Thorium-Based Fuels in Fast Breeder Reactors

Abstract

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 UO/sub 2/--PuO/sub 2/ mixed-oxide fuel. Their nuclear performance shows a substantially lower breeding gain, but a much lower positive sodium void coefficient than those for the UO/sub 2/--PuO/sub 2/ 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 UO/sub 2/--PuO/sub 2/ system. The Th-/sup 233/U metal alloy system has a slightly lower breeding gain than the UO/sub 2/--PuO/sub 2/ 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 UO/sub 2/--PuO/sub 2/ system for the same burnup constraint. Thermal-hydraulic calculations show that sodium-bonded thorium metal alloymore » fuel elements may be able to operate up to an approximate 82 kW/m (25 kW/ft) peak power rating in sodium coolant.« less