small amounts. It was felt during the discussion, that a more practical first objective should be sought. The establishment of a primary uranium standard, however desirable, would imply by necessity lengthy agreement procedures with many international and national bodies connected with chemical standards. The Panel considered that the IAEA should keep this question open and proceed further with exploratory measures in this direction because of its importance, but that what was of immediate necessity at the present time was a material that could serve as a common reference between laboratories and which could be used to check the accuracy of methods in a particular one. There was no need for this material to be a primary uranium standard; it would be sufficient if it had an accurately known content of uranium and if its assay could be easily reproduced in any laboratory.

After some discussion, it was considered that a sample of U3Og would be suitable. Its assay and the degree of reproducibility of this assay could be checked by loading laboratories in different countries against standard

29 potassium bichromate (K2Cr207) circulated (possibly) with the sample. After that, it could be assigned a certain value in uranium content and internationally used as a reference analysed sample sponsored by the IAEA. As to the amount necessary, Professor Alimarin suggested that 50 kg would be sufficient; the individual samples could be supplied in quantities of 25 g. The IAEA officers present at the'meeting agreed to continue the matter further in the Secretariat.

(ii) Ores

The question of the advantages of having reliably analysed ores to check ore analysis procedures was considered by the Panel. Dr. Rodden reported that years ago the New Brunswick Laboratory had prepared samples of some ores to be used for standardization of uranium assay by radiometric procedures. These ores were used by some people to check chemical procedures and the results were not good, because the samples were not homogeneous enough for the purpose and were intended to be used only for counting in 25 to 50-g amounts. Because of this experience, he considered that any intent to prepare reference ores for chemical purposes should take special care in the procedure of homogenization. Dr. Cellini, Dr. Rodden and Professor Alimarin pointed out that the number of ores of interest may be very large, as the ores of importance to one country may differ entirely from thosfe of interest to another. As a first step, it was advised that information be collected from Member States to find out which ores would be of interest. It might well be that this exploratory exercise shows that many of them are chemically similar and the total number will consequently be reduced. In any case, it was considered a very interesting proposition to explore the possibilities of the IAEA's provision of reference ores. These will be of particular importance to countries starting to evaluate their national resources, enabling them to control their analytical procedures on an internationally agreed basis. With regard to homogenizajion, Dr. Cellini reported that in Spain they have prepared reference ores to permit different laboratories to checktheir analytical procedures. It has been possible to reach a degree of homogenization where deviations of the results obtained from several samples taken from the same lot are practically negligible. When this condition is reached, the ore is considered as a standard one. He offered the collaboration of his laboratory in this respect, in case the IAEA decides to undertake such a programme. Dr. Cellini proposed the following steps for such a programme, after the number and kind of ores have been agreed on: (1) preparation of the ores; (2) analysis of these ores in different laboratories by the methods available there; (3) comparison of these results, and selection of one method as a tentative recommended method for the ore; (4) if necessary, further analysis by the same laboratories using the tentative method, as a definite check on its applicability; and (5) recommendation of the method. As to the amount of ore to be prepared in each case, a quantity of 200 to 500 kg, depending on the ore, was considered appropriate by most participants.

30 2. THORIUM ANALYSIS

In the Union of Soviet Socialist Republics small thorium concentrations are determined by colorimetry with the new arsenophenyl-azo compounds suggested by Kusnetzov, reported Professor Alimarin. These reagents are fairly sensitive and give very good results. For intermediate concentrations, morin and quercetin are used, and for high concentrations complexometric titrations with ethylenediaminetetraacetic acid and gravimetry are used. Professor Alimarin considered the latter techniques to be of similar quality and their use only a matter of preference. The same speaker mentioned also the use of phenylsulphine and phenylselenine acids which give precipitates of fixed composition and which he considered to be probably the best method. All these comments apply more or less to pure solutions and, of course, the problem is much more difficult when thorium-containing complex systems are considered. Dr. Rodden reported, answering a question of Dr. Kosta, that mesityl oxide, originally developed by Grimaldi at the United States Geological Survey, has been used with success to extract small thorium concentrations in ores but not for large amounts or pure compounds. In Spain they have used satisfactorily, for pure salts and concentrated solutions of thorium, complexometric titration and spectrophotometry with thorin. They have had difficulties in the use of spectrophotometry for low amounts and they currently use X-ray fluorescence with selenium as an internal standard for 0.01 to 0. 5%. Results by this technique show a standard deviation of 2 to 3.5%. It was the only one which worked satisfactorily with low concentrations. Those mentioned above gave poor agreement when previous separation was necessary.

PART II

TRACE IMPURITY ANALYSIS IN NUCLEAR MATERIALS

A. REPORT TO THE PANEL BY PROFESSOR DR. J. MINCZEWSKI

INTRODUCTION

The analytical chemistry of uranium and thorium was discussed on the basis of Dr. C.J. Rodden1 s lecture (Part I, this report). The present report is devoted to the problems related to methods of determination of trace amounts of impurities. Unfortunately I am not in a position to give a comprehensive lecture but will simply outline some of the main problems and, as we are all quite familiar with the subject, will select only those which seem particularly important. I will try to group them in a more or less logical system which, I hope, will be of help in further discussion. There are of course various possibilities of grouping problems related to methods of determination of trace amounts: for example (1) according to the elements or substances which form the impurities, (2) according to the methods of determination, or (3) according to the difficulties that are characteristic for trace analysis in general. Let me discuss these points in more detail.

ELEMENTS OR SUBSTANCES FORMING THE IMPURITIES

Among these we may distinguish the following important groups: (a) Elements with a high thermal neutron cross-section. In general they constitute the most important impurities in nuclear materials. (b) The so-called rare elements which most frequently present serious problems. For this reason I would rather call them the analytically difficult elements. (c) The common elements. (d) Gaseous impurities (oxygen, hydrogen, nitrogen and others) having an important influence on metal structure and requiring very specialized analytical techniques. (e) All other impurities, for instance water or the content of uranium (VI) in uranium (IV) salts. Group (a), elements with a high neutron cross-section, comprise roughly the following: B, Cd, rare earths, Li, Ag, In, Cs, Hf, Ta, W, Au, Co. Among these it is evident that B, rare earths, Cs, Hf, In, Ta and W are the most difficult to determine and they can therefore be counted among the second group (b). Difficulties may be encountered, such as those discussed later, with separation methods as well as methods of determination. The above elements have to be determined in practically all reactor materials

33 such as metallic uranium, uranium oxides and alloys [1, 2, 3, 4, 5], thorium, its oxides and alloys [6, 7], various construction materials [8, 9, 10, 11] as well as graphite or other moderators [12], cooling water, etc. Each ofthese materials calls for a special separation method since direct methods are in most cases not available. Of course a considerable amount of analytical research work has already been carried out on these elements. Nevertheless B, Hf, Ta, Cs, In, rare earths (in total and each individual element) as well as Zr, Th, Be, and Nb cause considerable difficulties and much work remains to be done. In this connection I should like to draw attention to a third group of elements (c), in particular those found in practically all materials, such as for example Na, K, Mg, Ca, Al, Si, S, P, V, Cu, Mo, Fe, Cr, Mn, Ni and Zn [6, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22]. They still present problems in certain cases, although the analytical chemistry of these well-known and widely-used elements is already well established. Mainly P and Si in trace amounts are difficult to determine. We are not yet familiar enough with the chemistry of heteropoly-acids which is the basis of all determination methods. Also fluorine should be mentioned as one of the elements difficult to determine in analytical chemistry and some difficulties arise with trace amounts of sulphur [23]. The fourth group (d) comprises all impurities in gaseous form. A sub- division in a group of gaseous impurities (mainly H, О and N) in metals such as uranium, various alloys, sodium and others [24, 25] could be made. These gases constitute, in my opinion, one of the most serious problems in trace analysis, firstly because they do not easily react and in most cases only a physical determination is possible, and secondly because it is unknown in which form they are contained in the metal structure. Are they in solution, do they form a compound or are they contained in various forms? As gases have considerable influence on the metal structure this is one of the most important facts to know. Unfortunately the methods usually employed, consisting of melting the metal under high vacuum and measuring either the pressure or the volume, do not guarantee reliable results. Direct methods will have to be found, enabling us to determine the gas atoms directly in the metal structure. One of these direct methods seems to be infra-red spectroscopy under extremely low temperature (near the absolute zero). I know from the literature that this method has been applied in the technique of semi-conductors but unfortunately I do not know whether it has also been used for nuclear materials. A second subgroup would comprise gaseous impurities in gases as far as these gases are of importance in reactor technology, as for instance C02. In my opinion methods of analysis are quite well developed and no particular difficulties should be encountered. The final group (e) comprises all other impurities. Water is of particular importance as its determination is frequently required and may cause considerable problems, as for instance when determining water in fluorides. Problems are also incurred in the determination of trace amounts of uranium (VI) in uranium (IV) salts and in the determination of oxide layers on uranium metal or uranium carbide turnings [26].

34 METHODS OF DETERMINATION OF IMPURITIES IN NUCLEAR MATERIALS

In any analytical determination (of any component of any material to be examined) we may distinguish three main processes: sampling, chemical preparation of the sample and final measurement. At the moment I shall only deal with the latter two processes. Chemical preparation of the sample consists, depending upon the material and the component to be determined, of a series of chemical or physical operations. The purpose of the chemical preparation is normally dissolution of the sample, separation of the component to be determined-from all other components that might interfere with the measurement and masking if required. All this refers, of course, only to the so-called indirect methods.. The dissolution of the sample does not normally present special problems. However, in cases where there is a content of carbides, as for instance in zirconium, tantalum and niobium, dissolution can become extremely difficult. The possibility of using so-called solid solvents (ammonium nitrates, chlo- rides, bromides in mixture) may be taken into consideration. A good separation is the most important aim of all chemical preparations and also the most difficult to obtain. Personally I should even say that developing methods of separation and masking is the most important task of analytical research work today. .In general there are two main methods of separation in trace analysis: either separation of the main constituent of the sample or separation of the impurities. The latter method is more commonly used since in this way impurities can be obtained in a purer form and quantitative results are better.

The following are the most important separation methods used: (a) Precipitation (for instance from homogeneous solutions) or co- precipitation [9, 27, 28], (b) Extraction — either periodically with a separatory funnel or con- tinuously with a chromatographic column [4, 16, 17, 19, 29], (c) Ion exchange [1, 2, 30, 31], (d) Electrolytic separation — usually on the mercury cathode [32], (e) Electrodialysis, and (f) Distillation — for instance after chlorination [3, 33, 34].

All these processes are well known and frequently used in analytical chemistry of nuclear materials. I should say that progress in the use of the extraction method in analysis depends largely upon a more expanded use of this method in the technology of nuclear materials. Extraction seems to me to be one of the most important separation methods and I think that future research should take this direction. Nearly all separation methods and masking processes depend in principle on our knowledge of the basic chemical processes (especially complexing processes) going on in the solution. We therefore appreciate all research work done in this field by physical chemists but I would like to mention that analytical chemists have also done interesting research work on this problem. Table I shows the methods used to determine trace impurities after separation.

35 TABLE I

METHODS FOR TRACE DETERMINATION

Standard Range of deviation Recent Method concentration of single references (ppm) determination Cfr)

Emission spectrography 0.01-1-10 ±50 [4,6,8,9,12,15, 16, 37]

Flame photometry 0.01-1-10 ±25

Atomic absorption 0.1-1 ±25

Colorimetry 0.1-1 ±10 [1,2,3,10,17,18, 19,20,21,23,27 28,38]

Fluorimetry 0.0001-0.01 ± 30-50 [29]

Turbidimetry 0.1-1 ±40

Polarography (classic square wave, hanging drop) 0.001-1 ±20 [22]

Coulometric titration 1-10 ±20

Activation (neutron, fast neutron, y-spectrometry) 0.00001-1-10 ±20 Г7,11.13,39]

Isotopic methods (dilution, exchange) 1-10 ±30 [14,25]

X-ray methods (fluorescence, absorption diffraction) 1-10 ±5, ±30 [26,30,40,41,42, 43,44]

Nuclear magnetic resonance

Electron paramagnetic resonance 0.1 ±10 [45]

Microwave techniques [46]

Mass spectrometry 0.01 [47,48]

SPECIFIC DIFFICULTIES IN TRACE ANALYSIS

At the end of my presentation to the Panel I should like to say a few words on the third problem, i.e. general analytical difficulties which are characteristic for trace analysis: Among these I want to list the following:

36 (a) Special requirements in trace analysis laboratories, such as pure reagents, pure substitutes for glass, special laboratory equipment to ensure chemical asepsis (to avoid contamination of the sample with the common elements), etc., (b) Problems related to sampling, and (c) Problems related to obtaining the required accuracy and precision of analysis. Nuclear materials — standards.

