The long-term nuclear explosives predicament : final disposal of military usable fissile material in nuclear waste from nuclear power and from the elimination of nuclear weapons

It is possible that the long-term global energy future does not turn out to be a breeder-reactor-based plutonium economy, but that a sustainable energy future based on renewable energy sources develops instead, i.e., a post-nuclear world. The thesis is based on a scenario where this is the case. Then large amounts of fissile material, that would otherwise to be consumed in the plutonium economy, will have to be disposed of as long-lived nuclear waste. This material is usable for the construction of nuclear explosives and consists of weapons-grade uranium and weapons-grade plutonium from nuclear weapons dismantled as a result of reductions of the nuclear arsenals, and reactor-grade plutonium produced in civil nuclear reactors, but not recycled. Regarding the possibilities of using reactor-grade plutonium for the construction of nuclear explosives, it is found that reactor-grade plutonium is an entirely credible fissile material for nuclear explosives, but that the increased spontaneous fission neutron background inherent in such material does provide an incentive for a nuclear explosives program to produce weapons-grade plutonium. On the other hand, laser isotope separation technology can be used to convert reactorgrade plutonium into weapons-grade plutonium. Present planning for the final disposal of spent nuclear reactor fuel that contains reactor-grade plutonium calls for the deposition of the material in mined geologic repositories. This disposal solution does, however, not make the fissile material “practicably irrecoverable” and safeguards would have to be put on the material for an indefinite time-period. Thus our generations, who utilize nuclear power, will leave a burden on future generations that do not. This is the long-term nuclear explosives predicament. In this thesis the predicament is examined. A scenario is described where the production of new military fissile material is halted and where civil nuclear power is phased out in a “no-new orders” case. It is found that approximately 1 100 tonnes of weapons-grade uranium, 233 tonnes of weapons-grade plutonium and 3 795 tonnes of reactor-grade plutonium has to be finally disposed of as nuclear waste, as the use of large-scale nuclear technology is phased out. This material could be used for the construction of over 1 million nuclear explosives and will be available for such purposes for a very long time. Reactor-grade plutonium is found to be easier to extract from spent nuclear fuel with time and some physical characteristics important for the construction of nuclear explosives are improved. However, the biggest problem, the large spontaneous neutron background, does not decrease. Alternative methods for disposal of the fissile material that will avoid the longterm nuclear explosives predicament are examined. Among these methods are dilution, denaturing or transmutation of the fissile material and options for practicably irrecoverable disposal in deep boreholes, on the sea-bed, and in space. Weighing in costs, environmental safety and public acceptance it is found that the deep boreholes method for disposal should be the primary alternative to be examined further. This method, which may make the fissile material more difficult to retrieve than from a mined repository, can be combined with an effort to “forget” where the material was put. This would, however, be a reversal of the present considerations where an attempt is planned to transfer as much information about the nuclear waste as possible into the future. Included in the thesis is also an evaluation of the possibilities of controlling the limited civil nuclear activities in a post-nuclear world. It is found that the opportunities for an effective safeguard regime are very favourable. Some surveillance technologies that might find widespread use in a post-nuclear world are described, including satellite surveillance. In a review part of the thesis, methods for the production of fissile material usable for the construction of nuclear explosives are described; the technological basis for the construction of nuclear weapons is examined, including the possibilities for using reactor-grade plutonium produced in civil nuclear power reactors for such purposes; also the present planning for the disposal of spent fuel from civil nuclear power reactors and for the handling of the fissile material from dismantled nuclear warheads is described. The Swedish plan for the handling and disposal of spent nuclear fuel is selected as a reference example of a spent fuel disposal system and is described in detail.