Analysis of nuclear fuel cycle of heterogeneous thorium fueled core for PWR

The neutronic characteristics, economics, proliferation resistance potential, and long-term radiotoxicity of heterogeneous thorium fuel option for PWR was analyzed. The HELIOS, group constant generation code used for thorium, has been qualified against the heterogeneous fuel assembly benchmark problem by comparing the results with CASMO-4 and MOCUP performed by US side as a part of NERI project. The infinite multiplication factors from HELIOS calculation are in good agreement with CASMO-4 except for SBU which uses metallic fuel for seed material. The mixed core with thorium and uranium fuel assemblies, the recycling of thorium fuel, and the mixed core with recycled thorium and uranium fuel assemblies have been proposed for the application of heterogeneous thorium fuel assembly to existing PWR cores. The refabrication with dry process of spent fuel was assumed in order to meet the proliferation resistant policy instead of wet reprocessing. Fuel economics of thorium cycle was analyzed by investigating the natural uranium requirements and the separative work requirements as well as the spent fuel disposal cost. The additional refabrication cost was also included in the fuel economic analysis only for the recycling of thorium fuel option. The fuel economics of the mixed core option with once-through thorium fuel increased compared to the previous homogeneous thorium fuel cycle. Compared to uranium fuel cycle, however, it does not show any economic incentives. Even though the fuel economics of the recycling of thorium options increased remarkably due to lesser requirement of enriched uranium, it does not show superior economics to that of uranium fuel cycle because of additional refabrication cost. However, the inventory of spent fuel of recycling option was reduced remarkably. In case of including the spent fuel disposal cost of 700US$/KgHM into fuel cost analysis, the fuel economics of the recycling of thorium option was comparable to uranium fuel cycle. From the view of proliferation resistant potential, the nonproliferation characteristic of thorium-based fuel such as critical mass, spontaneous fission rate, decay heat generation rate are superior to the conventional uranium fuel. The thorium fuel option has the advantage to reduce the inventory of plutonium production especially. The radioactivity level of thorium fuel options were proved to be lower than that of uranium fuel option till 104 years after fuel discharge. The proposed thorium options are less economical than uranium fuel option under the current circumstance, the thorium fuel option has the potential to be utilized in the future to consume the excessive plutonium effectively and to save the natural resource against the shortage of uranium resource. The recycling of thorium options have a superior economic potential to that of uranium fuel cycle when the spent fuel disposal cost is included in the fuel economic analysis