SCIENTIFIC AND TECHNICAL REVIEW OF THE EUROPEAN ^>|-f t? COMMUNITIES a DECEMBER 1972 VOL. XI NO. 4

^ /r

-λ"1. 91 VITTORIO PONS

WHY MUST A EUROPEAN CURRENCY BE CREATED ?

93 GIOVANNI PIATTI, ROBERT LUBEK, ROBERTO MATERA

CAVITATION Study of microcrack formation and propagation phenomena in creep deformed metals

102 JEAN DONEA

OPERATION "HOT MOLE" Self burial: an elegant solution to the problem of storing high-activity radioactive effluents?

110 MARTIN OBERHOFER

EXOELECTRON EMISSION DOSIMETRY

• AUTHORS' INDEX 1972

• SUBJECT INDEX 1972

• INDEX 1972 TO TECHNICAL NOTES

• JUST PUBLISHED

• CONFERENCES Five editions: English, German, French, Italian and Dutch

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Any article published In this Review may be reproduced In whole or in part without restric• tion, provided that the source is mentioned. euro spectra Within a short time during 1972 we lost two Scientific and personalities who, although from different walks Technical Review of the European of life, were both staunch and enthusiastic sup• Communities porters of the European cause — Paul-Henri (ex-Euratom-Review) Spaak and Count Coudenhove-Kalergi.

The summit conference recently held in Paris between the Heads of State of the enlarged Community has yielded practical, if not spectac• ular, results, especially as regards the Com• munity's monetary problems; it is therefore with gratitude, and not without a certain emotion, that we find the effigies of these European pioneers on the commemorative coins which were recently minted in remembrance of those who have been faithful believers in a united Europe.

The Commission of the European Commu­ nities or any persons acting on its behalf disclaim all liability with respect to the completeness of the information contained in this periodical as well as to any damage which might result from the use of information disclosed or of equipment, methods or processes described therein.

Picture credits: pp. 93, 102, 104, 105, 109: drawings by Gaston Bogaert, Brussels.

Printed in Belgium by Maison d'Edition s.c 6001 Marcinelle 90 Why must ON 9 FEBRUARY 1971, the Commis­ instructive precedents. In 1800. before sion of the European Communities, Napoleon's unifying undertaking, the a European following the work of the Werner 123 German States issued more than Committee, laid down the stages which 1 000 coins, and anyone travelling across currency should make way for the achievement of their territories had to "change" at Economic and Monetary Union in ten nearly every staging post. In 1814, there years. On 15 August 1971 the dollar were only 164 coins left in 29 currencies, be created? ceased to be the monetary standard of several of which had the same name, but the Western world; the international different values. monetary crisis which followed—and whose effects still continue to disturb The German Reich, founded in 1871 economic relations in Europe—pointed at Versailles, unified all this by adopting, within two years, a single Mark divided VITTORIO PONS quite clearly to the urgent need for an overall solution. into 100 Pfennige for all its territory. All these transformations took place, there­ Why is the creation of a European fore, in under 75 years and, to take currency necessary? The answer can be account of national sensibilities, it proved given in two ways. sufficient simply to allow each little State to have the head of its prince or the First of all, the absence of this currency emblem of its Republic on the reverse is harmful to Europe; the dollar standard side of all coins worth 2 Marks or more, has the continuing effect of reducing the while the Imperial Eagle adorned the intrinsic value of the national currencies, obverse. particularly since the dollar itself is now no longer fixed or covered. The national Since 1792 the United States has also banks, forced as they are to reckon with simplified its currency to the extent that the dollar, are coming more and more to six coins are sufficient to cross its territory resemble branches of the United States including Puerto Rico and Guam. And Federal Reserve, sometimes even yet there are still 12 monetary districts branches of the big American private managed by a Federal Bank. banks. The twelve governors regulate their The second answer is that the existence exchanges by an Interdistrict Settlement of a European currency would immediate­ Fund, which is unpublicized and which ly solve two problems. The first is that the user does not even have to know of tourists and travellers, who, for rea­ about. Moreover, who notices that these sons of pure convenience, have adopted twelve currencies, perfectly convertible the dollar as an "international cur­ between each other, bear a little distinc­ rency" for their journeys throughout tive sign: Β for Boston. C for Chicago, Europe. The second is that of the banks etc.? and big companies, which are tending Jacques Rueff1 once said: "Either more and more systematically to settle Europe will be created through currency, their foreign exchange transactions in or it will not be created at all". Euro­dollars, while the control of these transactions is daily becoming more The Chairman of the Banque Lambert, elusive for any monetary authority, obviously a man of experience, declared except that of the United States. recently: "Minting a currency has a huge political significance. In this interim The present state of monetary disorder, floating rates of exchange, and the aboli­ tion of any form of control, all contribute to general inflation which is tending to become permanent. This situation cannot ' Jacques Léon Rueff is a member of the Académie Française and was President of last for long without having a direct effect a Chamber at the Court of Justice of the on the value of real wages and on the European Coal and Steel Community from housewife's shopping basket. 1952 to 1958, and Judge at the Court of Justice of the European Communities from 1958 to 1962. He is the author of How can one create a European VITTORIO PONS, International Secre­ "Le péché monétaire de l'Occident", pub­ tary­General of the Paneuropean Union. currency? History contains a number of lished in 1971. period, when Europeans need so much al loans could be issued in units of name which came up the most often was to retain the hope that one day they will account, but the need for this is already EURO, which obtained 102 votes. After­ be united, acts are called for which are felt so much that, in January 1971, the wards came the COMMAR, mentioned both concrete and spectacular, unifying European Coal and Steel Community 37 times, the COMARK 36 and many the symbol and the reality. Few acts could issued a 8% 1970­85 loan for 50 million other names: Ducat, Talent, Euron, Pax, have so great an effect as the creation of European Monetary Units, symbolized etc. a European currency today." He thinks by the sign "f", a loan which, moreover, The Paneuropean Union questioned that such a unit of account must make was immediately taken up in its entirety. the editors­in­chief and directors of headway, first of all as a banking currency How should the new currency be European economic and financial news­ and then finally as common tender. This defined? In gold, special drawing rights papers in August 1972, and discovered currency would be issued by the Central and gold, or just special drawing rights? that they, too, preferred the term Banks in each Slate and guaranteed by Most numerous are the protagonists of EURO (''Handelsblatt", Düsseldorf, "La them, either jointly or by a European an evaluation in terms of gold, and the Stampa", Turin, "Luxemburger Wort", Reserve Fund. It would therefore have ambitions of Jacques Rueff are well for example). Along with extravagant to be governed by "a common monetary known. He summarizes them in the suggestions—a British paper proposed authority whose powers would, however, following way: HOMER—there was also the proposal be no wider than those which all the of " The Economist" of London which is members seem ready to grant it forth­ "Doubling the price of gold and worth noting: CROWN, as most of the with." generally revaluing reserves of the Community States are monarchies. The precious metal are the condition for "As soon as the new system is put into same paper opted in second place for refunding the dollar balances and the practice, its use could become generalized ECU, which is also favoured by "The special drawing rights. This revaluation for regulating international exchanges Financial Times", and "De Tijd" of should make it possible to establish a between banks and companies", giving Antwerp. "77;e Financial Times" also sort of Marshall Plan in reverse by the unit of account "a role equivalent proposes EUROPA. Whatever it may be lending to the United States the face­ to that which the dollar played before called, it is certain that United Europe value surpluses acquired by countries 15 August 1971." needs its own unit of account, and the which have gold but no balances to be sooner the Ministers of Finance, united This pragmatic banker describes the refunded. Practically, all the dollar in the European Community, decide on near future in the following terms: bank balances would disappear. The resulting its issue, the better it will be. assets in units of account, savings, inter­ reconstruction of the international mone­ national loans, (leaving the States "free tary system would cause a wave of Pending this decision, the Paneuropean to decide whether there is a case for prosperity and expansion in the West Union has issued a symbolic European retaining a system of exchange controls which would be without precedent in currency consisting of nine coins in two where it already exists, particularly for history, and would at the same time series, the aim being to commemorate in capital transactions"), and a free market greatly diminish inflationary pressures".2 this way the 50th anniversary of the first which would operate perfectly. call for unity launched by Count Couden­ To return to our unit of account. What hove­Kalergi in 1922. He concludes: "Because it will have should it be called, for the term "unit been in circulation as a means of pay­ of account" is not a popular one? French It is hoped that this currency will be ments for commercial and financial and English experts, and many others, more than a symbol: an incentive to spur transactions as a banking currency, the have shown a preference for the English on the Ministers responsible. currency will be created in fiduciary form. initials ECU (European Currency Unii) The name has not been chosen: Tourists in particular would use it for which, by a play of words, calls to mind EURO­ECU­EUROPA­CRO WN... their expenditure. In this way, the the écu, dating from the time of King psychological conditions for monetary Louis IX. On the obverse side the great figures of integration would be brought about to The Dutch advertising agency Ρ RA D European unification are portrayed. On the extent that what still remained to be the reverse are engraved the 12 stars of achieved later at the official level would thought of consulting the readers of the American magazine TIME in 1971. 1 464 the Council of Europe flag, surrounding merely seem the natural extension of what the symbols of European civilization: the answers were received, from 36 countries, was already being practised". sun of Greek wisdom and the cross of and suggesting 1 200 different names. The Christian inspiration. The whole is The suggestion of the Chairman of the rounded off by the inscription CONFOE­ Banque Lambert seems very realistic. The DERATIO EU ROP AEA and the sym­ proof is that the new unit of account bolic value of each coin expressed 2 would be used by tourists: 100 million When these notes appear, the Summit in f.. people going on seasonal migration across Conference will have taken place and we will know whether Mr Rueff's optimism Europe every year. The psychological has influenced the Heads of State or Gov­ effect would be considerable. Internation­ ernment meeting in Paris. EUSPA 11­16

