Core Design, Spent-Fuel Characteristics Assessment, and Fuel Cycle Analysis for Thorium-Uranium Breeding Recycle in Pressurized Water Reactors

This work is focused on core design, spent-fuel characteristics assessment, and fuel cycle analysis for thorium-uranium breeding recycle in a typical pressurized water reactor (PWR), without any major change to the fuel lattice and the core internals but substituting the uranium oxide (UOX) pellet with a thorium-based fuel pellet. Two mixed cores are investigated, one loaded with mixed reactor-grade plutonium-thorium oxide (PuThOX) fuel assemblies and the other with mixed reactor-grade ²³³U-thorium oxide (U3ThOX) fuel assemblies. The high purity of reactor-grade ²³³U extracted from burnt PuThOX fuel is used as seeds of U3ThOX for starting thorium-uranium breeding recycle.

The core design and analysis indicated that thorium-uranium breeding recycle is technically feasible in current PWRs. In the mixed core with U3ThOX loading, the well-designed U3ThOX assemblies were located on the periphery of the core as a "blanket" region, which remain in core for six cycles and get breeding with ²³²Th-²³³U. The feedback parameters and kinetic parameters are dominated by the UOX fuel in the inner core. For the UOX/PuThOX mixed core, the higher plutonium content leads to harder neutron spectrum, smaller reactivity worth of neutron absorbers, and smaller delayed neutron fraction and prompt neutron lifetime, which are similar to the current mixed cores partially loaded with the plutonium-uranium mixed-oxide (MOX) fuel.

The fuel cycle analysis has shown that ²³³U monorecycling with U3ThOX fuel could save 13% of natural uranium resource compared with UOX once-through fuel cycle, slightly more than that of plutonium monorecycling with MOX fuel. If ²³³U multirecycling with U3ThOX fuel is implemented, more natural uranium resource would be saved.