NEPTUNIUM SEPARATION THROUGH PHOTOCHEMICALLY INDUCED PROCESS

1激光光化学过程作为核燃料后处理中价态调整的替代手段提供了很大的希望。由于Np在有机相和水相之间的分布取决于Np的价态，因此可以使用激光光解来控制核燃料后处理厂中Np的浓度分布。大多数实际重要的情况涉及微量Np的调整。2为了在不能用吸收分光光度法测定的极低浓度下测定价态分数，研究了萃取色谱法的适用性。在TBP色谱柱上，用稀硝酸洗脱，可定性分离不同氧化态的Np离子，用α剂量法测定价态分数。该方法用于以下实验中 关于我们 通过光解测定氧化还原比。3当通过氨基磺酸亚铁完全调节为Np（IV）的Np硝酸溶液暴露于KrF准分子激光辐射（249 nm）时，即使在起始溶液中存在还原剂的情况下，也发生光化学氧化为Np（V）。实验结果表明，在一定的辐照时间后，平衡氧化率存在光致位移。氨基磺酸亚铁的初始加入量对光致位移影响不大，但延迟了光氧化的起始。反应温度也不影响光致位移。激光照射后，残余的Np（VI）被进一步氧化。4 Np（VI），这是由KMnO 4制备的光化学还原为Np（V）在硝酸溶液中通过激光光解，即使在存在的强氧化剂在初始溶液中。这种光化学反应最值得注意的方面是：1）还原率增加到由溶液条件控制的稳态值。2)较高的反应温度和较低的酸度有利于获得较高的还原率。3)5完成了萃取实验，为Np的光化学分离获得更实用的数据。预先用化学试剂将Np离子完全调整为Np（IV）或Np（VI）。使用30%TBP（70%正十二烷）作为有机相的溶剂萃取操作在激光照射之前和之后进行。实验结果表明，激光辐照导致Np的分配系数显著降低。因此，通过激光光化学方法调整Np价态可以与传统的Purex工艺结合，而无需进行重大修改。6 Np rebox反应的这些实验结果与Purex工艺模拟代码“ADVANCED MIXSET”相结合。利用这一改进的计算机程序，在混合澄清器中的激光照射已被证明是非常有价值的，以控制Np浓度分布和净化Np从U的Purex过程。少

1 Laser photochemical processes offer much promise as alternative means of valence state adjustment in nuclear fuel reprocessing The photochemically induced redox reactions of Np were shown to occur in nitric acid solution, such as used in the Purex process. Since Np distribution between organic and aqueous phases depends upon Np valence state, it is possible to control Np concentration profile in the nuclear fuel reprocessing plant using laser photolysis. Most practically important situations involve the adjustment of trace quantities of Np.2 In order to determine the valence state fraction under very low concentration where absorption spectrophotometry cannnot be used, the applicability of extraction chromatography has been studied. Np ions of different oxidation states can be qualitatively separated on chromatographic TBP-column by elution with dilute nitric acid and the fraction of valence state can be determined by alpha dosimetry. This method was used in the following experiments … More to determine the redox ratio by photolysis.3 when Np nitric acid solution adjusted completely to Np(IV) by ferrous sulfamate was exposed to KrF excimer laser radiation (249 nm), oxidation to Np(V) occurred photochemically even in the presence of a reducing reagent in the starting solutions. The experimental results show that the photo-shift exists in equilibrium oxidation ratio after adequate irradiation time. The initial amount of ferrous sulfamate had lettle effect upon the photo-shift but delayed initiation of photo-oxidation. Reaction temperature didn't affect the photo-hift either. The residual Np(VI) was oxidised further by dark reaction after the laser radiation bing off.4 Np(VI), which was prepared by KMnO4 was photochemically reduced to Np(V) in nitric acid solution by laser photolysis, even in the presence of a strong oxidising reagent in the initial solution. The most noticeable aspects of this photochemical reaction are; 1) Reduction ratio is increasing to a steady-state value governed by the solution condition. 2) Higher reaction temperature and lower acidity are preferred to obtain higher redution ratio. 3) Reduction ratio changes abruptly when laser radiation being off.5 Extraction experiments were accomplised, in order to obtain more practical data for photochemical separation of Np. Np ions were adjusted to NpnIV) or Np(VI) completely by means of chemical reagents in advance. Solvent extraction operations using 30%TBP(70%n-dodecane) as organic phase were conducted both before and after laser irradiation. The experimental results show that laser irradiation results in significant decrease of the distribution coefficients of Np. Therefore Np valence state adjustment by the laser photochemical method can be incorporated with the conventional Purex process without majour modification.6 These experimental results of Np rebox reactions were combined with the Purex process simulation code 'ADVANCED MIXSET'. Using this reformed computer code, laser irradiation in a mixser-settler has been shown of great value to control Np concentration profiles and to decontaminate Np from U in the Purex process. Less