The first point, provision of pure reagents, is not so difficult in the case of nuclear purity (assuming that determinations in nuclear-pure materials are in the ppm range, or on rare occasions in the 10"2 ppm range at the utmost). Only in semi-conductor analysis does this problem become most serious but some trouble may also arise in nuclear analytical chemistry. Graphite electrodes free of boron, for instance, as well as other boron-free reagents are very difficult to obtain and sometimes not available at all, or they are extremely expensive and besides not quite satisfactory. In many cases the purification of reagents is more difficult than the determination itself [34]. The problem of purest uranium compounds will be dealt with later in connection with standardized substances. The problem of pure containers is not so serious in analysis of nuclear materials. Silica ware or in special cases synthetic materials (polythene, Teflon) are in general quite satisfactory. The problem of chemical asepsis becomes more important when elements present in the laboratory air, such as silicon, calcium, magnesium and sodium have to be determined. The use of a very simple type of dry box filled with purified gas proved to be a very good solution. In the determination of Na20 in metallic Nal good results were obtained only when all the apparatus was kept hermetic in a box filled with nitrogen free of water and oxygen at very low pressure. The second problem — sampling — is one of the most important and in my opinion also one of the most serious problems in analytical chemistry. I believe that sampling can be responsible for many variations in results. Sufficient literature is available on sampling and many standards exist. Practically nothing remains to be done but to follow instructions exactly. As far as I can tell from my experience in Poland the problem lies in the practical application of the methods rather than in the methods themselves. In some cases (for example liquid sodium) sampling is still extremely difficult. Difficulties might also arise from the distribution of the impurities in the sample, particularly in metals and powder. The third problem mentioned above is accuracy and precision. May I quote here a few examples supplied to me by Professor Somiya in connection with oyr intercomparison project (see Table II). Certainly this is one of the most difficult determinations in analytical chemistry, although with recent analytical methods the problem should be solved without any particular difficulty. On the other hand I received another example from the same source on the determination of iron in uranium concentrate, carried out at three laboratories in three different countries. There was a considerable dis- crepancy between results (1500 ppm, 3000 ppm and 4700 ppm) although this

37 TABLE IV DETERMINATION OF HAFNIUM IN ZIRCONIUM OXIDE CARRIED OUT AT VARIOUS LABORATORIES

Laboratory Country (ppm)

A 1 0

В 1 60

С 2 15

D 2 30

E 2 25

F 2 10 determination can hardly be considered a trace analysis and although iron is one of the elements easiest to determine. Immediately two questions arise: 1. What accuracy and precision of the measurements are required, and 2. What accuracy can be expected from the methods used? The first question is very difficult to answer because the quality standards give normally only the upper limit of impurities. We say for instance: the boron content of nuclear-pure uranium cannot exceed 0.6 ppm. Therefore it is never quite certain whether (when using a method with an error of say ± 50%) results should not exceed 0.4 (±50%) ppm to be correct or whether 0. 5 ppm (which statistically could mean a value of 0. 75 ppm) could also be considered a correct result. The ¿ame material might thus be accepted by one and refused by another laboratory, although both have used the same method of determination and although there is no systematic error and both figures are statistically correct and derive from the same set of results. This question becomes even more important when determinations such as spectrography are used where we have to rely on one single determination with an average error of say ±50%. Another aspect of this question is what is the accuracy of the results actually required? Is it necessary to know that the content of boron in graphite is exactly 0. 10 ± 0.02 ppm or is it sufficient to know that it is 0. l±0.05ppm. There is always a certain misunderstanding between technologists who need analytical data and the analysts who supply them. The former would like the data in trace analysis to be just as accurate as those obtained when the percentage of impurities is higher. On the other hand analysts can only guarantee an accuracy obtainable with the methods known. The second question concerning the accuracy of the methods used is of course much easier to answer. I have already shown the relevant data on the table and we all know very well that colorimetric results give an average error of ±10%; polarographic results, an error of ± 20%;and spectrographic results, an error of ±50%. But then, how is it possible to obtain variations in results as quoted before in the case of iron in concentrates? What is the reason? In my opinion there are various reasons, for example lack of co-operation

38 TABLE m

TRACE IMPURITY ANALYSIS OF NUCLEAR MATERIALS

I. Elements and substances

A. Elements with high thermal neutron cross-section B, Cd, R^E., Li, Ag, In, Çs, Hf, Та. Co, W, Au B. Analytically difficult elements B, Hf, Ta, R.E., Cs, In, Zr, Th, Be, Nb C. Common elements Na, K, Mg, Ca, Al, Si, P, S, V, Cu, Mo, Fe, Cr, Mn, Ni, Zn D. Elements in gaseous form H, 0, N E. Other impurities

H20, U(VI) in U(IV), U0X in U, and others

II. Methods of determination

A. Chemical preparation 1. Dissolution - solid solvents 2. Separation (main constituent or impurities) a. Precipitation (e.g.homogeneous solution) b. Co-precipitation c. Extraction d. Ion exchange e. Electrolysis f. Electrodialysis g. Distillation (e.g. after or with chlorination) 3. Masking - co-ordination chemistry

B. Methods of measurement 1. Emission spectrography 2. Flame photometry 3. Atomic absorption 4. Colorimetry 5. Fluorimetry 6. Turbidimetry 7. Polarography 8. Coiilometry 9. Activation 10. Isotopic dilution 11. Isotopic exchange 12. X-ray absorption a. Diffraction b. Fluorescence 13. y-ray fluorescence 14. Nuclear magnetic resonance 15. Electron magnetic resonance 16. Microwave spectrometry 17. Mass spectrometry

IQ. Difficulties characteristic for trace analysis in general

A. Special laboratory equipment 1. Chemical asepsis 2. Pure reagents 3. Pure laboratory vessels B. Sampling - the distribution of impurities C. Accuracy, precision, standards, comparison of methods between laboratories, especially as far as accuracy arid precision in trace analysis is concerned. It should always be kept in mind that it is not sufficient to use the better method to obtain better results in trace analysis right away. Each laboratory usually has its own method and in general it is not very well known how this method compares with others. Instructions in the literature are also not quite satisfactory in general. An author des- cribing a new method with which he is already quite familiar usually does not take into account the difficulties an analyst who is just starting to use it might be faced with. Even if he does compare the method he has developed with other methods (which unfortunately happens in relatively few cases) he compares the results with his own results only. Literature hardly ever gives information on results obtained in normal routine laboratories. Another reason for variations in results is the lack of standards in trace analysis. They are especially important for laboratories in developing countries just starting on these problems. In my opinion it would therefore be extremely useful for any chief of laboratory to obtain standard samples of nuclear-pure materials. I know it is an enormous task to prepare these standard samples but there would be considerable profit. I présumé that Dr. Rodden would like to give us some more details on this matter. His paper published in Talanta shows many very interesting and useful aspects of this problem [36]. Table III is a summary of the points I have mentioned. It does not, I am sure, list all points of interest in trace analysis of nuclear materials. However, I should be glad if it proved to be of some help in further discussion.

REFERENCES

[1] YOSHIMORI, T. and TAKEUSCHI, T., "Colorimetric determination of boron with curcumin ; Determi- nation of boron in metallic uranium", Bunseki Kagaku 9 (1960) 354-9. [2] ROSENBERG, A.F., HIBBITS, J. O. and WILLIAMS, R. T. . Determination of cobalt in nuclear reactor materials, USAEC Rep. TID-7606 (1960) 3-13. [3] EBERLE, A.R. and LERNER, M. W., "Determination of boron in beryllium, zirconium, thorium and uranium; Dissolution in bromin-methanol", Analyt. Chem. 32 (1960) 146. [4] FELCHMAN, C. and ELLENBURG, J. Y., "Certain rare earths in purified thorium and uranium preparations ; Chemical isolation and spectrographs determination", Analyt. Chem. 30 (1958) 418. [5] PSZONICKI, L., "Spectrographic cadmium determination in uranium salts by predis"'11ation method" Chem. Analit. (Warsaw) 5 (1960) 261;Ph. D.thesiss Fractional predistillation of spectrographic samples in presence of spectroscopic carriers, Institute of Nuclear Research, Warsaw (1961). [6] NAKAZIMA, T. and FUKUSHIMA, H. , "Spectrographic determination of trace elements in thorium oxide", Bunseki Kagaku 9 (1960) 830-6. [7 ] NAKAI, T., YAGOMA, S., FUJA, S. et al, "Determination of rare elements in thorium and thorium oxide by activation analysis", Nippon Kagaku Zaschi 82 (1961) 197-200. [8] NAKAJIMA, T. and FUKUSHIMA, H., "Spectrographic determinations of traces of various elements in zirconium oxide", Bunseki Kagaku 9 (1960) 81-6. [9] WOOD, D. F. and TURNER, M., "The determination of traces of rare earths in zirconium and its alloys". Analyst 84 (1959) 725. [10] SAIKOVSKI, F.W. and GERHARDT, L. I., "Photometric determination of thorium with aid of Arsenazo in presence of Zr, Ti and rare earths", J. Analyt. Chem. 13 (1958) 274. [11] RICCI, E. and MACKINTOSH, W. D., "Neutron activation method for the determination of traces of cadmium in aluminium", Analyt. Chem. 33(1961) 230.

40 [12] PATERSON, J. E., WHITEHEAD, H. D. and BENNETT, R. К. , Spectrographs analysis of graphite raw material for boron and vanadium, USAEC Rep. Y-810 (1958) 17. [13] JOZEFOWICZ, K. and ADAMSHI, L. , "Determination of impurities in the WWR-S reactor cooling water using gamma-spectroscopy", Nukleonika 5^(1960) 617. [14] SILKER, W. B., "Separation of radioactive zinc from reactor cooling water by an isotope exchange method, Analyt. Chem. 33 (1960) 233. [15] GOLEB, J. A., "Analysis of unirradiated "fissium" alloy by optical emmission spectroscopy", Appl. Spectroscopy 15 (1961) 57-60. [16] HIRAUS, S. RAMADA, H. and SATO, H., "Determination of iron, nickel and copper in metallic uranium by an extraction-graphite spark method; Extraction of iron, nickel and copper with sodium diethyldithiocarbamate in chloroform", Bunseki Kagaku 9 (1960) 168-72. [17] SAITO, K. , ISHII, D. and TAKEUCHI, T., "Determination of trace impurities in uranium; V. Spectrophotometry determination of trace amounts of Cd in uranium metal; Studies on the determination using radioactive cadmium", Bunseki Kagaku 9 (1960) 299,801. [18] ISHII, D., "Determination of trace impurities of uranium; I. Photometric determination of traces of iron in uranium; II. Photometric determination of traces of manganese in uranium", Bunseki Kagaku 9 (1960) 693, 698; CA II (1961) 18441. [19] ASHBROOK, A.W. and RITEEY, G. M., "Spectrophotometric determination of aluminium in uranium metal and its compounds", J.Canad. Chem. 39 (1961) 1109-12. [20] STEVANCEVIC, D.B., "Direct spectrophotometric determination of microgram quantities of copper w in high purity uranium with oxaldihydraxide, Z. anal. Him. 165 (1959) 348. [21] SUZUKI, M., "Determination of trace impurities in uranium ; IV. Spectrophotometric determination of small amounts of copper in uranium metal", Bunseki Kagaku 8 (1959) 395-7. [22] JARMAN, L. and MA TIE, M. "A scheme for rapid analysis of uranium ore leach solutions ; Determi- nation of Al, As, Ca, Cd, Co, Cu, Mg, Ni and Zn in presence of excess iron and manganese", Talanta 9 (1962) 219. [23] GILBERT, T.W. and WHITE, J.C., Determination of trace amounts of sulphur in fluoride salts, USAEC Rep. CF-57-6-89 (1957) 11pp. L24] GULDNER, W.G., "The determination of oxygen, hydrogen, nitrogen and carbon in metals, a review", Talanta 8 (1961) 191. [25] HALEY, H.G. and SVEE, H.J., "The determination of nitrogen in metals by isotope dilution, Analyt. chim. Acta 21 (1959) 289. [26] PLUCHORY, M., "Quantitative X-ray analysis of oxide layers on uranium powders and uranium carbides", Planseeber. Pulvermet. 8(1960) 14. [27] HAYES, T. J., The determination of thorium in uranyl nitrate solutions, U.K.A.E. A. Rep. PGR-41(5). [28] HAYES, T. J., Analytic method for the absorptiometric determination of trace thorium in uranium solutions, U.K. A. E. A. Rep. PGR-2 (5) (1961) 6pp. [29] ATHANAK, V. T. and MAHAJAN, L.M., "Determination of microgram quantities of uranium in thorium", Analyt. chim. Acta 21 (1959) 353.

[30] VAN NIEKERK, J. N. et al., "Trace analysis by combination of ion exchange and X-ray fluorescence; Determination of uranium in sulphate effluents", Analyt. Chem. 33(1961) 213. [31] BOASE, D. G. and FOREMAN, J. K., "The separation of sub-microgram amounts of uranium from milligram amounts of iron, aluminium and plutonium", Talanta 8 (1961) 187. [32] MITCHELL, R. F., "Electrodeposition of Actinide Elements at Tracer Concentrations", Analyt. Chem. 32 (1960) 326. [33] ZIMMERMAN, J. B. and INGLES, J.C., "Isolation of the rare earth elements; A chlorination - volatilization procedure", Analyt. Chem. 32(1960) 241. [34] SPICER, G.S. et al., "The determination of microgram and sub-microgram amounts of boron; II. The separation of boron by distillation and the evaporation of distillates", Analyt. chim. Acta 18 (1958) 523. [35] MINCZEWSKI, J. et al., "Determination of trace amounts of Na,0 in metallic sodium". Acta chim. Acad. Sci. Hung. 28 (1961) 325. [36] RODDEN, C.I., "Standards in the nuclear energy program", Talanta 6 (1960) 3. [37] JOHNSON, A.J. and VEJVODA, E., "Specndchemical determination of trace impurities in plutonium nitrate solutions", Analyt. Chem. 31(1959) 1643.

