Validation of GAMMA-3D using inverse u-tube and HTTR-simulated air ingress experiments

One of the key safety issues for HTGRs is the ingress accident following a guillotine-type break at the coaxial pipe between the reactor vessel and the heat exchange system. We developed a multi dimensional GAs multicomponent mixture analysis (GAMMA) in order to investigate molecular diffusion, chemical reactions, and natural convection related to the air ingress phenomena during the primary-pipe rupture accident. In the simulations of both simplified inverse U-tube and HTTR- simulated air ingress experiments, the predicted results follow the experimental ones consistently regarding the concentration changes of each species and the onset times of natural convection show a level of agreement within a 10% deviation from the experimental data. Small internal leaks in the HTTR-simulated test facility have been found to significantly affect the consequence of air ingress