Thorium-Based Transmuter Fuels for Light Water Reactors

A light water reactor (LWR) fuel cycle is proposed where the reactor core mainly consists of standard uranium-dioxide (UO₂) fuel rods with typical ²³⁵U enrichment, along with thoria-urania (ThO₂-UO₂) or yttria-stablized zirconia fertile-free fuel rods containing the plutonium and minor actinides typical of 30-yr old UO₂ fuel in 1/9 to 1/3 of the positions. The goals of this mono-recycling strategy or "twice through fuel cycle" are to transmute the great majority of the long lived actinides in existing LWRs and to discharge a fuel form that is a very robust waste form and whose isotopic content is very proliferation resistant. The incorporation of plutonium into a ThO₂ or yttria-stablized zirconia fertile-free matrix results in the consumption of already-separated plutonium without breeding significant additional ²³⁹Pu. The minor actinides (i.e., neptunium, americium, curium, berkelium, californium, etc.) are also included in the ThO₂ or fertile-free transmuter fuel rods to further reduce the overall long-term radiotoxicity of the fuel cycle. Our analyses have shown that thorium-based or fertile-free fuels can reduce the amount of ²³⁹Pu needing further transmutation or going to a repository by ~90%. Also, thorium-based fuels produce a mixture of plutonium isotopes high in ²³⁸Pu. Because of the high decay heat and spontaneous neutron generation of ²³⁸Pu, this isotope provides intrinsic proliferation resistance.