41 [38] HOSHINO, J., "Separation of zirconium from hafnium and their micro-determination ; Ш. Spectro- photometric determination with quercetin-sulphonate", Nippon Kagaku Zashi 81 (1960) 1273-81. [39] COLEMAN, R. F., "The determination of trace elements by fast-neutron activation analysis", Analyst 86 (1961) 39. [40] WEDEPOHL, К. H., "X-ray fluorescence spectrometry of geochemical samples of eleifients with atomic numbers 25-40", Z. anal. Him. 180_(1961) 246-59. [41] HAKKILA, E. A. and WATERBURY, G.R., "X-ray fluorescence spectrographic determination of impurities and alloying elements in tantalum container materials", Talanta £(1960) 46. [42] BASTON, T. H. and NEFF, С. M., The determination of uranium in dibutyl carbitol by monochromatic X-ray absorption, USAEC Rep. Y-1351 (1961) 13 pp. [43] HAKKILA, E. A., "X-ray absorption edge determination of uranium in complex mixtures", Analyt. Chem. 33(1961) 1012. [44] McCUE, J.C. et al., "X-ray Rayleigh scattering method for determination of uranium in solution", Analyt. Chem. 33(1961) 41. [45] SARACENO, A.J. et al., "An election paramagnetic resonance investigation of vanadium in petroleum oils", Analyt. Chem. 33 (1961) 500. [46] ZEIL, W., "Anwendungsmoglichkeiten der Mikrowellenspectroskopie für die qualitative and quantitative Analyse", Z. anal. Him. 170 (1959) 19. [47] WEBSTER, R. K., "Isotope dilution analysis", Advances in Mass Spectrometry, (WALDRON, J. D., Ed.) Pergamon Press (1959) 103-19. [48] CRAIG, R. D. et al., "Determination of impurities in solids by spark source mass spectrometry", Advances in Mass Spectrometry (WALDRON, J.D., Ed.) Pergamon Press (1959) 136-56.

42 В. COMMENTS BY PROFESSOR DR. I. P. ALIMARIN

I listened with great pleasure to Professor Dr. J. Minczewski's report and it was particularly pleasant for me to see that my thoughts on this matter coincide fully, or almost fully, not only with Professor Minczewski's but, I dm sure, with those of all of you. If fifteen or twenty years ago I had been asked, for instance, if it were possible to determine 10"10 per cent of some- thing, I would have said that this was abnormal, just as Dr. C.J. Rodden said. But we must deal today with problems which remind us of the well- known case of Archimedes and the tyrant of Syracus who doubted the purity of the golden crown. This problem was difficult to solve and yet it was brilliantly solved by Archimedes. I think that we too are now in the position to solve very difficult problems satisfactorily.

What are the requirements at present? I think that I would list three: sensitivity, accuracy and speed. These three are dependent on each other. If we want to obtain high sensitivity and accuracy, the analysis cannot be done quickly. But modern industrial control often requires both accuracy and speed and therefore we must solve this problem. We should also note the evolution of the criteria for purity. Yesterday we spoke of chemical and spectral purity and now we shall speak of mass spectral purity. We have had figures for uranium purity of 99.98 or 99.99%, but those dealing with semi-conductors today, as Professor Minczewski rightly pointed out, have to deal with a purity of not 99. 99 but 99. 9999%, and therefore the problem is more difficult to solve than the problem of zirconium and thorium separation. Professor Minczewski's report also rightly points out the difficult elements: boron, aluminium, calcium, silicon, etc., that is to say, those elements that surround us. I will quote another example — the determination of gold which is a poison for semi-conductors. If you have golden teeth or a golden ring on your finger, you cannot determine this element. Another problem which I know from my own personal experience and which was also pointed out here is the determination of twin elements. Analysts have this problem with zirconium and hafnium. We know cases in atomic industry where zirconium or hafnium were of no use because of the difficulties in distinguishing them. But nevertheless we have solved and tackled this problem also. These examples show that there are many analytical problems and we cannot expect to solve them all here but we can say which have priority and what should be tackled first. We should programme our future work within the framework of the International Atomic Energy Agency. I would like to dwell for a minute on the methods of determination themselves. In the first place, one should mention the yield of the method. It is important for us to know whether all 100% or whether only 10 or 50% are being determined by our method. From the chemical point of view the important question is the form of the ions in the solution. Many elements,like niobium, tantalum, zirconium, etc. easily hydrolize, and if they are in a polymer form, the analyses do not give satisfactory results. That is why the rapporteur was quite right in stressing that it is very important to study

43 the problems of masking and the state of aggregation. This, of course, is known to radiochemists. The second problem is the sensitivity of the registration of the products of the reaction or of some physical phenomena that enable us to speak of the quantity analysed. The problem is that in making a certain measurement with any method (mass spectrometry, coulometry, spectrophotometry, etc.): we receive not only a useful signal but also other variable signals due to the background or noise. Let us quote an example in radio-astronomy for instance. An astronomer with the aid of a radio-locator captures a signal from outer space, but this signal is very small compared with all other noises from the entire space. This is the reason why modern astronomy uses cybernetic devices to accumulate the useful signals. For chemists too, it might be necessary to increase the sensitivity and accuracy with the aid of statistics and cybernetics. In fact, in spectrophotometry and some other methods, we have to measure very small flows of light. Spectrography also has problems connected with the background of the photographic plate.There- fore we could use the principle of signal accumulation and thus greatly increase the signal-to-noise ratio. In this way we could raise the sensitivity and accuracy, I would like to say a few words now about new instrumental methods, as I think we shall have to use them in future work. In my opiniori, mass spectrometry is the most important one. Modern mass spectrometers, for instance the MS-7 (Metropolitan Vickers) in the United Kingdom, make it possible to measure ion currents of 10~18to 10~19A and to determine concentrations of 10-w%. Secondly, we should consider X-ray spectral analysis. This method has a very high sensitivity and enables us to make rapid analyses. The device in Professor Maxwell's laboratory in Canada, for example, makes it possible to determine simultaneously approximately ten samples, with sufficient accuracy. But this X-ray method has another advantage: it makes local X-ray spectral analysis possible, i. e. the determination of the composition of very small surfaces. This is often required in semi-conductor analysis and in the scientific study of uranium. In the Soviet Union Borovsky works in this field. His articles were published in the reports of the Academy of Sciences. There is also a French device for this purpose, the microsonde électronique. I saw it in Moscow at the French exhibition. Instruments of this type are X-ray devices that make it possible to determine contaminations of 10"IS g on the surface of a few square microns. Of third place in importance, I think, is radioactivation analysis. In this case, of course, the sensitivity of the analysis can be raised by the use of short-lived isotopes. Another method which is not very frequently used (it was mentioned in my report at the Geneva Conference)* consists of using monochromatic bunches of neutrons. In this way we can determine some elements against a background of others. There is another possibility to improve activation analysis, i. e. by the use of other particles: deuterons, protons and gamma radiation.

* ALIMARIN, I. P., "Application of radioactive isotopes in chemical analysis", Proc. UN Int. Conf. PUAE 15 (1956) 60-72.

44 In connection with activation analysis I would like to mention that very good results have been obtained by the combination of activation analysis with chromatography or ion exchange. The next method in order of importance is probably emission spectrography. It is an excellent method, but the problems with spectrography are that the percentage of excited atoms in the plasma of the arc is very small, generally a few per cent or at best 10-20%. The sample analysed evaporates very quickly and in this connection it would be desirable that the atoms in the plasma would not dissipate but would remain in the excitation area as would be possible, for instance, by means of a device of the type of a Geissler' s tube. In this way we could expose photoplates a very long time. I think the problem in spectrography is not only to find devices that make possible high dispersion which means high resolution, but also to find new methods of excitation, new plasma sources with stable emission. In this way accuracy and sensitivity could be increased. In this connection I would like to mention the importance of the use of the isotope dilution method not only in mass spectrometry but also in emission spectrography. I should now like to speak about flame photometry and atomic absorption spectrophotometry. Here we have not too high sensitivities. This method helps us in determining the alkaline and alkaline-earth elements and it is a routine method in most laboratories. It seems to me that "light modulators" and photomultipliers with less noise would have to be used to increase the sensitivity and extend the applicability of these methods. One can also increase the sensitivity of instrumental methods of analysis in a chemical way, for instance by special treatment of the photoplates or their treatment, as was done by Ida and Walter Noddack with their special development technique. I can imagine that this method is also known to you because reports were made on the subject in Moscow. The sensitivity is about IO-14 g (abs. ). Ida Noddack stressed that they used this method for the analysis of very pure compounds. I would now like to speak about spectrophotometry which you have mentioned. The sensitivity of this method is determined by the molar coefficient of absorption and it is 100 000 at the best. This corresponds, for example, to approximately 10~7 g/ml of thorium if arsenazo-III is used. In spectrophotometry, when we use a combination of extraction and photometry, the final accuracy and sensitivity will depend on the selectivity of the extraction. In place of extraction, co-precipitation on organic reagents is also used as the first step, but in this case difficulties arise in the determination as many reagents have similar spectra. Only through extraction is it possible to achieve high sensitivity, and one important analytical task, very much stressed in the Soviet Union, is to find proper extractante for this purpose. This will enable us to improve the accuracy and precision. But it is important to consider the phenomena of co-extraction. In the literature there is some mention of the fact that the method of ex-^ traction is better than the method of precipitation because there is no effect of co-extraction corresponding to co-precipitation, but this is not so. I have been working a lot with extraction in theory and in practice and so have my assistants and a number of scientists. We have noticed phenomena of co- extraction connected with the formation of complex compounds. For instance

45 the oxyquinolinates of calcium and scandium (elements which are neighbours in the periodic system) extract under different conditions. However, when calcium and scandium are together in a solution, calcium is extracted partially with scandium. There are many similar examples, and I think that this problem of co-extraction should be further studied together with the role of the extractant, the selection of extractante, etc., as already mentioned. Another possibility of raising the sensitivity is catalysis. Otto Hahn said that the catalyst is the small cause for major consequences. Well, we want to take advantage of the small cause. In using a catalyst it is possible to measure concentrations of the order of 1СГ12 g/1. But we can use the vast sensitivity of the kinetic methods of analysis only in a small number of reactions. In the USSR Yatsimirsky works successfully in this field. Particularly the reactions of thorium and zirconium complex formation with hydrogen peroxide give good results. As is well known, this phenomenon is as follows: some reactions (for instance the oxidation of sodium thiosulphate to sulphate in the presence of hydrogen peroxide) do not go at all or go very slowly, but if molybdenum or zirconium is added the reaction is much quicker. In this case we are again following the principle of signal accumulation. Unfortunately this is not only a characteristic of zirconium but of many other elements. This makes the analysis difficult and an important scientific task is to raise the specificity of such reactions. Another very sensitive method is luminescent and chemi-luminescent analysis. Professor Erday of Hungary, for instance, is devoting much attention to this and we are working with quercetine and other derivatives of phlavon dyes. This method is very sensitive, but unfortunately this small cause has too many consequences so that the method can not always be used because the specificity is often low and other factors, for instance quenching effects, influence the accuracy and sensitivity. If we speak of the électrochemical methods mentioned by Professor Minczewski, I would list in the first place polarography and in particular amalgam polarography. Work on these lines has been done by Kemula in Poland and also in the United States. Vinogradova and Siniakova are working along these lines in my country. These are all hopeful experiments, the results are good, and, no doubt, it will be possible to raise a little the sensitivity limit by using radiofrequency and impulse and square wave polarography. I think the most prospective method for routine analysis is the electrolysis on a mercury drop followed by anodic dissolution. The catalytic wave method in polarography is still not used enough. This method can increase the sensitivity of polarography by one or two orders of magnitude. Let us speak about coulometry. I myself am working in this field but I wonder whether it would be very useful for small amounts. I cannot say anything about the accuracy of measurement in the case of small amounts. I would now like to draw your attention to microchemistry. It seems that microchemistry is also needed in the chemistry of nuclear materials, first for the analysis of micro amounts of uranium minerals dispersed in a matrix. In addition, it enables us to analyse concentrates that have been obtained by the extraction method or, as Professor Minczewski pointed out, by distillation of the basic component. Recently I purchased a book edited

46 by Professor Cheronis of the United States called Sub-microanalysis which encompasses a very broad field. It covers the problems of inorganic, bio- logical and other analyses and contains a number of interesting items. I'want to refer now to the problem of enrichment in analysis. Archimedes said "give me a point of support and I will move the world". Analysts can say: give me a method of enrichment and then I will be able to determine any element you want. Unfortunately, the coefficient of enrichment is still too small and there are, of course, many other difficulties. First we consider electromagnetic enrichment which is good but very expensive. We know also vacuum distillation and zone fusion, although the latter is used very little today. But it is a very good instrument in the hands of analysts as was shown at conferences in Poland, Czechoslovakia and the Federal Republic of Germany. Furthermore I would like to mention the extraction from melts, as for instance the extraction of rare earths from liquid uranium by yttrium which is not soluble in uranium. Perhaps this method is not easy for small laboratories but it should.be further perfected. Now we come to the chemical methods. Some of them are based on the removal of the basic component, in particular carbonyl compound formations work in this way, but they are little used and broad investigations are required in this field. The last thing I would like to talk about is speed. For research purposes we can spend two months or more on the determination of one single element, but if we have to solve practical problems, the question of speed and automation becomes particularly important. Therefore, I think, when speaking of spectro-analysis, we should also speak of quantometers. In my opinion work in the field of automation of spectral analysis with the aid of quantometers should be expanded. I also think that oscillographic polarography is a very interesting method, and in particular the work of Gokhstein on continuous oscillographic control may be of interest. In conclusion I would like to say that some of the questions related to the determination of contaminations in rare metals have been described in the Reports of the Commission of Analytical Chemistry of the Academy of Sciences of the USSR.

47 С. COMMENTS ON ANALYSES OF NUCLEAR MATERIALS IN JAPAN BY PROFESSOR DR. T. SOMIYA

INTRODUCTION

With the starting of the atomic energy programme in Japan, attention was given to the analysis of nuclear materials. The first nuclear reactor, JRR (water boiler), started it's operation in 1957 and the first domestically manufactured metallic uranium became available in 1959. This led to the systematic investigation of the analysis of uranium metal and other nuclear materials in an attempt to establish acceptable sampling and analytical methods. A Subcommittee on Nuclear Fuels was created and attached to the Atomic Energy Commission of Japan to work on the problem. This Subcommittee decided in 1958 to establish a Joint Committee for Uranium Analysis which is currently operating and with which 14 organizations co-operate. The committee has organized intercomparisons of analyses of samples of metallic uranium and other materials prepared as uniformly as possible. The present report gives typical examples of some of these comparisons and also data on the comparison of analyses made by Japanese and foreign laboratories on the same sample.