<>2 Cavitation (e.g.. nuclear installations) the standard problem of ductility loss is complicated even further by the fact that the choice of materials is greatly restricted by the requirements of neutron economy and the materials are stressed in service to the limit of their mechanical strength Study of microcrack formation and propagation phenomena in creep deformed metals (e.g., low wall thickness). Also, compo• nents which are exposed to intense radia• tion, such as fuel dads, have an additional tendency to lose ductility on account of GIOVANNI PIATTI, ROBERT LUBEK, ROBERTO MATERA the effect of the radiation. Lastly, men• tion must be made also of the influence of the chemical environment under nor• mal working conditions (oxidation, sur• THE FACT THAT SOME METALS the correlation between operating tem• face condition, surface microstructure, and alloys, e.g., certain types of steel, perature, operating load and creep rate, etc.) which causes intrinsically brittle undergo a loss of ductility at elevated so that it is theoretically possible to define materials to rupture more easily. temperatures is a frequent cause of the service parameters for a component Numerous theoretical and experiment• premature failure or breakage in com• in such a way that its useful life exceeds al studies have been conducted on the ponents or structural elements in high- the total life of the plant, it being assumed causes and mechanisms involved in this temperature industrial installations '. that the component will not fail. In prac• reduction of ductility with reference to The resultant plastic deformations tice, however, the metal may suffer a steels and other alloys. Broadly speaking, produced in the majority of cases are sudden loss of ductility within certain high-temperature embrittlement is char• time-dependent strain processes known temperature ranges which may cause pre• acterized by the transition from trans- as "creep". Some typical creep curves mature impairment of the material's crystalline to intercrystalline fracture. are shown in Fig. 1. They demonstrate properties, resulting in failure of the Studies on the formation and propaga- component. In order to remedy this, knowledge of the processes governing GIOVANNI PIATTI, ROBERT LUBEK this reduction in ductility and the various 1 and ROBERTO MATERA are employed factors which delay or speed up these The term "elevated temperatures" here is in the Materials Division of the Ispra Estab• taken to mean those temperatures above 30",, lishment of the European Communities' processes is of fundamental importance. or 50% of the absolute melting point, depend• Joint Research Centre. However, in certain forms of application ing on the alloy concerned.

93 t χ

\ 2 ν Φ+ 3 * ñ Fig. 1 : Schematic representation of a creep Working methods curve in the ε/t diagram. Three different phases can be distinguished: 1) transient creep (solid Until about ten years ago, the exper­ line) in which t lie rate of creep decreases from imental methods used for studying the high starting values when the stress is applied; formation and propagation of micro­ 2) steady­rate creep (broken line), where the creep rate is constant; 3) tertiary creep (in cracks were limited to metallographic colour), in which the rate of creep increases techniques (employing light and electron and rupture a/ways occurs (x = rupture point ). microscopes). However, it is almost Apart from sudden fracture due to ductility impossible to observe crack propagation loss, the lifetime of a material is determined accurately under the microscope since by its behaviour during steady­state creep. the size and shape of the microcavities are altered as a result of the polishing and etching of the ground sections. For some time now the differential density technique has hence been employed tion of microcracks 2 are of fundamental instead. This involves carrying out den­ importance among research into the sity tests on samples taken from the creep factors which lead to the premature specimens before or after fracture. The intercrystalline fracture of a material. real volume of the microcracks formed Investigations have therefore been carried can then be determined from the relative out by numerous workers to examine the density changes observed as a function entire complex of phenomena involved in of the parameters governing deformation, the various metals and alloys, from the namely, strain, time, temperature, load, formation of microcracks and their prop­ etc. agation (i.e., cavitation) to fracture It is, of course, impossible to distin­ occurring during hot deformation. The guish between the formation and prop­ results obtained so far are not only of agation of microcracks using this interest from the theoretical standpoint, technique alone. This must be done by but can also be applied in practice. Fur­ determining the number of microcracks ther research is under way in a number per unit volume as a function of the above of centres, including the Ispra Establish­ variables by means of quantitative metal­ ment of the Joint Research Centre. lographic analysis employing light or electron microscope techniques. It should also be pointed out that the changes in the shape of the microcracks due to 2 The terms "microcrack, microcavity, hair crack and micropore" are taken here to be preparation for metallographic analysis synonymous. are of no major importance as long as

94 Fig. 2: The time­dependence of the varia­ tion in relative density of various materials creep­deformed under different stress (n) and temperature conditions. Equation [I] may be applied. In the diagram, the variation ( — SD/D) in the relative density, which is AD τ—I 1 1ΙΠ1 -ι—ι—ι ι ι τ tr "τ—τ τ τ τ τ virtually equal to the porosity, is plotted vs ' D time.

one is only interested in counting the actual cracks present. Since the following 10 equation is true: (formation) ■ (propagation) cc (cavitation) the combination of these two methods (density measurement and quantitative 10 metallographic analysis) enables the parameters governing propagation to be determined accurately. In addition to this, there are other tech­ niques which can yield useful informa­ tion on the formation and propagation 10 of microcracks, especially as regards the nature of the fracture. Through analyses made using electron microscopes (trans­ mission microscopy) data can also be obtained on, for example, the interaction between grain boundaries and micro­ 10 cracks and between dislocations and microcracks. Studies such as these can provide valuable information on the physics of solid state which help to improve our understanding of the behaviour of materials. 10 _Ι ' ' ' ■ ' ' Scanning electron microscopes are also 10 10 10 10 10 t (sec. ) to be employed in this field on account of their unrivalled capacity for depth of focus, which is particularly useful for detailed analysis of the fracture surfaces 1 — Magnesium σ 0.5 kg/mm2 Τ = = 300DC of test samples. To obtain data on the 2 — Copper σ = 3.64 kg/mm2 Τ = = 400°C type of precipitation and inclusion which 3 — Copper σ = 3.5 kg/mm2 Τ = = 400°C are regarded as the origin of cavitation, 2 4a — Nickel 0.1 a/o Pd σ = 19.1 kg/mm τ == 503°C electron microprobes can be used to 4b — Nickel 0.1 a/o Pd σ = 16.1 kg/mm2 = 503°C 2 τ = perform point analyses of the inclusions 4c — Nickel 0.1 a/o Pd σ = 14 kg/mm τ == 503X and precipitations. 4d — Nickel 0.1 a/o Pd σ = 9.1 kg/mm2 = 503 °C 2 τ = 5 — Magnox Al 80 π = 1.61 kg/mm τ = = 275°C The combined results obtained with all 6a — Steel 20 Cr/25 Ni irradiated π = 4.2 kg/mm2 = 750°C 2 τ = these methods should provide a basis for 6b — Steel 20 Cr/25 Ni not irradiated η = 4.2 kg/mm τ == 750°C a phenomenological model of creep cavi­ 7 — Steel 20 Cr/25 Ni/Nb σ 9.5 kg/mm2 = 750°C = τ = tation behaviour in a given metal and 8 — Al—7 % AI2O3 σ = 5.9 kg/mm2 = 450°C 2 τ = make it possible to arrive at an equation 9a — Steel 1 % Cr/Mo σ = 19.6 kg/mm' τ = = 565°C 9b — Steel 1 % Cr/Mo σ = 5.6 kg/mm2 τ = = 565°C to describe the parameters governing 10a — Steel A1SI 310 π = 22 kg/mm2 = 600°C formation and propagation in order to 2 τ = 10b — Steel AISI 310 ΓΓ = 25 kg/mm τ = = 600°C determine the potential life of a metal. (σ = = specific load) Such models, which represent the rela­ tionship between measurable and observ­

95 Fig. 3: The time­dependence of the number of microcracks formed per unit volume; the black curve is for copper [II] and the coloured curve for Al—AÌ2O3 (16). Equation [3] may be applied. The number of microcracks (n) per cm3 is plotted vs time (sec).

τι/cm.ï

108 ,

10 7

103 IO4 IO5 f (Sec.) io6 ¿ A!­At203 5=5,9 k8/mm T=450°C Cu 6=3,64 kg/mm1 T*400°C

Fig. 4: Schematic representation of the forma­ planes A and C and tensile stresses perpen­ tion of microcavities at grain boundaries : a) dicular to them in plane Β (7). Other models formation of a microcavity due to grain bound­ have been suggested to describe these pro­ ary sliding near an embedded particle (8) ; cesses, but in all cases it is extremely difficult b) formation of a microcavity at a triple point to obtain sound evidence of their validity. in the grain boundary. Shear stresses act in

Grain boundary sliding Microcrack

Tensile stress

Microcrack Particle, impurity

96 able parameters, are particularly valuable method of age determination (testing of copper, austenitic stainless steels, ferritic for describing creep processes. Crussard samples to establish the extent to which steels, magnesium, nickel alloys, alumi•

(1) has shown that "an adequate explana• the properties of structural materials in nium, A1/A120, composites, zirconium tion of creep as well as a general view thermal installations are impaired) could, alloys, etc. These studies should be of its formation can be gained by observ• in practice, offer considerable economic extended to cover a wide range of ing the phenomena and building simple advantages. materials to facilitate evaluation of the models for each individual process Lastly, it should also be noted that results obtained, since it will then be involved (steady-state creep, temperature differential density measurement com• possible to distinguish between the effect and stress sensitivity, tertiary creep, bined with quantitative metallographic of the base metal (Fe, Ni, Al, etc.) and deformation fracture, cavitation fracture, analysis can also be employed in the that of structural peculiarities such as superplasticity, etc.)". investigation of other problems linked dispersed phases, precipitations, car• Apart from its theoretical aspect, with the brittle fracture behaviour of bides, etc. densimetric analysis also has further steels, such as shifts in ductile to brittle The relative density changes noted by practical significance in that combining transition temperature, radiation-induced it with a quantitative metallographic changes in tensile strength, etc. a number of different authors [(!())...( 18)] analysis should make it possible to are shown in the form of a graph in Fig. 2. The measurements are those made on determine with sufficient accuracy the Cavitation deterioration in the properties of a given various creep-deformed materials under metal, the previous history of which as The cavitation studies conducted hith• different test conditions. The variation in regards mechanical and thermal stress is erto in various laboratories have covered the relative density (V = - AD/D), virtually unknown. The use of such a a large number of materials, such as shown as the ordinate in the figure, can

Fig. 5: Schematic representation of cavitation microscope techniques but can be D — Reduction in area begins. Cavitation is in a creep sample under specified stress and detected by means of density measure• overlapped by the transition from the temperature conditions. The deformation e is ments (see Fig. 6). monoaxial to the triaxial stress condi• plotted as the ordinate and the test time t as C — Progressive deformation of the sample. tion. the abscissa. Formation and propagation of the E — Rupture of the sample due to merging A — Strain of the sample with inelastic strain microcracks, chiefly at the grain boun• of the microcavities and loss of material component. daries. In this phase microcavities are cohesion at grain boundaries. Figs. 7 B — Plastic deformation of the sample with also formed in the grains which can, and 8 show the fracture areas observed probable formation of microcracks. however, be removed by grain boundary in different materials. These can hardly be detected using migration.

