Study on Reactivity Control of Long-life Small Lead-cooled Fast Reactor

An effective reactivity control method is needed to compensate for the large reactivity swing during the long lifetime of small lead-cooled fast reactors. However, the compact core structure constrains the arrangement of the control rod system, and the control rod with high reactivity worth can bring safety problems to the core. In this study, the reactivity control of LFR-180 (lifetime reactivity swing is 6681pcm, 1pcm=10⁻⁵), a self-designed small lead-based fast reactor, is studied, the scheme of reactivity control based on flammable poisons is explored, and the transient safety characteristics of accidents are analyzed. The results show that the reactivity swing of LFR-180 can be reduced to 575pcm by using ZrH_1.6 as moderator and B₄C as burnable poison. At the same time, the reactivity control scheme significantly improves the temperature safety margin of the core under the accident of control rod withdrawal (CRW), and ensures the safety of the core under the accident of unprotected loss of primary flow (ULOF) and unprotected loss of heat sink (ULOHS). The burnable poison control scheme established in this study can be applied to the reactivity compensation of small lead-cooled fast reactors with long life.