RELAP5 analysis of gravity-driven core-cooling experiments with PACTEL

The RELAP5 calculation results for a series of gravity-driven emergency core-cooling (ECC) experiments with the parallel channel test loop (PACTEL) facility are provided. The simulated accident was a small-break loss-of-coolant accident with a break in one hot leg of the three loops of the facility. The ECC flow was provided from a core makeup tank (CMT) located at a higher elevation than the main part of the primary system. The CMT was pressurized with pipings from the pressurizer and a cold leg. The tests indicate that rapid condensation in the CMT influences the ECC flow. The experimental results are numerically analyzed using the RELAP5/MOD3.1 code. The calculations show good agreement with the tests except in the modeling of rapid condensation.