97 in practice be taken to equal the poros­ number of microcracks per unit volume ity 3. (n), the time and other variables. Fig. 3 In some cases the time dependence of shows some of the results published in the change in the relative density V (the the literature. From the equation cavity volume produced in a metal during η = Β · tq [3] a particular cycle, relative to the unit where Β is a constant, it is possible to volume) is given by the following determine the parameter q governing the equation: formation of microcracks. In a combina­ V = A· tp [1] tion of these equations, the individual where A is a constant dependent on the processes of microcrack formation (num­ load and temperature, and ρ represents ber of pores per unit volume) and growth the slope (generally stress­independent) (v) (the volume of one pore) can be of the curve in the log­log VT diagram. separated, the equation The exponent ρ can be regarded as one v = C­tp­q of the parameters describing the forma­ tion and propagation of microcracks. where v is the volume of one pore and C Other parameters can be deduced from is a constant, being used to describe the the variation of V as a function of other propagation. variables such as deformation, temper­ With regard to the formation phenom­ ature, etc. enon, there seems today to be wide­ Some authors have analysed the spread agreement that microcracks are influence of individual variables on the formed at elevated temperatures by a pore volume V and summarized their process of sliding at grain boundaries findings in the generally valid equation: during which the grain boundary has a V ­ f (σ, ε, t. Τ) [2] kind of entrainment effect on the impu­ rities and precipitations embedded in the where σ is the stress applied, ε the strain, structure. Since these particles hinder the t the time and T the absolute temperature. slip process, local stress peaks are set up For copper (2), the equation is written: around them which can exert the tensile V = Const, s­t­σ2·3 exp (— 22 500/RT). strength of the material and hence favour the formation of cavities. Other equations have been written to Fig. 6: Formation of microcavities ut lhe describe the relationship between the The growth phenomena, on the other interface matrix (Al)¡particles (~¡—AI2O3) in hand, are not yet fully understood. an AI/AI2O1 composite material (transmission Whereas on the one hand it is felt that electron micrograph) (9). Comparison of the 3 The porosity is the coefficient of propor­ grain­boundary sliding is essential for two parts of the micrograph a) and b), which tionality relating the total volume of a represent two successive observations, provides material to the sum of the individual volumes propagation, another theory considers an idea of the growth of microcracks (white) of all its defects (microcracks, dislocations, the diffusion and condensation of lattice near embedded particles (grey). vacancies). vacancies to be the fundamental mech­

a) b;

**?

A S^è <:é.-

1000Å Hfe*—ι 9,S anisms involved. The results of recent ena. The outlay in terms of time and mining technique referred to in this chap­ work in this field suggest, however, that money for experiments to establish long­ ter. Density measurements will also be both mechanisms interact in the sense time values is considerably reduced by carried out on samples taken from struc­ that sliding phenomena are predominant treating the problem of creep in this tural components of thermal installations at higher stresses and diffusion at lower way. This is also true if account is also in order to determine the extent of prop­ stresses. The complex nature of this taken of the superimposed effects of erty degradation, the results then being problem has, however, prevented a radiation in addition to the influence of compared with those obtained from complete understanding of these phe­ the temperature (3). laboratory tests on creep samples. nomena, and any attempt to obtain t— .J­jàj*. 4*.­ Lastly, tests are being carried out at detailed information on the processes present at the Ispra Establishment of the Measuring methods employed at lspra involved necessitates new and more Joint Research Centre to determine the Determination of the initial properties of subtle hypotheses (Fig. 4). practical applicability of the age deter- materials and creep test conditions Apart from this first stage in the deterioration of the material's properties, two further stages have been observed, namely, the merging of microcracks and the loss of cohesion in the material at grain boundaries, followed by fracture. A number of theories have also been put forward to explain these processes according to which the ultimate fracture could be caused by a pronounced reduc­ tion in the supporting cross-section due to the merging of the microcavities or by a break along the grain boundaries due to the propagation of microcracks by linking. During tertiary creep, the reduction in area of the test piece governs the transi­ tion from the monoaxial to the triaxial state of stress, as a result of which the interpretation of these processes is further complicated. If, however, a relatively rough investigation is felt to be sufficient, it is possible to obtain valid indications b) as to the nature of these processes. Fig. 5 represents an attempt to show the cavi­ s'. ;, - •η ■ ai tation process in simplified form as a Λ S- function of the test time. Figs. 6-8 à !: .» illustrate the beginnings of cavitation on \ micrographs of different metals. .'ΐ>~,-'·\ The literature [(4), (5), (6)] has pub­ lished a number of lifetime equations based on the results of differential density measurements. A comparison of the values calculated using these equations with the results obtained from exper­ imental tests indicates that a more detailed differentiation between the for­ mation and propagation processes will enable more sophisticated equations to be formulated. The large number of papers published hitherto on methods of Fig. 7: (a) Optical micrograph ( ■ 15) of extrapolating the creep rupture behaviour the fracture zone of a sample of AISI 3/0 of industrial alloys reveal the importance steel after premature rupture during a creep test (600 C122 kg/mm2) ; (h) Enlargement which is generally attached to these life­ ( :■ 75) of area in (a). Be formation at time equations to describe creep phenom­ grain boundaries is easily distinguishable.

99 Determination of the initial properties of a material inevitably covered the com• position (chemical analysis), the micro- structure (grain size, initial porosity, metallographic analysis of precipitations of oxides, carbide and intermetallic phases) and the evaluation of the degree of homogeneity required for the micro• scopic measurements planned, and par• ticularly those relating to differential density.

The creep tests arc then carried out under given test conditions (stress, tem• perature, deformation, etc.). During the ZircaIoy-2 durability tests, for example, the stress was applied in such a way that Fig. 8: Optical micro• fracture occurred after a maximum of graph of a creep sample 10 000 hours, the temperature being (400 C) of the zirconium maintained within the range 250-300 C, alloy Zircaloy-2. Compar• which is one of particular interest from ed with the previous pic• the point of view of nuclear applications. ture, the round shape of the microcavities can These test conditions must be deter• clearly be seen. This parti• mined individually for each material, due cular type of microcavity account being taken of the conditions formation is characteristic under which it will be used for industrial of creep processes which purposes. Since the aim of these creep take place at elevated tests is to obtain samples for differential temperature and under density measurements, the tests' must as low stress, and brittle fracture can also take far as possible be carried out under inert place under the same atmospheric conditions since (in the pres• conditions. ent state of the art) the absorption of even minute amounts of oxygen will make it impossible to obtain meaningful results.

Density measurements — A differential method had to be developed for precision density measurements. Other authors have devised similar techniques. Owing Fig. 9: Block diagram of the apparatus used 3) container for buoyancy liquid; in Ispra for differential density measurements. 4) thermostat ; to the high sensitivity of this method 1) Analytical balance (sensitivity 0.01 mg) ; 5) weighing box with temperature controlled (detection of density changes of less than 2) vacuum pump; immersion chamber. l()~f') it is possible to record the changes in density produced by extremely small plastic deformations. Suitable reference .QãjõõTj. samples are required, of course, since the difference in the densities of the actual sample and the reference can only be due to the deformation. All foreign influences, such as annealing, must be carefully elim• inated. It may, for instance, be neces• sary to subject the reference sample to a cycle of heat treatment which corre• sponds to the temperature cycle maintain• ed when the sample was deformed. In addition to this, further precautions are required to make sure that only the density changes caused by deformation are recorded. Fig. 9 shows a diagram

100 of the apparatus used to measure differ• analysis, it would be virtually impossible, ential density. in practice, to make a simple and signif• Quantitative metallographic analysis. — icant count of the microcracks present. In any study of microcrack formation EUSPA 11-17 and propagation aimed at establishing the number of microcracks formed as a function of the creep conditions (time, stress, etc.), use must be made of quan• Bibliography: (1) C. CRUSSARD: Mémoires titative metallographic techniques, as has Scientifiques Rev. Metallurg.. 66 (1969), p. 333. (2) D.A.WOODFOR: Metal Sei.J., 3 already been mentioned. Most of the (1969), p. 50. (3) W. SIEGFRIED, S. 2IM- measurements are performed using a TV MERING: Rapport EUR 3752 e (1968). (4) microscope with which enough samples D. HULL, D.E. RIMMER: Phil. Mag., 4 for a statistical evaluation can be ana• (1959), p. 673. (5) M.V. SPEIGHT, J.E. HARRIS: Metal Sci. J., J (1967). p. 83. (6) lysed reasonably quickly. By the com• R.P. SKELTON: Metal Sci. J., 2 (1968), puter-aided application of equations used p. 106. (7) C. ZENER: "Elasticity and Anelas- in quantitative metallographic analysis, it ticity" University of Chicago Press, Chicago, is possible to determine the spatial dis• (1948). (8) J.E. HARRIS: Trans. AIME, 233 (1965), p. 1509. (9) E. RUEDL: "Proc. Euro• tribution and morphology (number, pean Conference on voids by irradiation of diameter, surface characteristics, form reactor materials" (1971). (10) R.T. RAT- factors) of the microcracks in each CLIFFE. C.W. GREENWOOD: Phil. Mag., individual sample. Fig. 10 shows a 12 (1965), p. 59. (11) A. GITTINS: Metal Sci. J., 1 (1967), p. 214. (12) R.C. BOETT- block diagram of the apparatus used at NER, W.D. ROBERTSON: Trans. Met. Ispra. An automatically controlled pro• Soc. AIME, 221 (1961), p. 613. (13) gram is used to count the microcracks P. BOWRING, P.W. DAVIES, B. WIL- projected onto the screen, so that the SHIRE: Metal Sci. J., 2 (1968), p. 168. (14) A. GITTINS: J. Mater. Sci., 5 (1970), metallographer's subjective evaluation is p. 223. (15) A. GITTINS: J. Mater. Sci., 5 replaced by an objective test value of (1970), p. 233. (16) G. PIATTI, H. KELLE• Fig. 10: Block diagram of the automatic good reproducibility and all the data RER, G. GEEL: J. Inst. Metals, 99 (1971), evaluating apparatus used at the Ispra Estab• contained in the picture can be quantita• p. 283. (17) R.V. DAY: J. Iron Steel Inst., lishment of the Joint Research Centre for 203 (1965), p. 279. (18) D. BOERMAN, quantitative metallographic analysis. A similar tively assessed fairly quickly. Without the R. LUBEK, R. MATERA, G. PIATTI: use of TV microscopes for quantitative in preparation. layout can be used in conjunction with an electron microscope.

