Assessment of the Long-Term Waste Management and Proliferation Resistance of Different Fuel Cycles for the Generation-IV Canadian Concept of Super-Critical Water Reactor

Abstract

The Canadian concept of Super Critical Water Reactor uses a mixture of reactor-grade plutonium and thorium (Pu/Th) as a fuel, in a once-through cycle. The implications of using Pu/Th on long-term waste management and proliferation resistance were investigated in this study. Other fuels were investigated as well. These fuels are Low-Enriched Uranium (LEU), a mixture of LEU and thorium (LEU/Th), re-enriched reprocessed uranium (RepU), and a mixture of Pu/Th and natural uranium (Pu/Th/U). A quantitative estimation of the size of the deep geological repository (DGR) was done, and it was found that Pu/Th fuel would require three to four times larger DGR compared with uranium fuels. Criticality safety was investigated, and it was found that, even in the most reactive conditions, criticality safety is not hazardous. Assessment of the occupational dose to the workers in DGR from handling and storage of Pu/Th fuel showed a higher dose, around 8%, compared with LEU. The peak dose rate to the public, in case of an accident after the closure of DGR, was 75% higher in the case of Pu/Th compared with uranium, but it is still less than the regulatory limit. The attractiveness of the various fuel cycle for weapons were estimated using the Figure-of-Merit method. A numerical ranking system was proposed to facilitate the comparison between the different fuels from the proliferation point of view. It was found that RepU is the most proliferation-resistant fuel, while Pu/Th is the least one among all the studied fuels. Investigation of the reactivity coefficients of the studied fuel cycles showed that all fuels have the same sign of reactivity feedback. Regarding coolant void reactivity (CVR), the Pu/Th/U will have the most negative value which will help to bring the core to a safe state faster in case of an accident.