Alternative Applications of Homogeneous Thoria-Urania Fuel in Light Water Reactors to Enhance the Economics of the Thorium Fuel Cycle

Abstract

Since the thorium-based fuel has many incentives including the reduction of plutonium generation and long-lived radiotoxic isotope production, the research on the use of thorium as a nuclear fuel for nuclear power reactors has been performed and will last for a long time. Focus is on the fuel economics of the thorium-based cycle for light water reactors (LWRs). Analyses show that the neutronic behavior of a mixed thorium and uranium dioxide (Th + U)O2 core in a pressurized water reactor (PWR) will not be significantly different from that of a UO2 core. This implies that homogeneous (Th + U)O2 fuel can be used in PWRs instead of the current UO2 fuel without any significant mechanical modification of the fuel design and without any change in the nuclear design limits. However, homogeneous (Th + U)O2 has not shown any economic advantage over UO2 fuel when current fuel management strategies are used. Thus, alternative applications of homogeneous (Th + U)O2 fuel in LWRs have been investigated to enhance the economics of the thorium fuel cycle. Specifically, thorium-uranium fuel with a 235U enrichment significantly <19.5 wt%, mixed cores of both duplex (Th + U)O2 and UO2 fuel assemblies, and use of homogeneous thorium-uranium fuel in small-to-medium PWRs with a 5-yr cycle length have been investigated. The proposed alternatives result in far better fuel economics than the homogeneous thorium-uranium fuel cycle. However, the proposed alternatives do not show the economic merit of thorium-based fuel options for existing LWRs as compared to the UO2 fuel option. However, the inclusion of spent-fuel disposal costs in the fuel cost estimate makes (Th + U)O2 fuel competitive with UO2 fuel. In the case of a spent-fuel disposal cost higher than 700 US$/kg HM, the long-lived core with better economic potential than the UO2-fueled core may be realized with the homogeneous (Th + U)O2 fuel.