1. COMPARISON OF RESULTS ON URANIUM CONCENTRATES

Tables I and II give data on the assay of concentrates of uranium and on the determination of impurities in these concentrates as obtained by different laboratories.

TABLE I

ASSAY OF URANIUM IN CONCENTRATES Cpiriparison of Results obtained in Japanese Laboratories

Laboratory

(Data in и,08%) Sample Referee A В С D E F lab.

1 87.52 _ 86.64 86.94

2 - 88.25 - - - 89.07 -

3 - - 84.45 - - 84. 57 -

4 - - - 82.56 - 82.75 -

5 - 85.51 - - - 84.80 -

6 - - - - 92.98 91.83 91.97

7 - - 86.15 - - 86.16 -

48 TABLE II

ASSAY AND DETERMINATION OF IMPURITIES IN URANIUM CONCENTRATES Comparison of Results obtained in Japanese Laboratories

Sample 1 Sample 2 Determination Lab. A Ub. С Lab. В Lab. С

UsO, 82.75 % 82.56 % 87.52 86.64 %

AsjQ, 150 ppm ISO ppm - -

В 2 ppm 3.3 ppm 4.5 ppm 4.5 ppm

Cd 100 ppm 1000 ppm - -

CI 2500 ppm 1200 ppm - -

Co 10 ppm 9.6 ppm -

Fe,Os 4000 ppm 1200 ppm 1.23 % 2.0 *

HgO 4 ppm 0.5 ppm - -

Mo SO ppm 79 ppm - -

NiO 50 ppm 16 ppm - -

P2Os 200 ppm 75 ppm 0.095 <Я> 0.10 % SiO, 400 ppm 565 ppm 0.42 % 3.0 %

so4 90 ppm 100 ppm 0.77 % 1.5 %

ThO, 40 ppm 25 ppm - -

v,o6 160 ppm 36 ppm - - TABLE III (cont.)

DETERMINATION OF IMPURITIES IN URANIUM METAL BY SPECTROPHOTOMETRY Comparison of Results of Japanese Laboratories (Data in ppm)

Laboratory

Element Method A В С D E F G H I J К

Al Oxine,benzene extraction 12 - - - 14 14 27 _ 15.5 13.3

Oxine,benzene extraction (rapid) ------13.2 - - - 12.'9

Oxine,chloroform extraction 13 15.9 ------15.2 15.6

В Dehydration distillation-curcumine 0.12 0.16 - - - - 0.11 - - ' - 0.15

Cd Iodide extraction -dithizone -carbon

tetrachloride <0.02 - - - - <0.1 - - - <0.1 <0.1

Dithizone-chloroform - - - 0.025 <0.1 - <0.1 <0.1 0.24 - -

Cr Diphenylcarbazide 9.0 - 7.6 7.9 7.5 7.9 7.0 8.6 7.8 6.7 9.7

2-Methyl oxine 9.5 '7.9 - - - - - 8.3 - 7.4 7.9

Co Nitroso-R salt 1.6 1.6 1.1 1.3 - 1.2 1.3 - 1.9 1 1.1

Cu Diethyldithiocarbamate 1.7 - 2.1 1.8 1.9 1.6 1.9 1.5 1.9 1.8 1.5

Fe o -Phenanthroline 67 - 71 72 72 75 70 72 79 70 71

Oxine - 71 ------69 TABLE III (cont.)

Laboratory •

Element Method A В С D E F G H 1 J К

Mg Titan yellow 9.5 - - - - 18 11 5.1 15.6 <10

Phtalein complexone - 11.4 - - 10 - - - - - 10.3

Mn Permanganate 4.7 - 3.5 4.3 4.4 4.5 4.7 4.8 4.4 5.7 5.4

Ni Dimethylglyoxime extraction 19.3 19.8 7 17 19 19.1 - 19 18.8 19.3 19.2

Dimethylglyoxime -bromine 18 - 19.8 21 - - 20 19.7 - 19.4 20.2

N Distillation pyrazolone 23 __ ------22 - 20

Distillation -nessler - 25 - 20 25 21 24 - - - 20

P Methylisobutyl ketone extraction

Molybdenum blue 11 - ' - 13 13 12 - • 12 14 21.3 -

Molybdenum blue (direct) - 11 - 12 - - - 12 12 - 12

Si Methyllaobutyl ketone extraction

Molybdenum blue 45 40 42 55 60 40 TABLE IV

IMPURITY ANALYSIS OF URANIUM METAL Comparison of Results of one Japanese and one Foreign Laboratory (Data in ppm)

Determination Foreign Laboratory Japanese laboratory

Ingot 1 •

В 0.1 0.08

Cr 6 8

Cu 20 5.2

Fe 47 28

Mn 4 4.1

Ni 11 20

Si 80 ' 6

Ingot 2

Th 45 550

2. COMPARISON OF RESULTS OF THE DETERMINATION OF IMPURITIES IN URANIUM METAL AND IN SPECTROGRAPHIC ALL Y PURE U3O8

Table III gives results of 11 different Japanese laboratories on the determination of impurities in a common sample of uranium metal by spectrophotometry. Table IV gives also results for uranium metal, but in this case one of the laboratories analysing the common sample is of a foreign country. Finally in Table V the results obtained at a Japanese laboratory for the analysis of five samples of a U3Og spectrographic standard are given, compared with the results reported by the laboratory of origin.

3. GENERAL TRENDS

The examples quoted, and further material collected and published by the Uranium Analysis Committee, Japan, * show that inconsistencies appear more frequently in results of laboratories of different countries than between domestic ones. This general behaviour suggests the necessity of under- taking international comparisons in the field.

See, for example, "A Collection of Analytical Data of Common Samples", supplement to "Deter- mination of Trace Impurities in Uranium Metal". Uranium Analysis Committee, Japan (September 1962).

52 TABLE V

IMPURITY ANALYSIS OF SPECTROGRAPHIC STANDARD U308 * Comparison of Results of one Japanese and one Foreign Laboratory (Data in ppm)

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5

Element

Foreign Japanese Foreign Japanese Foreign Japanese Foreign Japanese Foreign Japanese

Cr 44 52.5 23 . 22 12 12.1 8 7.5 ~ 1 2.9

52(C) 22(C) 10 (C) С u 52,8 21.6 11.4 5(C) 5.9 0.7 53 (P) 13 (P) ~ 2(C) 24 (P) Fe 99.7 55.4 • 99 56 28 25.8 20 16.0 10 6.1 Mn 19.3 24 12 9.7 6 5.4 3 2.7 ~ 0.5 -0.8 100 (C) 50 (C) 22 (C) Ni 98.0 49.2 20; 5 12 (C) 10.8 6(C) 0.7 101 (P) 47 (P) 19 (P)

* Each result is the average of 3 - 5 determinations.

Methods of analysis used

Element Foreign Laboratory Japanese Laboratory

Cr Diphenylcarbazide, colorimetric 2-CH]. Oxine, extraction - colorimetric Diethyldithiocarbamate, colorimetric Cu Oxine, extraction - colorimetric Dithizone extraction, polarographic

Fe O-Phenanthroline, colorimetric Oxine, extraction - colorimetric

Mn Periodate oxidation, colorimetric 2-CHj.Oxine, extraction - colorimetric

Dimethylglyoxime, iodine oxidation, colorimetric Ni Dimethylglyoxime, extraction - colorimetric Dithizone extraction, polarographic D. SUMMARY OF DISCUSSION

(Chairman: Professor Dr. H. Malissa)

1. GENERAL COMMENTS

(i) Techniques

For trace analysis, it seems clear that emission spectroscopy and absorption spectrophotometry are now well known and proved methods that can be recommended for a laboratory interested in the subject on a routine basis. However, one must consider the newer methods which, in a few years' time may be of equal importance, such as X-ray and mass-spectrometric techniques. The latter could possibly be the most important trace analysis technique in the coming years, although the problem of speed of analysis must be solved. There are two conflicting points of view about techniques to be recommended for a new laboratory. When thinking of those to be used for some form of process control laboratory, it is no use choosing interesting or recently developed methods requiring very specialized and expensive equipment and highly specialized staff to operate them. One does not set up a laboratory to determine each element by a different technique, but concentrates on one or two techniques of general utility. This has great advantages in the training of staff and in keeping the cost of equipment low. With only one or two techniques, the staff can learn all the techniques and move readily from one method to another. For process control of uranium, in the United Kingdom the work is carried out by carrier distillation emission spectrography, using slight variations for different elements and by absorption spectrophotometry with or without a simple separation beforehand. Therefore, for a general process control laboratory for uranium analysis, Dr. F.J. Woodman would recommend emission and absorption spectrometry. On the other hand, from the point of view of research work with future deve- lopments in mind, for example, to provide alloy analyses etc., this would not be enough. It would be advantageous for a developing laboratory, if funds and manpower were available, to keep in touch with the more modern methods such as mass spectrometry to have the experience available when these methods become more generally useful. Professor Dr. H. Malissa reported on the advantages of the microprobe (microsonde électronique), a combination of the electron microscope and X-ray fluorescent analysis, already mentioned by Professor Dr. I. P. Alimarin. These are that it is capable of analysing an area of 1 /um2 both qualitatively and quantitatively and capable of being scanned. At the present time, elements up to sodium cannot be determined, so that important elements such as carbon are excluded. With the importance of metallurgy and metallurgical specimen analysis, the advantages of such an instrument are obvious and several of the Panel members reported their interest for analysis of in- clusions, phase and solid solutions, mixtures, of carbides, nitrides, diffusion zones, etc.

55 Dr. M. T. Keiley reported another technique similar to this. This is based on the use of a laser, the light beam from which is focussed through a microscope onto the surface of the specimen. The light intensity is such that the surface vaporizes and an arc may be struck between two approp- riately placed electrodes so arranged that an arc is produced only when vapour is present. The elements are determined spectroscopically. The advantages are also that a very small area may be excited (although larger than with the microprobe), the whole spectrum may be covered at once, vacuum operation is not required and it is much cheaper than the microprobe. This technique could be used on active samples so long as a handling technique is available. With the microprobe, the radiation from an active sample could interfere with the determination of fluorescent X-rays.

(ii) Speed

There was some discussion of the importance of the speed of analysis and the necessity of sacrificing accuracy to obtain rapid results which must be supplied to the people carrying out production. Dr. C. J. Rodden said that it may be necessary to have results with errors of say 30% because of the necessity of rapid results to control production. After all, in for instance the case of traces of boron (a few tenths ppm), it may be more important to have the result quickly than with high accuracy. An error of 50% may not be important to the production but a delay could be. This may leave the analyst uneasy, but it is his job to supply the best he can in the time available. In the early days of uranium production, each element was determined separately but this was too time consuming and it was necessary to sacrifice accuracy for speed by using relatively crude spectrographic methods. If the loss of accuracy is not acceptable, however, the analyst must say that he cannot do the job in time and the engineer must wait for the results, though it will be the task of the analyst to develop methods to satisfy the demands for both speed and accuracy. Dr. Woodman mentioned that in some cases, for example when a reactor loading of uranium is analysed in a series of batches, a poorer precision can be tolerated because only the total sum of the analysis is considered for the loading with a re- sultant improvement in precision because of the number of determinations involved.

Dr. R. F. Cellini mentioned that speed and economics are also inter- related and both are important. In Spain approximately 500 000 determinations are made a year under a programme of geological prospection. In this case the use of a quantometer had solved their problems, supplying results of sufficient accuracy quickly and because of the speed, economically. In spite of the greater capital cost of the quantometer, the cost per analysis was now 0.01 of that for spectrophotometry. The same general considerations apply to other auxiliary analytical activities as, for instance, when a large number of samples must be analysed in connection with a chemical engi- neering process in development.

56 2. INTERCOMPARISON OF RESULTS AND STANDARDIZATION OF METHODS

(i) General

From the data from Japanese laboratories supplied by Professor Dr. T. Somiya, Professor Dr. J. Minczewski pointed out that such wide variations of results in trace analysis are a common experience in many other laboratories. It was important, therefore, to obtain better results and one step on the way to achieve this is by the use of "standards". For a new laboratory starting work on this subject, it would be extremely valuable to have available some substance with exactly determined trace concentrations, but it is extremely difficult to obtain such a material relevant to the nuclear industry laboratory. Dr. Rodden stated that the preparation of such "standards" is extremely difficult. It is, for example, practically impossible to take pure uranium metal and add known concentrations of impurities. (It is very desirable to have a standard metal because this is the ultimate end product in many cases. ) This has been tried on simpler metals than uranium with only unsatisfactory results. An alternative is to take a piece of uranium metal, as it is fabricated, with the impurities normally present, and see if it is homogeneous. This is always necessary because of segregation on solidi- fication of the metal. The ingot must be sliced top and bottom until the slices analyse the same. Then the outside must also be removed to obtain a central piece of metal that should be homogeneous. To control homogeneity, some typical element such as iron can be chosen, but of course to be absolutely sure that all elements are uniformly distributed is very very difficult. The material should also be used in bars or sections of solid metal, because attempts to take turnings or chips and ballmill them are unsatisfactory as was shown with thorium. Appreciable increases in the oxygen and nitrogen content were detected and the samples were considered useless as "standards". Similar effects are to be expected in uranium. Another approach is to take the purest uranium oxide powder available, place it in a large dish and determine how much liquid is required to wet the solid. Then an aqueous solution is added containing all the impurities to be added and the whole evaporated to dryness and ignited. Here again, there are doubts of homogeneity and segregation, together with possible loss of elements on ignition. Boron is bad in this respect and can be lost, although addition of ammonia or mannitol prevents this. This seems the best approach to a solid standard or better-called "analysed sample" but it is not perfect. For example, such a sample was prepared to contain 1 ppm chromium and 2 ppm copper but the Japanese results were 2.9 ppm for chromium and 0.7 for copper. Even worse was nickel of which 6 ppm were added, but only 0.7 ppm was found in Japan. If lack of homogeneity was the cause or part of the cause of these discrepancies, then the use of different techniques may accentuate the trouble, as for instance a mass spectroscopist may take only 10 mg, the emission spectroscopist 100 mg and the chemist 1 mg so that the probabilities of obtaining a homogeneous sample vary.

