Characterization and Modeling of Gravity-Driven Flashing of Superheated Water in a Pool Heated from Below

Gravity-driven flashing of superheated water, the topic of this paper, is a phase change phenomenon that is tightly linked with some of the safety issues of a spent-fuel-pool loss-of-cooling accident. As detailed in this article, the phenomenon has been empirically studied and characterized within the Aquarius laboratory-scale experimental device. Primarily, the performed tests unveil the occurrence conditions of the gravity-driven flashing phenomenon in a pool heated from below and its coupling with the degassing of dissolved gases that may take place within the liquid. Next, a set of dimensionless correlations describing the studied heat and mass transfers is derived from the data and presented for both the single-phase and the two-phase regimes of any conducted test. Then, a lumped-parameter model, relying on those correlations and describing the studied physics, is introduced. The model resolves the coupled mass and energy balance equations of the heated liquid pool. Last, this model is used to simulate a selected reference test. The performed simulations are successfully compared with the available empirical data, with moderate discrepancies, thereby verifying the adequateness of the proposed model.