FLiNaK熔盐中CsF的定向凝固分离研究

Separation of CsF from FLiNaK molten salt via directional solidification

熔盐反应堆采用氟化物熔盐作为冷却剂和燃料载体,运行后的燃料成分为铀、钍、裂变产物和载体盐,对裂变产物进行分离并回收有效组分复用,可以提高反应堆的运行经济性,并且使放射性废物最小化。定向凝固技术是利用多元混合物的相平衡特性和凝固过程元素迁移机制实现物质分离,具有工艺操作简单、无副产物产生等优点,有望用于燃料盐中裂变产物分离。在自制的冷棒式定向凝固实验装置上,研究了FLiNaK熔盐体系内典型裂变产物CsF在不同工艺条件下定向凝固后的含量分布。研究结果表明:通过控制冷却凝固速度,得到的凝固盐中Cs元素的含量在径向上呈现出梯度分布,由内向外依次递减,外侧凝固盐中Cs含量相较液相中最高降低约90%,表明燃料盐中裂变产物定向凝固分离具有一定的可行性。

[Background]Fluoride molten salt servers as a coolant and fuel carrier in molten salt reactors(MSRs).Over time of operation,fuel composition of MSR includes uranium,thorium,fission products,and carrier salt.Separating the fission products and recycling the valuable components enhances the reactor's operational efficiency and minimizes radioactive waste.Leveraging the phase equilibrium properties of multi-component mixtures and elemental migration during solidification,can effectively separate materials.[Purpose]This study aims at the directional solidification technology of fuel composition of MSR with emphasis on the separation of CsF from FLiNaK molten salt.[Methods]Firstly,a certain mass of CsF and FLiNaK eutectic salt were taken to prepare simulated sample of typical fuel composition by mechanical mixing,and completely melt the mixed salt by heating and waiting for the molten salt to cool naturally before using it for directional solidification separation experiments.Then,the concentration distribution of a typical fission product CsF in the FLiNaK molten salt system,subjected to directional solidification under different technological conditions,was investigated using a self-developed cold-rod directional solidification experimental device.[Results]The experimental results indicate that,by controlling the cooling solidification rate,the Cs element concentration in the solidified salt exhibits a radial gradient distribution,decreasing from the inner to the outer layers.In comparison to the liquid phase,the Cs element concentration in the outer solidified salt shows a substantial reduction,with a maximum decrease of approximately 90%.[Conclusions]The results show that it is feasible to separate fission products via directional solidification in fuel salts.With its straightforward process and absence of by-product generation,this technology shows promise for separating fission products in fuel salts.