铀钍混合氧化物点阵参数及溶解性研究

Study on Lattice Parameters and Solubility of Uranium-Thorium Mixed Oxides

为了回收不合格铀钍混合氧化物燃料中的铀,研究了铀钍混合氧化物的晶格常数以及在硝酸中的溶解性。考察了反应时间、反应温度及钍含量对铀溶解率的影响。采用熔盐辅助焙烧法对高钍含量的铀钍混合氧化物进行活化,对比了不同焙烧助剂的活化效果。结果表明:铀钍混合氧化物的晶格常数与钍含量之间满足Vegard定律;铀钍混合氧化物的溶解性随钍含量增加而降低,适合直接使用硝酸溶解的钍含量上限为24.5%;硝酸钠、氢氧化钠、碳酸钠三种焙烧助剂均能活化铀钍混合氧化物,硝酸钠的活化效果最佳,在金属摩尔比为4,温度850℃下焙烧4.0 h后,铀溶解率≥98%。

In order to recover uranium from unqualified uranium-thorium mixed oxides,the lattice parameters and solubility of uranium-thorium mixed oxides in nitric acid was studied.The effects of reaction time,temperature,and thorium content on the solubility of uranium were investigated.Molten salt assisted roasting method was used to activate mixed oxides of uranium and thorium with high thorium content,and the activation effects of different roasting aids were compared.The results show that the lattice constants and thorium content of uranium-thorium mixed oxides follow the Vegard's law.The solubility of uranium-thorium mixed oxides decreases with the increase of thorium content,and the upper limit of thorium content suitable for direct dissolution with nitric acid is 24.5%.Sodium nitrate,sodium hydroxide,and sodium carbonate can activate uranium-thorium mixed oxides,and sodium nitrate has the best activation effect.After roasting with sodium nitrate at a metal molar ratio of 4 and a temperature of 850℃for 4.0 hours,the dissolution rate of uranium is≥98%.