Optical Preparation Electronic picture and analysis TV camera evaluating (micrograph of video apparatus or macrograph) signals

Printer Computer Magnetic Sample Monitor Numerical storage display etc.

101 Operation "Hot Mole" This value, which relates to only a minimum nuclear energy development programme in the Community, repre• sents the power generated by a fair-sized reactor. It is also interesting to ascertain the upper limit to the production and activity of solid waste. Self-burial: an elegant solution to the problem of storing high-activity radioactive effluents? The total energy consumed to date in the Community is of the order of 900 million tee (1 tee = 0.36 MWd). Let us imagine that this energy is at present JEAN DONEA * produced exclusively by nuclear means and that consumption increases by 5% a year. On the assumption that the effi• ciency of the power plants producing the energy vector (5) is 50% and that 10 000 Scale of the radioactive waste storage in the Community. The data on the MWd produce 25 litres of solidified waste problem production and activity of high-activity (2), by 2000 more than 110 000 m3 of waste were taken from an article which waste will have accumulated, generating The storage of radioactive residues appeared recently in this review (1). They something like 15 000 MW. from nuclear power plants is a crucial are based on the assumption of a mini• These figures show clearly that the problem, both because of the rapid mum nuclear energy development pro• problem of heat removal from nuclear increase in production levels forecast for gramme in the Six (40 000 MWe installed waste will, in a few decades, be extremely the coming years and because of the in 1980, 400 000 MWe in 2000). health and ecological implications of the grave. These considerations quite natu• question, and is one to which a solution On the basis of data supplied in a rally prompt the question as to whether must be found in the near future which recent American study (2), we have a storage technique is conceivable in will afford maximum security in matters estimated the thermal power generated which this heat could be used to bury of safety and protection. by all high-activity products accumulated waste in the lower strata of the subsoil. Such a solution is proposed in this Table I shows the importance which by the end of every decade. article. Before examining it in detail, we the problem of the disposal of waste In this evaluation, it has been assumed propose to review briefly the various from power reactors is likely to assume that the waste is stored for one year after storage techniques currently in use. the irradiated fuel is unloaded and that the reprocessing operations dilute the Techniques used for storing high-activity JEAN DONEA, Materials Division, Joint pure fission products by a factor of 10. waste [(2), (3)] Research Centre, Ispra Establishment of the The results are shown in the last line of Commission of the European Communities. Table I. It will thus be noted that the There is to date no long-term, large- power generated by the total waste scale industrial practice for the processing * With acknowledgements to Mr S. GIU• accumulated by the year 2000 will be of LIANI and Mr L. KESTEMONT for their of irradiated fuel from power reactors. assistance. the order of 700 MW. The disposal of high-activity effluents, in particular, is only just beginning to be a matter of concern to reprocessing plants. Storage in liquid form has been normal practice for some 20 years; the effluents, in the form of acid solutions, are contain• ed in stainless steel tanks or, if neutral• ized, in carbon steel tanks. The heat generated by radioactive decay is usually sampled during storage; this is done by immersing coils containing water in the active solution. Around 350 000 m3 of waste are currently stored in the United States in more than 200 underground tanks. Storage in liquid form by no means fulfils all the safety conditions necessary,

102 since some 15 carbon steel tanks have so cessing installations is an important Parametric study of self-burial far been known to develop leaks, causing problem in the usual storage techniques. contamination of the soil. Moreover, this It is obvious that the use of a self-burial type of storage takes up a great deal of The self-burial technique which we technique, like any other storage method, space and will not be practicable when suggest in this article, on the other hand, creates numerous problems. To name the quantities of effluent are much higher consists of using the heat generated by only a few, the containers must be made than at present. radioactive decay to dump the waste in of materials suited to the nature of the the deep strata of the subsoil. It is subsoil chosen for burial, care needs to Laboratories in a number of countries possible to pack high-activity solid waste be taken in filling and transporting the are thus considering the development of in suitable containers and bury these in containers, which are sources of consider­ other types of radioactive waste storage. the ground. If the heat generated by the able radioactivity and heat, and sites have To date, storage in solid form seems to products is higher than a critical value to be found in places where the subsoil is be the only technique offering an appre­ determined subsequently, after a certain uniform. ciable reduction in volume and an period of time the soil in contact with increase in safety. the container will melt and a further These problems, although important, burial process, this time automatic, will are not tackled in this preliminary study. Four high-activity liquid effluent solid­ take place. Provided that the container The need to investigate them will depend ification processes have been developed is denser than the soil and capable of on the answer to the question as to and tested in pilot installations during withstanding the melting point of the soil, whether self-burial can in fact work using recent years (2). They are: calcination in the self-burial process may be prolonged sources in the form of radioactive waste crucibles, spray solidification, phosphat- for as long as the power source, in the (limited thermal power and decay with ed glass encapsulation and fluidized-bed form of active waste, can supply the time) and containers of feasible dimen­ calcination. Each of these techniques necessary heat. sions. requires a supply of heat to rise the temperature and remove the volatile This, therefore, is a method of burying Accordingly we shall examine here only constituents (water, nitrates). The solid nuclear waste in the deeper strata of the the influence of the parameters directly left after cooling is relatively stable subsoil, with the threefold advantage of governing the self-burial phenomena, i.e.: chemically. being automatic, elegantly solving the — the external configuration of the The American regulations tend to problem of heat dissipation and minimiz­ containers and their overall dimen­ require compulsory solidification of fis­ ing the risks of soil contamination. sions; sion products in the five years after fuel unloading and storage in a "graveyard" (salt mine) in the 10 years following discharge. A different philosophy is beginning to emerge which recommends immediate solidification on leaving the Table I: Estimates of production and activity of radioactive waste in solid form in the Community. reprocessing plant and "cooling" in (a), (b): These figures are based on a minimum nuclear energy development programme solid form on site for three to five years. (40 000 MWe in 1980, 400 000 in 2000) (1). (c) : Volumes of waste accumulated at the end of each decade (1). In these cases, the process used would (d) : To give a tangible idea of the problems posed by storage, we have characterized probably be calcination of effluents with waste by the heat it generates. The thermal power existing by the end of the decade an inert diluent (e.g. aluminium nitrate). is due to all the solid waste accumulated at that date. It has been calculated from The cooled solid could be incorporated American data (2) on the assumption that the waste is stored for one year after in a less leachable medium (such as glass discharge and that reprocessing causes dilution of the pure fission products by a or metal) before being sent to the factor of 10. graveyard. In Europe no regulations or draft 1970 1980 1990 2000 regulations have so far been proposed. It should also be mentioned that studies (a) Curies discharged per year ( χ 10'J) 0.6 6 28 are currently in progress in the United 60 States to investigate the possibility of dumping the most active waste on other (b) Annual production (m3) 13 130 500 1 200 planets or the sun.

(c) Cumulated volumes (m3) 20 650 4 000 13 000 The principle of self-burial (d) Estimate of thermal power present As we have seen, the dissipation of heat (MW) — 60 250 700 in effluents from irradiated fuel repro­

103 Fig. 1 : Burial rates U altaìtìable with spherical containers are a function of: (a) radius R; (b) ratio between power Q generated by waste and critical power defined by equation [I]; (c) thermal diffusivity α of soil chosen for burial. At equal available power, the burial rate of a container depends on the mode of distribution of the heat flux over the outer surface of the container. The right­hand curve in the figure is for an isothermal container, and the left­hand curve for uniform distribu­ tion of the heat flux over the outer surface UR/2 cK of the container. G Experimental data on the 0,3 SÃ ft5 0,7 1,0 3 4 5 7 10 20 burial of a steel sphere in paraffin. _l I I I I ι ι ι _Ι Ι Ι Ι IIII

— the specific power of the heat source and its decay law; — the thermal properties of the subsoil. Any solution to the self­burial problem involves an examination of the movement in the subsoil strata of a heat source of finite dimensions and time­dependent power output. It will readily be realized that simplify­ ing hypotheses are necessary to make the solution of such a problem feasible. In order to linearize the differential equations governing the process, it is assumed that the thermal properties of the soil are independent of temperature. It is also assumed that the temperature field round the container appears station­ ary to an observer at the heat source. This % = = hypothesis entails a constant rate of burial in an infinite and homogeneous medium. As the power of the source Fig. 2: Isothermal sphere and uniform flux decreases in time, the time must be model. Illustration of the distribution of sur­ broken up so that the power of the source face heat flux. The isothermal sphere model can be considered as constant within each has a heat flux concentration in the burial interval. direction and thus, at equal available power, gives a higher burial rate than the model with Finally, dipole sources due to melting uniform flux distribution. (The arrow points and freezing of the soil and the effects of at the direction of burial). viscosity will be disregarded. In a first analysis, the presence of the container was simulated by applying to the edges of a cylindrical or spherical cavity made in the ground boundary conditions either of uniform thermal flux

