Simulation of the inhibition of water α-radiolysis via H2 addition

The continuous formation of H₂, O₂, and H₂O₂ observed in water during α-radiolysis may be suppressed by the addition of H₂ above the threshold hydrogen concentration (THC). Using the FACSIMILE simulation code, water radiolysis was reproduced in order to determine the THC and clarify the mechanism at room temperature. Using the reaction set and rate constants reported by Ershov and Gordeev together with the primary yields for water decomposition products generated using 12 MeV α-particles, the THC was found to be 165 μM. Further simulation results clearly showed that the value of THC is strongly dependent on the reaction set and rate constants. In addition, a possible mechanism involving a chain reaction governed by the two reactions OH + H₂ → H + H₂O and H + H₂O₂ → OH + H₂O was proposed. Furthermore, the same inhibition effect was found when a high-temperature simulation (300 °C) was performed, but the concentration range and THC were much smaller than the values obtained at room temperature. The importance of the reverse reaction OH + H₂ → H + H₂O was also investigated.     

Primary yields and reaction sets with corresponding rate constants for computer simulation of water radiolysis at elevated temperature

The chemical conditions of coolant water in light water reactors are important factors affecting the corrosive environment and the integrity of the structural materials. Computer simulations have commonly been used to predict chemical environment changes due to water radiolysis under extreme conditions. Initial parameters, including the chemical reactions, rate constants, and primary yields of water decomposition by radiolysis, have been reported by several groups in the past few decades. Using a FACSIMILE simulation, the variations caused by utilizing different sets of primary yields of water radiolysis, including γ-rays and fast neutrons, along with the chemical reactions and rate constants at 285 °C were evaluated in this study. The rate constant of the reverse reaction of OH + H₂ → H + H₂O was found to be the main factor controlling the variation between the different sets of chemical reactions and rate constants.