Thorium-based fuels in fast breeder reactors

A number of thorium-based fuels for fast breeder reactors using either sodium or helium coolant are considered. Thorium-plutonium mixed-oxide fuels have similar or slightly better material properties than those for mixed uranium-plutonium oxides. Their thermal performance is also very similar to that of the UO2--PuO2 mixed-oxide fuel. Their nuclear performance shows a substantially lower breeding gain, but a much lower positive sodium void coefficient than those for the UO2--PuO2 system. The material properties of Th-U-Pu and Th-U metal alloys are more suitable for reactor application than those of the uranium metal alloy. The Th-U-Pu metal alloy system has higher breeding gain, much lower positive sodium void coefficient, and a possibly higher negative Doppler coefficient of reactivity than the magnitude of those parameters for the UO2--PuO2 system. The Th-233U metal alloy system has a slightly lower breeding gain than the UO2--PuO2 system, but it has a negative reactivity coefficient for sodium voiding from the core. Equilibrium fuel cycle calculations reveal that all of the thorium metal alloy systems have a longer cycle length than the UO2--PuO2 system for the same burnup constraint. Thermal-hydraulic calculations show that sodium-bonded thorium metal alloy fuel elements may be able to operate up to an approximate 82 kW/m (25 kW/ft) peak power rating in sodium coolant