The use of zirconium hydride blankets in a minor actinide/thorium burner sodium-cooled reactor for void coefficient control with particular reference to UK's plutonium disposition problem

• We propose a new concept using zirconium hydride blankets for void coefficient control in a thorium-fuelled sodium-cooled reactor.
• We model a parfait arrangement with a homogeneous fuel distribution in a PRISM reactor.
• Mild moderation from blankets combined with a 3-batch fuelling scheme yields a negative void reactivity coefficient throughout the life of fuel.

The use of zirconium hydride (Th–ZrH1.6) blankets in a thorium-fuelled sodium-cooled reactor for void reactivity control with particular reference to UK's plutonium disposition problem is proposed and considered. It is shown that, with the use of such blankets, a mild moderation effect is produced during voiding which compensates for the general hardening of the spectrum, enabling a net negative void coefficient at pin level to be attained without the need to rely on traditional neutron leakage enhancement techniques or neutron poisons, and with negligible impact on transmutation capabilities. One important difference in comparison with the traditional methods is that the void coefficient is obtained at the pin level, eliminating or mitigating substantially the spatial dependencies on the location of the void. Combining the use of such blankets with a suitable n-batch fuelling scheme yields a negative void reactivity coefficient throughout the life of fuel. Additional research and development are required to explore further this concept's potential.