Stability of polyvinylpolypyrrolidone against gamma-ray irradiation in HNO3 media

Abstract

Polyvinylpolypyrrolidone (PVPP) is a resin with adsorption selectivity for U(VI) in HNO3 media. The stability of this resin has been examined against gamma-ray irradiation using HNO3 solutions of various concentrations. Samples of PVPP immersed in HNO3 solutions up to 6 mol·dm−3 (=M) were irradiated by a 60Co source at 3.6 kGy·h−1 to reach 0.90 MGy at room temperature under ambient atmosphere. As a result, no clear decrease in the capacity for U(VI) when added in 3 M HNO3 was observed for any samples, or rather the capacity was found to increase by approximately 50 % for PVPP irradiated in 6 M HNO3. It was indicated from some spectroscopic analyses of the irradiated samples that the irradiation causes the cleavage of the pyrrolidone ring of PVPP. This occurs by the addition of an oxygen atom originating from HNO3, followed by the formation of straight-chain groups with multiple coordinative atoms by the successive addition of oxygen, finally leading to the generation of a primary-amine-type weakly-basic anion exchange resin. The increase in the U(VI) capacity would be due to the formation of the straight-chain groups. However, such structural changes were not observed by heating at 323 K in up to 6 M HNO3 for 20 days. Thus, it was shown that PVPP is a heat-resistant resin.