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 2+/+ species under critical conditions of temperature and pressure. The reaction rates of hydrated nickel ions with water radiolysis products (e - aq , • OH, H, and H 2 O 2 ) 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 2+/+ 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 2+ with e - aq and Ni + with • OH, H, and H 2 O 2 were obtained. All measured rate constants increased with temperature and followed Arrhenius behavior.