Plutonium End Game

Press Release

Table of Contents

Preface

Summary and Recommendations

Chapter One: Nature of the problem of commercial plutonium

Chapter Two: A Brief History of Commercial Plutonium

Chapter Three: Assessment of the current situation

Chapter Four: Disposition of US-Russian Surplus Military Plutonium

Chapter Five: Alternative Disposition Options

References

Plutonium is one of the most important links between the commercial and military nuclear industries. Plutonium is made by irradiating relatively abundant, naturally-occurring uranium-238 in a nuclear reactor. This can be done for military purposes, whereby the plutonium is extracted from the fuel and targets rods irradiated in a nuclear reactor (called irradiated reactor fuel, or spent fuel). Plutonium is also created in commercial nuclear reactors, since uranium-238 is present in large amounts in commercial nuclear reactor fuel. Since there are a large number of such reactors (more than 400 worldwide), the total quantity of plutonium that has been generated in the commercial nuclear power industry has been far greater than that produced in military nuclear weapons programs. By the end of 1999, the total plutonium created in commercial power reactors amounted to over 1,400 metric tons, compared to about 270 to 300 metric tons in military programs.

Commercial plutonium can be used to make nuclear weapons. It does not have the same isotopic composition as weapon-grade plutonium - that is, it does not contain as much plutonium-239, the fissile isotope of plutonium that is the most suited for making nuclear bombs. But any grade of commercial plutonium - that is any essentially any isotopic composition of plutonium derived from a nuclear reactor - can be used to make nuclear bombs.

One metric ton of weapon-grade plutonium could be used to make about 200 nuclear bombs - more, if sophisticated bomb designs are used. It takes roughly 40 percent more commercial-grade plutonium to make a similar bomb. Commercial reactor spent fuel contains enough plutonium to make hundreds of thousands of nuclear bombs, if it were first separated from the other radioactive material in the spent fuel. An Interagency Working Group of the US government on plutonium disposition has clearly stated that:

The main physical barrier to the use of commercial plutonium in nuclear bombs is that when it is in reactor spent fuel, it is mixed up with a far larger quantity of uranium and with highly radioactive fission products generated in the course of the nuclear chain reaction. In order to be usable for making nuclear bombs, the plutonium must first be separated from the uranium and fission products. Further, the spent fuel is so radioactive that approaching it in an unshielded state even for a few minutes would result in a lethal radiation dose.⁷ Hence plutonium in spent fuel is secure because spent fuel is resistant to theft and the plutonium in it would be very difficult re-extract should the spent fuel be stolen.

Commercial plutonium is less attractive as a nuclear weapons material for designers in the nuclear weapons states since it contains far less plutonium-239 than weapon-grade plutonium. However, the larger amount of plutonium-240 in commercial plutonium could actually make it less difficult to design a weapon. This is because the higher rate of spontaneous fission of plutonium-240 provides a source of neutrons that helps trigger the nuclear weapon. This same property also makes the yield less predictable in relatively crude bomb designs.

Plutonium extraction from commercial spent fuel is a chemical process, known as reprocessing. Commercial reprocessing plants are large and result in large amounts of liquid radioactive waste, some of which is highly radioactive and must be stored in special tanks. They also emit large amounts of radioactive krypton-85 gas into the atmosphere, which can be detected offsite. As a result, reprocessing plants are easily detectable.⁸ It would be difficult for non-state parties, such as terrorist groups, to construct and operate reprocessing plants, even if they somehow got access to spent fuel. Hence, officially sanctioned commercial reprocessing plants are among the principal potential sources of proliferation risk arising from separated plutonium.⁹ Commercial reprocessing plants are still operating in France, Britain, Russia, Japan, and India. Table 1 shows the operating commercial reprocessing plants and their capacities. The incomplete Rokkasho-mura reprocessing plant in Japan is not shown. It will be the most expensive reprocessing plant ever built.

