Numerical Analysis of 1/28 Scaled HTGR Reactor Building Test Facility Response to Depressurization Event

Depressurized Loss of Forced Cooling (DLOFC) accident is an important type of accident scenario in High Temperature Gas-Cooled Reactor (HTGR) design which is initiated by a break in Helium Pressure Boundary (HPB). This class of accident scenarios results in a depressurization of primary helium coolant system with subsequent release of helium into the Reactor Building (RB) and to the atmosphere through Vented Low Pressure Containment (VLPC). After the total depressurization of helium depending on the specific accident scenarios, it is also possible that air enters into the Reactor Pressure Vessel (RPV) through the RB which can potentially react with fuel and the reactor internal components such as nuclear-grade graphite. In this study, GOTHIC model of a 1/28-scaled simplified test facility was developed to analyze the depressurization scenarios and validate them against the experimental data. Simulations were conducted in three phases by following the experiment sequence. In the first phase, natural leakage from the RB was modeled with two different methods to prepare the model for further analysis. In the second phase, post-depressurization refill of air into the RB compartments was analyzed and results were validated against experimental data. In third phase, two hypothetical depressurization scenarios were analyzed and results were compared with experimental data. Simulation results were found to be consistent with experimental data