Modeling of ESBWR passive containment cooling system with MELCOR

Capability of the MELCOR code to model the passive containment cooling system of the GE Hitachi ESBWR reactor design was investigated. The system consists of vertical tubes immersed in a water pool. Steam from the containment flows through the tubes and condenses on their inner surfaces. Results from three test facilities were utilized in the model development. In some cases MELCOR underestimated the condensation rate significantly when using default heat transfer parameters. This problem was corrected by modifying the Reynolds number limits for classifying the condensate film flow as laminar or turbulent to values found in literature. After this modification, it is possible to achieve better than 10 % accuracy in the condensation rate. Also aerosol deposition in the condenser tubes is reproduced well. In order to avoid oscillation and excessively short time steps, careful modeling of drainage of the condensed water out of the condenser is important.