ALTERNATIVE APPLICATIONS OF HOMOGENEOUS THORIA-URANIA FUEL IN LIGHT WATER REACTORS TO ENHANCE THE ECONOMICS OF THE THORIUM FUEL CYCLE

摘要

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)O_2 core in a pressurized water reactor (PWR) will not be significantly different from that of a UO_2 core. This implies that homogeneous (Th + U)O_2 fuel can be used in PWRs instead of the current UO_2 fuel without any significant mechanical modification of the fuel design and without any change in the nuclear design limits. However, homogeneous (Th + U)O_2 has not shown any economic advantage over UO_2 fuel when current fuel management strategies are used. Thus, alternative applications of homogeneous (Th + U)O_2 fuel in LWRs have been investigated to enhance the economics of the thorium fuel cycle. Specifically, thorium-uranium fuel with a ~(235)U enrichment significantly <19.5 wt%, mixed cores of both duplex (Th + U)O_2 and UO_2 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 UO_2 fuel option. However, the inclusion of spent-fuel disposal costs in the fuel cost estimate makes (Th + U)O_2fuel competitive with UO_2 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 UO_2-fueled core may be realized with the homogeneous (Th + U)O_2 fuel.