Coupling Gothic and RELAP5 for Passive Containment Cooling Modeling

GOTHIC and RELAP5 have been coupled to model the containment and passive containment cooling system (PCCS) for the Korean advanced containment designs. In the coupled system, GOTHIC models the containment and the outer shell (mid tube wall to outside surface) of the PCCS heat exchanger tubes and RELAP5 models the inner shell (inside surface to mid tube wall) and the coolant loop to the external heat sink. The coupling approach leverages the modeling capabilities of RELAP5 for piping load analysis and the capabilities of GOTHIC for containment and heat/mass transfer with noncondensing gases. With the coupled model, it is possible to apply the thermal-hydraulic load analysis on the PCCS supply and return piping considering the containment conditions predicted by GOTHIC during a loss-of-coolant accident (LOCA). This paper describes the coupling approach, a coupling dynamic linked library for GOTHIC, modifications to RELAP5, and verification of the coupling. Last, demonstration results from a LOCA simulation with four PCCS trains is provided and the results of the GOTHIC/RELAP5–coupled model are compared to a GOTHIC-only result, where GOTHIC was used to model both the containment and the PCCS.