UCRL-TT-112792 T RA N S L A T 1 0 N

Report on The Useability of Reactor Plutonium in Weapons

TRANSLATED FROM ORIGINAL TITLE

Bericht zur Waffentauglichkeit von Reaktorplutonium

AUTHORS

Egbert Kankeleit-Christian Küppers-Ulrich Imkeller

SOURCE Institute fur Kernphysik Technische Hochschule Darmstadt December 1989

TRANSLATED DATE LLNL REF NO: 21 january 1993 04191

TRANSLATED FOR: TRANSLATED BY:

Lawrance Livermare Berkeley Scientific National Laboratory Translation Service Livermore, CA 94550 510 548-4665

Report on the Useability of Reactor Plutonium in Weapons

Egbert Kankeleit Christian Küppers* Ulrich Imkeller

Institute of Nuclear Physics Technical College Darmstadt

December 1989

Expanded report on the occasion of the testimony given by experts on the issue I'Danger of Atomic Weapon Proliferation1' in the Hessian Parliament on 6/15/1984

*Christian Küppers is with the Ecology Institute of Darmstadt

1 Introduction

This report endeavors to explore the issue of whether it is possible to build atomic weapons by making use of “reactor plutonium,” i.e., plutonium obtained in power-generating reactors. In the USA, scientists who were themselves active in atomic weapon projects have made public statements of their fear of misuse of reactor plutonium for weapons purposes since the early seventies.

In the Federal Republic, the question of possible misuse continues to be important, even after the stoppage of construction of the reprocessing plant at Wackersdorf, since the processing of fuel elements and the separation of reactor plutonium continue to be the primary goal of the disposal policy. There are also horizontal proliferation problems associated with a transfer of technology. The boundary between civilian and military use is blurred.

The so-called "home-rigged bomb" is, to be sure, unrealistic. All the more reason to inquire into the capabilities of a country, whether a highly developed industrial nation or a nation of the so-called Third World, which is using nuclear energy. As well as assess the capabilities of a technically trained group of terrorists.

This version is a revision of the report with the same title of May 1988. The bibliography has not been updated. The situation discussed is as of July 186.

The first chapter consists of a historical survey and contains:

· a review of international literature regarding opinions as to the useability of reactor plutonium for weapons,

· a survey of proposed methods of making plutonium artificially unsuitable for weapons,

· an evaluation of the discussion held in the Federal Republic of Germany on the useability of reactor plutonium for weapons.

The second chapter deals with special problems in the handling of reactor plutonium for weapons purposes and several additional physical aspects, including:

· projectile techniques for compacting "subcritical" masses into "critical" ones,

· formation and composition of plutonium isotopes in fuel elements,

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· handling of reactor plutonium with respect to effects of radioactive radiation and the concomitant release of heat,

· influences of radiation and heat output on a chemical explosive charge,

· reasons for the use of weapons-grade plutonium by the established nuclear- armed states.

The third chapter discusses the preignition problem of a plutonium fission bomb. The intention is to refine the figures cited on the statistics of the energy liberation (yield).

Of course, in the time allotted to us for this work, we were not able to examine all existing material, or to cite, much less evaluate, all material examined. But neither have we made a onesided choice of the material cited by us.

First, an explanation of some of the concepts used hereafter:

By weapons-grade plutonium is generally meant plutonium having less than 7% of the isotope plutonium-240, in addition to plutonium-239. Chapter 2.1 and 3 explain in greater detail why plutonium-240 influences the quality of the plutonium for weapons purposes.

By reactor plutonium we mean - in keeping with the conventional definition - plutonium that has been produced in light water reactors for production of electricity. For reasons of economy, the fuel is allowed to remain in the reactor until the isotopes plutonium-238, plutonium-240, plutonium-241 and plutonium- 242 are formed in significant quantities, in addition to plutonium239. A typical isotope composition of reactor plutonium might 2 be, e.g.: 1. 5% 238pU; 56.5% 239Pu; 26. 5% 241pU; 11. 5% 241 Pu and 4 l% 42pU [ALKE82].

The brisance (in English, Ilyield") of an atomic weapon is generally given as the TNT (trinitrotoluene) equivalent. For example, an atomic weapon of 1 kiloton (kT) TNT has the same explosive power as 1 kiloton (1000 tons) of the explosive TNT.

The burn-up of fuel elements is a measure of the energy produced from them by nuclear fission. Typical thermal powers of nuclear power plants (e.g., Biblis A) lie in the range of 3 GW (3 109 W) , and the fuel inventory amounts to roughly 100 T uranium. With an operating life of around three years for the fuel elements, the energy produced is (3 GW/100 T) 3 365d = 33 GWd per T. For weapons- grade plutonium, the burn-up is under 5 GWd/t. 3 Table of Contents

1. State of Discussion Of the Useability of Reactor Plutonium for Weapons in Retrospect

1.1 International Developments Since the Discovery of Plutonium

1.2 Proposals for the Denaturing of Plutonium Since the Mid Seventies

1.3 Views Regarding the Useability of Reactor Plutonium for Weaponry in the Federal Republic of Germany

2. Special Problems in the Handling of Reactor Plutonium for Weapons Purposes

2.1 Blasting Techniques in Plutonium Bonds

2.2 Formation of Pu-Isotopes in Fuel Elements and the Neutron Background

2.3 The Neutron Source for Initiation of a Chain Reaction

2.4 Handling of Reactor-Grade Plutonium

2.4.1 Dose Load from Radioactive Radiation

2.4.2 Heat Liberated by Radioactivity

2.4.3 Self-Ignition in Plutonium Processing

2.5 Influences of Reactor Plutonium on an Explosive Charge

2.5.1 Influences of Radioactive Radiation

2.5.2 Influences of Thermal Output

2.6 Traceability of Reactor Plutonium Through Its Radiation

2.7 Reasons of Nuclear-Armed States for the Use of Weapons-Grade Plutonium

3. Estimates on the Likelihood of Preignition

4. Supplement

4 1. State of Discussion of the Useability of Reactor Plutonium for Weapons in Retrospect

1.1 International Developments Since the Discovery of Plutonium

The plutonium--239 used for the first experiments had been produced in the cyclotron of Berkeley (USA) from 1940 on. The first larger quantities were obtained in a reactor at Clinton, Tennessee, and they contained the first significant amount of the spontaneously fissioning isotope, plutonium-240. Studies on this (at the time) reactor-grade plutonium revealed, in July 1943, a much larger emission of neutrons than that of pure plutonium-239. This was a heavy setback for the Manhattan Project, occupied in the development of the first atomic bombs, since this plutonium could no longer be used with the colliding-impact techniques of critical configurations developed at the time [HAWK61). But suf f icient quantities of plutonium f or construction of bombs could only be produced by means of a reactor, so that the goal of a plutonium bomb was quickly placed on the back burner.

The much-cited "Los Alamos Primer" [SERB43] of April 1943, being an introductory course to the Manhattan Project, declassified in 1961, is still unaware of the isotope plutonium-240 and the difficulties associated with it. The configurations of subcritical masses that are supposed to form critical masses when hurled together, as explained in the primer, although very diversified, did not yet include the implosion method. Within a year, the then-new explosive lens technique was developed, also making this plutonium suitable for the first test in July 1945. The energy yield produced was far greater than most expectations of the scientists involved in construction of the bomb (see also Chapter 2.1). Such plutonium, which is unsuitable for weapons purposes because of its isotope mixture, had already been termed 11denatured.11 One of the discoverers of plutonium, Glenn T. Seaborg, reported in 1976 that he had explicitly pointed out already in 1945, especially in written opinions on drafts of the so-called Franck Report, that such a "denaturing" with the isotope plutonium-240 alone is not possible [WOHL77]. He was disappointed in not finding this fact mentioned either in the Franck Report of 11 June 1945 or the Acheson-Lilienthal Report [ACHE46] of 16 March 1946. (These two reports constitute an early common effort of scientists, the military, and politicians to assess and influence, as they saw fit, the consequences of the newly-emerging atomic technology.)

The Acheson-Lilienthal Report stated that plutonium could be denatured so as to prevent the construction of effective atomic weapons by any (then) known technique. A technical development that made possible such construction would require more strenuous scientific and technical exertions. On the other hand, reactors could be allowed to operate with the denatured material. In any case, the Acheson-Lilienthal Report stipulated: 5 "only a constant re-examination of what is sure to be a rapidly changing technical situation will give us added confidence that the line between what is dangerous and what is safe has been correctly drawn; if it will not stay fixed."

The representative of the United States in the United Nations Atomic Energy Commission, Bernard M. Baruch, submitted a plan to the United Nations on 14 June 1946 for handing over all fissionable material to an international agency. The proposal was known as the "Baruch Plan" [BARU46] and it contains a passage taken from a press release of the Department of State on 9 April 1946:

"In some cases denaturing will not completely preclude making atomic weapons, but will reduce their effectiveness by a large factor... Further technical information will be required ... before precise estimates of the value of denaturing can be formulated. Denaturing though valuable in adding to the flexibility of a system of controls, cannot itself eliminate the dangers of atomic warfare."

"Denaturing" meant, explicitly, the transformation into a weapons-unsuitable mixture by adulteration with an isotope of the same chemical properties. Like the Acheson-Lilienthal Report, Baruch mentioned no specific denaturants. In any case, the establishment of Baruch's proposed "limited form of a World Government11 [WILL74) foundered because the USA would only destroy its atomic weapons if all other fissionable material produced on earth were handed over to the international agency and an international supervision set up.

For a long time thereafter, there was no more public mention of a possible use of the plutonium produced in energy reactors for atomic weapons. A statement by the U.S. Atomic Energy Commission in 1952 that, contrary to former assumptions, reactor plutonium would indeed be suitable for weapons, apparently went unheeded [TAYL73]. Also, as the Shippingport Reactor in the USA was the first atomic reactor in the world intended exclusively for generation of electricity, being placed in operation in December 1957, and the so-called peaceful use of atomic energy becam; increasingly widespread, few people pointed out the possibility of further spread of atomic weapons in this connection. Only in the early seventies was this issue, so to speak, rediscovered in the USA. In other countries - such as France - this occurred somewhat earlier, though exciting no attention [LOVI80].

One of the first warning voices, J. Carson Mark, has been often cited, and shall continue to be. Mark, for many years the director of the Department of Theoretical Physics at Los Alamos and also involved in the Manhattan Project, said at the tenth Pugwash

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Symposium in Racine, Wisconsin (26-29 June 1970), published in 1971 MARK7 1 ] :

"I would like to warn people concerned with such problems that the old notion that reactor-grade plutonium is incapable of producing nuclear explosions - or that plutonium could easily be rendered harmless by the addition of modest amounts of plutonium-240, or "denatured," as the phrase used to go-that these notions have been dangerously exaggerated. This observation is, of course, of no direct practical interest to the United States or the USSR, who have adequate supplies of weapon-grade plutonium, and have proved designs for weapons much better than could easily be made with plutonium from power reactors. To someone having no nuclear weapons at all, or no source of high-grade materials, however, the prospect of obtaining weapons - even of an "inferior" or "primitive" type could present quite a different aspect."

Mark also reported that he spoke at the conference with Jan Prawitz of the National Research Institute of Defense in Stockholm and learned that one of Prawitzl colleagues could prove, mathematically, that all kinds of reactor-grade plutonium could be used in bombs [MARK71, PRAW74].

