Fuel Cycle Optimization of a Helium-Cooled, Sub-Critical, Fast Transmutation of Waste Reactor with a Fusion Neutron Source

Abstract

Possible fuel cycle scenarios for a helium-cooled, sub-critical, fast reactor with a fusion neutron source for the transmutation of spent nuclear fuel have been analyzed. The transmutation rate was set by the 3000MWth fission power output. The primary objective was to achieve greater than 90% burn of the transuranic (TRU) fuel obtained from spent nuclear fuel. A secondary objective was to examine the possibility of achieving this deep burn without reprocessing after initial fabrication of the TRU into coated particle TRISO fuel. Four sets of 5-batch fuel cycle scenarios, differing in the constraints imposed on the beginning of cycle (BOC) k-eff and the end of cycle (EOC) neutron source strength (characterized by the fusion neutron source power level), were evaluated. In scenario A, BOC k-eff was required to be 0.95 and EOC Pfus less than 200 MWth was required. In scenario B, the restriction was removed to allow less reactive BOC fuel loadings, while the 200 MW upper limit on EOC Pfus was retained. It was found that the primary objective of greater than 90% TRU burn-up could be achieved by repeatedly reprocessing the TRISO TRU fuel particles to remove fission products and add fresh TRU makeup at the end of each 5-batch burn cycle, without needing to increase the fusion neutron source power above 100 MWth when the BOC k-eff is restricted to 0.95. The secondary objective of obviating processing could only be accomplished when the restriction was removed and recycling was employed or when both EOC Pfus and BOC k-eff restrictions were removed in a single-pass deep burn fuel cycle. In scenario C, with both the BOC k-eff limit and the fusion power limit unrestricted, greater than 90% TRU burn-up was achieved without reprocessing the TRISO TRU fuel particles, which could then be buried intact in a high-level waste repository, but a neutron source rate of 3370 MWth was required. In scenario D, with only the BOC k-eff limit unrestricted, greater than 90% TRU burn-up was achieved without reprocessing by the continuous recycle of TRISO particles through the reactor.