Reactions of Nickel Ions in Water Radiolysis up to 300 °C.

Radiation chemistry of hydrated metal ions plays a significant role in the field of nuclear energy, especially regarding water radiolysis in coolant water in nuclear reactors. This work reports new experimental data on the reactivity of Ni species under critical conditions of temperature and pressure. The reaction rates of hydrated nickel ions with water radiolysis products (e, OH, H, and HO) have been investigated for a 25-300 °C temperature range and 200 bar pressure using electron pulse radiolysis/transient absorption. Extensive experiments with the Ni species in various salts and pH up to 300 °C were performed. Kinetic decay traces of short-lived monovalent nickel ions were fitted to extract the rate constants versus temperature up to 300 °C. A blue shift of the absorption spectrum of the monovalent nickel ion with increasing temperature was demonstrated, which may indicate a change in the average coordination number. The Arrhenius parameters for the reactions of Ni with e and Ni with OH, H, and HO were obtained. All measured rate constants increased with temperature and followed Arrhenius behavior.