In the early seventies, Theodore B. Taylor began his persistent warnings against possible misappropriation of reactor plutonium by terrorists. He did so, for example, at the Symposium on Implementing Nuclear Safeguards at the University of Kansas, 25-27 October 1971, published in 1972 [TAYL72). Taylor was entrusted with the development of atomic weapons from 1946 to 1956 at Los Alamos, then served as Technical Director of the Nuclear Space Propulsion Project and Senior Research Advisor at the General Atomic Division of General Dynamics Corporation, moved to the Defense Atomic Support Agency in Washington, spent two years in Vienna at the International Atomic Energy Agency and finally, in 1967, founded the International Research and Technology Corporation, devoted primarily to the social effects of technical developments.

At the aforesaid symposium, Taylor left it to David B. Hall [HALL72] to answer the question of whether terrorists could build a working bomb with reactor-grade plutonium; later on, Taylor summarized these two related issues in his own publications. Hall, Manager of the Safeguard Program at Los Alamos Scientific Laboratory, confined himself in 1971 to discussing explosions with a strength of several tons of high explosives. However, he is on record in stating that even smaller energy yields could produce enormous destruction and are unacceptable. Hall [HALL72] remarks: 7

"Commercial grade plutonium will have a large fraction of its content as plutonium-240 with its high spontaneous fission rate. This constitutes a large neutron presence of more than a million neutrons per second and complicates the design. one can imagine rapid assembly methods that will to some extent overcome this difficulty and result in an explosive yield. In general, it can be stated that the high plutonium-240 content will make the explosive performance quite unpredictable but not impossible. The degree of sophistication required for a successful device with this material is greater than the types previously discussed. However, one should not assume that such sophistication does not exist in the criminal or fanatic world."

Victor Gilinsky, Physicist at the Rand Corporation, in an article of the book "Civilian Nuclear Power and Internal Security" (WILL71], had advanced the view in 1971 that reactor-grade plutonium might greatly restrict the serviceability of an atomic weapon, even when the implosion technique is used. Gilinsky therefore considered civilian plutonium as generally unsuitable in simple, reliable and effective weapons. In 1972, however, in a reprint of this article in the journal Environment (GILI72], he already added a quotation from J. Carson Mark (see above) in a separate box as "A Warning Note." Gilinsky wrote that Mark's warning utterances added a new dimension to the problem. Afterwards, Gilinsky was one of the members of congress pointing out proliferation problems with greatest vehemence.

Also noteworthy is the book "International Safeguards and Nuclear Industry," published by Mason Willrich in 1973, which was the outcome of a study commissioned by the American Society of International Law's Panel on Nuclear Energy and World Order, with financial support from the National Science Foundation. Willrich himself was a professor of law dealing with disarmament issues. In his own contribution to the book (WILL73], he wrote:

"While the plutonium produced in the course of normal commercial operation of most types of power reactors is very difficult to use in an efficient explosive, it is relatively easy to use in a crude, inefficient explosive device."

The al ready- introduced Theodore B. Taylor also contributed an article to this book [TAYL73]. He also added to his discussion of issues of the diversion of plutonium, whether by a country or by terrorists, a section dealing with the construction of a possible device. However, he confined himself essentially to stating that all necessary knowledge was now freely accessible, and only had to be brought together from various publications.

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The book published together by Willrich and Taylor in 1974, "Nuclear Theft: Risks and Safeguards" (WILL74), received much attention. Years later, many authors have tried to refute the thesis of this book; we shall take up several of these works hereafter. Willrich and Taylor wanted to make the public aware of the danger of theft of bomb-capable nuclear material in order to force the authorities to take countermeasures. The book was a report written by Willrich and Taylor on a project of the energy policy of the Ford Foundation. The original intention was to include a list of freely available literature providing the necessary information on construction of simple nuclear explosives. Representatives of the U.S. Atomic Energy commission, who received a manuscript for examination, stated that this list contained no classified literature. However, various reviewers advised against the publication of such a list and ultimately had their way. This shows how concerned expert circles already were with respect to a "do-it-yourself bomb." (This would not yet have been available with the naming of a classified source.) Willrich and Taylor believed it possible to attain a level of information greater than that prior to ignition of the first plutonium bomb, by means of unclassified literature. The authors estimated the possible energy yields in the area of kilotons of TNT ("very likely") and emphasized that terrorists could kill 100,000 or more people by setting off a simple bomb in the right place.

In 1974, the Stockholm International Peace Research Institute (SIPRI) brought together the contributions to a review conference on proliferation problems of June 1973 in a book (SIPR74). John C. Hopkins of Los Alamos Scientific Laboratory stated herein that the production of enormous quantities of plutonium in power reactors would not be such ground for concern were it not possible -contrary to earlier assertions - to employ this reactor plutonium in nuclear weapons (HOPK74]. Jan Prawitz of the Ministry of Defense in Stockholm [PRAW74] cited the Finnish physicists P. Jauho and J. Virtamo, according to whom an explosion intensity of up to one kiloton TNT could be achieved with reactor plutonium, even under the most unfavorable conditions. Jorma K. Miettinen, professor at the Institute of Radiochemistry of the University of Helsinki (MIET74], then examined special possibilities of use of reactor plutonium. According to Miettinen, one Robert M. Lawrence, in an article written in 1969 but published only in 1971 in the journal General Military . Review, had already underscored the advantages of atomic weapons in the range of tons of TNT equivalent CLAWR71]. These weapons could also be used in the vicinity of one's own troops and have a "more favorable" ratio of dead and wounded as compared to conventional weapons (3:1 instead of 1:3). Miettinen further argued that it was already possible to achieve such relatively low energy yield with reactor plutonium, although its exact magnitude could not be reliably predicted. In using such weapons, however, one need only make sure that his own troops are as far away from the explosion site as would be necessary if the maximum possible explosive force were attained. In any case,

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Miettinen also admitted that nations in possession of definite weapons-grade plutonium would not put up with the disadvantage of the unreliable explosive force, along with the somewhat more clumsy form of such a "mini weapon."

Note: In an interview on 13 April 1972, the former American head of the Def ense Department, Melvin Laird, gave the f irst indication that such "mini weapons" had actually been developed [SIPR74, SIPR76]. Arkin, et al., CARKI84] estimated that the USA in 1984 had more than 922 IIW48 explosives" (explosive power under 100 T TNT) and 260 IIW54 explosives" (explosive force between 10 and 1000 T TNT).

Yet it was the detonation of an Indian atomic bomb in May 1974 that first began a process in the USA that led, within three years, to the problems of proliferation being discussed not only by individuals in the U.S. Congress and scientists. In the spring of 1976, proliferation became an issue in the presidential election of the United States. (This turn of events is described in detail by Michael J. Brenner of the University of Pittsburgh [BREN81J.) The then-President of the United States, Gerald R. Ford, and his opponent, Jimmy Carter, declared that reactor plutonium was basically useable for weaponry and feared a proliferation by widespread closure of the civilian fuel cycle with reprocessing plants and Fast Breeders. Ford justified his reservations against the commercial closing of the fuel cycle in a statement of 28 October 1976 [FORD76] with the words:

"Unfortunately - and this is the root of the problem -the same plutonium produced in nuclear plants can, when chemically separated, also be used to make nuclear explosives."

Thus, after many years of efforts, especially on the part of politically committed scientists, acknowledgement of the useability of reactor-grade plutonium for weaponry finally gained admittance to the highest policy level - at least, in the USA.

Robert W. Selden, who was developing atomic weapons at the Lawrence Livermore Laboratory, is said to have sent a letter in November 1976 to certain representatives of the atomic industry 5f various countries - including the Federal Republic of Germany - and the International Atomic Energy Agency, in which he pointed out the direct useability of all kinds of plutonium in nuclear weapons [ALBR84). Selden emphasized the possibility of a military-use device with reactor plutonium, which could achieve an explosive force in the range of kilotons of TNT, even with low-level technology. The first plutonium bomb, according to Selden, would have had at least one kiloton TNT explosive force if it had been ignited with reactor plutonium [ALBR84, COCH84, LOVI80].

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On 16 November 1976, the journal Nucleonics Week [NUCL76] reported that even the U.S. Energy Research and Development Administration (ERDA), entrusted with the development of Fast Breeders, believed that a bomb whose design was specially adapted to reactor plutonium could produce a powerful nuclear explosion ("All grades of plutonium must be considered strategically important and dangerous"). ERDA commissioned the Science Applications Incorporation, MacLean, Virginia, with the quantitative assessment of proliferation risks of various alternative reactor types. Although one might dispute the meaning of such quantitative investigations, we shall mention two of the findings here: Science Applications Inc. estimated the difficulties as equally great in weapons production using practically pure plutonium-239 for subnational or national groups. If other fissionable materials are used, the difficulties of the subnational groups would be not quite twice as great as those of national groups [SCIE77].

An important part in the U.S. nonproliferation policy was played by a report of the Nuclear Energy Policy Group, a one-year study financially supported by the Ford Foundation and supervised by the MITRE Corporation - known as the Ford/MITRE Report [KEEN77]. This study was published on 21 March 1977 and was also the foundation of the famous statement of then-newly elected U.S. President Jimmy Carter on the American nuclear policy of 7 April 1977 [CART77]. In this statement, Carter announced the United States' abandonment, for the time being, of commercial development of breeders and reprocessing plants. Carter appointed the co-authors of the study to high government positions - Joseph S. Nye became head of the Nonproliferation Coordination Group in the State Department, Harold Brown became Minister of Defense (PATE77b).

Although the Ford/MITRE Report stated that the difficulties of terrorists in the design and construction of an atomic weapon should not be underestimated, on the other hand it considered the construction of a bomb with explosive force of several hundred tons TNT by a well-organized group, supported by a few technicians, to be feasible. The report did not expressly assume the assistance of actual weapons experts. However, for a small group or even individual persons, the report considered it unlikely to achieve such an explosive force.

The Office of Technology Assessment (OTA) of the U.S. Department of Commerce also submitted a lengthy proliferation study in 1977 [OTA77). According to the OTA, an explosive force of up to 10 or 20 kT TNT could be achieved with weapons-grade plutonium, even in a design of obsolete technology. (By obsolete technology, the OTA meant that which was available to the USA in 1945.) With reactor-grade plutonium, the OTA anticipated a reduction of the possible brisance by a factor of 3-10, i.e., a brisance still in the kT-TNT range. With this (obsolete) technology - as was

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specially pointed out - it should be possible to make reliable weapons of military value with reactor plutonium. To be sure (according to the OTA), a design with preignition might result in almost-zero explosive force, but a better design could muster a minimum brisance of military usefulness.

Amory B. Lovins, at a hearing of the California Conservation and Development Commission on Safeguards, Proliferation, and Alternative Fuel Cycles on 17 June 1977 [HEAR77], added further considerations to the statements of the Office of Technology Assessment under the assumption of highly developed technology. Lovins considered it possible, with very good technology, to eliminate the differences in magnitude and predictability of the explosive force of bombs with reactor plutonium and those with weapons-grade plutonium.

Ted Greenwood, Harold A. Feiveson and Theodore B. Taylor published a book of the Council on Foreign Relations in 1977 [GREE77]. In this book, they claimed that criminals and terrorists were capable of putting together simple bombs of at least 100 T TNT brisance with reactor-grade plutonium. The necessary facts were published and thousands of people already possessed the necessary knowledge.

