Characterization and prediction of flow-conditions in the hot-leg of PWR during loss of coolant accident

Abstract

Numerical and computational attempts are made to investigate and characterize the flow-condition in the hot-leg of a Pressurized Water Reactor (PWR) during the loss of coolant accident (LOCA). Finite Volume-based Volume of Fluid (VOF) model is employed for transient numerical simulations of the two-phase hydrodynamics in hot-leg during LOCA. The turbulence effect is captured using ‘k-w’ model. Effect of individual fluid-flowrates and stored water (initial water-level), on the developed counter-current two-phase flow-structures in hot-leg are extensively studied. Variations of the spatial distribution of phases with time are evaluated. Flow-structures in the hot-leg are characterized and parameterized in terms of statistical parameters extracted from the time variation of pressure drop (PD) and volume fraction (VF) across the flow domain. Computational intelligence-based methodologies are developed to capture the complex nonlinear relationship between obtained flow-conditions (occurrence or absence of plugging/blocking) in the hot-leg and the extracted statistical parameters. A computational approach is also developed to find the dependency of occurrence or absence of plugging on the physical working conditions. Plugging is found to be most responsive to the gas-flowrate. Plugging/blocking is easily occurred at high gas-flowrate. It may occur even at moderate gas-flowrate when initial stored water-level in hot-leg crosses the threshold limit. It is found that the developed methodologies are able to perfectly capture the relationship between the flow-condition (occurrence or absence of plugging) in hot-leg and the said statistical parameters. The relation between the flow-condition in the hot-leg and the working conditions is also perfectly correlated by the developed computational approach.