104 Fig. 3: Distribution of isotherms round a The power densities can be estimated sphere undergoing burial in salt, on the on the basis of a standard fuel described assumption that the sphere surface is at a in an American study (2) and normally uniform temperature equal to the melting chosen as a reference for future repro­ point of the salt. (The arrow points at the cessing installations (3). direction of burial). The reference reactor is a PUR burn­ 235 ing U02 enriched with 3.3",, U . It operates at a mean power level of 34.8 MW/t and has a burnup of 33 000 MWd/t. 200"C or of uniform temperature equal to the melting point of the soil. This twofold The information in the work cited in analysis enables the top and bottom the bibliography enables the specific limits to the actual behaviour of a con­ power of the pure fission products to tainer to be defined and should permit a be evaluated as a function of the time definition of the most interesting areas elapsing since reactor shutdown. Thus, for a subsequent more detailed study. after 90 days of cooling, the pure prod­ ucts have a power density of 6 W/cm3; after 150 days, the power density drops Spherical containers to 4.4 W/cm3; after one year, it would be 2 W/cm3. Critical powers — It can readily be demonstrated (4) that the minimum Assuming that reprocessing dilutes the thermal power Qcr which a spherical pure products by a factor of 10, radio­ container of radius R (cm) must generate active waste of an initial power density to initiate the self-burial process is given equal to several times the final critical by the equation densities given in Table II should thus be available. Qcr == 4 π R k Tm (watts) [1] Burial rates — The burial rates obtain­ where k (W/cm Ό is the thermal able with spherical containers are a func­ conductivity of the soil and Tm (°C) its tion of their dimensions, the power melting point. density available and the thermal prop­ erties of the soil. The self-burial of a spherical container holding radioactive waste of power den­ In fact, the problem is a fairly simple 3 sity q (W/cm ) is therefore conceivable one, since all these parameters can be only if incorporated in two non-dimensional quantities, namely: 3kTm

q > -^ Η — the ratio Q/Qcr of actual thermal power to the critical power defined To establish an order of magnitude for by equation [I]: the power densities involved, let us take 2 Q/Qcr R · q/3 k · T,„ [3] the case of burial in salt, for which the ratio: k ~ 0.06 W/cm °C; T ~ 800 'C. m U · R [4] The minimum power densities are shown in Table II as a function of the of the product of the burial rate and the container radius. container radius divided by twice the It is not very easy to determine the thermal diffusivity of the soil. values of the power densities available The full investigation of self-burial of in radioactive waste. These depend very spherical containers thus reduces to the much on the type of fuel, the burnup, construction of a diagram giving the ratio the time elapsing between reactor shut­ Q/Qcr as a function of the quantity Z. down and storage of the waste and also on the dilution of pure fission products It is, however, obvious that the value Wk achieved when the fuel is reprocessed. of Ζ (and therefore the rate) correspond- 105 q = 0,2 q =0,3 q=o,4 q=o,6/ w/cm3

Fig. 4: The curves show the self-burial depth attain• able in salt. They are plotted as a function of the radius R of the spher• ical container and of the initial power density q of the waste. The sphere is assumed to be isothermal; the maximum depth is reached when the power density of the waste is reduced to a value equal to the critical density de• fined by equation [2].

ing to a given value of the ratio Q/Qcr sphere with uniform flux and the same from the waste, by a process of numerical depends on the way in which the heat diameter. The explanation is that, unlike integration at short time intervals during flux is distributed over the surface of the the uniform flux model, the isothermal which the burial rate may be regarded as container in contact with the soil. As was sphere model has a heat flux concentra• constant. previously mentioned, two configurations tion in the direction of burial. Fig. 2 have been devised in order to describe shows the heat flux distribution for the The burial depths obtainable were the actual behaviour of a spherical two models in question, while Fig. 3 calculated on the assumption that the container. shows the distribution of isotherms round subsoil consists of salt. a sphere in motion, it being assumed that In the first configuration, it is assumed the sphere surface is at uniform temper• Salt was not chosen at random. Firstly, that the edge of the spherical cavity ature. geologists tell us that there are numerous simulating the container is at a uniform salt domes in Europe several miles in diameter and more than 1 000 m high temperature equivalent to the soil melting Burial depths — The diagrams in (7). Secondly, the melting point of salt point Tm, whereas at a considerable dis• Fig. 1, expressed in polynomials, con• is 800 °C, whereas that of other rocks, tance away the temperature remains tain all the information required for such as granite, is often over 1 500 °C. undisturbed. calculating the burial depths obtainable It should also be noted that salt domes as a function of container radius and The numerical resolution of the tem• are integral geological structures, i.e., initial power density. perature field for various values of the they contain no faults or other defects. ratio Z, followed by integration of heat In this calculation, account was taken This characteristic is due to the fact that flux to obtain the power generated by of the decay in time of the thermal power salt is viscous under pressure. the container, gave the behaviour de• scribed by the right-hand curve in Fig. 1.

The second configuration assumes a heat flux uniformly distributed round the Table II: Critical power densities as a function of radius of spherical containers. Burial in salt edge of the spherical cavity. The results is assumed (melting point 800 °C). Self-burial is possible only if the power density of the waste obtained lead to the behaviour law exceeds the values given. It should be noted that, for containers with a radius of over 30 cm, described by the left-hand curve in the critical power densities are very low. Fig. I. R (cm) 10 20 30 40 50 It will be observed that, for equal power, the burial rate of an isothermal 3 q,r (W/cm ) 1.44 0.36 0.16 0.09 0.06 sphere is much higher than that of a

106 Fig. 5: The dynamics of the self-burial phenom­ enon are illustrated by the time curves for the depth reached by four spherical containers of which the radii R and the initial power densities q are given \M month(s)]. The IM IM isothermal sphere model is used ; burial takes 200 place in salt. —2M 2M --4M 4M IM ©6M 6M 400 4-2 M

600 4M

800 -8M (8>12M

-1000

Θ :R-30cm q=04 w/cm

3 0:R=4Ocm q=0 4w/cm » :R=30cm q=0 6 w/cm3 m 3 (g):R^4ocm q= 0 6 w/cm

Fig. 6: A preliminary check on the theoretical results was carried out by burying a steel sphere 5 cm in diameter in a paraffin block. The thermal power was supplied by the Joule effect of a resistor at the centre of the sphere with an external power supply. The results obtained are shown in Fig. I ; they are in fairly good agreement with the estimates id 'he is/flux model, as might have been expected from the type of experimental device used (low level of internal conduction).

107 Fig. 4 shows the self­burial depths containers, as in the case of spherical obtainable in a salt dome. In order to containers: visualize the dynamics of the phenome­ — calculation of critical powers; non, Fig. 5 shows the penetration in depth as a function of time. The diagrams — evaluation of burial rates as a func­ refer to isothermal spheres of a radius of tion of power available, geometry 30­40 cm ; the initial power density of the and subsoil characteristics; 3 waste is 0.4 or 0.6 W/cm . — estimation of burial depths attain­ Experimental verification — In order able. to check the theoretical data on the burial Only the case of a vertical cylinder has rates attainable, we carried out an exper­ been considered, i.e., with its axis of iment involving the self­burial of a stain­ rotation parallel to the direction of less steel sphere 5 cm in diameter in a burial. block of pressed paraffin. The thermal power required is obtained, as Fig. 6 It is shown (6) that the minimum shows, by the Joule effect in an electrical thermal power which has to be generated resistor at the centre of the sphere. This by a cylindrical container of radius R resistor is supplied by an external source, (cm) and height/diameter ratio equal to / the wiring being passed through a zone to start the self­burial process can be of liquid paraffin above the sphere. found from the equation c After an experimental determination of Q cr = 4 π R k T„ the critical power, we measured the burial 2/ rates for various values of the ratio Q/Qcr. Watts [5] log, [21 _1_ / 4 /2] The experimental points are plotted in V Fig. 1 ; it will be noted that they lie well inside the area delineated by the Compared with equation [1], this theoretical curves. expression shows that the critical power of the cylinder is equal to that of a sphere of equivalent diameter multiplied by a Cylindrical containers form factor greater than unity and There are three main phases in increasing with the value of the height/ the study of the burial of cylindrical diameter ratio (see Table III).

<¡o R(cm)

Fig. 7: Burial depths attainable in salt with cy­ lindrical containers. Two values (0.5 and 1) of the height ¡diameter ratio were considered. The cylinder 10 20 50 100 200 10001 surface is assumed to be IIII L_ I ι ι L_ ι ii I isothermal ; the initial l­_ 0.5 power density of the waste 1 = 1,0 is shown.

108 The burial rates are obtained by plott­ shown that the self­burial phenomenon 91­94. (2) "Siting of fuel reprocessing plants ing diagrams giving the ratio Q/Qç is a fact. and waste management facilities", Report r compiled and edited by the Staff of the Oak (actual power/critical power) as a func­ The power densities involved are of an Ridge National Laboratory, July 1970. tion of the parameter Ζ defined in order which allows the use of such a (3) E. DUTILLEUX, Eurochemic, Mol, Bel­ equation [4] and the ratio /. Only the process to be contemplated for the gium, personal information. (We acknowl­ isothermal model was used in order to edge with gratitude Mr Dutilleux'sinterest in definitive storage of high­activity radio­ approximate the behaviour of a real our work and the valuable information he has active waste. cylinder. provided.) (4) CR. EASTON: "Conduction from a finite­size moving heat source applied The thorny problem of the removal of The burial depths obtainable were to radioisotope capsule self­burial", (Dou­ the heat generated by radioactive decay calculated for salt and for height/diameter glas Aircraft Company, Santa Monica, is elegantly solved by using this heat as ratios of 0.5 and 1. Fig. 7 shows the California) pp. 209­218 of Thermal Conduc­ a driving force for the self­burial process tivity, Flynn et al., editors, Washington, depths obtained for the two cylinder types tiself. It even becomes desirable for the National Bureau of Standards, 1968. (The as a function of radius and of the initial fission products accumulated in solid power for thermoelectric generators on board power density of the radioactive waste. form not to be cooled down or diluted satellites usually obtained from radioisotope sources. The study in question was under­ too much, so that significant burial taken to estimate the consequences of fall­out Conclusions depths can be achieved with capsules of from a capsule of radioisotopes in the event acceptable dimensions. A preliminary theoretical study, con­ of an abortive launching). (5) G. de BENI, C. MARCHETTI: Hydrogen, key to the firmed by laboratory experiments, has At the same time, it is obvious that energy market, euro­spectra, 9 (1970) No. 2, we cannot claim, on the basis of the pp. 46­50. C. MARCHETTI: Hydrogen, arguments put forward in this article, master­key to the energy market, euro­spec­ to have solved all the problems connected tra, 10 (1971) No. 4, pp. 117­129. (These Table III: Form factor affecting the critical articles show how nuclear energy can cover power of a cylindrical container. with the application of a means of not only electric power requirements but also disposing of high­activity waste by most requirements of the energy market). Form factor self­burial. (6) J. DONEA, S. GIULIANI, L. KESTE­ MONT: Process of self­burial of contai­ What we have tried to do rather is to ners holding high­activity nuclear waste 1 1.39 point out a promising line of research. Report, EUR4903 ƒ (1972). (7) H. KRAUSE et al.: Project for storing radioactive wastes 2 1.90 EUSPA 11­18 in a salt cavity. Proceedings of the Sympo• sium organized by the IAEA and ENEA 3 2.41 on the Disposal of Radioactive Wastes into the Ground, Vienna, 29 May-2 June 1967. References: (1) G. GRISON: The creation Published by the International Atomic 4 2.88 of a Community system of radioactive waste Energy Agency. dumps, euro­spectra, 10 (1971) No. 3, pp.