But there were also voices of dissent. In August 1977, William E. Nelson completed his dissertation entitled "The Homemade Nuclear Bomb Syndrome" [NELS77] at the University of Missouri in Virginia. This dissertation was intended as a direct response to the thesis of Taylor and its echoes by official representatives. In his dissertation, Nelson tried to show that the construction of an atomic weapon was often represented as being much too easy, which greatly confused the atomic industry. It should come as no surprise, according to Nelson, that the opponents of atomic power immediately took up the arguments. According to Nelson, Taylor had especially overlooked the difficulty of atomic weapon construction from toxicity, radiation, and self-heating of the plutonium. Nelson considers the "Los Alamos Primer" [SERB43], quoted by Taylor as being important, of little use ("not a handbook on design") ; even so, he was only able to obtain a copy of this after applying to various organizations and finally to Taylor himself. Note: We ourselves obtained the "Los Alamos Primer" privately, here in thf27 Federal Republic and without any connections - through the Hessen Regional College Library within five weeks.

On balance, Nelson was not particularly convincing in pointing out the difficulties of building an atomic weapon. In his remarks on radiation damage and preignition, he confuses pure plutonium-239 with reactor-grade plutonium. Thus, the comparison yielded a more than 10,000 times higher rate of spontaneous fission (which also produces the overwhelming majority of the radiation dose in the surroundings) for reactor-grade plutonium, as compared to plutonium-239. But it is only permissible to compare reactor-grade

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plutonium with "weapons-grade plutonium" that is actually still used in weapons. This comparison would have shrunk the difference in dose power and neutron background to much less than a factor of 10 (see Chapter 2.1). Nelson even claimed that the radiation of reactor plutonium is so high that additional adulteration with radioactive emitters ("spiking") to make it difficult to handle might be needless. Nor in his discussion of the thermal output of reactor plutonium does Nelson succeed in pointing out real problems: he himself considered a sufficiently active cooling to be feasible. An article under the title "The Homemade Nuclear Bomb Syndrome," submitted by Nelson along with Walter Meyer, Sudarshan K. Loyalka and Raymond W. Williams, also appeared in the journal Nuclear Safety in the summer of 1977 (MEYE77). It pursued the same purpose and gave the same findings as Nelson's dissertation.

In the summer of 1977, the voices of warning received support when a successful U.S. bomb test with reactor plutonium was announced. The journal Nuclear Engineering International published a report on this (NUCL77], which is given here in its entirety:

"U.S. exploded bomb made from power reactor plutonium: It was revealed in a public inquiry held in Britain, and later confirmed by U.S. officials, that the U.S. has exploded a nuclear device using reactor grade plutonium. Albert Wohlstetter, Professor of Political Sciences at Chicago University, made his announcement at the Public Inquiry over the expansion of Britain's Windscale reprocessing plant. While it has never been denied that power reactor generated plutonium could be used to produce a nuclear weapon, there has always been question about the stability of such a device because of contamination with certain plutonium isotopes. It also had not been known that one actually had been produced and detonated."

Previously also, according to Lovins (LOVI79], J. Griffin, ERDA, in a press release of 4 August 1977, and Albert Wohlstetter, in the aforesaid Windscale Inquiry (14 June - 19 October, 24 October - 4 November 1977), had mentioned the test. The Honorable Justice Parker, in a report [PARK78] to the British Ministry of Environment, summarized the arguments presented at the Windscale Inquiry. According to the report, there was consensus on the usefulness of reactor plutonium for weapons:

"A nuclear bomb can be constructed with the grade of plutonium recovered by reprocessing."

However, there was disagreement on whether the reprocessing plant for LWR fuel elements, planned at Windscale, increased the risk of proliferation. It was argued that Great Britain is already a nuclear weapon state and the plutonium obtained from the

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processing of the Magnox fuel element was sufficient for British bomb production, so that the new facility could not imply a British proliferation. Yet many experts feared a possible theft of plutonium or felt that the facility would encourage non-nuclear weapon states to build their own reprocessing plants. To this it was replied that the filling of orders for interested foreign parties could indeed prevent the operation of their own plants; it would be possible to recycle the plutonium separated for non-nuclear weapon states in fuel rods manufactured by Great Britain with short radiation exposure.

The test conducted by the USA was frequently mentioned in the aftermath, whenever it was necessary to buttress the theoretical proof of the useability of reactor plutonium for weaponry. This was done, for example, by Joseph Rotblat (ROTB79], who in 1979 indicated the kT TNT region as the lower end of a statistical distribution of explosive force with reactor plutonium and mentioned the above test: "(A) high yield was obtained."

Bhupendra Jasani, SIPRI, (JASA80] made similar remarks in 1980. David Widdicombe, Chairman of the Administrative Law Committee of Justice, London, (WIDD80], even went so far as to state, in 1980, that the useability of reactor plutonium for weaponry is now commonly accepted.

Before we demonstrate that this conclusion - at least insofar as authoritative circles in the Federal Republic of Germany are concerned - is unfortunately quite wrong, we shall insert a special chapter on the deliberate denaturing of plutonium.

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1.2 Proposals for the Denaturing of Plutonium since the Mid Seventies

Increasingly, as it became evident in the USA how little is the denaturing effect of a lengthy stay of fuel elements in power reactors on the thus-produced plutonium, new possibilities f or denaturing were proposed.

Prompted by Willrich and Taylor ("Nuclear Theft: Risks and Safeguards") [WILL74], Bruce A. Hutchins [HUTC75] investigated possibilities of preventing the theft of plutonium by high natural radiation. He considered the admixture of various emitters to achieve a dose power of 5000 roentgen per hour at a distance of one meter for five kilograms of plutonium. Within 200-300 days before the radiation declined too much -the plutonium was to be recycled in new fuel elements. However, it remained unclear how such an extremely radioactive plutonium could be manipulated in a fuel element factory. Maximum allowable doses have been legislated for employees in fuel element factories. On the other hand, a terrorist would have little concern for these limit values, as long as he stays within the range of statistical radiation injury, i.e., he must only count on a certain probability of coming down with cancer at some time due to this radiation.

In the FRG, Gerhard Locke of the Fraunhofer Society (Institute for Scientific-Technical Trend Analysis, Stohl iiber Kiel) has discussed possibilities of denaturing of plutonium. In 1976, Locke said that the great powers "could effectively produce an explosion of reactor plutonium whatever the neutron background" CLOCK77]. At the reactor conference of 30 March to 2 April 1976 in Dusseldorf, he presented his thoughts in the lecture "Possibilities of Making Reactor Plutonium Unfit as Nuclear Explosive" [LOCK76]. Locke recommended immediate adulteration of the separated plutonium with uranium and avoidance of unadulterated plutonium in metallic form. In order to further increase the neutron background, Locke advised the denaturing with curium-244 or beryllium. Locke's lecture was largely ignored; the journal Atomwirtschaft/Atomtechnik stated only briefly in its report on the conference (KARW76]:

"In order to make reactor plutonium unusable for bomb purposes, it was proposed in a lecture from the Fraunhofer Society of Kiel to blend the plutonium with uranium-238 already during its production, to use only compounds of lower density, and to add neutron-creating elements."

On 7 April 1977 (as already mentioned above), the newly elected American President Jimmy Carter announced the temporary abandonment of commercial development of reprocessing facilities and Fast Breeders by the USA [CART77]. Shortly thereafter, efforts were made in many places to develop "denatured fuel cycles" and awaken hopes in the industrialized Western nations and developing

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countries, which did not respond very friendly to the moratorium, and in parts of the U.S. industry, that the moratorium would soon become needless as a result of solving the proliferation problem.

New denaturing concepts developed by Alexander DeVolpi of the Argonne National Laboratory were presented by F. C. Olds in the summer of 1977 in the journal Power Engineering [OLDS77]. High critical masses (25-30 times greater than that of pure plutonium-239), in conjunction with a tenth to a hundredth of the possible energy yield as compared to plutonium-239, should reduce the attractiveness of such plutonium so much that its actual use in weapons could be virtually excluded. However, Henry C. Ott of Ebasco Services Incorporation, in a reader's letter (OTT77], found the proposed denaturing to be economically unfeasible. The Technical Director of the General Atomic Company, Peter Fortescue, also in a reader's response to the article of Olds, totally refuted the possibility of denaturing of plutonium (FORT77]; on the other hand, Fortescue could imagine a proliferation-resistant uranium-thorium cycle.

Alexander DeVolpi himself responded to these two reader's letters in the journal Power Engineering (DEV077]. He conceded that many questions of economy, neutron balance in reactors, and waste treatment remained open. DeVolpi subsequently devoted himself intensively to many of the open questions. His findings shall be discussed later on. Here, we shall first examine many of the denaturing methods proposed by various sides.

There were proposals to develop fuel cycles in which plutonium would be present only at an "international energy center," taking charge of the fuel elements at the end of their use, and in the spent fuel elements (PIGF78]. other authors considered new processing technologies. In one economically attractive processing method (AIROX process) , not all fission products were to be removed (ASQU78]. In "co-processing," uranium and plutonium would not be present separately [BR0078], except possibly with a certain proportion of fission products left behind in the uranium/plutonium mixture (Civex process) [BR0078, NUCL78]. But the Civex process had been developed for the processing of Fast Breeder fuel elements, and thus could not help solve the urgent problem (JASA80]. Furthermore, in "co-processing," the separation i:;f uranium and plutonium remained possible with relatively simple technical modifications, so that a strict international monitoring of the facilities would still be necessary (BR0080].

In the case of so-called "spiking," strongly emitting radioisotopes were to be artificially added to the plutonium, e.g. , cobalt-60, zirconium-95, niobium-95, ruthenium-106, silver-110m, cesium-134, cesium-137, Cer-144, europium-154; all of them being radionuclides that accrue in large amounts in nuclear technology (FELD79, BR0078, PINE77]. Depending on the intensity of the radioactivity, a distinction was drawn between "spiking for

16 detection," in order to make it easy to observe the removal of fuel from a particular location, "spiking for delay," to enable the finding of the fuel once abstracted, and "spiking for deterrence," in order to make it impossible to pilfer the fuel due to its strong radiation (BR0078]. Curium-244 CLOCK77), californium-252 [FELD79, NELS77, PINE77], and beryllium [FELD79, LOCK77] were mentioned as additional neutron sources in the fuel. Many authors also considered the addition of plutonium isotopes with the advantage of chemical inseparability. In this regard, plutonium-238 was mostly recommended, which can be produced with relative isotope purity by neutron bombardment of neptunium-237. Plutonium-238 generates a high degree of heat through its strong alpha-activity. Some authors, on the basis of purely arbitrary assumptions, felt that even 5% of plutonium-238 in the plutonium mixture would be enough for denaturing (HEIS80], others would not completely rule out the weapons-suitability of a mixture with 20% plutonium-238 (LOVISO] or even a mixture of any given concentration of plutonium-238 (WALT80] and contented themselves with the reduced attractiveness of such plutonium. Scientists of the Sandia Laboratory could come up with no feasible material for denaturing of plutonium, as long as the denatured plutonium was to be reusable in fuel element factories and reactors (WILL78].

In the meantime, DeVolpi developed an extensive denaturing concept (DEV078), which he also presented in a detailed book [DEV079] and a lengthy journal article (DEV082], based primarily on the book. DeVolpi stressed the denaturing action of the plutonium isotopes Pu-238, Pu-240 and Pu-242 in general - apart from individual considerations [DEV078, DEV081]. He even factored in a deliberate addition of plutonium-242 in his calculations. According to DeVolpi, plutonium with only 18% of fissionable isotopes in the reactor should still be economically useable. DeVolpils concept should not be viewed without the restrictions that he himself mentioned:

• Denaturing was for him the lessening of the weapons-suitability, as opposed to the definition of other authors, who understood by denaturing the total unfitness for weaponry.

