基于熔盐快堆的模型优化与Th-U增殖性能研究

Model optimization and analysis of Th-U breeding based on MSFR

作为四代堆6种候选堆型中唯一的液态燃料反应堆,熔盐堆对未来核能和钍资源利用具有重要意义,特别是熔盐快堆(Molten Salt Fast Reactor,MSFR)还具有较大的增殖比和较好的温度负反馈。由于启动新的熔盐快堆需要较高的燃料装载量,若能改善MSFR的增殖性能,则有利于提高233U产量并缩短燃料倍增时间。首先应用SCALE6.1针对MSFR的径向增殖盐、新增轴向增殖盐和新增石墨反射层这三方面分析了初始增殖比,同时从核素吸收率角度说明增殖比变化的原因和MSFR的设计不足并对其进行了优化;然后应用基于SCALE6.1开发的熔盐堆在线处理模块(Molten Salt Reactor Reprocessing Sequence,MSR-RS)进行燃耗分析。结果表明,新增轴向增殖盐可以进一步提高增殖性能;新增石墨反射层可以节省增殖盐装载量。改进后的堆型运行时增殖比可以维持在1.1以上,233U年产量提高至133 kg,倍增时间缩短至36 a,并且堆芯在整个运行寿期都能保持足够的温度负反馈。

Background： As the only one of liquid fuel reactor among the six candidate reactors chosen by the Generation IV International Forum （GIF）, Molten Salt Reactor （MSR） shows great potential for future nuclear energy and thorium usage, especially for Molten Salt Fast Reactor （MSFR） with characters of high Th-U Breeding Ratio （BR） and large negative Temperature Coefficient of Reactivity （TCR）. Purpose： Th-U breeding capacity of MSFR is expected to be further improved for more 233U production and shorter Double Time （DT）, and bum-up analysis is necessary to demonstrate the breeding characters with time, as well as TCR for safety. Methods： Based on SCALE6.1, three aspects are explored including fertile in radial direction, newly added fertile in axial direction and appended graphite reflector, followed with explanations from the point of nuclide reaction rate. Furthermore, bum-up analysis is carried out with time by using the self-developed code Molten Salt Reactor Reprocessing Sequence （MSR-RS） specifically for on-line reprocessing of MSR. Results： Initial BR of 1.17 is obtained when axial fertile is included, and about 50% of fertile salt is saved with graphite reflector. BR above 1.1 in equilibrium and DT of 36 a are achieved, and the production of 233U is about 133 kg·a^-1, while TCR can be kept at about -6× 10^-5 K^-1. Conclusion： Newly added axial fertile improves the BR obviously, while about half inventory of thorium can be saved with graphite reflector. The self-developed module MSR-RS is suitable for simulating the reprocessing of MSR, and 233U production for the optimized geometry increases markedly while TCR is kept negative enough at all the running time for safety.