VIPRE-W / MEFISTO-T, a Mechanistic Tool for Transient Prediction of Dryout in BWR Fuel Assemblies

Abstract

The VIPRE-W/MEFISTO-T code package constitutes a simplified approach to sub-channel filmflow analysis whereby the transport equations for the liquid films are decoupled from each other. The approach allows fast and robust simulation with high axial resolution of realistic BWR transients. It has previously been shown that a steady-state version of the model agrees well with dryout measurements in full-scale fuel assembly mock-ups performed at the Westinghouse FRIGG loop. In this paper, we present validation of the transient version of the code with around 300 transient dryout experiments from the same loop. The transients involve realistic variations of flow and power and three different axial power distributions at conditions typical for BWR operation. The results from the film-flow analysis show high precision in the dryout prediction but a hitherto unexplained bias that reduces the accuracy.