Improvement of direct contact condensation model of relap5/mod3.1 for passive high-pressure injection system

A simple set of the transition criterion of the condensation regimes and the heat transfer coefficients on the direct contact condensation in the core makeup tank was developed, and implemented in RELAP5jMOD3.1. The condensatin regimes were divided into two ones: supply limit and condensation limit. In modeling the transition criterion between two regimes, a large-eddy model developed by Theofanous was used. The modified code better predicted the experiments on the core makeup tank using small scale test facility than the original code did.