Breeding and void reactivity analysis on heavy metal closed-cycle water cooled thorium reactor

Design parameters of heavy water (D2O) cooled thorium breeder reactors for actinides closed-cycle cases have been investigated to find a design feasible area of breeding and negative void reactivity. Heavy metals (HMs) closed-cycle shows narrower feasible area compared with feasible area of 233U closed-cycle. In thorium fuel cycle, the breeding capability of the reactors becomes worse when all HMs are recycled. The result shows an opposite profile of breeding capability compared with uranium fuel cycle which obtains higher breeding capability when more HMs are recycled. Feasible design area which has a breeding and negative void reactivity can be estimated for higher burnup, even higher than 60 GW d/t for 233U closed-cycle; however, it is limited to 36 GW d/t for HM closed-cycle. Contribution of capture 235U is more significant to reduce breeding capability and contribution of 234U is also more effective to make the reactor more positive or less negative void coefficient for HM closed-cycle case in thorium fuel cycle system.