Zirconium Matrix Cermet for a Mixed Uranium-Thorium Oxide Fuel in an SBWR

The thorium oxide fuel cycle has been a viable technology option since the beginning of the nuclear era. By placing (Th,U)O₂ in a zirconium matrix, the resulting cermet nuclear fuel properties create a strong negative void reactivity coefficient, which is especially appealing for boiling water reactor applications. The combination of the thorium fuel cycle and zirconium matrix cermets has enabled a new core design for a simplified boiling water reactor (SBWR). Core design simulations show that an 8-yr fuel cycle is achievable using this fuel concept. Further, if burnable poisons are added to the powder fabrication mix, an essentially flat reactivity swing is created that could enable an autonomous control system. In addition to the SBWR core design, a preliminary investigation is presented for experimental fuel fabrication methods designed to simplify cermet fabrication. Spray drying and sintering were used to create mixed-oxide (Th,U)O₂ powders with a nominal diameter of ~200 m, with ~10 vol% uniformly distributed porosity and nominal grain size of 5 m. In addition, a low-temperature cermet fabrication method was used to fabricate simulated fuel pins with a porous zirconium matrix. Results from these initial development experiments are promising for the future application of the cermet fuel, but further work is required to demonstrate their viability.