Limited Proliferation-Resistance Benefits from Recycling Unseparated Transuranics and Lanthanides from Light-Water Reactor Spent Fuel

Keeping LWR plutonium mixed with other transuranics and with lanthanide fission products other than 154Eu does not make it significantly more self protecting or more difficult to fabricate into a nuclear weapon. Gamma-ray and neutron doses at one meter, heat generation, and spontaneous-neutron emission are calculated from 1-kg metal balls of weapon-grade plutonium, reactor-grade plutonium, and the full mix of transuranics in high-burnup light-water-reactor (LWR) spent fuel with and without the lanthanide fission products from the spent fuel. The total radiation dose rate from transuranics without the lanthanides is more than three orders of magnitude lower than the IAEA's threshold for self-protection, 1 Sv/hr (100 rems/hr) at 1 meter. Inclusion of either of two lanthanide fission products, 144Ce and 154Eu, could increase the dose rate above the self-protection threshold. However, 144Ce has a half-life of only 0.8 years and has already decayed away in all but the most recently discharged LWR spent fuel. 154Eu has a half-life of nine years but is not recycled with the transuranics in the pyroprocessing fuel cycle that was developed for the Integrated Fast Reactor.

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