57 (ii) International Atomic Energy Agency's (IAEA) intercomparison project

The Panel examined the work already done by the IAEA Laboratory in international comparisons of analytical techniques, namely a study on the accuracy and precision of some techniques when applied routinely at the trace level. This work consisted in the analysis of copper, mercury, manganese and chromium from diluted nitric acid solutions by spectrography, spectrophotometry, polarography and activation analysis. The Panel considered that the project should continue and discussed the next step of the comparison. It was agreed that the determination of important iihpurities in uranium would be an appropriate subject.

(a) System to be used

In view of the difficulties of the preparation of an "analysed sample" of a solid, it was agreed as first step that a solution of uranyl nitrate should be used because there is no problem of homogeneity. Two samples should be used, one prepared from the purest uranium compound available and the other the same solution but containing known additions (in the ppm range) of the nine elements given below for the oxide case. This would not be a sample stable for many years but would allow comparison of methods of different laboratories and the possible unification of methods. After this, an "analysed sample" of oxide followed by one of metal would be the working order to aim at. It was pointed out that at any time a guaranteed homogeneous sample of a production product would be very valuable.

(b) Elements to be considered

It was agreed that "trace impurities" in this connection was misleading and that "impurities" was what was meant, whether boron at 0.1 ppm or carbon at 5000 ppm. The question of what elements should be included in the "analysed sample" was-discussed at some length. It was agreed that they should be commonly occurring and be of practical interest to the chemist or metallurgist and should not contain those of purely academic interest only. Also the number should not be large. For an oxide sample B, Cr, Co, Fe, Ni, Mo, Mn, Cd and Cu were agreed and for a metal sample the same with the addition of C, N and O. The elements Al, Ag, P, Si, S, Li, rare earths, Zr, Nb and Ti were discussed but it was agreed not to include these in the first experiment.

A question was raised as to whether, in the comparison, methods or techniques should be specified. There was general agreement that they should not be. It was better to obtain results by a variety of methods so that a better comparison could be made. Analysis should not be limited to, for instance, spectroscopic methods, but should also include, for example, polarography and colorimetry and where applicable mass spectrometry.

58 In addition, it would be useful to obtain data on separation methods such as precipitation, ion exchange, chromatography. There is a danger, however, that if every laboratory does the analysis as it likes, there will be a large number of results by many different methods making it very difficult to decide on the standard one. Alternatively, with say uranium oxide, if only the spectroscopic method is reported, then this must become the standard method. Another approach is to allow free choice, compare values and then from the most promising methods make a further comparison of a limited number of selected methods. Dr. Rodden commented on the difficulty of getting laboratories to use a common method; they like to use the one they have most experience with. Even on a national scale, for instance for the determination of uranium, some laboratories will use Jones reductors, others lead reductors with titration by dichromate or eerie sulphate, but he saw no problem in having two or three accepted methods, but they should be the same general procedure or technique. It would not be satisfactory to have a determination by colorimetry and one by say X-ray fluorescence. Professor Alimarin commented on the preparation of manganese standards in the Soviet Union. Official methods are recommended but each laboratory has an alternative method of its choice. He thought that obligatory methods could be recommended but each laboratory could be allowed to submit results based on other methods. Then with this data, a committee could consider the results and allow each laboratory to uphold the method it feels is best. If results are given only on obligatory methods, there may be mistakes in establishing contents as a result of systematic errors.

(d) Containers

The containers for the samples for the international comparison were more or less limited to polythene because of the boron problem with glass. Polytetrafluoroethylene (PTFE) might be an alternative, but was not possible at the present time. There may be some absorption on polythene but it was felt that this would be low and not affect results after a relatively short storage time. There appears to have been difficulty with polythene containers for kerosene tributyl phosphate (TBP) solutions of uranium, when in a relatively short time there were detectable changes in concentration. This did not seem relevant in this case. In certain cases, however, inorganic ions were believed to be difficult but there seemed to be no alternative in this case. One suggestion raised to test the extent of absorption was to use, in separate containers, radioactive tracers for the principal impurities and check the adsorption in this way.

PART III

ANALYTICAL CHEMISTRY OF IRRADIATED NUCLEAR FUEL PROCESSING

A. REPORT TO THE PANEL BY DR. F. J. WOODMAN

INTRODUCTION

The first purpose of this survey is to provide a critical review of the analytical methods and techniques necessary and available to permit operational control of irradiated nuclear fuel processing plants. The second object is to attempt to indicate what are likely to be the most necessary and profitable lines of future analytical methods and technique development in support of fuel processing facilities. When it is remembered that there are some 300 reactors operating or scheduled to operate within the next three years and that these are based on a variety of fuel systems using uranium, thorium, and plutonium separately or in admixture and in the form of a metal, an alloy, or an oxide, carbide or sulphate, it will be appreciated that the task of discussing the analytical chemistry of re-processing is truly a formidable one. However, the picture can perhaps be logically simplified by concentrating on the 50 nuclear power stations and prototype stations operating or planned to operate in the near future in 11 different countries (see, for example, [1 ]). Con- sidering these we find that on the basis of electrical output some 66%operate on uranium metal fuel and some 29% on uranium dioxide fuel; the remaining .5% use uranium alloys or carbides. For the present purpose, therefore, it will not be unreasonable to concentrate on analytical support for the operation of plants designed to handle uranium metal and oxide fuels from reactors providing 95% of the world's nuclear power over the next few years. At a nuclear fuel re-processing plant the analyst has, of course, other commitments besides the provision of a service in support of plant operation. He has, for example, to provide a comprehensive analytical service for health and safety purposes including urinalysis and environmental contamination survey analyses; such work, which is essential to the safe and efficient operation of the plant, may amount to 10% or more of the total analytical effort. Nevertheless it is not proposed to consider it in this survey but to concentrate on the analytical commitments closely associated with the actual re-processing operations. Similarly, it is not proposed to deal with the analysis of raw materials or the analysis of final products such as uranyl nitrate, plutonium metal or oxide since such discussion might well overlap with other contributors. Because of the existence of various processes for handling irradiated nuclear fuels based on different types of solvent extraction plant(e.g. counter current columns, mixer-settlers) and the range of solvents (dibutoxydiethyl ether, tributyl phosphate (TBP), hexone) and the choice of techniques (solvent

61 extraction, ion exchange, precipitation), it would seem most appropriate in attempting a reasonably comprehensive review of this sort to consider the analytical requirements under the headings of plutonium, uranium, fission products, etc. rather than in terms of a generalized flow sheet. Since uranium metal and oxide fuels dissolve directly in nitric acid without special additions (such as hydrofluoric acid, hydrochloric acid) irradiated fuel dissolver solutions will be regarded as straight nitrate systems. In discussing the relative merits of different methods critically it must be borne in mind that there are a number of competing factors and that performance characteristics such as precision, accuracy, speed, operational cheapness, radiological safety and general ruggedness all have to be taken into account in assessing the suitability of a particular method in a particular application; this naturally makes firm recommendations on the best method very difficult.

THE DETERMINATION OF PLUTONIUM

In an irradiated fuel processing plant determinations of plutonium may be required at a range of concentrations varying from say 100dpm/ml in raffinates and effluents through the 50-200¿ig/ml level in fuel element dissolver solutions to the 10-300 mg/ml level in the purer concentrates approaching final metal or oxide preparation.

Raffinates and effluents

In concentrations up to the ng/ml region, plutonium is invariably determined by alpha counting with preliminary separation, if necessary. The procedures have been frequently described [2, 3, 4] and it is not proposed to go into detail here. The Hanford Technical Manual [4] contains an excellent discussion on the technique, for example. Broadly, four cases present themselves: (a) Straight evaporation from aqueous nitric acid onto a stainless steel tray followed by heating to dull redness and counting; non-volatile solids must be limited to about 0.1 mg in this case; (b) Co-precipitation with lanthanum fluoride from aqueous nitric acid solutions after reduction with hydroxylamine to the (III) state followed by traying and counting; (c) Direct evaporation from solvent solutions by dropwise addition to the centre of a tray heated at the periphery followed by flaming and counting; and (d) Co-precipitation with lanthanum fluoride in the presence of ammonium sulphate followed by washing, traying and counting; this is useful for traces of plutonium (100 dpm/ml) in concentrated uranium solutions, the ammonium sulphate helping to achieve precipitates of low uranium content by forming a soluble uranium complex. Clearly none of these procedures is specific for plutonium and in cases of doubt alpha pulse amplitude analysis has to be resorted to on specially prepared trays followed, if necessary, by chemical separation and determination of the alien alpha emitters to permit corrections to be made. In

62 this connection, the use of thenoyltrifluoracetone (TTA) in benzene or xylene as an extractant permits the separation of plutonium (previously conditioned to the (IV) state) from americium, curium, neptunium and an excess of uranium. The TTA-solvent phase can be directly evaporated, ignited and counted [4].

Dissolver solutions

The estimation of plutonium in dissolver solutions being fed to a processing plant is clearly of great importance from the point of view of accountancy. Good precision and accuracy are required in this analysis although the determination has to be carried out in the presence of several thousand times as much uranium and in the presence of a high level of associated beta-gamma active fission products. Four main approaches to the problem have been made: (i) Alpha counting with corrections for uranium alpha contributions and for americium-curium alpha contributions; (ii) Chemical separation of plutonium followed by absorptiometric or titrimetric determination; (iii) Coulometric determination; and (iv) Mass spectrometric determination using the isotope dilution method.

(i) Alpha counting

This, the earliest method, and one which still has much merit provided the irradiation level of the feed fuel elements remains relatively constant, needs little description. A small aliquot of the dissolver solutionis evaporated on a platinum or stainless steel counting tray and alpha is counted in a conventional proportional alpha-counter adjusted to minimize errors re- sulting from the beta-gamma background. Corrections to the observed alpha count for uranium and americium-241 and curium-242 are essential so that extra analyses are necessary for these elements. The frequency of these corrections is dependent upon the constancy of the feed concentration of uranium and on the constancy of the irradiation level of the fuel; since the order of the uranium correction is only a few per cent, relatively infrequent analyses may be sufficient, but for all but fairly low irradiation levels the americium-curium correction is appreciable and must be frequently made, although recourse may be had to the bulking of dissolver samples over periods of time to reduce'the frequency, if irradiation levels do not fluctuate to any great extent. By the use of standard samples of plutonium the method can be made free of bias. As regards precision, the generally accepted figure is ± 5%(Зет). If the irradiation levels of the feed fuel elements show much variation frequent isotopic analysis of this plutonium is essential to permit the evaluation of the specific activity, which in turn will enable the results of the alpha counting to be translated into units of mass. The isotopic analysis frequency can again only be decided from a knowledge of irradiation history variation but in any case will involve plutonium-238 determination by alpha kick-sorting and plutonium-240 and plutonium-242 determination by mass spectrometry. The alpha-counting method is described in various papers, including the Hanford Analytical Technical Manual [4] and the Windscale analytical

63 method [5] . The americium-curium determination in dissolver solutions to serve as a correction can be carried out by TBP and TTA extraction [4] or by trioctylphosphine oxide (TOPO) extraction [6]. Summarizing, the alpha-counting method is relatively simple and straight- forward and acceptable in terms of precision, accuracy and operational cheapness, provided the irradiation level of the feed elements is reasonably constant with a consequent minimization of the necessary ancillary esti- mations of specific activity and americium-curium. If however a range of fuels of varying irradiation history have to be processed the alpha counting method becomes less satisfactory and operationally expensive because of the frequent need for supporting alpha kick-sorting, mass spectrometry and americium-curium determinations. Generally this method requires the least remote control handling.

(11) Chemical methods

Several chemical methods have been described which get round some of the difficulties associated with the alpha-counting method but these methods in their turn introduce other problems. In the first place chemical methods tend to use larger samples and consequently fully remote handling is essential, at least in the earlier analytical stages; secondly, when relatively impure solutions are involved a preliminary separation becomes necessary. This can be achieved by extraction of the plutonium from 2M to 4M nitric acid into a solution of Hyamine 1622 in benzene. Hyamine 1622 is essentially £-di-isobutyl phenoxyethoxyethyl-, dimethyl-, benzyl-, ammonium chloride and its behaviour as an extractant has been described [7] . Plutonium after conditioning to (IV) valency is extracted as the anionic species Pu(N03)s~ with decontamination factors of 102 for uranium and 105 for fission products. After separation the plutonium at the 100 ng level can be determined ab- sorptiometrically using the coloured thoronol complex with a precision (3a) of about ±4% 18]. Considerably better precision can be achieved by sub- stituting a titration finish [9]; in this very useful procedure an excess of ethylenediaminetetraacetic acid (EDTA) is added to form plutonium; EDTA complexes and the uncomplexed EDTA are then determined by photometric titration with zinc chloride using dithizone as an indicator. With this technique a precision (3a) of ±1.2% is possible. Because of the good decontamination from fission products in the preliminary separation all subsequent stages of the analysis can be done under semi-remote conditions. At high irradiation levels neptunium-237 will interfere and must be corrected for. The method has the advantages of good precision and accuracy and uses only relatively cheap and readily available apparatus; two operators can carry out eight to ten determinations per day.

