Steam condensation simulation in a scaled IRWST-ADS simulator with GOTHIC 8.1

Abstract

The AP1000® advanced reactor passive safety systems are based on natural phenomena to ensure the containment integrity during an accident. One of the most important passive systems is the Passive Core Cooling System (PXS) which includes the In-containment Refueling Water Storage Tank (IRWST), a pool that serves as a heat sink for the Passive Residual Heat Removal Heat Exchanger (PRHR) and the Automatic Depressurization System (ADS). The thermal-hydraulic behavior of the pool is quite complex under accidental conditions: the pool receives steam at high velocity and temperature from the Reactor Cooling System (RCS), the pool is the heat sink of the PRHR, and eventually, it is the source for the low pressure safety injection. In order to study the behavior of the AP1000 IRWST during a steam discharge from the ADS at different stages of a SBLOCA, an experimental test rig was constructed in cooperation with the Technical University of Munich (TUM). The results obtained in the IRWST-ADS experiment were used to test the capability of GOTHIC 8.1 to simulate the phenomena observed experiments such as thermal stratification, direct contact condensation, and flashing. The GOTHIC model is based on two control volumes, one represents the channel test and the other the laboratory room. These control volumes are connected with a 3D-Connector between each other and with flow-paths to the boundary conditions. Pressure boundary conditions has been applied to the laboratory room control volume to maintain a constant pressure and temperature. Simulations were able to reproduce major occurring phenomena. Thermal stratification and flashing were predicted plausibly, however the direct contact condensation of steam and void fraction distribution are not perfectly simulated probably because of the selected mesh size. A sensitivity analysis has been conducted to the discretization scheme, the turbulence model, and the heat transfer correlation in order to test their effect upon GOTHIC model simulation.