• By "denatured -grade plutonium, 11 DeVolpi meant plutonium with 20% or less fissionable component in reactors. Thus, according to DeVolpi, the risk of proliferation could be reduced by several orders of magnitude with isotopic denaturing (DEV079, Conclusion No. 6] and, in conjunction with safeguards, could be converted to the level of or below other accepted technological risks (DEV079, Conclusion No. 26]. There has already been lengthy discussion about the meaning and nonsense of "risk assessments" in connection with nuclear technology - with no reconciliation of the different viewpoints being in sight.

17

This chapter should demonstrate one thing, first and foremost: The plutonium currently manipulated in the Federal Republic of Germany has nothing whatsoever to do with these denatured mixtures ("denatured-grade plutonium") . The described discussion in the USA did not revolve around whether or not reactor-grade plutonium can be used for weaponry, but rather methods that could make reactorgrade plutonium unfit for weaponry through artificially added ingredients. In the Federal Republic of Germany, no one is considering the introduction of a plutonium operation using plutonium with less than 20% of reactor-fissionable isotopes. At the only plutonium fuel element factory in the Federal Republic, the ALKEM company, the handling of this plutonium would be prohibited by the legally mandated protection of workers and the neighboring population. The same applies to ALKEM's newly requested facility.

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1.3 Views Regarding the Useability of Reactor Plutonium for Weaponry in the Federal Republic of Germany

Examples of comments by various parties, starting in 1975 and continuing until recent time, will illustrate the discussion in the Federal Republic of Germany. A special significance attaches to the reporting in the popular journal Atomwirtschaft/Atomtechnik, which has contributed much to the formation of public opinion with its technical, as well as political information. The title of this journal is usually abbreviated 11atw.11 It is the official organ of the Kerntechnische Gesellschaft e.V.

"Is there a plutonium problem?" asked the managing director of the plutonium fuel element factory ALKEM, Wolfgang Stoll, 1975, in atw (STOL75]. With regard to the useability of reactor plutonium for weaponry, he limited himself to denying that it is easy to make a nuclear device. The fact that special plutonium with a high percentage of plutonium-239 is used in atomic weapons, according to Stoll, would be incomprehensible if it were easy to build bombs with reactor plutonium (here, Stoll forgot the aspects of reliability and predictability). In other respects, Stoll's article was the revised version of a survey report, presented by him at the 1975 reactor conference of the German Atomic Forum and the Nuclear Technology Society of 8-11 April 1975 in Nuremberg.

At the next conference in 1976, Gerhard Locke of the Fraunhofer Society pointed out the suitability of reactor plutonium for weaponry (cf. Chapter 1.2) and at the same time indicated methods for denaturing, although their effectiveness was far less than that of DeVolpits (ibidem). Although this report was briefly mentioned in atw (KARW76], no special attention was ever given to it thereafter. Nor was a single comparable report ever given at any of the annual reactor conferences.

At no time did atw devote so much attention to proliferation as in 1977, when the commercial development of breeders and recycling were halted in the USA. Since the German atomic industry at this time was striving to export such proliferation-prone technologies, the atomic industry felt itself on the defensive. The USA expected that its Western alliance partners would join its moratorium. Yet the last sentences of Jimmy Carter's famous statement on 7 April 1977 are worthy of note [CART77]. They make some of the criticism subsequently uttered against the USA, especially in the Federal Republic (and some of this criticism will turn up later on in this chapter), appear unjustified:

"We are not trying to impose our will on those nations like Japan and France and Britain and Germany which already have reprocessing plants in operation. They have special need that we don't have in that their supplies of petroleum products are not available. But we hope that they will join with us - and I believe that they will

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in trying to have some worldwide understanding of the extreme threat of the further proliferation of nuclear explosive capability.,,

Contrary to popular opinion - for understandable reasons also disseminated by the German atomic industry, technical problems and the more strict radiation protection and operating tasks imposed on the supervisory agencies (Nuclear Regulatory Commission, NRC, the mandate having been withdrawn from the lax and corrupt Atomic Energy Commission, AEC, in 1975) were mostly responsible for the freezing of commercial U.S. breeder and reprocessing programs (NWG82]. The tendencies of the U.S. nuclear export policy were repeatedly criticized in atw, e.g., by C. Patermann of the West Germany Embassy in Washington [MUEL77, PATE77a, PATE77b].

J. Scharioth in 1977 examined the "Nuclear controversy from social and psychological standpoint" in atw [SCHA77], without even mentioning proliferation(!) ; this was a revised version of a survey report at the reactor conference in Mannheim, 1977. Karl Wirtz reported on the ANS-ENS Conference of 5-19 November 1976 in Washington [WIRT77] and called proliferation "Issue No. 111 of this conference. He described the situation and discussion in the USA without mentioning an important factor, namely, that the useability of reactor plutonium for weaponry was again in the public mind.

The atw published mostly articles which, under the slogan "nonproliferation policy," emphasized the Federal Republic's forswearance of its own atomic weapons, the existence of the nonproliferation treaty, and the international controls of Euratom and the IAEA, such as the articles of Hans-Hilger Haunschild, State Secretary at the Federal Ministry of Research and Technology [HAUN77] and Federal Economic Minister Hans Friderich [FRID77]. Heinrich Mandel, then President of the German Atomic Forum, stated [MAND77]:

"Naturally we understand the concern of our American friends.... There should be total agreement between the USA and ourselves in that everything must be done to hinder the proliferation of nuclear weapons. We here in Germany have done especially much in this direction through the unilateral forswearance of production and national possession of nuclear weapons, submission to the safety supervision of Euratom, the nonproliferation treaty, and cooperation in the London Export Guidelines."

The export of nuclear know-how, according to Mandel, is in fact a proliferation-reducing measure, for "any other procedure must result in such countries feeling themselves discriminated against and carrying out their own projects behind closed doors, which may be detrimental to the world peace."

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Only G. Hildenbrand of the Kraftwerk Union AG pointed out "but even reactor-grade plutonium with a content of 20-30% of Pu-240 can be used for production of nuclear explosives, the effectiveness of which depends on the arrangements to achieve the required speed of bringing the ingredients together" (HILD77]. In summation, however, Hildenbrand stated "that the proliferation of nuclear knowledge has already become irreversible, and that it is essential to resort to effective nonproliferation programs involving the force of political conviction, instead of the vain attempt to turn back events."

The overwhelming majority of articles published by atw on the proliferation topic considered proliferation an essentially political and not a technical problem. One may mention an atw article in 1977 by the head of the Fast Breeder Project at the Nuclear Research Center of Karlsruhe, Ganther Kessler, who in a "critical review" [KESS77] of proliferation issues in connection with the ERDA-breeder program of the USA presented a picture with possible proliferation pathways. The possibilities discussed were theft of nuclear weapons, enrichment of uranium-235 or uranium-233, chemical separation of uranium-233 and chemical separation of "Pu-239 with a little Pu-240.11 Kessler mentioned "U-233, U-235, Pu-23911 as a weapons-capable nuclear fuel. The text also dealt entirely with plutonium-239, so that one could not deduce that reactor-grade plutonium can be used for weaponry from this "critical review." Already by 1978 the discussion of nonproliferation problems had again declined considerably in the atw; the export control law that took effect on 10 March 1978 in the USA was again attacked as "the wrong way to nonproliferation," which had "seriously shaken the trust in the USA as a reliable trading partner" (MUEL78].

One result of the breeder and reprocessing moratorium of the USA was an international evaluation of the fuel cycle (INFCE) with the goal of developing the most proliferation-safe cycles. The atw doubted the value of such an evaluation in 1979 [LEV179]:

"It is therefore extremely doubtful whether the attempt to influence the risk of proliferation by selection of fuel cycles simply misses the heart of the matter, which is political."

The atw presented the findings of INFCE several times during 1980 and 1981 CHOSS80, PATE80, PATE81, POPP80, ROTH80]. "Nothing really has come of it (INFCE] that was not already known before," namely, "that a certain proliferation potential is inherent in all fuel cycles, although it can be reliably controlled in the opinion of international experts." The assistant editor-in-chief of atw, Radiger Hossner, commented [HOSS80):

"Yet concern grew particularly in the country that was the first to open the way to the proliferation of nuclear

21

energy, the USA. It was not entirely clear whether this concern was not also influenced by motives of competition... 11

Representatives of the Federal Ministry of Research and Development presented "The basic findings of INFCE11 [POPP80]: Proliferation is "a political and not a technical problem," there is no fuel cycle that is absolutely resistant to abuse, safeguards are to be further developed and the aspects of safety of supply, environmental protection, and economy should also be considered. And the especially important finding, that "nuclear energy can in fact be made available worldwide." Also "very meaningful in light of the history of INFCE11 was the statement "that large breeders or reprocessing facilities are also quite Isafecjuardable'.11

In 1981, the Assistant General Director of the IAEA, H. Griimm, discussed possible proliferation in the atw [GRUE81]: Once again, nothing was said as to the possibility of building a bomb with reactor plutonium. Instead, Griimm declared that the "imaginary danger of nuclear power plants" had diverted attention from the "millions of times greater actual danger of atomic weapons.... In this regard, the nuclear power plant hysteria is contributing to the continuance of an immeasurable danger potential of 40,000 to 50,000 nuclear explosives in the arsenals of the great powers." (This source was an offprint of a speech given by Griimm on the occasion of his induction as honorary member in the Nuclear Technical Society on 23 October 1980 in Bonn.)

The attack of Israeli airplanes on the research reactor Osirak in Iraq on 7 June 1981 was worth a mention of the proliferation problem in atw [ATW81]:

"Fissionable material requirement for a nuclear weapon.... The critical masses for a nuclear weapon in the form of unreflected balls of metal of the highest density for fast neutrons are 44 kg for U-235 and 10 kg for Pu-239. It must be assumed, first, that the required quantities are larger on account of losses and suboptimal conditions upon ignition of the device, and second, that the necessary quantities can be roughly halved with reflectors and extreme compression upon ignition. But this latter technology requires nuclear weapons testing and an extremely highly developed technology in this specific field, the existence of which outside the USA is not yet known."

Contrary to this is the fact that the first plutonium bomb (Trinity Test) already functioned better than most of its inventors had assumed. Furthermore, the technology of atomic weapon construction must also surely be in existence outside the USA today, since there are at least five atomic weapons powers in

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addition to the USA, and they also employ plutonium in their weapons.

So much for the reporting in the atw. We should like to point out, once again, that the quotations from the atw have not been chosen to falsify their general tenor. At no time did the atw report on the discussion of the capability of using reactor plutonium for weapons on a level approaching that of the quotations in Chapter 1.1. On the contrary, one gets the impression that such discussion was deliberately ignored in the soothing and suppressing articles of the atw. The articles published in the atw mostly argued for accelerated entry into the plutonium economy.

A somewhat more far-reaching discussion of the fitness of reactor plutonium for weaponry appeared in the journal Atomkernenergie-Kerntechnik - but only in 1976. The discussion began with an article on the criticality of reactor plutonium by the Turkish engineer Sdmer Sahin (SAH176a], who was serving as Assistant Professor in Switzerland. Carl M. Fleckf Professor at the Atomic Institute of the Austrian Universities of Vienna, provided "some remarks" on Sahin in the journal [FLEC76a], to which Sahin responded in turn (SAH176b], and Fleck published "final remarks" on this (FLEC76b].

