Review of Canadian Experience With the Fabrication of Thoria-Based Fuels for Advanced Reactors and Fuel Cycles for Long-Term Nuclear Energy Sustainability and Security

Abstract

Advanced fuels and fuel cycles are important for the current and next generation of advanced reactors, small modular reactors, and microreactors, in order to maximize the utilization of fissile and fertile nuclear fuel resources, and also to minimize the mass and volume of radioactive waste to be placed into long-term storage. Thorium-based fuels are a potentially attractive option for both advanced fuels and fuel cycles, since neutron irradiation will lead to the conversion of fertile 232Th to fissile 233U. Thus, thorium-based fuels can be used to augment and extend uranium resources. Through work done at Canadian Nuclear Laboratories (CNL), Canada has gained extensive experience over more than 50 years of how to fabricate thorium-based fuels. This paper provides an overview of Canada's experience in the fabrication of thorium-based fuels (mainly ThO2, (Th,U)O2, and (Th,Pu)O2) at CNL at its Chalk River Laboratories (CRL). Thoria (ThO2) fuel pellet fabrication uses processes and equipment similar to that of uranium dioxide (UO2) fuel pellet fabrication. However, since thorium lacks a fissile isotope, most ThO2 pellet fabrication processes must include a step to add a fissile component, such as enriched UO2, plutonium dioxide (PuO2), or U-233 in the form of 233UO2. Along with a review of the fuel fabrication effort that has taken place at CNL, the potential impact that CNL's extensive experience with thoria fabrication could have on the future Canadian nuclear energy landscape is also discussed.