1 09 Exoelectron tion of heat by Klaphecke (2) about 40 years ago. emission dosimetry Many data have been accumulated since then, mostly since 1950. Kramer (3) introduced the term "exoelectron emis• sion", and the abbreviation EE used MARTIN OBERHOFER today stems from his early attempt to explain the emission observed as a result of exothermal processes. Although the phenomenon is now known to be structure-dependent, the ONE OF THE METHODS most com• It was only very recently, i.e. some term "exoelectron emission" is still used monly applied in personnel dosimetry is, years ago, that work was commenced as well as the name "Kramer effect", it will be recalled', film dosimetry, which on a new dosimetric method, based on honouring J. Kramer's outstanding con• is based on the blackening of photograph• the observation that the surfaces of many tributions in this field. It was also ic emulsions. In the last few years solid materials emit low-energy electrons Kramer who extensively discussed the another technique has been developed during and after various kinds of possible application of exoelectron emis• —in addition to that using radio-photo- influences, of either a mechanical or a sion in dosimetry (4) when, in 1957, he luminescence (metaphosphate glasses)— chemical nature, such as crystallization noted a linear relationship between which is based on thermoluminescence processes, phase changes, exposure to exposure to radiation and exoelectron and is increasingly employed in present- light or irradiation with particles, X- or emission (5). day dosimetry. gamma-rays. Emission after these in• In 1966, then, Kramer succeeded in fluences can be obtained by illuminating observing dose-linearity over a dose- the materials with light or by heating range of more than six orders of magni• them up. MARTIN OBERHOFER. head of the tude by mixing his dosimeter substances Personnel Dosimetry Laboratory, Ispra Emission by means of illumination was establishment of the Joint Research Centre with graphite (6), a discovery which of the Commission of the European Com• observed back in 1896 by Elster and resulted in the systematic study of munities. Geitel (1), and emission by the applica• promising materials for their application in exoelectron dosimeters in laboratories here and abroad. An attempt is made below to explain in some detail the mechanism underlying exoelectron emission on the basis of the band model (7) and to give an idea of the measuring techniques used now, following this with a brief survey of the present state of the art.

Mechanism of exoelectron emission By analogy with luminescence, a process which is observed parallel to exoelectron emission [(8), (9)], it is at present assumed that the emission of electrons from the surfaces of solids is connected with the energy deposition in the crystallites of the materials in question by electron transitions between lattice imperfections. The energy deposition, which will subsequently be referred to here as the "excitation process", causes electrons to move the valence band to

1 See K. Becker: "Film dosimetry: a thing of the past?" euro-spectra, Vol. VI (1967), No. 3, pp. 78-83.

1 10 the conduction band, as is shown in path of thermal electrons [(11). (12)]. counter, which is at present employed Fig. 1. More recent studies indicate that the de• together with high-resolution propor• The energetic position of the traps (the tectable exoelectrons originate in a mate• tional counters in various laboratories "trap depth") is characteristic of the rial layer not thicker than 100 A (13). for dosimetric studies. Details of the material used. There may be different sample-detector arrangement shown in Fig. 2 can be seen in Fig. 3. Fig. 4 gives kinds of trap with various trap depths. Detection of exoelectrons The higher the deposited energy (e.g. the the block diagram of the accessory absorbed radiation dose), the more traps In early work exoelectrons were mainly instrumentation for the counter. will be filled up with electrons from the counted with point counters, Geiger- The result is a curve with one or more valence band. Müller counters and multipliers later emission maxima at characteristic tem• After the excitation process the elec• being used also. In some special cases peratures corresponding to traps of trons can be liberated from their traps the electron emission was measured with different trap depths. As in thermo• luminescence work, this curve is called by putting more energy into the solid, electrometer systems. Owing to their low the "glow curve", or more specifically either optically in the form of light, or energy the exoelectrons must pass directly the "TSEE curve", sometimes also the thermally in the form of heat. This into the detector. Thus, in the case of a "trap spectrum". Figs. 5 and 6 show process is called "stimulation", the term Geiger counter, the counter must be of such curves obtained with gamma- optical and/or thermal stimulation being the open type. Fig. 2 shows such a used. This process is indicated by number 4 in Fig. 1. In both kinds of stimulation electrical conductivity, luminescence and Fig. 1: Fairly simplified schematic band (number 4}. If fiotti there they return then exoelectron emission are noted. model for explaining luminescence and under emission of light (h\>) into their ori• Luminescence (thermoluminescence— exoelectron emission from solids. ginal place passing the so-called "accep• TL—if the stimulation is thermal) occurs By way of radiation absorption electrons tors" (number 5), one talks of lumines• are lifted from the valence band into the cence [thermoluminescence (TL) if the sti• if the electrons return from the conduc• conduction band (number I). After having mulation is thermal}. Exoelectron emis• tion band to their ground state, passing stayed there for a while (number 2), they sion occurs if the electrons leave the sur• through so-called "acceptors". This is drop into the so-called "traps" (number face of the solid (number 6). This case shown by the vertical line numbered 5. 3) which may be located within the solid requires an energy supply not less than Optically stimulated exoelectron emis• (volume traps) or at its surface (surface the sum of the trap depth and the work traps). The energetic position of the traps function. In the case of thermal stimula• sion (usually abbreviated to OSEE) and — "trap depth" — is characteristic of the tion, otie talks of "thermally stimulated thermally stimulated exoelectron emission material used. By putting more energy exoelectron emission" (abbreviated: TSEE); (TSEE) occur when electrons leave the into the solid (stimulation) the electrons in the case of optical stimulation, of surface of the material either via the can be liberated from the traps by lifting "optically stimulated exoelectron emis• conduction band, if they were trapped them first up into the conduction band sion" or. abbreviated, OSEE. in volume traps, or without passing through the conduction band in the case of the surface traps. The energy neces• Conduction sary for this process is given by the trap band traps depth and the work function. The intensity of the exoelectron emis• sion is related to the number of trapped |^ work electrons and thus to the excitation function energy or dose. Proportionality is expect• trap ed as long as the available traps are not depth exhausted. With increasing filling up of the traps saturation takes place (satura• tion effect). photons A low trap depth may cause "fading" at room temperature, as the thermal energy present is then sufficient to empty the traps with time. The fading charac• teristics of a material improve for increasing trap depth. The mean energy of the exoelectrons is about 1 eV (10). It was estimated that the exoelectrons originate within a surface layer of a valence excitation band thickness of the order of the mean free activators stimulation energy surface

111 Fig. 2: Overall view of a high-tempera• Fig. 3: Cross-section of the ORNL coun• ture TSEE Counter used at Oak Ridge ter shown in Fig.2. The counter, a gas- National Laboratory (ORNL) (24). flow counter, was designed ¡or thermal stimulation, which presents less several problems than optical stimulation. The irradiated beryllium oxide and with sample, which is inserted into a slide, is lithium fluoride powder, both mixed with heated with a small plate underneath it. In order to avoid heating up the counter graphite, the heating-rate being LC/sec. and thus impairing its counting cha• For integral dosimetric purposes either racteristics (plateau shrinkage), the lower the peak height is measured or—and this part of it is cooled with water. In a later gives better results—the area under the version of the same type of counter the peak by taking an integral count within whole sample-slide was cooled.

counter cooling loop brass slide

heater opening for marmite thermocouple container

1 12 a suitable temperature interval, e.g. 150- ting electrically conductive substances, Fig. 8 shows the TSEE curves for 350°C in the case of BeO. e.g. graphite, and by making use of CaS04 exposed to alpha and gamma electrometer-type readers in addition to radiation. The peak/height ratio can be Dosimetric properties counting devices. used for determining the effective linear energy transfer (LET) (19). Neutron of promising EE materials By means of optical stimulation dosimetry in mixed radiation fields might Kramer (18) even obtained linearity over Many substances, mostly ionic crystals, be possible in this way if a proton eight orders of magnitude with SrS0 have been investigated as potential exo­ 4 mixed with graphite, as can be seen in electron dosimeters [(4), (14), (15), (16)]. Fig. 7. In the course of these studies it was found that some substances are extremely sen­ With EE it might be possible to Fig. 4: Block diagram of the accessory sitive to radiation. Kramer (15) had measure doses even as high as I08R. instrumentation for the counter. The pulses previously reported that doses as low as Another feature of TSEE is the LET2 from the counter are fed into an emitter- a few μR can be detected with CaS04 dependence of the EE for some sub­ follower preamplifier; from there they en­ and that it might be possible to detect ter a gated decade scaler which is followed stances, which makes it possible to a tenth of a u.R. This is the main reason by a linear count-ratemeter. The output why exoelectron dosimetry is attracting differentiate between various kinds of of the ratemeter is fed into the Y-input so much interest at present. radiations. Typical examples are the of an X-Y recorder, the X-input of which alkaline earth sulphates CaS04, SrS04 is connected to a thermocouple mounted Exoelectron dosimetry offers other and BaSO,,. on top of the healing clement. The re­ striking advantages, such as the wide corder thus registers the count-rale of the dose range obtainable by "diluting" the TSEE counter as a function of the sample EE materials with non-exoelectron-emit- 2 Linear Energy Transfer temperature.

