Improvement of Low-Pressure Subcooled Boiling Models in RELAP/MOD3.2 Code for Predicting Flow Instability

A proposed model for low-pressure subcooled boiling flow is incorporated into the RELAP5 reactor safety code to enhance its performance to predict the occurrence of the Ledinegg-type instability. The modified code is validated against experimental data. A marked improvement in the predictive performance is obtained. Although the results are encouraging, discrepancies between the modified codeʹs predictions and the experiments are observed, particularly regarding the influence of subcooling on the flow instability.