Plutonium utilization in a small modular molten-salt reactor based on a batch fuel reprocessing scheme

Abstract

A molten salt reactor (MSR) has outstanding features considering the application of thorium fuel, inherent safety, sustainability, and resistance to proliferation. However, fissile material \({^{233}\hbox {U}}\) is significantly rare at the current stage, thus it is difficult for MSR to achieve a pure thorium-uranium fuel cycle. Therefore, using plutonium or enriched uranium as the initial fuel for MSR is more practical. In this study, we aim to verify the feasibility of a small modular MSR that utilizes plutonium as the starting fuel (SM-MSR-Pu), and highlight its advantages and disadvantages. First, the structural design and fuel management scheme of the SM-MSR-Pu were presented. Second, the neutronic characteristics, such as the graphite-irradiation lifetime, burn-up performance, and coefficient of temperature reactivity were calculated to analyze the physical characteristics of the SM-MSR-Pu. The results indicate that plutonium is a feasible and advantageous starting fuel for a SM-MSR; however, there are certain shortcomings that need to be solved. In a 250 MWth SM-MSR-Pu, approximately 288.64 kg \({^{233}\hbox {U}}\) of plutonium with a purity of greater than 90% is produced while 978.00 kg is burned every ten years. The temperature reactivity coefficient decreases from \(-4.0\) to \(-6.5\) pcm K\(^{-1}\) over the 50-year operating time, which ensures a long-term safe operation. However, the amount of plutonium and accumulation of minor actinides (MAs) would increase as the burn-up time increases, and the annual production and purity of \({^{233}\hbox {U}}\) will decrease. To achieve an optimal burn-up performance, setting the entire operation time to 30 years is advisable. Regardless, more than 3600 kg of plutonium eventually accumulate in the core. Further research is required to effectively utilize this accumulated plutonium.