Core design and reactivity control optimization of small lead-cooled reactor LFR-180

Small lead-cooled fast reactors with a long lifetime generally refer to the core does not need refueling for a long time. The high excess reactivity and compact structure of the core restrict the design of control rod system. Therefore, effective reactivity control is the key to achieving longevity goals and safety enhancement. The study is carried out on a self-designed reactor LFR-180 with a reactivity swing of 6681 pcm. The combination of moderator and burnable poison (BP) is explored for reactivity compensation in the work. From the aspects of material selection, moderator design, and abundance optimization of BPs, a core control scheme is designed adopting ZrH1.6 as moderator and B4C as BP, which achieved a reasonable excess reactivity compensation. The abundance of 10B is determined according to the neutron fluence distribution in the core. The reactivity swing of the core could be reduced to 575 pcm. Although the moderator has certain unfavorable effects on power distribution and coolant void effect, the compensation design significantly improves the core safety margin under the CRW accident while the safety performance under ULOF and ULOHS transients needs further improvement. The simulation results in this paper provide ways for further design and research of small long-life LFRs.