氯化锂熔盐中二氧化铀电解还原工艺研究

Study on Electrolytic Reduction of Uranium Dioxide in Molten Lithium Chloride Molten Salt

  • 摘要: 氧化铀的电解还原是当前混合氧化物乏燃料干法后处理流程的重要组成单元之一,掌握其电解还原工艺对于后处理流程具有重要意义。本文以二氧化铀为研究对象,通过热力学计算和循环伏安测试等方法,测定了二氧化铀在氯化锂熔盐中的还原电位。在工艺研究中,以装载十克量级二氧化铀片体的金属篮为工作电极、装载金属锂的金属篮为对电极、镍-氧化镍为参比电极,通过控制电位或控制电流电解的方式研究了熔盐杂质、还原电位、电量比、阴阳极距离和阴阳极面积比等因素对二氧化铀电解还原的影响。在初步确定工艺优选的参数后,开展了百克量级二氧化铀还原实验,通过X射线粉末衍射、酸碱滴定和金属离子测定等方法对阴极产物和熔盐组成进行了分析。实验结果表明,还原产物主要由金属铀和碳化铀组成,二氧化铀XRD特征峰面积占比仅为6.9%。还原后的片体内部还有约11.4%的氯化锂、5.83%的氧化锂和0.11%的金属锂。本文研究不仅验证了二氧化铀电解还原的可行性,还确定了还原工艺的关键影响因素,为后续更大规模还原实验的开展奠定了坚实的基础。

     

    Abstract: The electrolytic reduction of uranium oxide is recognized as playing a pivotal role in the current mixed oxide fuel (MOX) spent fuel pyroprocessing. This technology is crucial for the entire reprocessing process, as it directly influences the efficiency and effectiveness of the process. In this paper, the reduction potential of uranium dioxide in lithium chloride molten salt was investigated with rigorous methods such as thermodynamic calculations and cyclic voltammetry. During the experimental study, an electrochemical setup was designed. A metal basket loaded with a ten-gram uranium dioxide pellet was utilized as the working electrode, while another metal basket loaded with lithium metal as the counter electrode, and nickel-nickel oxide as the reference electrode. By meticulously controlling either the potential or the current, the intricate effects of various parameters on the electrolytic reduction of uranium dioxide were systematically investigated. These parameters include molten salt impurities, reduction potential, charge ratio, cathode-anode distance, and cathode-anode area ratio. Following preliminary determinations of the optimal process parameters through extensive experimentation, uranium dioxide reduction experiments involving a substantial amount of material, up to 100 g, were conducted. The cathode products and molten salts obtained from these experiments underwent rigorous analysis using advanced techniques such as X-ray powder diffraction, acid-base titration, and metal ion analysis. The experimental results reveal that the reduction products are predominantly composed of uranium metal and uranium carbide, with the characteristic peak area of uranium dioxide accounting for only 6.9%, indicating a high degree of reduction is achieved. Furthermore, the analysis results of the reduced particles show that they contain approximately 11.4% lithium chloride, 5.83% lithium oxide, and 0.11% lithium metal. This work not only validates the feasibility of uranium dioxide reduction but also sheds light on the key influencing factors of the reduction process. The findings obtained provide foundation for subsequent large-scale reduction experiments in the field of MOX spent fuel pyroprocessing.

     

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