Numerical Simulation of RCCS under LPCC Accident in PMR600 Using CFD

The Reactor Cavity Cooling System (RCCS) is the ultimate heat sink of the core decay heat under accident conditions. RCCS has a capability to limit the reactor pressure vessel temperature under the design safety limit following accidents such as High Pressure Conduction Cooling (HPCC) and Low Pressure Conduction Cooling (LPCC). The initiating event for LPCC is the guillotine rupture of a coaxial pipe or a simultaneous break of all the connecting pipes between the reactor pressure vessel and the heat transport system. A simulation for LPCC accident of PMR600 was conducted by using the GAMMA+ code. The GAMMA+ code, which is developed to analyze the thermo-fluid transients in HTGR, is a system code and it treats the momentum and energy transfer differently from the computational fluid dynamics (CFD). There might exist the difference between the estimations using GAMMA+ and CFD. In a previous study the steady state performance of RCCS in HTGR (High Temperature Gas-Cooled Reactor) was calculated using the computational fluid dynamics with the porous medium approach and the axisymmetric assumption. Even though this assumption reduces the computational time significantly, it changes the RCCS tube shape. This may change the behavior of RCCS. In this study, we develop three candidates of RCCS for CFD, conduct the unsteady simulations for the LPCC accident, and compare the results with the GAMMA+ code. By doing this, we can find a suitable model for RCCS when CFD is conducted with the axisymmetric assumption