In this debate, Sahin had pointed out the different neutron lifetimes in reactor-grade plutonium, as compared to weapons-grade plutonium, which should affect the attainable explosive force. on the other hand, Fleck considered the problem of preignition and the concomitant expansion of the fissionable material before reaching maximum supercriticality, thus also reducing the attainable energy yield, to be more significant. Regrettably, Sahin and Fleck constantly spoke past each other.

Finally, Sahin performed calculations, although they were published in the Annals of Nuclear Energy 1978 (SAH178], instead of Atomkernenergie-Kerntechnik, and in these he attempted to determine quantitatively the lengthening of the neutron lifetime in reactorgrade plutonium. Sahin was aware of the uncertainty of his calculations, for they did not include any dynamic influences during the compaction time. From his calculations he drew the conclusion that the explosive force of reactor-grade plutonium can only be reduced in limited extent with respect to weapons-grade plutonium. As Sahin added the quantitative finding to his previous discussion with Fleck in the Atomkernenergie-Kerntechnik 1979 (SAH179), the aforesaid consequence, of only limited reduction of the explosive force, was not presented in this journal. Fleck responded (FLEC79] that this still does not eliminate his reservation with respect to preignition.

In 1980, Sahin presented further improved calculations in Atomkernenergie-Kerntechnik [SAHI80a], which led to higher neutron lifetimes - even for pure plutonium-239. But the percentage

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increase in the neutron lifetime in reactor-grade plutonium, as compared to pure plutonium-239, did not agree with his earlier calculations. The new calculations of Sahin were presented in greater detail in the journal Nuclear Technology (SAH180b], where he explained that 15% of plutonium-240 with an ingenious technology could achieve an explosive force of 1 kT of TNT, while with 25% of plutonium-240, the explosive force almost always remains below 100 T of TNT. In a reader's letter in the journal Nature [SAH180c), replying to an article by Amory B. Lovins [LOVI80], however, Sahin slightly modified his view: with an ingenious technology, it is not possible to exceed an explosive force of 1 kT TNT (for 15% Pu-240) or 100 T TNT (for 25% Pu-240).

Next, we shall devote ourselves to the remarks of a representative of the Jalich Nuclear Research Plant, Erwin Manch. In March 1976, he wrote [MUEN76]:

"The composition of the plutonium created in commercial nuclear power plants of fissionable and around 40% nonfissionable isotopes makes it impossible to produce effective nuclear weapons from this material that exceed the brisance of conventional weapons."

Later on, Miinch claimed that he had coined his statement implicitly only for misuse by terrorists without access to modern ballistic techniques (EHRE79]. In 1979 (MUEN79), Manch considered it possible for a state to build explosives in the range of several kilotons of TNT with reactor-grade plutonium, though stating:

"The production of an effective and reliably igniting atomic bomb by terrorists from the mixtures of fissionable materials accruing in the reactor can be ruled out."

A somewhat shorter version of Minch's article (MUEN79], although verbatim in many essential points, was reprinted in a pamphlet of the Nuclear Research Plant Jalich [BORS78]. The 1980 edition of this pamphlet [BORS80] has been amplified with respect to its 1978 edition by the sentence "However, the production of nuclear explosives with limited explosive force might be possible for a state. 11 In a handbook published by Minch ("Facts Aboui Nuclear Energy") , in its second edition of 1980 (MUEN80), Minch describes the difficulties in the use of reactor-grade plutonium, again identically with his treatment in the 1979 article [MUEN79]. Similar to Manch are the remarks of Klaus-Detlef Closs in Bild der Wissenschaft in July 1979 [CLOS79]. According to Closs' opinion, reactor-grade plutonium would have to be compressed at a rate of at least 10 km/s and only the nuclear weapon countries have experiences in this regard. One of the article's illustrations has the caption in bold letters "reactor plutonium not suitable for bombs." The Society for Reactor Safety (GRS) in its report "Plutonium" (MUEL79] of April 1979 designated reactor-grade

24 plutonium as "useable for weapons construction"; the production of an explosive device is "much more dif f icult" than in the case of weapons-grade plutonium, "but basically possible." The authors of the GRS set the required implosion rate for reactor-grade plutonium at around 10 km/s, but considered only 100 m/s achievable by "do-it-yourselfers-" However, this 100 m/s could still produce an explosive force of 20 T TNT.

Even the opponents of atomic power for a long time overlooked the proliferation problem of reactor plutonium. Relatively early, but still only in September 1977, the Citizens League of Environmental Initiatives (BBU) wrote in its pamphlet "Plutonium" [BBU77]: "It is considered certain today that one can build atomic bombs from plutonium created in atomic power stations." (This pamphlet is based on (KOLL78).) On the other hand, for example, the handbook "Reactors and Missiles - Atomic Dangers and Citizen Protests," published by Joachim Grumbach in 1980 [GRUM80] and written by critics of atomic power, despite its much-promising title, contains no indication of the fitness of reactor-grade plutonium for weaponry. Quite the contrary: It even denies such fitness of reactor plutonium.

The earliest time at which one can speak of a broad-based discussion of the possible fitness of reactor-grade plutonium for weaponry in the Federal Republic is probably the so-called "Gorleben Hearing. it During the Gorleben Hearing, from 28 March till 3 April 1979, more than sixty experts discussed the fundamental safety of the then-planned "Nuclear Disposal Center" of Gorleben (a revised record of the hearing was published by the German Atomic Forum (ATOM79].)

The discussion was based on the "Gorleben Report," a 2200 page thick report by twenty internationally renowned scientists. Several of the scientists took up the fitness of reactor-grade plutonium for weaponry. A survey of the hearing and the report is provided by the handbook "The Gorleben Report," published by Fischer Alternativ in July 1979 CHATZ79].

In the chapter "Safeguarding of Fissionable Material," the book quoted Amory B. Lovins - bombs can be produced with reactor-grade plutonium and they are not fundamentally weaker or more reliable than those with weapons-grade plutonium - and the report of the "Gorleben International Review" (GIR). According to GIR [BARN79], a nuclear explosive of the "Nagasaki" type could be produced from reactor-grade plutonium, and even with preignition it would still have the brisance of 1 kT TNT; with an explosion of several hundred tons TNT brisance, terrorists could cause devastating damage in a population center, and a terrorist organization was probably capable of building such a bomb. However, the fitness of reactor-grade plutonium for weaponry was not accepted by all scientists at the hearing. Thus, for example, ALKEM's General Manager Wolfgang Stoll, in the papers submitted,

considered reactor-grade plutonium "highly unsuitable" f or bombs (STOL79a], "extremely unpredictable in its effects" and "only very high rates of combination ... oppose the otherwise highly likely inertness of a nuclear explosive charge made f rom reactor-grade plutonium due to preignition (STOL79b]." Stoll cast doubt on the statements of American scientists and considered them mere political expediency (STOL79b]:

"The alleged simplicity of making nuclear explosive charges was always contested by the armed nations prior to 1975 (the appearance of the book by Willrich and Taylor). The denials suddenly stopped when the new U.S. nonproliferation policy took effect. Statements not proven in practice, without ever being officially confirmed, were used as argument against the separation of plutonium. Thus far, it seems, no one has really got beyond the intelligent copying of published weapons cross sections."

The following statement by Stoll is also important in this connection [STOL79b]:

"A ball of at least 13 kg reactor-grade plutonium metal is required to trigger a chain reaction with fast neutrons (official information of the NRC). However, in the military realm, there are special geometries of explosives, the details of which have been kept strictly confidential thus farl which produce spherical -centric compression waves of appropriate intensity to make even small amounts of fissionable material go critical. Even light water/Pu has been detonated in this way - albeit with modest energy yield (figures not published)."

According to DeVolpi (DEV079), it is possible to use a reflector of natural uranium to reduce the critical mass of the typical light water plutonium in the delta phase to around ten and that in the (much harder to achieve) alpha phase to around six kilograms. One cannot deny that a reflector may be used in the fabrication of a nuclear device - whether by terrorists or by a country. The principle of the so-called "explosion lens" - as used in implosion weapons - has also become common in the civilian reaAn today (see Chapter 2.1).

In 1984, a hearing was organized in the Hessian Parliament of Wiesbaden to clarify the proliferation risks of the fuel element factories NUKEM and ALKEM in Hanau [HESS84]. Once again, Stoll attempted to refute his opponents with the same arguments. He continued to deny the reasons (see Chapter 2.6 for this) why reactor-grade plutonium is not used by the atomic weapon nations in their explosives:

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"I have clearly stated that we are not weapons experts. But naturally, we read the literature. So far as one can find in this literature, the material that we have is unsuited for military use. I conclude from this that no serious weapons expert has ever thought of using it, if only because the ef f ect cannot be predicted with any certainty. The fact that an experiment with light water material allegedly succeeded once - no one knows exactly - in the USA under the strictest seal of secrecy in the Carter era in March 1977 - as has already been stated -changes nothing. No one knows the conditions or results. All that is certain is that this requires an especially sophisticated and complicated technology.... The peaceful use of light water plutonium really has nothing to do with nuclear weaponry."

Another speaker at the hearing, Professor Karl Kummerer of the Nuclear Research Center of Karlsruhe, considered reactor-grade plutonium "on principle, fit for weaponry." However, he pointed out several obstacles that should make it "damnably difficult" to build a useable weapon. Strangely enough, Kummerer stressed the neutron impulse at the correct time - down to a microsecond required to initiate the chain reaction. First, the neutron impulse at the correct moment is not the greatest technical problem (see Chapter 2.3), and secondly preignition and neutron impact cannot both present a major difficulty. Should a preignition occur with high likelihood, the additional deliberate neutron impulse is simply superfluous.

Already in his written presentation before the hearing (Committee Exhibit WTA/11/30 and HAA/11/4) of 30 May 1984, Kummerer informed the Hessian Parliament that "no atomic weapons or intermediate products for these would be produced" at NUKEM and ALKEM and there was "no experience in this area" there. The uranium and plutonium processed there, "because of its chemical composition and because of its isotopic composition is unsuited for atomic weapons." We should further quote here the remarks of two experts invited to the Wiesbaden hearing. Ministerial Councilor Hagen represented the Federal Ministry of Research and Technology:

"The company representatives have already stated that a detailed evaluation of the quality of the material that is stored or processed there for peaceful use as fuel in power and research reactors is not possible. The same applies to the information of the Federal Government on this. We, the Federal Government, quite consciously and in keeping with the contractually assumed international obligations, in our research projects carried out for example in the development of the peaceful use of nuclear energy in the Federal Republic have refrained from examining the weapons grade or the quality in respect of weapons production of such materials, or even allowing

27

such work to be carried out. I am certain, on the basis of extensive knowledge, as well as discussions within the German scientific scene, that such a request, by any federal government and at any time, would have been clearly rejected in the past twenty-five years and will be rejected in future.... once again: As far as detailed information goes, especially the deliberate production of an effective nuclear device with calculable effectiveness, we do not have this knowledge, and we do not want to have it."

Professor Karl Kaiser, Director of the Research Institute of the German Society for Foreign Policy in Bonn, once again underscored:

"The federation ... cannot be interested in acquiring the specific knowledge necessary to produce weapons, because we as a country do not want to produce any weapons."

