Modeling of the Gamma Radiolysis Process in Light and Heavy Water Nuclear Reactors

In water-cooled and moderated reactors, radiolysis is the source of hydrogen, deuterium, and oxygen production, as well as hydrogen peroxide (deuterium peroxide). Modeling the radiolysis phenomenon from a safety perspective is crucial for predicting the production of corrosive or explosive compounds. In this study, a gamma radiolysis model was developed for light and heavy water, and ode15s was selected as the appropriate solver for the model. The validation results of the developed model indicate an error of less than 5%. The absorbed dose effect in the range of 0.5 to 100 Gy/s, temperature in the range of 20 to 70 °C, and the effect of initial hydrogen (deuterium) concentration in the range of zero to 50 ppb were investigated for both light and heavy water. The results showed that gamma radiolysis has more obvious effects on light water compared to heavy water, and the rate of change in the concentration of oxidizing compounds, oxygen, and hydrogen (deuterium) peroxide, is lower than the rate of change in hydrogen (deuterium) concentration. The maximum difference between the final concentration of hydrogen and deuterium occurs at an absorptive dose of 100 Gy/s, where the produced hydrogen concentration is 3.5 times higher than the produced deuterium concentration from radiolysis. As the temperature increases from 20 to 70 °C, the stable concentration of radiolysis-produced compounds decreases by a maximum of 70% for hydrogen and 50% for deuterium. Increasing the initial concentration of hydrogen (deuterium) always reduces the concentration of oxidizing species (oxygen, hydrogen (deuterium) peroxide). However, the graph of produced hydrogen (deuterium) exhibits an optimal threshold (20 ppb for hydrogen and 10 ppb for deuterium). Therefore, by controlling the absorptive dose, temperature, and initial hydrogen concentration to the optimum values, corrosion resulting from the production of oxidizing agents and hydrogen (deuterium) explosions can be prevented.