Validation of mechanistic dryout and rewetting model based on the three-field model with single-tube experiments

Abstract

ABSTRACT A mechanistic model for dryout and rewetting in boiling water reactors, is necessary in safety evaluations since it could be commonly applicable to various fuel assemblies and wider ranges of thermal-hydraulic conditions. A dryout and rewetting mechanistic model based on the three-field model in the COolant Boiling in Rod Arrays-Three Field (COBRA-TF) code was validated in this study. The dryout and rewetting criteria were introduced into COBRA-TF with the critical liquid film thickness correlation proposed by Chun et al., taking into account the disappearance and reformation of a liquid film. The calculated results were compared with not only the experimental results on critical powers and rewetting velocities measured in single-tube experiments, but also those calculated with the original model in COBRA-TF. It was shown that the model had a good predictive capability for the dryout. Although the dependencies of the calculated rewetting velocities on wall surface temperatures were qualitatively consistent with the experimental results, there were quantitatively significant differences between the experimental and calculated results. The sensitivity analyses on the rewetting predictive capability showed a critical liquid film thickness model for the rewetting, which would consider the rewetting front behaviors, is necessary for an improvement of the rewetting prediction.