(Hi) Coulometric methods

With the development in the last five years of improved electronic instruments for coulometry [10, 11] attention has been directed to the determination of plutonium by this procedure. One of the earlier methods reported [12] described the generation of the ferrous ion titrant electrolytically at constant current; the plutonium adjusted to the (VI) state by chemical pre-

64 treatment was then titrated to an accurate end point and no correction for iron was necessary. The long and rather complex chemical pre-treatment and the need for titration to an exact end point militated however against the method finding wide favour despite the advantages of reasonably good precision and freedom from ion interference. The construction and success- ful operation of controlled potential.coulometers paved the way for a fresh attack on the problem and resulted in the development of a procedure [13] involving separation of the plutonium and lanthanum fluoride followed by coulometric titration of 50-150^g with a precision (3a) of ±0.9%. More recently still [14] further development along similar lines has resulted in the provision of a method for several types of dissolver solution which gives no bias and a precision (3a) of ±3%. In this procedure the plutonium is adsorbed as the anionic complex in 8M HN03 onto an anion-exchange resin and after washing is eluted with dilute acid and determined using the controlled potential coulometer. Summarizing, coulometric methods have good precision, are readily adapted to remote control operation, the equipment is dependable arid not too expensive and interference from other elements, if present, can be controlled or eliminated by a relatively simple separation procedure.

(iv) Isotope dilution method

Recently a method of good precision and accuracy has been developed [15, 16] utilizing the well-known isotope dilution principle.. Plutonium-242 tracer is added to the dissolver solution and after equilibration the plutonium is adsorbed on an anion-exchange resin. After elution from the resin the isotopic composition of the plutonium is determined in a surface ionization mass spectrometer and the plutonium çoncentration present in the sample is calculated. This technique gives a precision (3a) of about 2.5% and a biàs less than 0.1%. The preliminary treatment is not critic ally dependent on valency conditioning as is the case with chemical methods. It provides an excellent referee method but naturally calls for extremely expensive equipment and expert mass spectrometer operators; despite these objections, because most nuclear fuel processing plants must have such equipment and expertize for other purposes, it may well serve as a semi-routine method at least. A further advantage is that ura'nium can be determined on the same sample by a closely analogous technique using uranium-233 as tracer.

Concentrates and pure products . . , -

At the. milligram level and above, many other methods become available to the analyst in addition to some of the procédures already mentionéd for dissolver solutions, such as coulometry [13,17]¿ Of the more useful methods [18, 19, 20] we may first consider absorptiometry. Here the plutonium is reduced to the trivalent state with hydroxylamine and this absorbency measured at 565nm. The more recent referènces quoted utilize the very precise technique of differential spectrophotometry and attain a precision (3a) of ±0.3% on solutions at the 5 mg/ml level with zero bias and ±0. 2%

65 on metal. The method is convenient and does not call for equipment not usually available in a normally equipped analytical laboratory; on the other hand, the preparation of the appropriate range of standards can be an exact- ing and somewhat tedious task. Once established, operators can analyse five samples per day. A complexometric titration procedure has been described [21] in which excess EDTA is added to a chloride solution and the excess titrated with thorium nitrate using Alizarin Red S/methylene blue as indicator. Iron, titanium, thorium, gallium and vanadium may interfere however and there is therefore likely to be a small variable bias unless corrections are applied. A number of methods using redox titrimetry have been advocated. One of the earliest [22] involving reduction to the trivalent state with titanous chloride followed by oxidation of excess titanous chloride and oxidation of plutonium (III) to (IV) with eerie sulphate; at the 5-mg level a precision (3a) of about ±0.5% was obtained. Another early technique [23] using zinc amalgam as the reducing agent followed by potentiometric titration with eerie sulphate gave similar precision. A further variation was the use of the ferrous o-phenanthroline as indicator in place of the potentiometric finish [24] giving a precision of about 0. 75% at the 2. 5-mg level. More recently [25] by using a photometric end point this method has been improved to give ±0. 21% precision (3a). All these methods have the drawback of requiring iron corrections, thus calling for separate determinations and generally are not really specific. Other methods utilizing oxidation-reduction principles include one using the silver reductor prior to eerie sulphate titration [26] which has the virtue of excluding interference from uranium and a somewhat different approach in which the plutonium is oxidized to the (VI) state with argentic oxide and titrated to the (IV) state with ferrous iron using an amperometric end point [27]. Thé latter procedure can give a precision (3a) of about ± 0.15% at the 20-mg level and has the merit of being free of interference from both iron and uranium although chromium and manganese would interfere; in our hands at the 100-mg level the precision could not be maintained over a period, however, and over-all precision was about 0.4%. The reduction stage can also be accomplished with chromous chloride [28] followed by back titration with eerie sulphate; this method gives a precision of about 1.2% (3a) at the 20-mg level but requires an iron correction. Finally in this category we have the very useful procedure in which the plutonium is oxidized to the (VI) state with perchloric acid, reduced to the (IV) state with ferrous iron in excess and this excess titrated potentiometri- cally with eerie sulphate [29] . Iron and uranium do not interfere and the very good precision of about 0.06% (3a) is obtained at the 400-500-mglevel. Using an automatic burette some 15 determinations can be done a day and it is therefore probably faster than the differential spectrophotometric method. The analysis of plutonium in solution in the 5-250mg/ml range by X-ray fluorescence has been described 130]. Using yttrium as internal standard a precision (3a) of about 4% has been reported; the method has the advantages usually associated with the X-ray fluorescence technique, namely that it is independent of the isotopic constitution of the plutonium and reasonably free from interferences from other cations and anions. Other advantages of the

66 technique are its applicability to sludges and solids generally by using an aluminium hydroxide-magnesium oxide matrix but here particle size uni- formity becomes important and sample grinding complications arise. For liquids certainly the method is fast and has definite attractions. A disadvantage is the relatively high capital cost of X-ray fluorescence equipment. Unspecific but precise methods of analysing plutonium solutions are provided by X-ray absorption [4] and y-ray absorption [4]; for relatively pure solutions under routine control conditions the bias can be kept to 0. 3% and the precision (3a) about ±2%. If desired a preliminary separation stage can be applied when other solutes cause appreciable absorption. Probably the y-ray absorption technique is the more convenient since the source (usually encapsulated americium-241) is smaller'and requires no maintenance compared with the conventional X-ray tube source. Perhaps these techniques, particularly the y-absorptiometer, are more useful as "in-line" methods rather than laboratory methods. Finally, mention must be made of the gravimetric determination of plutonium as the dioxide [31]. The plutonium salt solution is fumed with sulphuric acid and the sulphate ignited at 1250°C to a non-hygroscopic stoichiometric dioxide. The bias is less than 0.05% and the precision(3a) ±0. 2%. The method is useful for standardizing pure plutonium solutions.

THE DETERMINATION OF URANIUM

Determinations of uranium are required at a range of concentrations from say the /ug/ml level raffinates and effluents through the 100 mg/ml level in fuel element dissolver solutions to pure depleted uranium nitrate solutions and uranium trioxide.

Raffinates and effluents

In concentrations of the order 0.01 to 10 Mg/ml uranium is invariably determined fluorimetrically by measuring the fluorescence of a fused sodium fluoride base melt under ultra-violet light excitation. The method and its numerous variations have been frequently described, a particularly good discussion being that included in the Hanford Analytical Technical Manual [4]. The principal variations are: (i) The inclusion of a preliminary separation procedure to isolate uranium from excessive amounts of such well-known quenching agents iron, chromium, and nickel; extractante advocated have included diethyl ether, ethyl acetate, and hexone; for sub-microgram levels of uranium in the presence of milligrams of iron, plutonium and aluminium an anion-exchange procedure is very useful [32]. (ii) The composition of the fluoride flux which has included sodium and lithium fluorides and sodium carbonate or bicarbonate. (iii) The procedure for fusion which has included gas burners, electric furnaces, and induction furnaces. (iv) The type of fluorimeter used for the final measurement - reflection or transmission. It is extremely difficult to make a clear-cut recommendation as to the best procedure for general use; it is accepted that the extra time and trouble

67 expended in preliminary separation is justified in the presence of high concentrations of quenchers (as opposed to correction by internal standard additions); it is accepted that carbonate fluxes are more readily fused than straight fluoride fluxes; it is accepted that the addition of a few per cent of lithium fluoride to the sodium fluoride assist in subsequent removal of •the melt from the platinum (which facilitates a separate measurement in a .tray of constant background) and reduces the tendency for melt cracking. jWhàt is extremely important is that whatever procedure is adopted all the many variables must be strictly controlled and the same technique rigidly followed each time.; only then с an the best precision — abouti 25% (3c) at the 0. ¿-/и g "level - be secured. Well-tried and tested versions are given in references [4, 33, 34J. We believe that in the procedure given in reference [33J the use of sodium bicarbonate is advantageous in producing a carbon dioxide atmosphere during melting which probably reduces platinum dissolution, and thus subsequent quenching effects due to platinum are eliminated. Another well-known method of value for the determination of uranium around the 50-мg level depends upon the formation of a yellow complex with the thiocyariate ion; iron interference.is overcome with stannous chloride whilst chromium only interferes slightly (1 mg Cr^lOjjg U); plutonium interferes if present at levels of the same order as the uranium. Traces of organic matter if present, e.g. entrained or dissolved solvent, must be removed by preliminary ignition. The method has a limit of detection of about lOjug and a precision (3a) at the 50-^g level of about 10%. '•••• Polarography has been successfully used for traces of uranium in the presence of an excess of plutonium down to the microgram level; a perchloric acid-hydrazine base is used with a commercial AC polarograph [42]. At the milligram level a precision (3a) of about±5% is possible.

Dissolyer solutions

Sometimes it is possible to obtain an indirect measure of the uranium content of dissolver solutions by density measurements with suitable corrections being applied for nitric acid and other minor constituents if present; a favoured procedure for density is the well-known falling drop method [4] because it readily lends itself to remote control and calls for only a very small sample. An adaptation of Hare's classical balancing column method is also applicable to remote control conditions. Since the uranium concentration in the dissolver solution is an important accountancy figure the density method may not be sufficiently accurate and precise, especially if the plant is subject to fluctuations in general operating performance.' In these circumstances actual uranium determination may be performed. In selecting the procedure it must, of course, be borne in mind that the sample will be highly bëta-gamma active and the technique adopted must be readily used under remote control conditions. Of the multitude of available methods for uranium, those which have been successfully reported for use with dissolver solutions can be roughly classified as follows: (i) - Redox titrimetry; (ii) Coulometry;

68 (iii) X-ray absorption after separation; (iv) Mass spectrometric determination using isotope dilution.

(i) Redux titrimetry

In this method [35] after removal of nitrate the uranium is reduced to the (IV) state with aluminium metal and is then titrated to uranium (VI) with standard eerie sulphate solution. The precision (3cr) is ±0.7% and the preferred concentration range in the sample aliquot, 20-30 mg. It has the advantage of being readily operated on a remote control basis and of requiring no special expensive apparatus or equipment.

(ii) Oculometry

The controlled potential coulometers previously mentioned underplutoni- um analysis were earlier used for uranium under fully active conditions, only the titration cell itself being placed in the shielded facility [36]. A precision (3a) of about±2%was achieved. Controlled potential coulometry offers a fast, precise method readily usable under fully remote operation. Perhaps the only drawback is the need to construct the equipment which, so far as the author is aware, is not available commercially.

(iii) X-ray absorption

After an appropriate solvent extraction procedure with TBP the measurement of uranium in dissolver solutions is practicable by the X-ray absorption method mentioned previously [4] . This is a reasonably precise method but calls for somewhat expensive and specialized equipment. The final measurement is made directly on the solvent containing the uranium.

(iv) Isotope dilution

Mass spectrometry using the well-known isotope dilution principle affords a very precise and accurate method of determining uranium in dissolver solutions. It can readily be combined with the determination of plutonium by the same technique [16]. Uranium-233 tracer is added and after equilibration the isotopic composition is determined in a surface ionization mass spectrometer. The bias is less than 0.1% and the precision (3a) about 2.5%. This is an excellent method, especially when combined with the plutonium determination, but has the disadvantage of cailing for extremely expensive equipment and expert mass spectrometer operators.

Concentrates and pure products

Once we reach the milligram level of uranium in relatively pure solutions there is a very wide range of methods available and it would seem inappropriate to consider them in much detail here since they have been frequently discussed critically before [cf. 37, 38, 39] . When pure products are being handled perhaps pride of place must go to the classical gravimetric method in which sample aliquots containing upwards of 50 mg are

69 precipitated as ammonium diuranate and the precipitate after washing is

ignited at 900°С and weighed as U3Og. At concentrations above 10 mg/ml the X-ray absorption or у-ray absorption technique provides a convenient but unspecific method of measurement [4]. X-ray fluorescence methods are also quick and convenient but more specific and can be used with success down to about 50 ng of uranium in TBP for example with a precision (3

THE DETERMINATION OF FISSION PRODUCTS

The effectiveness of decontamination from fission products needs to be measured through any nuclear fuel re-processing plant. Usually gross beta or gross gamma measurements will be sufficient for this purpose but in solvent extraction processes some fission products, notably ruthenium, niobium and zirconium, may tend to follow the solvent stream under some conditions and must be separately measured. In effluents and washes it may also be important to measure specific radionuclides for control purposes. Direct gross beta and gamma measurements present no special problem using conventional counting equipment and techniques apart from the vexed question of the appropriate standard to use. Since the energy spectrum of the mixed fission products is not precisely known gross measurements can only be approximate and the usual practice is to use a standard with a similar energy to the average energy of the mixed fission products encountered. Thallium-204 has been advocated [43] for beta measurements, particularly for low-level waste streams and the use of strontium-90/yttrium-90 in equi- librium is described in a method for beta activity in solutions and effluents [44]. The determination of a specific radionuclide does not, of course, present this problem since the method can be standardized using a standard source of the actual nuclide being measured. As mentioned previously such determinations are less frequently required and where possible are carried out by gamma spectrometry [cf. 45, 46, 47] although well-tried but more time-consuming radiochemical procedures are readily available for all the significant fission products [48-53, 54].

