Synthesis and characterization of uranium trichloride in alkali-metal chloride media

Given a growing interest in uranium salts for pyrochemical processing of used fuel and uranium-fueled molten salt reactors, the synthesis of uranium trichloride in alkali-metal chloride media was investigated in a series of four experiments. Specifically, uranium metal powder and uranium hydride powder were prepared and separately blended with ammonium chloride and lithium chloride – potassium chloride eutectic in two runs, while the same powders were separately blended with ammonium chloride and sodium chloride in two additional runs. Each of the lithium chloride – potassium chloride containing blends was slowly heated to 923 K, while those containing sodium chloride were heated to 1123 K. During each heat up, the ammonium chloride sublimed into gaseous ammonia and hydrogen chloride, leading to the chlorination of uranium metal or uranium hydride and the formation of molten salt solutions of the respective chlorides. Experimental conditions were incorporated in the runs to promote formation of uranium trichloride over uranium tetrachloride in the respective media. Molten samples of each run product were taken and characterized via chemical analyses, diffractometry, and microscopy. The final products from each run were dark dense ingots of the respective salt systems with uranium concentrations ranging from 44 to 51 wt%. Chemical analyses and diffractometry identified the predominant presence of uranium trichloride in these systems; however, a possible minor presence of uranium tetrachloride could not be conclusively dismissed.

鉴于铀盐在乏燃料高温化学后处理以及铀基熔融盐反应堆（molten salt reactors）领域的关注度与日俱增，本研究通过四组系统实验，探究碱金属氯化物（alkali-metal chloride）介质中三氯化铀（uranium trichloride）的合成方法。具体而言，本研究制备了金属铀粉末与氢化铀（uranium hydride）粉末，将二者分别与氯化铵（ammonium chloride）及氯化锂-氯化钾共晶盐（lithium chloride – potassium chloride eutectic）混合，开展两组实验；同时将同种粉末分别与氯化铵及氯化钠（sodium chloride）混合，额外完成两组实验。每组含氯化锂-氯化钾共晶盐的混合物料均以缓慢升温速率加热至923开尔文，而含氯化钠的混合物料则升温至1123开尔文。升温过程中，氯化铵升华生成气态氨与氯化氢（hydrogen chloride），进而实现金属铀或氢化铀的氯化反应，生成对应氯化物的熔融盐溶液。本研究在各实验批次中优化实验条件，以在对应介质中优先生成三氯化铀而非四氯化铀（uranium tetrachloride）。采集各实验批次产物的熔融态样本，通过化学分析、衍射分析及显微观测对其进行表征。各实验批次的最终产物为对应盐体系的深色致密铸锭，铀元素质量分数介于44%至51%之间。化学分析与衍射分析结果表明，该体系中主要存在三氯化铀；但仍无法完全排除微量四氯化铀存在的可能性。