Radiolysis of Diisodecyl Phosphoric Acid and its Effect on the Extraction of Neptunium

Radiolysis of diisodecyl phosphoric acid (DIDPA) in n-dodecane containing tributyl phosphate (TBP) was examined by analyzing concentrations of acidic extractants and H₃PO₄, and its effect on the extraction of neptunium was studied from the aspect of the extraction rate. For the solvent containing 0.5 M DIDPA and 0.1 M TBP irradiated in the absence of HNO₃, G-values for degradation of DIDPA and for production of dibutyl phosphoric acid (DBP) were found to be 0.47 and 0.14, respectively. For the solvent irradiated in stationary contact with 0.5 M HNO₃, G-value for DIDPA degradation was found to be 0.73, which was 1.7 times larger than the value for the solvent irradiated in the absence of HNO₃.

In the experiment on the extraction of neptunium initially in the pentavalent state from the solution containing 0.5 M HNO₃ and 0.5 M H₂O₂, it was found that the extraction rete tas determined by the concentration of MIDPA forted by radiolysis when the solvent was irradiated with lower dose than 1 MGy in the absence of HNO₃. When the solvent absorbed higher dose or was irradiated in the presence of HNO₃, the extraction rate was influenced by the other radiolysis products. Even in this case, when the solvent contained TBP, the rate varied little until absorbed dose increased over 0.5 MGy.