thermocouples

113 radiator were used together with the EE material. Some of the materials, such as LiF 400 and BeO, are also very attractive because the photon energy dependence of the exoelectron emission is rather flat. Further advantages of exoelectron dosimetry are the large variety of suitable 300­ substances. Besides the curves already mentioned, these include CaF2, BaF2, SrF2, some sulphides, Li2B407 and other metallic oxides apart from BeO. The materials can be taken from the chemist's shelf, are inexpensive and need 200 no complicated pretreatment (often an­ nealing by the heating­cycle itself within the reader is sufficient). Sample prepara­ tion is also simple, no sophisticated technique is necessary for evaluation and 100 the samples may be re­used if the reading does not require excessively high temper­ Fig. 5: TSEE curve obtain­ atures (deep trap depth). ed with BeO (UOX, raw­ material from Brush Beryl­ Particular attention is at the moment lium Co.) irradiated with being devoted to sintered ceramic BeO gamma radiation. as a highly radiation sensitive material Heating rate: I "C'/sec (24). 700 TCO with a low energy dependence of its response and with excellent storage prop­ erties (no observable fading at room and elevated temperatures). TSEE work TSEE ^135 °C with this material started in Oak Ridge in 1969 after it became evident that it might be difficult to build a rugged personnel dosimeter with any of the materials used hitherto for TSEE dosi­ 800 metry (20). Ceramic BeO, known to be also a good thermoluminescence material (21), prov­ ed to be such a good exoelectron emitter that even a few hours' exposure to back­ 600 ground radiation is sufficient to produce évaluable peaks, as can be seen in Fig. 9. The trap spectrum is similar to the one shown earlier for powdered BeO. Here also three emission maxima are observed if the radiation dose is sufficiently high. 400 Ceramic BeO has excellent mechanical features. It is solid, can be obtained in all kinds of shapes (as rods, discs and plates of various thickness), is impervious to water and resists nearly any chemical. 200 Besides its advantageous mechanical properties, ceramic BeO possesses a high thermal conductivity. Fig. 6: TSEE curve obtain­ 330 °C ed with LiF (Baker Anal.), 1 Some drawbacks, which might possibly irradiated with 154 R Cs­ be overcome, help up the design of a 137 gamma radiation. ^_J personnel dosimeter with ceramic BeO. Heating rate 1 "C/sec. J ΛΑ 100 200 300 400 500 600 700 τ CO

14 The first is that the ceramics used now 10' OSEE exhibit a non-linear dose response. This t ■ is demonstrated in Fig. 10, which shows 108 how the sensitivity, expressed in counts À per R of gamma-radiation, decreases for 7 S: increasing doses. 10

If the surface conductivity of the C IO6 ê samples is increased, this sensitivity -Ί / decrease with the dose is reduced (22), which is one way to overcome the 5 10 / / drawback. Another problem at the j moment is the energy dependence of the IO4 material, which has not hitherto been """*■ P measured correctly. Also, calculation is Dt U difficult, as the exoelectron emission is io3 a surface effect. Unless the radiation Fig. 7: Optically sensitive layer is covered by a sufficiently io2 thick electron equilibrium layer, the stimulated exo• surface layer will respond to electrons electron emission of SrSO, and from surrounding materials like the air BeO powder /> and supporting materials. More work is mixed with gra• being done on this subject at present. A phite, after irra• 10° more serious problem—and this applies diation with 10 IO*5 IO"4 IO-3 IO"2 10"' 10° IO1 IO2 IO3 IO4 Xn to the whole field of exoelectron dosi• keV X-rays (18). metry—is the poor reproducibility of the data. The reason for this is, again, that exoelectron emission is a surface effect. Many outside influences may cause exo• electron emission which can be eliminated mereiai EE dosimeter is available yet ; a only with the greatest care. first model of a TSEE reader with a p¡g g. TSEE curves obtained with CaSO. gas­flow counter is on sale by an elee­ (non­linear heating rate) after exposure to In one case a reproducibility of ± 2 % tronies company in Munich. alpha particles and gamma radiation (19). for 10-20 successive measurements using gold-plated and brass-framed ceramic BeO samples is reported (23). In another laboratory the standard deviation obtain• ed with Thermalox 995 varies from ± 5 to ± 15 % for the repeated exposure and reading of gold-plated ceramic BeO samples with no heat treatment between the individual readings. Nude samples showed better results. Here the standard deviation varied from ± 7 to ± 13 %. More effort has to be devoted to this problem in order to obtain better results.

Actual dosimeter design Owing to the present problems with ceramic BeO, the design of dosimeters made of this material is in its infancy. There is some work going on at Oak Ridge National Laboratory, while further studies are being carried out by CNEN at Bologna under a Euratom contract. Various TSEE dosimeters, mainly using BeO powder as the active layer, are described by Kramer (15). No corn- 100 150 200 250 300

1 15 400 CPS

300 15.3 h The very thin active layer of EE materials points to their suitability for measuring doses at interfaces (e.g. 200 bone/tissue interfaces) and dose profiles of narrow beams and for certain micro­ 4.5 h dosimetric problems. The high upper dose limit of some 100 materials might lead to new in­pile dosimeters, while the extreme sensitivity of others might produce very small dosimeters with a diameter of the order J TCO of some tenths of a micron. Q >■ Much attention will be paid to optical 100 200 300 400 500 stimulation, which makes it possible to cover dose ranges with one reader which with thermal stimulation could be covered only by several measuring methods. Fig. 9: Background radiation TSEE curves Further development of EE dosimetry (1 "C/sec) for ceramic BeO (Thermalox EUSPA 11­19 995 background exposure). Storage time: Certainly more effort will have to be 4.5 and 15.3. made in order to improve the dosimetric characteristics of the ceramic BeO which might be contemplated for use not only Bibliography: (1) J. ELSTER, H. GEITEL: in routine personnel dosimeters, but also Ann. Phys. (Leipzig), 59 (1896), p. 487. as a highly sensitive dosimeter for gonad­ Fig. 10: Gamma radiation sensitivity of (2) J. KLAPHECKE: Z. Phys., 67 (1931), dose measurements around X­ray instal­ p. 478. (3) J. KRAMER: Der metallische ceramic BeO us a function of exposure. lations, as a device for measuring Zustand, Göttingen, Vandenhoeck und Ru­ Upper line: counts/R obtained by eva­ background radiation (site survey, for precht (1950). (4) J. KRAMER: Ζ. Angew. luating first peak (175­375 °C); Phys., 15 (1962), p. 20. (5) J. KRAMER: Lower line: counts/R obtained by eva­ example) and for special low­level Acta Phys. austriaca, 10 (1957), p. 392. luating second and third peaks (375­ radioactivity studies, such as the mea­ (6) J. KRAMER: Z. Angew. Phys., 20 600 °C). surement of the distribution of gaseous (1966), p. 411. (7) W. HANLE: Acta effluents from reactor stacks or of the Phys. austriaca, 10 (1957), p. 339. (8) J. (23). As can be seen, the sensitivity (ex­ activity of low­energy particle­emitting KRAMER: Z. Phys., 133 (1952), p. 629. pressed in counts per R of gamma radia­ (9) J. KRAMER: Naturw., 41 (1954), p. tion) decreases with increasing doses. radionuclides in liquids. 160. (10) G. BARTHOW: Naturw., 45 (1958), p. 381. (11) B. SUJAK: Acta phys. polon., 20 (1961), p. 969. (12) A. R. KRASNAJA et al.: Opt. Spektr., 12 (1962), p. 526. (13) G. HOLZAPFEL: Phys. Stat. Sol., 33 (1969), p. 235. (14) W. HANLE, 1 ^____^ Z. SCHARMANN, G. SEIBERT, J. SEI­ BERT: Nukleonik, 8 (1966), p. 129. (15) • "■*»~_ » —„ J. KRAMER: Proc. Second Inter. Conf. on Luminescence Dosimetry ­ USAEC 9 ^^^ > Rep. Conf. (1968), p. 180. (16) K. BEC­ 5 KER: Proc. Second Inter. Conf. on Lumi­ 10 ­^ ; nescence Dosimetry ­ USA ES Rep. Conf. (1968), p. 200. (17) W. KRIEGSEIS, A. \ SCHARMANN, J. SEIBERT: Kernlech­ s nik, 13 (1971), No. 1, p. 11. (18) J. KRA­ 6 MER: Proc. Third Inter Symp. on Exo­ 5 electrons, PTB­Mitteilungen 80, No. 5 o (1970). (19) K. BECKER, N. CHANTA­ NAKOM: Nucí. Insti: a. Meth., 66 (1968), ρ 353. (20) E.M. ROBINSON, M. OBER­ HOFER: Health Phys., 18 (1970), No. 4, ) p. 434. (21) E. TOCHILIN, N. GOLD­ STEIN, W. G. MILLER: Health Phys., 16 2 (1969), p. 1. (22) J. F. WILSON: M. S. Thesis, Univ. Tennessee, to be published. (23) K. BECKER: Proc. Third Inter. Symp. on Exoelectrons, PTB­Mitteilungen IO4 80, No. 5 (1970). (24) M. OBERHOFER, R E. M. ROBINSON: Kernt. Isotopent. u. 10-2 10 10° Chemie, 12 (1970), No. 1, p. 34.

1 16 subject

Issue Page

APPLICATIONS OF ISOTOPES AND RADIATIONS

KOWALSKI Η. — Nuclear radiation exposes art forgers and coin counterfeiters 2 47­55

CHEMISTRY, METALLURGY

PIATTI G., LUBEK R., MATERA R. ­ Cavitation : study of microcrack formation and propagation phenomena in creep deformed metals 4 93­101

DOCUMENTATION AND INFORMATION

BREE R. — Cash, please ! •Spec 25­28 BUNTROCK H. — Agricultural documentation Spec 20­24 CAVARA L., PARFAIT A.F. — Documentation ma­ chines ? 1 24­28 d'OLIER J.H. — The european contribution to the world network of scientific and technical infor­ mation Spec 1­3 DUSOULIER N., van WESEMAEL A.L. — The working party on biomedical information and docu­ mentation: work and prospects. Spec. 14­19 MAUPERON A. — The latest child of a great fa­ mily Spec. 4­9 ROLLING L. — S.D.l.M. : the system of documen­ tation and information for metallurgy of the European Communities Spec. 10­13 WINTERS A.A. — User needs in an information system Spec 29­33

ECONOMICS, INDUSTRY AND LAW authors MORENZ A. — The importance of venture capital as a means of financing innovation 1 2­7 N"/Page BARAZZONI L. 1/12 BREE R. *Spec./25 HEALTH & SAFETY BUNTROCK H. Spec.'20 LEMOINE P. — The war on pollution: desulphur­ CAVARA L. 1 /24 ization of fuels and fuel gases 1 8­11 COLLING Α. 1/12 OBERHOFER M. — Exoelectronemission dosimetry 4 110­116 d'OLIER J. Η. Spec/1 RAVERA O. — Water, water everywhere, nor any DONEA J. M. 4/102 drop to drink... 2 34­46 DUSOULIER Ν. Spec/14 SANDRONI S. — Remote sensing of atmospheric pollution 2 56­64 EHRENTREICH J. 1/12 HIPP G. 3/66 KOWALSKI H. 2/47 INTERNATIONAL COOPERATION LEMOINE P. 1/8 HIPP G. — Sun or rain ? Use of European Centre LUBEK R. 4/93 for medium­term weather forecasting 3 66­85 MATERA R. 4/93 PONS V. — Why must a European currency be MAUPERON A. Spec/4 created ? 4 91­92 MORENZ A. 1/2 NACFAIRE H. 1/12 REACTORS OBERHOFER M. 4/110 BARAZZONI L„ COLLING Α., EHRENTREICH J., PARFAIT A. F. 1/24 NACFAIRE H., SIEBKER M. — Light­water nu­ PIATTI G. 4/93 clear plants in the Community : the present PONS V. 4/91 position and development prospects 1 12­23 RAVERA 0. 2/34 ROLLING L. Spec/10 WASTE DISPOSAL AND PROCESSING SANDRONI S. 2/56 DONEA J. — Operation « Hot Mole ·· ­ Self­burial : SIEBKER M. 1/12 an elegant solution to the problem of storing van WESEMAEL A. L. Spec/14 high­activity radioactive effluents ? 4 102­109 WINTERS A. A. Spec/29

•Spec. = Special issue devoted to scientific in­ 'Spec. = Special issue devoted to scientific information in the Com­ formatlon ¡η the Community. munity.