So much for the statements at the hearing. These two utterances should be contrasted with the following fact: Though not intensively or with great expenditure, but nevertheless constantly since the late sixties, scientists of the Fraunhofer Society, Institute for Scientif ic-Technical Trend Analysis at Stohl bei Kiel, have been working on the theoretical treatment of the functioning of nuclear weapons [LOCK74, LEUT75, LOCK82]. They even mention a commission from the Federal Minister of Defense (see the foreword to the works [LOCK74] and [LEUT75]). According to them, the suitability of reactor plutonium for weaponry CLOCK76, LOCK77] was also found in projects for the Federal Ministry of Defense. The foreword of one work of 1982 [LOCK82) states that this research should also continue in future, in order to assimilate "developments in the area of a miniaturization and greater efficiency of nuclear fission weaponry."

Thus, contrary to the statements of Hagen at the Wiesbaden hearing, scientists of the Federal Republic have been continuously occupied with the functioning of nuclear weapons since the late sixties on order of the Federal Minister of Defense; not with experimental projects, but with theoretical treatments as the first step in an actual development of nuclear weapons. While the~ construction of such weapons is not a necessary consequence, it is a temptation. We could mention the development in France, which led to the "force de frappe." In France, for a long time there was no top-level decision of the government on atomic weapons production. However, scientists carried out the preliminary work and the government's decision for construction and testing of weapons came only after certain scientists were very close to a solution. One can read about this, for example, in the Office of Technology Assessment [OTA77] in brief and more extensively in Scheinman (SCHE65].

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In many of the remarks quoted in this chapter one is struck by how little importance is often given to the question of whether a nation with the resources at its disposal can construct a useable bomb from reactor-grade plutonium. Mostly, mention is only made of difficulties, the relevance of which is assessed for subnational groups - to the extent that any background conditions at all are given. Alexander Rossnagel [ROSS83] in 1983 pointed out that one should not inquire into the capabilities of terrorists to build a modern weapon, but rather "which are the minimum requirements for subnational groups to produce the simplest possible atomic explosive, granting the appropriate motivation and willingness of its members to accept danger."

The electricity supply industry itself has been unaffected by any concern over the establishment of a plutonium supply industry in the Federal Republic. For example, in 1975, its central information office attempted with pamphlets "to clarify concepts, eliminate concern, and awaken understanding" [GRUP75], which reads as follows:

"Only Pu-239 is suitable for use in nuclear weapons. During the long operating time of the fuel elements in the reactor (one year or longer) necessary for an economical reactor functioning, only such large quantities of the nonfissionable isotopes Pu-240 and Pu-242 are created as make a use of this "reactor plutonium" not possible for weaponry."

Evidently, the authors have overlooked the fact that plutonium-240 and plutonium-242 are quite fissionable in weapons; these isotopes cause difficulties for other reasons. Even in a more recent edition of this booklet in August 1984 [GRUP84, KFK76, KFK81], the above-quoted passage has been retained. Only the second sentence has been modified, changing "not possible" to "not suitable."

In this work, we have intentionally refrained from examining the records of the German Parliament to determine whether a consensus exists or ever existed with respect to the fitness of reactor plutonium for weaponry. This shall be left to another work.

In summary, the findings of this chapter are:

• A discussion in research reports, at conferences or even in technical journals among scientists of the Federal Republic as to the possible usefulness of reactor plutonium for weaponry took place much later than was the case in the USA.

• In the USA, several years passed before such a discussion reached the government level and led to the corresponding consequences there.

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0 In the Federal Republic, this latter process does not seem to have occurred.

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Special Problems in the Handling of Reactor Plutonium for Weapons Purposes

2.1 Blasting Techniques in Plutonium Bonds

In the Manhattan Project, two ballistic techniques were investigated: shooting together individual subcritical masses to form a single supercritical mass ("shooting method") and the "implosion technique." The implosion technique was supposed to make it possible to compact a plutonium sphere so fast that a preignition by neutrons from the spontaneous fission of plutonium-239 would be unlikely.

During the implosion, a hollow plutonium sphere surrounded by an explosive is compacted and thus achieves a supercritical configuration. The plutonium sphere should be compacted as a sphere during the implosion; it should not deviate from the spherical shape as a result of nonuniform shock waves on its surface. But if a plutonium sphere is surrounded with a layer of explosive and this layer is ignited at certain spots, the shock wave will always reach certain points of the plutonium sphere sooner than others. Already in March 1943, Seaborg feared that plutonium generated in reactors might not be useable with the shooting method due to the possibly intense spontaneously fissioning isotope plutonium-240 [HEWL62]. With the shooting method, compaction rates up to 3000 feet/s (914 m/s) were deemed possible (HAWK61). Therefore, work was done on the implosion technique starting in 1943, although initially it did not appear very promising. The first implosion test without nuclear explosive occurred on 4 July 1943 [HAWK61]. Subsequently, in the summer of 1944, when Seaborg was confirmed in his apprehensions, the implosion technique was vigorously developed, for only this could make a plutonium bomb feasible.

Explosives that detonate with different rates were therefore put together in such a way that the shock waves generated at one point on the outer surface of the layer of explosive reached the surf ace of the hollow plutonium sphere simultaneously at all points ("explosive lens") [TSIP83].

The first nuclear test occurred on 16 July 1945 at Alamogordo, in the desert of New Mexico. Almost all scientists involved underestimated the achievable explosive force prior to the test [BLUM76, JUNG64].

The explosive lens technique is also widely used in the civilian sector today. It is mostly employed to achieve a straight shock wave front with a pointlike ignition. A further possibility of shaping the shock wave, besides the use of several explosives with different rates of detonation, is the insertion of cavities or nonexploding bodies in the explosive charge [SCHA71]. The necessary physical and chemical data on a number of high explosives

31

are available in a handbook from the Lawrence Livermore Laboratory [DOBR74).

There is frequent mention of the large number of scientists and technicians of the Manhattan Project, in order to justify the enormous difficulties of bomb construction. However, it should not be forgotten that this group of people had to work on many problems that are long since solved today, such as the determination of critical masses or reaction activation cross sections with primitive methods compared to the present state of the art. Furthermore, at that time there were no high-performance computers available, so that theoreticians had to struggle with calculations that can today be carried out in the shortest of time by means of

• machine.

At this point, we should like to call attention once more to

• widely held misunderstanding. When considering the weaponsfitness, one should not compare the neutron background of pure plutonium-239 and reactor-grade plutonium (e.g., [SEIF84, NELS77)). The neutron background of our reactor-grade plutonium, as defined at the outset of this report, is actually around 17,000 times greater than that of pure plutonium-239. But if we compare our reactor plutonium with low-quality weapons-grade plutonium (7% 240pU) , though still qualifying as weapons-grade plutonium, then the neutron background of reactor plutonium is only 4.6 times as large.

2.2 Formation of Pu-Isotopes in Fuel Elements and the Neutron Background

The relationship between the burnup of the fuel element and the neutron background is relevant to an assessment of the preignition problem. The breeding of plutonium isotopes from 238U, so-called inventory computations, can be simulated with nonlinear coupled differential equations [FISH83, KIRC85]. Figure I shows a schematic layout of this process. By virtue of the neutron flux sustained by the fissioning of 235U, the 238U changes into 239Pu through several intermediate steps (n-capture & 8-decay) . The capture of additional neutrons results in the "higher" plutonium isotopes 240, 241, 242. The neutron background can be determined as a function of the burnup, using the Pu-composition resulting from the inventory calculation and the specific neutron rates given below.

where P is the proportion 0 f 141 Pu and 142pU in all plutonium isotopes and A is the fuel burnup in GWd/T, which with a time constant of around 11 GWd/T reaches a maximum value of about 32%. one should not overlook the fact that there is considerable scatter in the experimental values (FISH83]. The specific neutron rate for 240Pu and 242pU may be roughly estimated at 106 neutron/s/kg. If the burnup is not too low, the proportion of 239Pu can be disregarded. The specific neutron rate N is then found to be:

approximation formula that is better than (2). Kirchner's inventory calculations are based on the ORIGEN Code [Oak Ridge

Isotope Generation and Depletion Code], amplified by a program package SAS2, which takes into account the effective activation cross sections that are heavily time-dependent, owing to resonance.

Figure 2 shows the production of Pu isotopes as a function of the burnup for UO, fuel elements in DWR for an average target burnup of 33 GWd/T and for planned high burnup elements with 55 GWd/T. The enrichment amounts to 3.2% and 4% 235-U, respectively, the mean 9P, ower density 37.5 MW/T and 41.25 MW/T. Note the decrease in the 23 Pu component at high burnup, due to its dominant fission rate as compared to 235U, and the considerable production of 23BPu.

Figure 3 shows the percentage composition of plutonium as a function of the burnup.

Figure 4 presents the neutron production rates [WICK67] of the isotopes and their sum. The even-numbered isotopes, particularly 240pU, dominate as a result of their spontaneous decay rates. The approximation of formula (2) overestimates the neutron rate for burnup below 33 GWd/T and underestimates it for burnup above 33 GWd/T. The data on probability of preignition remain unaffected for burnup of 33 GWd/T.

The shaded area is the region in which so-called weapons-grade plutonium is bred. The fuel elements exhibit a burnup of no more than 5 GWd/T. This means that the fuel rods spend only several hundred days in the reactor.

At the time of maximum supercriticality - during several millionths of a second - a neutron must initiate the desired chain reaction in the plutonium of a nuclear weapon. In the case of the first implosion bomb, a spherical capsule containing polonium and beryllium powder, separated by a foil, at the inside of the hollow plutonium sphere, was crushed at the instant of maximum supercriticality. In this way, the two powders mixed and the reaction 9Be(a, n)12C provided a neutron burst (BARN79]. (The polonium-210 was obtained by neutron bombardment of bismuth-209 in the Clinton Pile.) The intensity of a polonium-210/beryllium source is around 2.5 106 neutrons per second and curie of polonium (JAEG74?; the specific radioactivity of polonium-210 is 4600 curie (1.7,104 Bq) per gram. Thus, with a milligram of polonium-210, as many as 1.2,107 neutrons per second can be generated, which would suffice as source intensity inside the plutonium sphere. Ignition by means of a polonium/beryllium source is a relatively primitive method. An electronic neutron generator with tritium/deuterium target is also considered as a neutron source. If, for a given ballistic technique, preignition is extremely likely on account of a neutron from spontaneous fissioning of plutonium or an (a, n) reaction at impurities of the plutonium, the additional neutron source can be dispensed with.

Figure 4. Rate of neutrons per second per kg plutonium as function of the burnup, according to Figure 2.

2.4 Handling of Reactor-Grade Plutonium

2.4.1 Dose Load from Radioactive Radiation

Ten kg of typical light water reactor-grade plutonium (1.5% 238Pu, 56.5% 239Pu, 26.5% 241pU, 11.5% 241pU, 4.1% 242pU) , according to Campbell and Gift [CAMP78], produce a dose power of 1. 56 mSv/h (156 mrem/h) at a distance of 30.5 cm. Within one year of separation of plutonium from spent fuel elements, the dose power increases to 1.74 mSv/h (174 mrem/h). The largest contribution comes from the neutrons of spontaneous fission. But if there are light element contaminants or plutonium dioxide present, the neutrons from (a, n) reactions may also be decisive for the local dose power (ARN058]. Even at a concentration of 18.5% of the very a-active isotope, plutonium-238, the overall dose power of 10 kg plutonium dioxide at a distance of 30.5 cm should amount to no more than 8.5 mSv/h (850 mrem/h), according to Campbell and Gift (CAMP78]. The values given by Campbell and Gift contain no X-rays or B-radiation and no I-radiation from spontaneous fission; this radiation plays no major role at the distance in question [ROES58).