70 MISCELLANEOUS DETERMINATIONS

Acidity

The determination of acidity in processing plant solutions falls into two categories. In the first category are solutions with relatively low concentrations of hydrolysable ions where normal titration methods are applicable; in the second category are solutions with relatively high concentrations of hydrolysable ions from uranium, plutonium, iron or aluminium where recourse has to be made to the addition of a complexing agent prior to titration. The complexing agents normally used are either oxalate or fluoride, or ferrocyanide may be added to precipitate the uranium or plutorjium. It is convenient, especially for more highly beta-gamma active solutions, to carry out the titration with one of the several available types of automatic titri- meter. Excellent discussions on the determination of free acidity in processing plant solutions are available [4,54]. Quite recently, the use of sulphate has been advocated as a complexing agent in preference to oxalate and fluoride, particularly where one wishes to use a glass electrode [56].

Other determinations

Most other determinations required (e.g. ferrous iron, dichromate, nitrite, sulphamate) are carried out by classical procedures and do not present special problems apart from the possible need for partial shielding during an analysis. One miscellaneous determination of importance, worth mentioning, however, is the estimation of TBP in the usual hydrocarbon inert diluent. Vari- ous techniques have beën utilized for this determination including: (a) Density measurements which are cheap but unspecific and liable to error unless careful control of each fresh batch of raw diluent is exercised; (b) Dielectric constant measurement which is quick but also unspecific and open to some minor objection as density; (c) Infra-red absorption measurement which calls for relatively expensive equipment but is more specific; (d) Acid equilibration which is simple and cheap to operate and probably the best procedure for ordinary process control purposes [54]; and (e) X-ray absorption using an iron-55 source which is quick, fairly simple but unspecific [57j.

FUTURE DEVELOPMENT

„ So far as the processing of irradiated uranium metal and oxide fuels in solvent extraction plants is concerned there are probably only minorim- provements to be made in the very large and formidable array of laboratory techniques and methods available to the analyst. However, some success has been achieved at several establishments in the use of "in-line" analysers and one would expect that the further development of rugged and fool-proof in-line analytical instruments would pay dividends from the aspect of over- all economies. The determination of acidity, nitrite, ferrous/ferric ratio,

71 uranium, plutonium, fission-product activity etc. are all feasible on an automatic basis and indeed instruments have been successfully utilized for some of these measurements (e.g. gamma absorptiometers for uranium and plutonium) . With the increasing introduction of newer types of nuclear fuel such as cermets, ceramics, carbides etc. some additional analytical laboratory problems are bound to crop up and a number of reports already exist des- cribing the solution of analytical problems arising in pilot-plant and small- scale operations handling these materials. Finally, for large-scale processing plants where a mass of analytical data are forthcoming in the course of control operations, much benefit from the point of view of economics can be gained by the development of appropriate data processing devices and the use of computors; this applies particularly to gamma spectrometers, and counting equipment generally.

REFERENCES

[1] Nuclear Power, World Reactor Chart, 3rd ed. (1962). [2] Determination of plutonium in reactor fuel processing and effluent plant solutions, U.K. A. E. A. Rep. PGR-199 (W). [3] CETEMA: Method No. 38, CEA, Paris. [4] Hanford Analytical Technical Manual (SCHNEIDER, ,R. H. and HARMON, K. M., Eds.) HW-53368, USAEC, Off. Techn. Services, Dept. Comm., Wash., D.C. [5] Determination of plutonium in the feed and product solutions of the plutonium purification plant, U.K. A. E.A. Rep. PGR-300(W). . [6] Determination of americium and curium in the feed solution to the primary separation plant, U. К. A. E. A. Rep. PGR-280 (W). [7] POWELL, R., Analyst 83 (1958) 252. [8] The absorptiometric determination of plutonium in the feed solution to the primary separation plant, Rep. IGO-AM/W 115. [9] BOASE, D. G., FOREMAN, J. K. and DRUMMOND, J. L., "Complexometric determination of plutonium in reactor fuel processing plant solutions", Talanta 9 (1962) 53-63. [10] BOORMAN, G.L., Analyt. Chem. 29 (1957) 213. [11] KELLEY, M.T., JONES, H.C. and FISHER, D.J., Analyt. Chem. 31 (1959) 488. 956. [12] CARSON, W.N., VANDERWATER, J. W. and G1LE, H.S., Analyt. Chem. 29 (1957) 1417. [13] SCOTT, F. A. and PEEKEMA, R. M., Determination of plutonium in irradiated uranium fuel solutions by controlled potential coulometry, Hanfoid Lab, Rep. HW-58491. [14] HANDSHUH, J. W., Ion exchange separation and coulometric titration of plutonium in irradiated fuel element solutions, Hanford Lab., Rep. HW-66441. [15] WEBSTER, R.K., SMALES, A.A., DANCE, D.F. and SLEE, L.J., Analyt. chem. Acta 24 (1961)371. [16] Determination of plutonium/uranium ratio on the feed solution of the Windscale primary separation plant, U.K. A. E.A. Rep. PGR-340 (W). [17] SHULTS, W. D. ; "Coulometric generation and back titration ot intermediate reagents at controlled potential", Analyt. Chem. 33 (1961) 15. [18] ALLISON, G.M., Atomic Energy of Canada, Ltd. Rep. PDB87. [19] PHILLIPS, G., Analyst 83 (1958) 75. [20] Determination of plutonium in the product from the plutonium purification plant (differential spectrophotometry). U.K. A. E.A. Rep. PGR-297 (W). [21] MILNER, C.W.C. and WOODHEAD, J. L., Analyst 81 (1956) 427-9. [22] METZ, С.F., "Analytical chemistry of plutonium", Analyt. Chem. 29 (1957) 1748. [23] METZ, С. F., "Analytical chemistry of plutonium", Analyt. Chem. 29 (1957) 1748. [24] KOCH, C. W., "The transuranium elements", National Nuclear Energy Series, Div. IV 14B Mcgraw-Hill, New York (1943).

72 [25] CALDWELL, С. E. et al., Analyt. Chem. 34 (1962) 346. [26] BARKER, F., Titrimetric determination of plutonium in plutonium nitrate solution: silver reduction eerie sulphate method, U. K.A.E.A. Rep. WSL-M-692A. [27] SEILS, C.A., LARSEN, R. P. and MEYER, R.J. , Gatlenberg Conf., USA, ТЮ-7606 (1960) 178. [28] FUDGE, A. et al. U.K.A.E.A. Reps. AERE R/3264 and Rep. PGR-309 (W). [29] METZ, С.F. and WATERBURY, G. R., Analyt. Chem. 31(1959) 1144. [30] TURNLEY, W.S.,"X-ray fluorescence analysis сf plutonium", Talanta 6 (1960) 189-195. [31] DRUMMOND, J. L., Gravimetric determination of plutonium as oxide at 1250°C, U. K.A.E.A. Rep. IGO AM-W-64 (1956). [32] BO ASE, D. G. and FOREMAN, J. K., "Separation of sub microgram amounts of uranium from milligram amounts of iron aluminium and plutonium", Talanta 8 (1961) 187. [33]' Fluorimetric determination of trace amounts of ura nium in effluent treatment plant solutions, U. К. A. E. A. Rep. PGR-200 (W). [34] CETEMA: Nos. 43 and 44, CEA, Paris. [35] Determination of uranium in uranyl nitrate solutions (eerie sulphate titration), U. К. A. E. A. Rep. PGR-126(W). [36] HORTON, A. D., FARRAR, L. G., HOBBS, B.B. and SMULTZ, W. D., "Coulometric titration of H.R,T. fuel in the high radiation level analytical facility", Gatlenberg Conf.,USA,ТШ-7568 (1958) 96. [37] MILNER, G. W.C., "Non-ferrous metallurgical analysis: a review". Analyst 81 (1956) 619-650. [38] RODDEN, C.J., "Analysis of uranium and its compounds", Gatlenberg Conf., USA, ТЮ-7555 (1957) 24. [39] DeSESA, M. A., "Determination of uranium in cires, leach solutions and mill products", Gatlenberg Conf., USA, ТШ-7555 (1957) 57. [40] McDONALD, B.J., U. K.A.E.A. Windscale Works, unpublished work. [41] PISH, G. and HUFFMAN, A. A., Analyt. Chem. 27 (1955) 1875. [42] Determination of uranium in plutonium metal, plutonium compounds etc. .U.K. A. E. A.Rep. PGR-236(W). [43] REYNOLDS, S.A. and BROOKSBANK, W.A., Jr., "Thallium 204 as standard for radioassays", Nucleonics 11 (1953) 46-47. [44] Determination of beta activity in plutonium plant solutions and effluents, U. К. A. E. A. Rep. IG-212(0/W). [45] LEBOEUF, M.B. and CONALLY, R.E., "Analysis of radionuclide mixtures", Analyt. Chem. 25(1953) 1095. [46] CONALLY, R. E., "Instrumental methods of garnira ray spectrometry", Analyt. Chem. 28 (1956) 1847. [47] PERKINS, R. W.. Proc. 2nd. UN Int. Conf. PUAE 28 (1958) 445. [48] Analytical method for the determination of ceriurr -144 in reactor fuel processing and effluent treatment plant solutions, U. K.A.E.A. Rep. PGR-205 (W) (1961). [49] Analytical method for the determination of niobium 95 in reactor fuel processing and effluent treatment plant solutions, U. K.A.E.A. Rep. PGR-211 (W) (:1961). [50] Analytical method for the determination of caesium 137 in reactor fuel processing and effluent treatment plant solutions, U.K.A.E.A. Rep. PGR-202 (W) (1961). [51] Analytical method for the radiochemical determination of ruthenium 103 and 106 in reactor fuel processing plant solutions, U. K.A.E.A. Rep. PGR-78 (W) (1960). [52] Analytical method for the radiochemical determination of strontium 89 and strontium 90 in plant solutions, U. K.A.E.A. Rep. PGR-84 (W) (i960)., [53] Analytical method for the determination of zirconium 95 in plutonium plant solutions, U. K.A.E.A. Rep. IG-109 (O/W) (1959). [54] Master Analytical Manual, Oak Ridge Nat. Lab. ТШ-7015. [55] HAMLIN, A.G. et al., "The separation of uranium by means of reversed phase partition chromatography", Pittsburgh Conf. on Analyt. Chem. (1961). [56] AHRLAND, S., New methods for the determination of free acid in the presence of large amounts of uranyl salts, Eurochemic Rep. ETR-74. [57] EDWALL, B. and WICHMANN, P., X-ray absorption method for determining the TBP content of kerosene- based extraction solvents, Eurochemic Rep. ETR 132.

73 В. SUMMARY OF DISCUSSION

(Chairman: Professor Dr. H. Malissa)

« 1. ANALYSIS OF FUELS

(i) Plutonium determination

Gravimetric plutonium dioxide determination has been used as a standard method, but only for pure, relatively concentrated solutions. The lower limit for this is potentially low, because the quartz microbalances are very sensitive, but these are difficult to use on a routine basis because they are slow and require very skilled operators not normally available in sufficient numbers. Thus this method has been restricted to the use of a normalsemi- microbalance, i.e. five decimal places, which must also be installed in a dry box. The use of a more sensitive balance in a dry box gives rise to difficulties, for example, the variations in pressure produced when the gloves are used. In general, the feeling in the United Kingdom was that routine gravimetric determinations requiring high sensitivity were not suitable for application in a dry box. Using coulometry, plutonium can be determined directly in dissolver solutions without uranium and iron separation, provided the solution does not contain more iron than plutonium and provided the medium does not complex plutonium strongly (e.g. perchlorate, nitrate or even chloride). When larger quantities of iron are present, as in the determination of plutonium in fuels containing stainless steel, then separation is necessary. Dr.M. Corpel reported that when applied to amounts of the order of 1 mg of plutonium, it is difficult to obtain a precision of better than 2 to 3%. There is little interference by neptunium in the determination of plutonium in alpha-counting methods because neptunium-237 has a relatively low specific activity. With chemical methods, such as solvent extraction followed by an ethylenediominetetraacetic acid (EDTA) titration, a small correction is necessary with fuels irradiated to the extent of 2000 to 3000 MWd/t or more, when the neptunium concentration is significant. There is no interference in mass spectrometric method's, nor in coulometry as the potentials of neptunium are sufficiently different from those of plutonium.

(ii) General comments

As fuels, such as uranium and plutonium, are subjected to longer irradi- ations, appreciable quantities of the elements such as americium and curium will be produced. Purely chemical methods of analyáis for these are not readily applicable because of the relatively small mass concentrations involved, and the only available approaches are by a-counting with energy discrimination after preliminary separations using ion-exchange or solvent- extraction techniques. Professor Dr. F. Hecht and Dr. R.F. Cellini pointed out that many small countries have no possibility of producing the transuranium elements in quantity but that they have nevertheless a direct interest in their analysis

74 as a research project. Joint ventures by several countries (i. e. Eurochemic) provide opportunities that do not exist in a country alone. It is extremely useful if these countries have analysts experienced in actinide and fission- product analysis and such work should be encouraged. It was-too early to recommend particular approaches to these problems. The same remarks apply to the newer types of fuel where there are also many general problems.