1I7 Index to Technical Notes 1972 (left: serial number of notes; right: issue and page.;

786 Air filter for a hot eel 3/87 868 A circuit arrangement for digitalizing an analog value of short duration 1/III 769 Capsule slitter 3/87 1062 A process for the prevention of carbon deposits on iron and steel surfaces in an environment containing carbon monoxide 3/III 1062 A process for the prevention of carbon deposits on iron and steel surfaces in an environment containing carbon monoxide 3 llf 868 A circuit arrangement for digitalizing an ana­ log value of short duration 1/III 66/C Device for collecting and filtering Seston 3/86 639 Device for bleeding gas from a sealed enclosure or for introducing it into such an enclosure 1/31 920 Device for milling and drilling grooves and radial holes in the inner walls of tubes 3/88 66/C Device for collecting and filtering Seston 3/86 921 A device for extracting radioactive samples from a reactor and maintaining them at the temperature of liquid nitrogen 3/88 868 A circuit arrangement for digitalizing an analog value of short duration 1/III 920 Device for milling and drilling grooves and radial holes in the inner walls of tubes 3/88 836 A method for the production of an electrical and mechanical connection between a GeTe semi­ conductor and a metal electrode 1/32 836 A method for the production of an electrical and mechanical connection between a GeTe semiconductor and a metal electrode 1/32 639 Device for bleeding gas from a sealed enclosure or for introducing it into such an enclosure 1/31 725 Heat exchanger 1/31 921 A device for extracting radioactive samples from a reactor and maintaining them at the temperature of liquid nitrogen 3/88 786 Air filter for a hot cell 3/87 66/C Device for collecting and filtering Seston 3/86 845 Investigation of gamma- or X-radiation 1/32 639 Device for bleeding gas from a sealed enclosure or for intro­ ducing it into such an enclosure 1/31 920 Device for milling and drilling grooves and radial holes in the inner walls of tubes 3/88 725 Heat exchanger 1/31 64/C High-speed motor 1/30 920 Device for milling and drilling grooves and radial holes in the inner walls of tubes 3/88 786 Air filter for a hot cell 3/87 920 Device for milling and drilling grooves and radial holes in the inner walls of tubes 3/88 6B8 Thermal insulation 1/31 1062 A process for the prevention of carbon deposits on iron and steel surfaces in an environment containing carbon monoxide 3/II A device for extracting radioactive samples from a reactor and maintaining them at the temperature of liquid nitrogen 3/88 61/C Remote-controlled sectioning machine 1/29 65/C Optical measuring rig for wall-thickness measure­ ments on tubes 3/86 836 A method for the production of electrical and mechanical connection between a GeTe semiconductor and a metal electrode 1/32 729 Welding of composite metal/metal oxide tubes 1/32

I IS First European congress on documentation systems and networks

836 A method for the production of an electrical and mechanical connection between a GeTe semi-conductor and a metal electrode 1-32 729 Welding of composite metal/ metal oxide tubes 1 32 836 A method for the production of an electrical and mechanical connection between a GeTe semiconductor and a metal electrode 1/32 Metrology rig 1.29 Device for milling and drilling grooves and radial holes in the inner walls of tubes 3 88 High-speed motor 1/30 A method for the production of an electrical and mechanical The Commission of the European connection between a GeTe semiconduc­ Communities will hold a First European tor and a metal electrode 1.32 Storage system for radioactive probes 3/III Congress on Documentation Systems and A process for the prevention of carbon Networks from 16 to 18 May 1973 in deposits on iron and steel surfaces in an environment containing Luxembourg. carbon monoxide 3 III Storage system for radioactive probes 3/111 There will be three sessions dealing A device for extracting radioactive samples from a reactor and main­ taining them at the temperature of respectively with: liquid nitrogen 3 88 A device for extracting radioactive - Input operations: data collection and samples from a reactor and maintaining them at the tem­ storage; perature of liquid nitrogen 3/88 Remote-controlled sectioning machine 1/29 - Processing methods - products and Optical measuring rig for wall-thickness measurements on tubes 3/86 services ; A device for extracting radioactive samples from a reactor and maintaining - Financial and management aspects. them at the temperature of liquid nitrogen 3/88 Device for bleeding gas from a sealed enclosure or for introducing it into The working languages wil be: En- such an enclosure 1/31 Remote-controlled sectioning machine 1/29 glish, French and German. A method for the production of an electrical and mechanical connection The congress will be preceded by a between a GeTe semiconductor and a metal electrode 1/32 Device for collecting and filtering Seston 3/86 Seminar entitled "the Anatomy of Capsule slitter 3/87 an Operational Documentation System" A process for the prevention of carbon which will be held on 14 and 15 May deposits on iron and steel surfaces in an environment containing carbon monoxide 3/III 1973. Storage system for radioactive probes 3/III A process for the prevention of carbon deposits on iron and steel surfaces in an environment containing Persons intending to submit papers carbon monoxide 3/III should contact one of the three orga• Storage system for radioactive probes 3/III A device for extracting radioactive nizers before 15 November 1972: samples from a reactor and maintaining them at the temperature of liquid nitrogen 3/88 - Institut français de Formation perma• Thermal Insulation 1/31 nente (I.F.F.P.) 14, Rue Gramme, Welaing of composite metal/metal oxide tubes 1/32 e Optical measuring rig for wall-thickness Paris (XV ) (attn. Mrs. STERN Tel. measurements on tubes 3/86 727 75 09). Device for milling and drilling grooves and radical holes in the - Bureau Marcel van DIJK, 409, Avenue inner walls of tubes 3/88 Louise, 1050 Bruxelles (Tel. 48 66 97). Underwater X-ray apparatus 1/30 Optical measuring rig for wall-thickness measurements on tubes 3/86 - Commission of the European Commu• Device for milling and drilling grooves nities, DG Dissemination of Informa• and radial holes in the inner walls of tubes 3'88 Welding of composite metal/metal oxide tion, 29, rue Aldringen, Luxembourg tubes 1/32 (attn. Mr. EMRINGER - Tel. 2 92 41, Investigation of gamma- or X-radiation 1/32 Underwater X-ray apparatus 1/30 ext. 360).

119 variables avec la température. EUR • JN-METD2 - A Fortran—IV pro• 4809 /. gramme for solving neutron trans• port problems with isotropic scatter• • Extraction du plutonium des com• ing in multilayer slabs by the ¡N bustibles eau lourde par le procédé method. EUR 4839 e. Saltex. EUR 4812 f. • Measurement of correlation proper• • Viscosity measurement of fuel sus• ties of the bubble field in two-phase pension under irradiation by means flow. EUR 4840 e. of VISIR-2 measuring device. EUR 4817 e. • C.C.R. ISPRA - Caratteristiche del ¿Just pHÚti&AeÁ sito. EUR 4841 i. • Transient heat conduction through Reports 1972 heat producing layers. EUR 4818 e. • Filling alloys for fast breeder fuel element conditioning. EUR 4857 e. • Trace level determination of oxygen in organic coolants and ultra-micro • Radioaktive Kontamination von determination of oxygen in C-H-O Lebensmitteln in den Gemeinschafts• organic compounds. EUR 4822 e. ländern im Jahre 1970. EUR 4858 dl f Hin. • Etudes préliminaires sur le rôle du zooplancton dans la constitution et • Transient heat conduction through a le transfert de la matière organique cylindrical three-layer hollow fuel au sein de la chaîne alimentaire element with internal and external marine en Mer Ligure. EUR 4823 ƒ. cooling. EUR 4862 e. • Etude par absorption différentielle • Studies on the radioactive contami• dans l'infrarouge des lipides et des nation of the sea. EUR 4865 e. • Deep penetration of neutrons in polymères irradiés. EUR 4828 f. • Recommandations sur les mesures hydrogenous shields. EUR 4743 e. • Calculations for fission neutron and des irradiations reçues par les maté• gamma multiplicity measurements. riaux de structure de piles. EUR • Collectrons, self-powered neutron EUR 4829 e. 4867 f. flux detectors. EUR 4775 e. • Spectrometer using NaI(Tl)-Ge(Li) • Application of atomic energy in • Mikrodosimelrische Untersuchungen detectors in coincidence and anti• agriculture. EUR 4868 e. zur Energieübertragung schneller coincidence for (n,gamma) investiga• Neutronen an weiches Gewebe. • Isolamento e determinazione di pro- tions. EUR 4831 e. EUR 4787 d. toattinio-231 nelle urine. EUR 4870 • La formation postgraduée des scien• • Kalibrierung von Vakuummessgerä- tifiques dans la Communauté Euro• ten. EUR 4797 d. péenne. EUR 4832 f. A possible function for RNA to DNA inverted transcription in anti• • Variable dead time neutron counter • Four computer codes for dynamic body biosynthesis and irreversible for tamper resistant measurements process inventory determination differentiation. EUR 4871 e. of spontaneous fission neutrons. application in safeguards. EUR EUR 4801 e. 4833 e. Survey of fusion reactors technology. EUR 4873

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