A 1 kg sphere of metallic weapons-grade plutonium (93% 239Pu, 7% 240pU) , according to the International Atomic Energy Agency CIAEA74], exhibits a dose on the surface of around 18 mSv/h (1800 mrem/h) [X-rays 13 mSv/h, T-rays 3 mSv/h, neutron radiation 2 mSv/h].

For reactor-qrade plutonium (1.5% 238Pu, 58.6% 239Pu, 23.8 % 240pU, 11. 0% 141pU , 4.8% 242pU) , we would have 137 mSv/h (13,700 mrem/h), disregarding the I-rays (X-rays 108 mSv/h, I-rays 3 mSv/h, neutron radiation 10 mSv/h) , i.e., 7.6 times the dose power of weaponsgrade plutonium. This difference shrinks with increasing distance from the surface, since short-range X-rays contribute disproportionately to boost the radiation level of reactor-grade plutonium as compared to weapons-grade. For 10-kg spheres, a dose power significantly less than 10 times the above-indicated value is to be expected, since one must factor in the self-absorption of the plutonium metal.

An acute radiation syndrome is generally anticipated only above 1 Sv (100 rem) total-body exposure. Conspicuous clinical symptoms are not to be expected under a lower radiation burden and organ damage can only be demonstrated in the laboratory using special research methods. Recovery is still likely up to a total-body exposure of 2 Sv (200 rem) [MOEH72). Thus, even without shielding measures, acute radiation syndromes do not occur with reactor-grade plutonium, when handled carefully. Subsequent,

37 late-term damage, especially in the case of terrorists, must not be seen as a deterrent to working with reactor-grade plutonium.

2.4.2 Beat Liberated by Radioactivity

The individual plutonium isotopes have different thermal output CALKE82]:

From this we have around 2.2 W/kg for the plutonium used in weapons (6% 240pU) , compared to somewhat more than 10 W/kg for reactor plutonium. The thermal power of reactor plutonium is thus around five times greater than that of weapons-grade plutonium. Figure 5 shows the production of heat as a function of the burnup. At burnup over 14 GWd/T, the thermal power is primarily due to 238Pu. With a quantity of 6.1 kg Pu, the thermal power for 33 and 55 GWd/T corresponds to approximately 60 W and 120 W, respectively, i.e., a common lightbulb. A sphere of 6 kg reactor-grade plutonium without explosive jacket reaches an excess temperature of about 1000C under natural air convection (NELS77].

Figure 5. specific thermal power per kg Pu as function of burnup with a composition of the plutonium vector according to Figure 2.

2.4.3 Self-Ignition in Plutonium Processing

One possible problem in the processing of plutonium is self-ignition with consequent contamination of the surroundings. According to Waltz, et al., [WALT80], plutonium filings ignite at 1750C, shavings at 2650C, and large metal pieces at 300-3500C, even if one atom-percent gallium has been added to the plutonium. Wick [WICK67] claimed that unalloyed plutonium (a cylinder of 10 mm diameter and 10 mm length, corresponding to a mass of around 15 g) would ignite in air at 500-5200C. Ignition temperatures in air between 266 and 280*C are said to have been observed for foil of 0.12 mm thickness, and temperatures between 378 and 408*C for foil of 1 mm thickness.

The self-ignition of plutonium can be hindered by cooling and inert gas - usually argon or nitrogen. cooling and inert gas are not a problem, as long as the plutonium is not installed in a nuclear device. Stout [STOU61] has made a number of suggestions, based on experiences gathered at Los Alamos, as to how to minimize the danger of a plutonium fire and the possible ways of putting out a fire (see also [IAEA74]). Furthermore, difficulties may arise from gradual oxidation of the metal. According to Sackman (SACK61], plutonium metal at the surface is first oxidized to PuO (a black layer is formed), and on the surface of this PuO to PuO 2 (yellow layer). Yet oxidation scarcely occurs in dry air and the best experience has been gained at Los Alamos in the storage and handling of plutonium metal in freely circulating dry air [WICK67]; mere surface oxidation is not in itself particularly troublesome. The corrosion resistance can be substantially improved [WICK67] by stabilization of the so-called 6-phase of plutonium metal, as is achieved in nuclear weapons by alloyage with several percent gallium (COCH84). In the 6-phase, plutonium metal exhibits the greatest affinity for alloying elements, e.g., 8 atom-% gallium at room temperature, 12.5 atom-% at higher temperatures (TAUB74]. Ifi experiments, a foil alloyed with 3.5 atom-% gallium revealed no significant deterioration in quality from oxidation after two and a half years in laboratory air and a foil with 6 atom-% revealed no deterioration after six years [WICK67]. The production of plutonium/gallium alloys is extensively described in the publicly available literature [BLAN62, WICK67].

39

2.5 Influences of Reactor Plutonium on an Explosive Charge

2.S.1 Influences of Radioactive Radiation

For use in the first atomic bombs at Los Alamos, experimentation was done primarily with the explosive Composition B, but also less frequently with Torpex, Pentolit, Baronal and Baratol [HAWK61]. Until the mid fifties, for both safety and security reasons, the fissionable material of nuclear weapons was kept separate from the rest of the weapon in the USA [COCH84]. The problem of possible long-term radiation damage to conventional explosives therefore did not arise. Even so, experiments were soon carried out with radiation exposure of high explosives, and the findings of several of them shall be summarized below.

In 1948, at Oak Ridge and Los Alamos, 5 g samples of the explosives RDX, Tetryl, TNT and Composition B were exposed to 8.6 106 X-rays over 10 days; at Aberdeen and elsewhere, TNT, Pentolit, Composition B, Tetrytol, Tetryl and lead azide were exposed to 4.32 104 X-rays within one hour [ROSE55]. In all cases, no significant changes were observed in the explosives. Experiments with a large number of additional explosives and high I -doses ensued. For a specimen of 5 g TNT after exposure to roughly 2,108 X-rays, no significant change was found in the melting point, ignitability, or brisance. Similar results were found for RDX, Tetryl, and lead styphnate [ROSE55, KAUF58].

Bowden and Singh [BOWD54] exposed explosives to high-energy electrons, slow neutrons, fission products and X-rays, the main goal being to investigate the ignitability through radiation exposure., According to a so-called "hot spot" theory (see, e.g.,, [PHUN70]), many explosives were supposed to explode when a region of 0.1-10 gm diameter reaches a temperature of 400-500*C. Thus, in order to ignite, the explosive need not be heated uniformly to its ignition temperature. During the exposure, the explosives were also heated to temperatures up to 290*C. Lead azide and calcium azide when exposed to several 107 of slow neutrons per CM2 per second and temperatures up to 2900C could not be caused to detonate [BOWD54, BOWD58]. Groodcock [GROO58) exposed 2 mg specimens of a-lead azide to 1 MeV X-rays and reactor radiation. The X-rays resulted in changes of the detonation properties of the explosive only after 104 roentgen; the reactor radiation, even at the highest dose used of 107 roentgen, produced no such changes.

Urizar, et al., [URIZ62] exposed 3 g specimens of TNT, Tetryl, NC, RDX, HMX, PETN and four mixtures to neutron radiation and I-rays from a reactor. Up to 5 106 roentgen, they observed only slight changes in the explosive properties, but at 2 108 roentgen some of the changes were significant. They also tested the effects of extremely large, but transient neutron fluxes on TNT S HMX, and three mixtures in a critical layout. Exposure to 5 10 roentgen

40

within 90 gs resulted in neither explosion nor notable damage to the explosives. The findings of radiation exposure experiments with organic substances - including explosives - were assembled in a book by Bolt and Carrol in 1963 [BOLT63].

A comparison with the surface dose powers of reactor-grade plutonium, cited in Chapter 2.4.1, reveals that no damage to the explosive from exposure to plutonium is to be anticipated, even over the course of years. (The shielding action of a uranium reflector is to be noted.)

2.5.2 Influences of Thermal output

Information on the thermal power of reactor-grade plutonium has already been presented in Chapter 2.4.2. Here, we shall investigate the temperatures produced in this way in the explosive charge of a nuclear weapon. For this, we must make assumptions regarding the amount of plutonium, the thickness of reflector, explosive layer, and outer shell, and assumptions on the thermal conductivity of the individual components. Starting with Fourier's law, we can compute the quantity of heat flowing through the shell of a hollow sphere [MICH64]. Converting to a system of concentric hollow spherical shells, the quantity of heat flowing through the individual shells in the steady state should then be equal. For masses of 10 kg reactor-grade plutonium, using two different geometries as a basis, we found (see also Figure 6, temperature profiles):

Outer radius plutonium sphere 5.6 cm 8 cm outer radius uranium reflector 7 cm 15 cm Outer radius explosive layer 66 cm 66 cm Outer radius housing (only marginal influence) 70 cm 70 cm

Maximum temperature rise of explosive over ambient temperature 280 K 115 K

This shows that, even without active cooling, the maximum temperature of the explosive can be kept in noncritical limits. It is only necessary to factor the aspect of heat output into the design. We chose the value of 0.4 W/mK as the thermal conductivity for the explosive, corresponding to the high explosive HMX. In addition to a high detonation rate and high specific energy, HMX has the advantage of a relatively high melting point (285-2870C) (DOBR74]. In selecting the indicated quantity of explosive, we relied on the information of Cochran, et al., [COCH84] that the mass of the explosive in the Trinity Test was around 5000 lb, which is consistent with the published outer dimensions of the first two

41

Another example is provided by the time behavior of heating of a layout by reactor-grade plutonium. If we assume a specific power of 11 W/kg Pu for a burnup of 33 GWd/T, a thermally insulated mass of the Hiroshima bomb of 6.1 kg Pu per second will initially be heated around 5 degrees per minute for a specific heat of 134 J/(kg K). This sphere of 9 cm diameter would reach an excess temperature in air of around 300 degrees, with a time constant of several dozen hours (around 70 h, see Figure 6). With strong convection, the temperature can be reduced by a factor of 2-3. If this sphere is surrounded by a 0.5 cm U jacket, the latter by 9 cm of explosive and the latter by a 0.5 cm thick steel jacket, we obtain the temperature profiles of Figure 6. This imaginary arrangement, assuming ideal thermal contact, merely serves to exemplify the problems in the use of reactor-grade plutonium. It should be noted that the excess temperatures for high-burnup

42

elements are roughly twice those of Figure 6. Without artificial cooling, the temperatures would approach the melting point of the relatively heat-resistant explosive HMX. The poor heat conduction of the explosive causes the plutonium sphere to heat up. on the other hand, the time constants for the temperature buildup are relatively slow, so that it would be conceivable to assemble a previously refrigerated Pu sphere. In any case, the temperature problem alone makes clear that reactor-grade plutonium is of little interest in the military sector, as long as plutonium from reactor elements with low burnup, i.e., slight proportion of 240Pu and MPu, is available and obtainable.

The melting point of plutonium metal is around 640*C [WICK67], and thus is not reached in these sample layouts.

