Stability of pyrrolidone derivatives against γ-ray irradiation

To evaluate the stability of N-alkylated pyrrolidone derivatives （NRPs）, which are supposed to be used as precipitants for U（VI） and Pu（IV, VI） species in HNO3 media, under irradiation environment, some candidate NRPs were irradiated by γ-ray. Irradia- tion to HNO3 solutions up to 6 mol dm-3 （= M） containing 2 M N-n-butyl-2-pyrrolidone （NBP）, one of NRPs with lower hy- drophobicity, has revealed that the residual ratios of NBP in the samples of HNO3 up to 3 M decreased identically and linearly. Approximately 20% of NBP was found to be degraded after the irradiation at 1 MGy. It was also found that the decrease in the precipitation ratio of UOf＋ （P.R., %） was gentle and that the P.R. values were relatively in accordance with the residual ratios of NBP. On the other hand, the degradation of the samples irradiated in 6 M HNO3 was found more distinguished. It was pro- posed from the analyses of degraded compounds that the degradation of NBP in HNO3 by γ-ray irradiation started from the cleavage of the pyrrolidone ring by the addition of oxygen atom originating from HNO3, followed by the formation of chain compounds by the successive addition of oxygen, leading to the generation of oxalic acid and acetic acid. The stability of other NRPs in 3 M HNO3 was evaluated to be nearly identical with that of NBP except lower P.R. values of the samples containing NRPs with higher hydrophobicity irradiated at more than 0.5 MGy.