Development of the Water Radiolysis Model in the AERMOD Module

In the case of accidents involving loss of fuel pin tightness in pressurized water reactors (specifically, their Russian version known under the brand name VVER), it is necessary to take into account their potential interaction with the radiolysis products accumulated in the coolant for correctly modeling the fission products' behavior. Since such interaction can entail generation of a significant quantity of volatile compounds, which may pose a threat in the case of release into the environment, a relevant block in the integrated code was developed, using which this phenomenon can be modeled. The article describes the water radiolysis model used in the AERMOD, which was developed for numerically analyzing radiation-chemical transformations in water occurring under the influence of ionizing radiation. By using the model, it is possible to trace changes in the concentrations of individual radiolysis products for different values of initial concentration of impurities in water and absorbed dose rate. The model is also supplemented with an interphase transfer mechanism for determining the release of volatile radiolysis products (e.g., hydrogen) into the gas volume. A method for numerically solving the obtained equation systems is presented, and the model is compared with the existing domestically developed analogs. The results obtained from validation of the model describing water radiolysis and hydrogen release into the gas gap against experimental data are given.