2.6 Traceability of Reactor Plutonium Through Its Radiation

One could speak of a chance of detection of purloined plutonium if the latter could be demonstrated by its radiation within a reasonable measurement time on the outside wall of the building in which the plutonium is concealed. The neutron radiation, in particular, should be considered for such a detection. A space-saving, multilayered neutron shield to screen out fast neutrons can be assembled from four layers:

1. Material of medium or large nuclear charge number -e.g., heavy metal - to reduce the neutron energy by means of inelastic scattering.

2. Material of small nuclear charge number - e.g., polyethylene, paraffin, water, graphite - to reduce the neutron energy by means of elastic scattering.

3. Material with large capture cross section for absorption of the thermalized neutrons - e.g., cadmium, boroncontaining steel.

4. Material of large nuclear charge number - e.g., heavy metal - to absorb the I-radiation given off by neutron capture (SAUT83].

As the plutonium mass, we assume 7 kg of reactor-grade plutonium, which means an emission of around 2 106 neutrons per second. Neutrons from spontaneous fission of plutonium-240 and plutonium-242 have a mean energy of 1.7 MeV and 1.8 MeV, respectively [SMIT72]. If the plutonium is being kept 2 m away from a 1.5 m thick concrete wall, the neutron flux density at the end of this concrete layer, for purely geometrical reasons (disregarding 2 the scattering) would still be 1.3 neutrons per second per cm . The neutrons would quickly be thermalized in the concrete and any layer of lead placed in f ront of it. 1.5 m of normal concrete already reduces the f lux of f ission neutrons by

43

more than f ive orders of magnitude (escape cross section per (SCHM70]). If the available space is unusually cramped, a shielding of lead, concrete and boral or cadmium/lead plate can be chosen. With the help of a 13 mm thick lead plate with 5% dispersed cadmium, the thermal neutron flux would be attenuated to 1/500 (JAEG60], with a 4.45 mm thick boral plate (30% B4C) to 1/1000 [PRIC57], and with a 6.5 mm thick boral plate (35% B C) to

1.8 4

0' [JAEG60]. A 3.2 mm thick boral plate (35% B4C) attenuates the thermal neutron flux to 10-4 CROCK56]. Boron has the advantage over other shielding materials of emitting no hard I-rays upon absorption of thermal neutrons; the secondary I-radiation lies below an energy of 500 keV [ROCK56]. This shows that it is entirely possible, with a somewhat clever choice of shielding materials, to reduce the neutron flux from stolen reactor-grade plutonium at the outside wall of the hiding place to levels that are no longer practically detectable.

2.7 Reasons of Nuclear-Armed States for the Use of Weapons-Grade Plutonium

In 1945, the USA commenced a large-scale plutonium production with three reactors in Hanford. In 1954, there were already six reactors in operation in Hanford and two reactors in Savannah River. In 1964, finally, there were a total of fourteen reactors running in Savannah River and Hanford. At this time, the USA had accumulated so large a supply of fissionable material for weapons purposes that the President in those days, Lyndon B. Johnson, allowed its production to be curtailed; the USA no longer supplemented its atomic weapons arsenal with highly-enriched uranium and the plutonium production was drastically cut back. The number of reactors in operation to produce plutonium steadily decreased; in 1984, there was only one reactor in Hanford and three in Savannah River in operation [HIPP85]. The youngest of these reactors is the multipurpose Hanford-N reactor, commissioned in 1962, which supplies electricity (860 Mwe) in addition to plutonium and commenced operation in 1966 [HIPP85, KEMP85].

In December 1957, the Shippingport reactor (72 MWe) was the first reactor placed in operation in the USA for the sole purpose of commercial generation of electricity. At this time, there were thirteen reactors used in the USA for production of plutonium; a-C no time were there more than fourteen reactors operating in the USA for this purpose. This means that, at the time when commercial utilization of atomic energy began, the reactor potential for production of weapons-grade plutonium was already fully constructed in the USA; the last plutonium production reactor (Hanford-N) to be built was already intended to generate electricity as well. Even as a test demonstrated the fitness of reactor-grade plutonium for weaponry, there were still serious reasons against a subsequent conversion of the armament program to reactor plutonium:

• The required number of reactors for production of weapons-grade plutonium were already running.

• Reprocessing of reactor plutonium and its use for weapons engineering would have demanded enormous retrofitting costs, if not entirely new construction of reprocessing facilities and weapons laboratories, since the processing of highburnup fuel elements is more difficult and additional radiation protection measures would have been necessary for reactor-grade plutonium. According to Donald Kerr, Director of the Los Alamos National Scientific Laboratory, the radiation exposure of the personnel was to be further reduced in 1980 by even lower plutonium-240 content [KERRSO]. The only commercial reprocessing facility ever to operate in the USA, West Valley, only functioned from 1966 to 1972. In this time, it processed around 600 T of spent fuel elements, 390 T of which had a burnup of less than 1000 MWd/TU, taken from the Hanford-N reactor [NWG82].

• The price of plutonium is of no great importance, given the overall costs of modern rockets and cruise missiles.

• Modern weapon designs were developed especially for weapons-grade plutonium (MARK71]; conversion to reactor plutonium would have necessitated reworking of the designs.

• The target accuracy of the weapons has been increasingly improved in order to destroy important targets of potential adversaries with minimal use of rockets and greatest possible probability. An explosive force that could not be predicted exactly would run counter to these efforts, since an uncertain explosive force is tantamount to worse target accuracy and the problem of casualties from "friendly fire" is increased in a salvo-type bombardment.

• The somewhat larger and heavier weapons with reactor plutonium would have been a serious hindrance to the desired miniaturization, e.g., in multiple warheads.

In Great Britain, the first reactors for production of weapons-grade plutonium were already being used for electricity generation as well. The reprocessing plant at Windscale, initially purely military, was expanded with a commercial section in 1964. The British gas/graphite reactors produced a plutonium better suited for weapons purposes than that generated in light water reactors, while the rate of formation was also higher.

In France as well, the first reactors were gas/graphite reactors, which produced electricity in addition to plutonium for military purposes (GSP083]. Soviet reactors allow removal of fuel elements during operation. In this way, weapons-grade plutonium can be obtained from short-exposure fuel elements while electricity

45 production continues - India separated its first plutonium probably from breeder elements of a heavy water-moderated reactor [KWG82].

A decision for or against reactor-grade plutonium for weapons purposes might be made in f avor of reactor plutonium in other countries if, in particular,

• the technique of the light water reactor is established,

• a facility exists for processing of reactor plutonium,

• the development of nuclear weapons has just begun (building of the laboratory, development of the design),

• a large number of atomic bombs is desired at the outset, instead of ultramodern missiles. Even the possession of a few atomic bombs tremendously alters the political status of a nation.

For terrorists who are able to gain possession of already separated plutonium, questions of predictability, weight, and size of their weapons play no part whatsoever. The only factors important to them would be an adequate minimum explosive force and the transportability of their weapon on a truck. But these goals can be achieved with some likelihood using reactor-grade plutonium.

46

3. Estimates on the Likelihood of Preignition

In this chapter, we shall assemble the current state of knowledge in respect of the mode of functioning of fission bombs and the preignition problem in the publicly available literature. At the same time, the information cited above on the statistics of energy release (yield) should be made more precise in this way. only fission bombs in the 20 kT TNT range will be taken as examples. First, technical data is only available for these bombs from the Trinity Test and from Nagasaki; secondly, they should be of particular interest as igniters for fusion bombs or fusion-boosted bombs. once again, it is pointed out that all statements rely solely on theoretical estimates. Experiments in the non-nuclear realm, especially involving implosion techniques, could surely have been conducted in the Federal Republic and would have greatly improved the quality of the estimates. The following technical data is publicly available on the aforesaid bombs:

• The plutonium bombs of the Trinity Test and of Nagasaki allegedly contained 6.1 kg 239Pu (COCH84).

• The "brisancell (yield) of both was allegedly 22 kT TNT. The large variance of around 30% is not significant in this connection (COCH84).

• Oppenheimer is said to have estimated the probabilities of the brisance of the Trinity bomb as follows:

The probability of reaching the full yield might be 88%. The probability of a preignition, i.e., a yield beneath the maximum value, is accordingly 12%. If a preignition occurs,

• yield under 5 kT can be expected with 6% probability and

• yield under 1 kT with 2% probability (wrongly quoted in (COCH84], in reference to the Hiroshima bomb).

• Moreover, it is suggested [ALBR84] that the same arrangement with reactor-grade plutonium and presentday ballistic techniques would achieve a yield of at least 1 kT.

The estimate given below is based on the works of Locke and Leuthduser [LEUT75, LOCK74, LOCK82] and the publications cited therein, to which we shall. no longer refer individually. only the newly obtained evaluations shall be marked with an asterisk (*). This information should make it possible to achieve a rough estimate of the rates of compaction already achieved in 1945, but not published, and to obtain a parametric description of the very complicated relationships.

As often mentioned above, the preignition is caused by neutrons that are primarily produced by the "heavier" even-numbered Pu isotopes, 240 and 242, through spontaneous fission and through (a, n) reactions induced by a-decay. A sufficient estimation of

4 Anhang

Literatur

[ACHE46] A Report on the International Control of Atoniie Energy, U.S. Department of State, Publ. 2498, 16 March 1946

[ALBR84] Albright D., Can Civilian Plutonium be Used in Nuclear Explosives?, A Review on Statements by Nuclear Weapons Experts, 24 August 1984, Draft

[ALBR88) Albright D, Taylor T.B.; A Little Tritium goes a Long Way. Bulletin of Atomic Scientists, Jan/Feb 1988, p39

[ALKE82] ALKEM GmbH, Sicherheitsbericht Gesamtanlage, ALKEM-SB-3/82, Hanau 1982

[ARKI841 Arkin-W.M., Cochran T.B., Hoenig M.M.,Resource Paper on the U.S. Nuclear Arsenal, Bulletin of the Atoraic Scientists, Aug/Sept 1984, p. Is-15s

[ARNOSS) Arnold E.D., Radiation Limitations on Recycle of Power Reaetor Puels, Proc. 2nd United Nations Int. Conf. on the Peaceful Uses of Atoraic Energy (1958), Vol. 13 p. 237-250

[ASQU78) Asquith J.G., Grantham L.F., A Low-Decontamination Approach to a Proliferation-Resistant Fuel Cycle, Nuclear Technology Vol. 41(1978) p. 137-148

[ATOM79) Deutsches Atomforum e.V., Rede - Gegenrede, Symposium der Niedersächsischen Landesregierung zur grundsätzlichen sicherheitstechnischen Realisierbarkeit eines integrierten nuklearen Entsorgungszentrums, 28.-31. März, 2.-3. April 1979, Bonn 1979

[ATW81) Hätte Osirak den Weg zu einer irakischen Atombombe verkürzt?, Atomwirtschaft/Atomtechnik Aug./Sept. 1981, S. 462-464

[BARN79] Barnaby F., Jones G., Sieghart P., Bericht der Gorleben International Review, Hannover, Februar 1979

[BARU461 U.S. Department of State, The International Control of Atornic Energy, Publ. 2661 (1946), US and UN Report Series No. 5

[BBU 171 Bundesverband Bürgerinitiativen Umweltschutz e.V., PlutonJum - über die Beratungspraktiken der offiziellen Strahlenschutzkommission, September 1977

65

IBLAN621 Blank H., Brossmann G., Keminerich M., Zwei- und Mehrstoffsysteme mit Plutonium, Literaturübersicht. Phasendiagramme und Daten, Teil I, Pu-Ag bis PuSn, Kernforschungszentrum Karlsruhe, KfK 105, Juni 1962

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