Radiation stability and radiolysis mechanism of hydroxyurea in HNO3 solution: Alpha, beta, and gamma irradiations

Abstract

Hydroxyurea (HU) is a novel salt-free reductant used potentially for the separation of U/Pu in the advanced PUREX process. In this work, the radiation stability of HU were systematically investigated in solution by examining the effects of the type of rays (α, β, and γ irradiations), the absorbed dose (10–50 kGy), and the HNO3 concentration (0–3 mol L−1). The influence degree on HU radiolysis rates followed the order of the absorbed dose > the ray type > the HNO3 concentration, but the latter two had moderate effects on HU radiolysis products where NH4+ and NO2− were found to be the most abundant ones, suggesting that the differences of α, β, and γ rays should be considered in the study of irradiation effects. The radiolysis mechanism was explored using density functional theory (DFT) calculations, and it proposed the dominant radiolysis paths of HU, indicating that the radiolysis of HU was mainly a free radical reaction among ·H, eaq–, H2O, intermediates, and the radiolytic free radical fragments of HU. The results reported here provide valuable insights into the mechanistic understanding of HU radiolysis under α, β, and γ irradiations and reliable data support for the application of HU in the reprocessing of spent fuel.