Flow instability prediction in low-pressure subcooled boiling flows using CFD codes

A proposed model for low pressure subcooled boiling flow was incorporated into the safety reactor code RELAP5/MOD3.2 to enhance the performance of the reactor code to predict the occurrence of the Ledinegg-type of instability in two phase flows. The nodalization scheme employed for the particular geometry as modeled in the RELAP5 code is described. The modified code was validated against experimental data and a marked improvement in predictive performance was noted. Simulation results using the modified RELAP5 code and CFX were also compared. Discrepancies between the modified RELAP5 predictions and the experimental benchmark were observed, particularly on the influence of subcooling on the flow instability.