The United States operates two military reprocessing plants at its Savannah River Site in South Carolina, ostensibly for the purpose of "environmental management." In any case the result of the operation of these plants is an increase in the stock of weapon-usable separated plutonium.¹⁰ Russia also operates two military reprocessing plants in Siberia, one at its Tomsk-7 plant near the city of Tomsk, and the other at Krasnoyarsk-26, near the city of Krasnoyarsk, also ostensibly for the purpose of managing spent fuel.

Once plutonium has been separated from spent fuel, the main barrier to proliferation has been overcome. Many of the principles and some of the details of nuclear weapons technology were first published in an unclassified report by the United States government as long ago as 1945.¹¹ There are so many details publicly known by now, that it is widely considered that if the materials have been acquired by a party determined to make nuclear weapons clandestinely, it could do so. According to a US National Academy of Sciences report,

The main current use of plutonium separated from commercial spent fuel is the fabrication of the plutonium into mixed oxide, or MOX, fuel for use in light water reactors. MOX is a mixture of a few percent (generally 5 to 7 percent total plutonium) plutonium dioxide (PuO₂) with the rest being depleted uranium dioxide (UO₂), which consists almost entirely of uranium-238. The MOX fuel is used in some of the same light water nuclear power reactors that now use uranium oxide fuel, containing 3 to 5 percent uranium-235, which is the fissile isotope of uranium. Essentially, the plutonium-239 and plutonium-241, both fissile isotopes of plutonium, replace the uranium-235 as the fuel.¹³ Both uranium and MOX fuel contain mostly uranium-238. ¹⁴ In both cases, some of the uranium-238 is converted to plutonium-239 (and higher isotopes) during reactor operation. Some of this new Pu-239 is fissioned during reactor operation and the rest remains in the spent fuel. Spent fuel derived from uranium-fueled light water reactors contains about 1 percent plutonium, while that derived from MOX-fueled light water reactors would contain 1.6 to 3.9 percent plutonium depending on the length of irradiation of the fuel, the reactor type and the percentage of MOX fuel loading.¹⁵

Fresh MOX fuel is a far greater proliferation risk than fresh uranium fuel for commercial reactors. In the latter case, the low-enriched uranium, if stolen, would have to be further enriched in huge, costly and complex uranium enrichment plants, present in only a few countries. In the case of MOX, the plutonium and uranium in the fuel, being different elements with differing chemical properties, can be chemically separated with relative ease in smaller scale facilities that would be difficult to detect. Since the principal uranium and plutonium isotopes are alpha-emitting radionuclides, with weak gamma rays, thick shielding and remote operation are not necessary for processing fresh MOX fuel so as to separate the plutonium from the uranium in it. While glove boxes and complex worker protection are desirable, this is unlikely to be a significant restraint on plutonium recovery from fresh MOX fuel, should non-weapons states or terrorist organizations acquire it for the purpose of acquiring sufficient plutonium for making nuclear weapons.

The chemical separation of the components of fresh MOX fuel yields relatively pure plutonium that can be used to make nuclear weapons. Assuming that commercial MOX fuel would have five percent plutonium, about 140 kilograms of MOX fuel (about 14 liters volume) would be needed to get enough commercial plutonium to make a relatively simple nuclear bomb.¹⁶

By contrast, commercial reactor uranium fuel is a mixture of uranium isotopes, which are chemically essentially identical. The concentration of the fissile isotope is 3 to 5 percent by weight for light water reactors (less for other types). Nuclear weapons cannot be made with this uranium without further enrichment. The minimum enrichment needed is at least 20 percent, but deliverable weapons require 50 percent or more uranium-235 content. Nuclear weapons states use uranium enriched to over 90 percent uranium-235 in their weapons, in which case 10 to 20 kilograms is required.

Uranium enrichment is a difficult and expensive process done in very large plants. Hence, fresh low-enriched uranium fuel is far more proliferation-resistant than MOX fuel, even though both contain comparable concentrations of fissile material (a few percent). Since MOX fuel is only a few relatively simple chemical processing steps away from yielding nuclear weapons-usable material, it must be safeguarded in facilities that are as secure as those that would be used for nuclear weapons. Failure to do so invites increased proliferation risks.

Next: Chapter Two: A Brief History of Commercial Plutonium