氟氯混合盐体系熔盐萃取分离锆铪的实验研究

发布时间：2018-05-23 11:14

  本文选题：锆铪分离 + 氟氯混合盐体系　； 参考：《安徽工业大学》2017年硕士论文

【摘要】：锆热中子俘获面小,是核反应堆的重要堆芯结构材料、核燃料包覆材料,与铪相反。锆铪在自然界中一般共生,且铪在锆中含量为2%左右,而核级锆要求铪的含量小于0.01%,因此锆铪分离十分重要,但两者化学性质很相似、分离困难。目前锆铪分离方法主要分为湿法和火法两种,工业上主要采用溶剂萃取法,但流程复杂,环境负担重。本文采用熔盐萃取法分离锆铪,具有流程短、效率高的优点。主要工作包括母合金的制备、母熔盐的制备以及锆与铪的分离实验。母合金体系为72.8%Cu-18.2%Sn-8%Zr-1%Hf,母熔盐体系为5%CuF_2-32%NaCl-63%CaCl2。分离实验考察了CuF_2/Hf的摩尔比、反应温度、反应时间和盐中CuF_2含量对锆铪分离效果的影响,探讨了较为合适的分离条件,并且与纯氯盐体系的分离结果进行了比较。实验结果表明:(1)CuF_2/Hf摩尔比对分离过程的影响较为复杂,总体上Zr损失率γ、Hf去除率α均随着摩尔比的增大而增大,特别在温度较低时,但是摩尔比太大会导致Zr损失率过大,较合适的摩尔比为4/1;(2)温度对分离过程有较大影响,在905~970℃的范围内,随着温度的升高,Zr的损失率γ下降,此时热力学因素占主导,在1010℃的高温条件下,Zr的损失率γ有所提高,此时动力学因素——离子扩散占主导;Hf去除率α在905~1010℃均维持在一个较高的水平(97~99.6%);分离系数β总体上随温度升高而增大;(3)时间的影响:4h是比较合适的反应时间,既能保证高的Hf去除率,也能将Zr的损失控制在较低水平;(4)盐中CuF_2含量下降,对Zr-Hf分离效果略有提高,但效果不明显。(5)总体来说,同样条件下,氟氯混合盐体系的分离效果要优于纯氯盐体系,分离系数最高可达79.353和85.200。氟氯混合熔盐分离锆铪的最佳条件为:反应温度1010℃、CuF_2/Hf摩尔比4/1、反应时间4h,此条件下得到的锆中铪含量最低,为0.107%。通过实验条件的进一步优化,有望获得符合要求的核级锆。
[Abstract]:Zirconium thermal neutron capture surface is small, and it is an important core structure material of nuclear reactor, nuclear fuel coating material, contrary to hafnium. Zirconium and hafnium are generally symbiotic in nature, and the content of hafnium in zirconium is about 2%, while the nuclear level of zirconium requires that the content of hafnium is less than 0.01. Therefore, the separation of zirconium and hafnium is very important. At present, the separation methods of zirconium and hafnium are mainly wet and pyrotechnic. Solvent extraction is mainly used in industry, but the process is complicated and the environment is heavy. The separation of zirconium and hafnium by molten salt extraction has the advantages of short flow and high efficiency. The main work includes preparation of master alloy, preparation of master molten salt and separation of zirconium and hafnium. The master alloy system is 72.8Cu-18.2and Sn-8Zr-1Hf. the master molten salt system is 5%CuF_2-32%NaCl-63Cl2. The effects of molar ratio of CuF_2/Hf, reaction temperature, reaction time and CuF_2 content in salt on the separation of zirconium and hafnium were investigated. The experimental results show that the effect of 2 / HF molar ratio on the separation process is more complex. In general, the removal rate of Zr, 纬, HF, increases with the increase of molar ratio, especially when the temperature is low, but the molar ratio too large leads to the loss rate of Zr. The suitable molar ratio is 4 / 1 / 2) temperature has a great influence on the separation process. In the range of 905 ~ 970 鈩，

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