Extraction and retention of plutonium with gamma-irradiated 30% trialkylphosphine oxide-kerosene solution

Extraction and retention of plutonium by irradiated 30% trialkylphosphine oxide (TRPO) in kerosene were investigated. Factors that influence the retention of plutonium are discussed. The experimental results show that when 30% TRPO-kerosene-HNO3 is irradiated above a dose of 2 x 10(6) Gy, it produces a few Pu-complexing radiolytic degradation products. Radiation dose was the primary factor affecting retention of plutonium in the organic phase. At a radiation dose of 5 x 10(6) Gy, about 40% of the plutonium extracted by the solvent was left in the organic phase even after five back-extraction contacts with 0.6 mol/L oxalic acid. The reasons for plutonium retention were investigated. The products causing the retention were the polymeric ones with high molecular weight, and these were recovered by vacuum distillation of the irradiated 30% TRPO-kerosene. The phosphonic and phosphinic acids produced by irradiation of TRPO had no effect on the retention of plutonium.