2. ANALYSIS OF OTHER MATERIALS

The question of chemical analysis of active materials (for instance, liquid sodium coolant, cladding materials, etc.) which are not fuel elements was also raised. Dr. G.A. Welch reported that at Dounreay, the analysis of the liquid sodium-potassium coolant was normally carried out on the "cooled material". Analysis of the coolant for oxygen at the 5- tolO-ppm level is a considerable problem. This is normally done by distilling the alloy in an inert atmosphere; the requirements with regard to absence of oxygen and humidity are so extreme that they had found it necessary to use three pairs of rubber gloves, because moisture from the skin penetrates both the surgical rubber gloves and the dry-box gloves. Even so, with three pairs, there is a limited working time. Because of the lack of experience in the particular field, the Panel did not feel competent to discuss the problem of the analysis of radioisotope preparations commonly used in many sciences, particularly medicine. The problem was considered important and requires attention, but it was felt that a meeting of specialists on the particular subject was necessary to cope with it.

3. COMMENTS ON TECHNIQUES

(i) Analytical techniques

High-frequency titration methods seemed to have some relevance to the analysis of radioactive solutions as the technique seems suitable to remote control. In general, it appeared that although the method was nowadays not widely used, it could take microsamples and probably be useful for acidity determination. However, Dr. M.T. Kelley pointed out that automatic titrators are commercially available for acid determination and these are readily used in "hot cells", so that they could not see a clear advantage in favour of the high-frequency method. On the relative merits of ion exchange and solvent extraction as general techniques in this type of work Dr. F.J. Woodman felt that the quality of staff available was an important factor. Solvent extraction gives better results than ion exchange in the hands of moderately skilled operators, because the latter requires more attention to details. However, in certain cases, ion exchange gives better results and if sufficiently skilled operators are available this would be preferred. . Kelley has noticed that when plutonium is separated using an anionic resin in a nitric acid system prior to its determination by coulometry, the resinproducts cause difficulty in the coulometry titration unless the extract is fumed to dryness.

75 (ii) Handling techniques

One of the most immediate considerations in the chemical analysis of radioactive materials is the effect of remote handling techniques and there was some discussion on this point. The comment of Dr. Corpel on the use of titanium chloride instead of a Jones reductor to reduce uranium in shielded areas (see Summary of Discussion, Part I, this report) is relevant to this. To the question "Is it worth while to make the remote handling fit the analytical method", there seemed to be considerable agreement that this is not the best philosophy. It is not worth while to select the best, most accurate and precise method and make this work using remote handling, come whatmay. It is in general better to sacrifice a little on accuracy and precision to obtain a method which could be readily adapted to remote control. The normal aim in any case is to carry out the finish of the determination in the simplest way without remote handling. Thus, plutonium would be extracted from fission products remotely, and the final determination by titrimetry or absorptiometric measurement would be made under semi- remote conditions or in a fume hood. For these reasons Dr. Kelley said that the United States particularly liked coulometry because only the cell need be placed in the shielded area and all other equipment is outside. This was an example for a general point of view. Dr. Woodman said that at one time they spent a long time trying to make the simpler instruments, such as absorptiometers working inside shielding by remote control. This, however, created difficulty over a period of time owing to maintenance difficulties, "fogging up" of optics, etc. Now they place only the minimum in the shielded area. Absorptiometers and spectrophotometers are now operated with only the cells in the shielded areas, the light being "piped" through the shielding to the instrument. Feldman of Oak Ridge, for example, uses a mirror system to make the light out of the shielded cell to an emission spectrograph. Dr. Woodman preferred to extend the pans of a balance into an active area, but maintain the remainder outside.

There seemed to be satisfaction with the remote manipulators available, but it must be realized that they are a very poor substitute for a pair of hands, and to improve them to that extent would be prohibitively costly. When there'is a fairly clear plan of action, say 10 or 15 methods routinely used, it is possible to use a system called in the United Kingdom "gantry manipulators", which run over the wall and move laterally, embodying a series of devices for pipetting and stirring, simple tongs, etc. Dr. Welch commented that shift operation staff seem to adapt themselves better to this limited type of manipulator than to the more expensive and versatile master slave. Master slaves were considered to be more appropriate where the exact nature of the work could not be predicted, as in research and development laboratories.

In general, viewing systems using lead glass or zinc bromide windows seem to be satisfactory also. The latter is usually preferred because of price and availability. There are problems with these systems, but in general they are not prohibitive. There seemed to be no general desire for closed-circuit television.

76 The decrease in precision of a method under remote control which is generally observed Was felt to arise from the unusual conditions of operation. Operator fear in handling active material was not considered to be significant provided it was obvious that the operator was adequately protected. However, when working remotely, the operator is conscious that he has his equipment 1 m or more away from him instead of 30 to 40 cm as in normal practice, and there is some distortion through windows when the direction of sight is oblique. Lack of sound may play a part and nowadays there is a tendency to put microphones into the remote handling cells to pick up and relay the sounds and noises which one normally expects to hear. It was felt that the lack of feel, which is present in even the best manipulators, also plays a part. Corrosion is normally a considerable problem in hot-cell and dry-box work, and although ventilation is always provided, there is always increased corrosion above that normally experienced in the open laboratory. One solution which the United Kingdom is experimenting with is to carry out every- thing that involves the possibility of fumes in an inner box. This has had some success. Dr. Kelley reported a similar approach, but still had some difficulties. In France, the approach has been to limit the corrosion by the use of all-plastic dry boxes for both analytical and fabrication purposes, although of course metallic parts which must go into the area, such as manipulator tongs, will still be corroded. The safety services in France were satisfied that such plastic boxes were safe after a series of explosion tests. It appeared that the rubber gloves constituted a safety valve to the pressure wave under such conditions. The plastic boxes have thé advantage that it is easier to drill holes in them than in glass and as the boxes are often used for research work, modifications are often required. In the United Kingdom, "fiber glass" boxes with a "Perspex" front were used successfully, although they did not find that the rubber gloves acted as a safety valve in case of explosion.

(iii) Futyre fields of work

In a discussion of useful subjects for further work. Dr. Woodman suggested that some of the more basic aspects in the development of "in line" instruments would be appropriate. There are many problems connected with increase of background which are common to any technique so applied. He felt that studies on these problems and means of dealing with them were suitable basic research subjects of wider interest than the development of a particular instrument for a special application. Such common problems were: (a) corrosion; (b) adsorption of radioactivity on surfaces and studies of surface finishes; (c) darkening of transparent materials; and the like. Dr. Kelley reported that work on the general development of instrumental analysis not particularly aimed at "in line" instrumentation, but aimed at techniques which would be appropriate for this type of work, was proceeding at Oak Ridge.

PART IV

RECOMMENDATIONS OF THE PANEL

1. The International Atomic Energy Agency (IAEA) should print and supply all members of the Panel and interested countries with a summary report of the working discussions,- papers and comments. 2. The consensus of opinion of the Panel was that there exist satisfactory methods for the determination of uranium at the present time but that methods for the determination of thorium have not reached the same level. It was suggested that useful work can be done on methods for the separation and precise and accurate determination of this element at high concentrations. 3. The Panel, recognizing that it is extremely difficult to establish a real and in every respect satisfactory uniform chemical standard of uranium, recommended that, until one is established, the IAEA take the necessary steps to provide an internationally analysed sample of U3O8, as pure as possible, which would be available on request for purposes of comparison. 4. The Panel recommended that, to help analytical laboratories in developing countries, the IAEA study the possibility of providing analysed samples of uranium ores. It suggested that a survey of the most important types of ores be initiated and efforts to choose a representative selection be made. The aim of this programme would be the establishment of a practical number of useful analysed samples which could be used for purposes of comparison. 5. The opinion of the Panel was that, at present, fluorimetric, radiometric and emission spectrographic methods are advisable for routine determinations of uranium in ores, such as is necessary in prospection and primary laboratory control. For the more exact determination of uranium these methods are not to be applied and absorption spectrophotometry or titrimetry should be used. It was agreed that the possibility of making routine analyses by these techniques would be enough to cover the analytical needs of a country surveying its uranium resources. 6. It was the consensus of opinion of the Panel that there exist atthe present time useful methods (for example emission spectrography and absorption spectrophotometry) which have proved satisfactory in a number of laboratories for the determination of all the more important elements at trace concentration in the mçre common nuclear materials, such as uranium, graphite, light and heavy water, etc. For some elements it was felt desirable to develop better techniques to improve speed, accuracy or precision. The Panel thought that the following elements fell into this category - hafnium, hydrogen, niobium, oxygen, phosphorus, rare earths, silicon, tantalum, thorium, tungsten and zirconium. It was considered that a fruitful field of approach may be the usé of techniques recently developed for other purposesi 7. The Panel considered that it was desirable to establish the inter- laboratory precision and accuracy of some methods of trace analysis. There- fore it was recommended that the IAEA prepare a solution of uranylnitrate with addition of traces of elements and have that analysed, together with another solution without additions, by various laboratories in different

79 countries. In this connection it was felt that there is a lack of available, reliable analysed samples or of samples established by other means. It was then recommended, as the next step, that studies be made to prepare more suitable samples. 8. In the field of analytical chemistry of fuel reprocessing it was felt that the problems associated with analytical chemistry are now perhaps less of a chemical nature than mechanical, as they involve principally the adaptation of known chemical techniques to special conditions and possibly their automation. As new fuels come into prominence so fresh analytical problems will emerge and must be assessed at an appropriate time. 9. It was apparent from all discussions that the most important stage in an analysis is the securing of a representative sample and this can often be a problem. This is specially important for nuclear materials because of their toxicity, radioactivity, inhomogeneity, variety and cost. Considering this, the Panel recommended that the IAEA organize in the near future a special meeting devoted to this problem. 10. The Panel advised that another meeting be convened when the results of the planned experiment on trace analysis in uranyl nitrate solutions and of the analysed sample of U3O8 are ready for evaluation. It also felt that in future small panels on particular subjects of analytical chemistry should be convened. These panels should review particular techniques or problems and aim at establishing methods of analysis to be recommended officially by the IAEA. Participants should be recruited from specialists having worked in the particular field for some years. 11. The Panel recommended that it is desirable to have close collaboration with the Analytical Section of the International Union of Pure and Applied Chemistry.

80 LIST OF PARTICIPANTS

Professor Dr. I. P. Alimarin Institute of Geochemistry and Analytical Chemistry, Academy of Sciences, Moscow, USSR

Dr. R. Fernandez Cellini Junta de Energia Nuclear, Serrano 121, Madrid, Spain

Dr. M. Corpel Centre d'études nucléaires, B. P. No. 6, Fontenay-aux-Roses (Seine), France

Professor Dr. F. Hecht Analytisch-chemisches Institut der Universität Wien, Währingerstraße 38, Vienna EX, Austria

Dr. J. Huré Centre d'études nucléaires, B. P. No. 6, Fontenay-aux-Roses (Seine), France

Dr. M. T. Kelley Oak Ridge National Laboratory, P.O. BoxX, Oak Ridge, Tennessee, United States of America

Dr. L. Kosta Nuklearni Institut Jozef Stefan, Jam ova 39, Ljubljana, Yugoslavia

Professor Dr. H. Malissa Technische Hochschule Wien, (President, Analytical Section, Getreidemarkt 9, International Union of Pure Vienna IV, Austria and Applied Chemistry)

Dr. C. J. Rodden United States Atomic Energy Commission, New Brunswick Area Office, P.O. Box 150, New Brunswick, New Jersey, United States of America

Professor Dr. T. Somiya Atomic Energy Bureau, The Science and Technics Agency, Kasumigaseki, Chiyoda-ku, Tokyo, Japan

81 LIST OF PARTICIPANTS

Dr. G. A. Welch United Kingdom Atomic Energy Authority, Dounreay Experimental Reactor Establishment, Thurso, Caithness, Scotland, United Kingdom

Dr. F. J. Woodman United Kingdom Atomic Energy Authority, Windscale and Calder Works, Sellafield, Seascale, Cumberland, United Kingdom

Agency staff members:

Professor Dr. J. Minczewski (Scientific Secretary) Dr. G. B. Cook Dr. M. B. Crespi OTHER IAEA PUBLICATIONS ON RELATED SUBJECTS

THERMODYNAMICS OF NUCLEAR MATERIALS (Proceedings Series)

Proceedings of an IAEA symposium held in Vienna, May 1962, to present and appraise current work, to assess the reliability of nuclear materials and to discuss application of such information to current problems in nuclear technology. i 808 pp. (16 X 24 cm) Price: US ill. 00; Elsewhere 66s. stg

THE URANIUM- CARBON AND PLUTONIUM- CARBON SYSTEMS: A THERMOCHEMICAL ASSESSMENT (Technical Reports Series No. 14)

Report of a panel on data discrepancies revealed at the Symposium on Thermodynamics of Nuclear Materials.

44 pp. (16x24 cm) Price: US $1.00; Elsewhere 6s. stg

GEOLOGY OF URANIUM AND THORIUM (Bibliographical Series No. 4)

A selection of 892 items on geology and related subjects such as prospecting, exploration, reserves and geochemistry.

134 pp. (16 X 24 cm) Price: US $1.50; Elsewhere 9s.stg

REVIEW SERIES

No. 5: MASS SPECTROMETRY FOR URANIUM ISOTOPIC MEASUREMENTS by C. D. Tabor

A description of instruments, sample-preparation techniques and analytical methods.

48 pp. (14.8x21 cm) Price: US Jl. 00; Elsewhere 6s.stg

No. 22: METALLURGY OF THORIUM PRODUCTION by B. Prakash, S.K. Kantan and N.K. Rao

A monograph on the occurrence of thorium ores and their processing and the present status of thorium in nuclear energy.

56 pp. (14. 8 x 21 cm) Price: US Jl.00; Elsewhere 6s.stg

No. 23/24: CHEMICAL PROCESSING OF URANIUM ORES by E. T. Pinkney, W. Lurie and P.C.N, van Zyl

TRATAMIENTO DE MINERALES DE URANIO by L.G. Jodra and J.M. Josa

Two monographs. The first outlines uranium mineralogy, reviews physical concentration, outlines extraction and describes three typical plants. The second deals with preliminary concentration, roasting, acid and alkaline leaching, solid-liquid separations and final preparation for delivery.

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