Hydrazine Radiolysis by Gamma-Ray in the N₂H₄-Cu⁺-HNO₃ System

Radiolysis of chemical agents occurs during the decontamination of nuclear power plants. The γ-ray irradiation tests of the N₂H₄-Cu⁺-HNO₃ solution, a decontamination agent, were performed to investigate the effect of Cu⁺ ion and HNO₃ on N₂H₄ decomposition using a Co-60 high-dose irradiator. After the irradiation, the residues of N₂H₄ decomposition were analyzed by Ultraviolet-visible (UV) spectroscopy. NH₄⁺ ions generated from N₂H₄ radiolysis were analyzed by ion chromatography. Based on the results, the decomposition mechanism of N₂H₄ in the N₂H₄-Cu⁺-HNO₃ solution under γ-ray irradiation condition was derived. Cu⁺ ions form Cu⁺N₂H₄ complexes with N₂H₄, and then N₂H₄ is decomposed into intermediates. H⁺ ions and H^● radicals generated from the reaction between H⁺ ion and e_aq^- increased the N₂H₄ decomposition reaction. NO₃^- ions promoted the N₂H₄ decomposition by providing additional reaction paths: (1) the reaction between NO₃^- ions and N₂H₄^●+, and (2) the reaction between NO^● radical, which is the radiolysis product of NO₃^- ion, and N₂H₅⁺. Finally, the radiolytic decomposition mechanism of N₂H₄ obtained in the N₂H₄-Cu⁺-HNO₃ was schematically suggested.