Simulation of Ex-Vessel Steam Explosion with a General Purpose Computational Fluid Dynamics Code

An ex-vessel steam explosion might occur when during a hypothetical severe reactor accident the reactor vessel fails and the molten core pours into the water in the reactor cavity. A steam explosion is a fuel coolant interaction process where the heat transfer from the melt to water is so intense and rapid that the timescale for heat transfer is shorter than the timescale for pressure relief. This could lead to the formation of shock waves and production of missiles at later times, during the expansion of the highly pressurized water vapour, that may endanger surrounding structures. The purpose of the article is to present how steam explosions can be treated with a general purpose Computational Fluid Dynamics (CFD) code, to give an insight of the steam explosion phenomenon in a typical Pressurized Water Reactor (PWR) cavity, and to provide a rough assessment of the vulnerabilities of cavity structures to steam explosions. Ta achieve this a fit-for-purpose steam explosion model was developed, followed by a comprehensive and reasonably conservative parametric steam explosion study. The multiphase flow in the reactor cavity during the high-pressure premixture expansion was simulated with the CFD code CFX-5.7.1 and the stresses in the reactor cavity walls were determined with the stress analysis code ABAQUS/Explicit