THE ATTRACTIVENESS OF MATERIALS ASSOCIATED WITH THORIUM BASED NUCLEAR FUEL CYCLES FOR PHWRS

This paper examines the results of a study in which Low-Enriched Uranium Oxide/Thorium Oxide (LEU/ThO2) fuel is substituted for the standard natural uranium fuel used in Pressurized Heavy Water Reactors (PHWRs). The goal is to assess the ability of this fuel mixture to closely match operating characteristics of the standard fuel, while minimizing the material attractiveness of the fuel and maximizing the number of spent fuel assemblies required to accumulate a Bare Critical Mass (BCM) of plutonium. In meeting these criteria, the optimized LEU/ThO2 fuel will represent a significant improvement in Safeguards by Design for the PHWR fuel cycle. A central focus of this study is the idea that the proposed fuel will be exported from a nation-state as a finished product. Results from this research indicate that the proposed LEU/ThO2 fuel can indeed meet the criteria mentioned above, though differences in reactivity coefficients were observed between the cycles. All LEU enrichments (modeled using the SCALE code package) increased the number of fuel assemblies required for a BCM of plutonium by a factor of 2.5-7 over standard PHWR fuel. However, it is important to note that a lower material attractiveness does not lessen the need for stringent safeguarding of spent nuclear fuel. This study was performed at the request of the United States Department of Energy/National Nuclear Security Administration (DOE/NNSA).