Improvement of two-region nonequilibrium model for noncondensable gas

The homogeneous equilibrium model has been widely used to simulate the nuclear reactor transient. However, the homogeneous equilibrium model is not sufficient to model some components of nuclear reactor system, such as pressurizer and accumulator, where the phase separation phenomenon occurs. To compensate such weakness, RETRAN-3D uses the two-region nonequilibrium model. The two-region nonequilibrium model is consistent with the homogeneous equilibrium model and it allows phase separation and thermal nonequilibrium between vapor and liquid phase. However, the two-region nonequilibrium model in RETRAN-3D does not consider the presence of noncondensable gas. Therefore, RETRAN-3D cannot simulate the noncondensable gas effect in the nonequilibrium control volume and, as a result, it cannot be used to the analysis of the reactor system which has a steam-gas pressurizer. In this study, the improvement of the two-region nonequilibrium model in RETRAN-3D has been done to consider the effect of the noncondensable gas. In addition, the results from the improved model are compared with the results from pressurizer insurge experiment conducted in the Massachusetts Institute of Technology. (author)