Study Of Tributyl Phosphate/Dodecane Solvent Radiolysis Products On Retention Behavior Of Zirconium Ruthenium Metal

Spent fuel reprocessing is the top priority of the nuclear fuel cycle system.In the most commonly used Purex spent fuel reprocessing process,the TBP-diluent-nitrate solvent extraction system is subject to radiation damage from the spent fuel and nitric acid,resulting in radiolysis and chemical degradation,producing a series of temporary and permanent irradiation products.The temporary radiolysis products such as DBP and MBP can be removed by recycling the used TBP extraction system after acid-base washing,but the permanent irradiation products will accumulate in the organic phase with recycling,causing retention of fission products such as zirconium and ruthenium,resulting in poor decontamination of them,and also aggravating radiolysis and generating interfacial contamination,which seriously affects the extraction process.The normal operation of the extraction process is seriously affected.Therefore,it is important to investigate the metal retention behavior of radiolysis products.In this study,several simulated radiolysis products（dodecanol,lauric acid,HDEHP）were selected and the following studies were carried out to investigate their extraction retention behavior of zirconium and ruthenium metals:（1）The extraction retention behavior of three simulated radiolysis products for zirconium（IV）and ruthenium（III）was investigated.By comparison with the pure 30%TBP-n-dodecane system,it was shown that the addition of HDEHP,a long-chain acidic phosphate with branched chains,had the effect of increasing the distribution ratio for both zirconium and ruthenium,while the other simulated radiolysis products did not have this effect.Through the reverse extraction and alkali elution experiments,it was found that the metal at this point was difficult to elute and was retained in the organic phase,which further supports the long-chain acidic phosphate hypothesis of the metal retention mechanism.（2）The extraction and retention behavior of zirconium（IV）by HDEHP was investigated,and its extraction distribution ratio（D）and metal retention value（R）were determined.The laws of nitric acid concentration,radiolysis product concentration,metal concentration and temperature on the extraction distribution ratio（D）and metal retention value（R）were investigated,and the infrared spectra of its complexes were analyzed.The results showed that the extraction process of zirconium is a heat absorption reaction;increasing the concentration of nitric acid can effectively reduce the distribution ratio and retention value of zirconium,which is presumed to be related to the competition effect of nitric acid and the hydrolysis reaction of zirconium;adding rhenium can greatly increase the retention of zirconium,which is related to the co-extraction effect of rhenium（VII）and zirconium（IV）;the retention of zirconium is not related to the anti-micellar group formed by HDEHP,and may be related to the P=O group is related to the solvation effect between the metal cation;the complex formed by the ligand and zirconium also contains nitrate.（3）The extraction and retention behavior of ruthenium（III）by HDEHP was investigated,and its extraction distribution ratio（D）and metal retention value（R）were determined,and the influence of nitric acid concentration and other factors was also investigated,and the IR spectra of the complexes were analyzed.The results show that the extraction and retention processes of ruthenium are exothermic;increasing the nitric acid concentration effectively reduces the distribution ratio and retention value of ruthenium,and it is assumed that the competitive effect of salt precipitation with nitric acid is related to the morphology of the ruthenium complexes,which should be retained in the organic phase in a 3:1 configuration;adding rhenium reduces the distribution ratio and retention value of ruthenium,which indicates that there is no co-extraction and co-retention effect between rhenium（VII）and ruthenium（III）,but rather The retention of ruthenium is not related to the formation of anti-micellar groups by HDEHP,nor to the formation of complexes linked to water molecules in Ru NO³⁺ligands through weak interaction forces of hydrogen bonding,but probably to the ligands bound to the inner coordination sphere through anion-cation exchange reactions;the complexes formed by the ligands and ruthenium also contain nitrate.