Burn-up characteristic and proliferation resistance of uranium and plutonium in multi-recycling of HALEU

The effects of multi-recycling of HALEU fuels with initial 235U enrichment from 5% to 19.9% on the burn-up characteristic and the proliferation resistance (PR) of uranium and plutonium in LWR are studied. The effects on the burn-up characteristic and PR of uranium and plutonium of 4 recycles such as Basic cycle: the irradiation of natural uranium HALEU, RepU-1 cycle: the irradiation of re-enriched RepU from the spent nuclear fuel (SNF) of the basic cycle, RepU-2 cycle: irradiation of re-enriched RepU from the SNF of the RepU-1 cycle and RepU-3 cycle: the irradiation of re-enriched RepU from the SNF of RepU-2 cycle are summarized in the present paper. Presence of 236U produced from 235U during the irradiation decreases the maximum burnup and enhances the Proliferation Resistance (PR) of uranium and plutonium in multi-recycled SNF. For example, in the case of the initial 235U enrichment 19.9% of HALEU, the maximum burn-up decreases by a factor of 0.71, from Basic cycle to RepU-3 cycle. Based on Enrichment Coefficient of 236 U which was proposed by Saito et.al and defined as a ratio of 236U to 235U after the centrifuge enrichment to that before the enrichment, Attained Maximum Possible Enrichment (AMPE) of multi-recycled RepU of HALEU was predicted. For example, in the case of the initial 235U enrichment 5%, AMPE decreases from 0.759% at Basic cycle to 0.256% at RepU-3 cycle. On the other hand, in the case of the initial 235U enrichment 19.9%, AMPE decreases from 0.684% at Basic cycle to 0.184% at RepU-3 cycle. The production of highly enriched weapons-grade uranium becomes more difficult from the multi-recycled RepU. PR of plutonium in RepU is discussed based on decay heat and spontaneous fission neutrons. Multi-recycling of RepU from SNF increases PR of plutonium more because the increase of 238Pu produced from 236U.