Prediction of large vapor mass formation under subcooled flow boiling

Ono, Ayako ; Okawa, Tomio*

We aim to establish a new prediction method for departure from nucleate boiling (DNB) in fuel assemblies, contributing to the design and safety evaluation of next-generation reactors. Since the formation of a large vapor mass on the heating surface is considered the initial trigger of DNB, we focus on predicting the heat flux required for its formation. To achieve this, we integrate two-phase flow computational fluid dynamics (CFD) with a mechanistic large vapor mass formation model. In this study, we develop a simplified numerical analysis method that simulates bubble generation, growth, motion, and coalescence to predict large vapor mass formation. Additionally, we investigate the vapor volume on the heating surface at the onset of large vapor mass formation and predict their formation conditions.