Effects of the reprocessed uranium (RepU) multi-recycle on proliferation resistance of plutonium (Pu) and uranium (U) has been studied. Non-fissile isotope 236U is generated from 235U during the burn up in the reactor. Typical isotope ratio of 236U to the remaining 235U isotope in the RepU from the used fuel in light water reactor varies from 0.4 to 1.0, depending on the initial enrichment and the burnup. During burnup, by further absorbing neutrons, some of 236U becomes 238Pu via 237Np. 238Pu has strong proliferation resistance because of the high decay heat and spontaneous fission neutron emission. During the centrifuge re-enrichment of 235U in the RepU, 236U is also re-enriched together with 235U. The ratio of 236U to 235U after re-enrichment of the RepU is roughly 0.3 to 0.4 up to 5% 235U enrichment. Hence, the centrifuge re-enriching of the RepU makes it difficult to produce weapon-grade high-enriched 235U because 236U is also enriched together. After the re-enriched RepU is burned again in the reactor, naturally 235U is reduced by fission to release energy during the burning and the content of 236U after the first recycle is further increased compared to that after the first cycle. The content of 238Pu after the first recycle is also further increased compared to that after the first cycle, which means the proliferation resistance of Pu is further increased after the first recycle. By repeating this process, the production of highly enriched weapon-grade U becomes more difficult from the multi-recycle RepU. 236U in RepU is an attractive isotope to make protect Pu and U from adversarial use. Recycle of minor actinides for protected Pu production (P3), proposed earlier by Saito elsewhere, and the recycle of the RepU proposed here are both useful and important for the peaceful uses of nuclear energy.
- M. Saito, S.S. Chirayath, "Effects Of Reprocessed Uranium Multi-recycle On Proliferation Resistance Of Plutonium And Uranium", INMM and ESARDA Joint Annual Meeting, Virtual Meeting, August 23 – September 1, 2021.