Void effect research on MOX-fueled lead-cooled fast reactor

Abstract

Liquid metal-cooled reactor (LMR), including lead-cooled fast reactor (LFR), may have strong positive void reactivity coefficient due to the hard neutron spectrum, which is unfavorable for reactor reactivity control. This paper presents a detailed research on the lead void effect for deeper understanding on the causes. Through analytical analysis and numerical simulation, the lead void effect was decomposed into several components, and the spatial distribution of lead void worth was also calculated. The calculation results have shown that spectral hardening effect, which will cause an increase in fertile fission (mainly 238U) and decrease in the capture rate of all heavy nuclides, accounts for the high positive lead void reactivity. Meanwhile, it has been further concluded that high positive lead void reactivity mainly exists in active region. Finally, comparison between two different lead coolant lost scenarios were carried out to further prove these conclusions.