Prepared for US Department of Energy Advanced Fuel Cycle Initiative

A task was undertaken at INL to establish specific technical capabilities to perform neutronics analyses in order to further assess several key issues related to the viability of thermal recycling. The initial computational study reported here is focused on direct thermal recycling of IMF fuels in a heterogeneous Pressurized Water Reactor (PWR) bundle design in a multi-recycle strategy using legacy 5 year cooled LWR SNF. These analyses provide comparison of direct thermal recycling of four actinide partitioning options: PuNpAmCmCf,, PuNpAm, PuNp, and Pu. The TRITON depletion code (a component of the SCALE5.1 suite) was used to simulate depletion of an infinite-lattice (2-D) PWR fuel assembly, containing both IMF and UO2 pins. The TRU loading in the IMF pins was adjusted to ensure a pin power peaking factor no greater than 1.2. The enrichment of the uranium in the UO2 pins was adjusted to achieve a 1500 day fuel life in a 3-batch strategy. Transuranic recycling was assumed where the selected TRU elements of the given strategy are recycled from UO2 and IMF pins in the previous cycle and loaded into IMF pins of the current cycle. In the cases where the bundle design was constrained to have a constant number of IMF pins (44 pins), some of the partitioning scenarios required that a portion of the transuranic mass would have to be discarded to repository storage. The reasons for this mass expulsion from an otherwise closed fuel cycle was the requirement to maintain a peaking factor no greater than 1.2. Additional calculations described in Section 5.3 allowed variation of the number of IMF pins between 44 and 60 per assembly as needed in each pass in order to accommodate all TRU in the fuel cycle with no material (aside from separation losses) being discarded.