Rate constant for the H˙ + H2O → ˙OH + H2 reaction at elevated temperatures measured by pulse radiolysis

Maintaining the structural integrity of materials in nuclear power plants is an essential issue associated with safe operation. Hydrogen (H₂) addition or injection to coolants is a powerful technique that has been widely applied such that the reducing conditions in the coolant water avoid corrosion and stress corrosion cracking (SCC). Because the radiation-induced reaction of ˙OH + H₂ → H˙ + H₂O plays a crucial role in these systems, the rate constant has been measured at operation temperatures of the reactors (285-300 °C) by pulse radiolysis, generating sufficient data for analysis. The reverse reaction H˙ + H₂O → ˙OH + H₂ is negligibly slow at ambient temperature; however, it accelerates considerably quickly at elevated temperatures. Although the reverse reaction reduces the effectiveness of H₂ addition, reliable rate constants have not yet been measured. In this study, the rate constants have been determined in a temperature range of 250-350 °C by pulse radiolysis in an aqueous I^- solution.