Implementation of the Phase Change Model between Aerosol and Gaseous Fission Products in the GAMMA+ Code

One of the unique features of a Very High Temperature Gas Cooled Reactor (VHTR) is Vented Low Pressure Containment (VLPC) containing two separate vent paths where both have two gravity operated relief valves in a series. Because VLPC strategy allows the release of a relatively small amount of radioactive fission products(FP) into the environment during the blowdown phase, behavior analyses of the fission products circulating in the primary coolant loop and in the containment are major consideration factors for safety evaluation. For thermal-fluid analysis of a Very High Temperature Gas Cooled Reactor (VHTR), the GAMMA(GAs Multicomponent Mixture Analysis)+ code is under development. The multi-component analysis modules of aerosol fission products has been developed based on the MAEROS model and the aerosol transport model of the CONTAIN code. Furthermore, Yoo et al. developed and incorporated gaseous fission product transport phenomena into the GAMMA+ code. In this study, the phase change of fission products between condensed and vapor forms are modeled by thermochemical equilibrium, and the thermochemical and physical data of 288 species and 26 elements are implemented as a form of look-up table in the FP module of the GAMMA+ code