Ex-vessel steam explosion may happen as a result of melting core falling into the reactor cavity after the failure of the reactor vessel and interaction with the coolant in the cavity pool. It can lead to the formation of shock waves and production of missiles that may endanger surrounding structures. Ex-vessel steam explosion energetic is affected strongly by three dimensional (3D) structure geometry and initial conditions. In this article, ex-vessel steam explosions in a typical Chinese pressurized water reactor cavity are analyzed with the code MC3D, which is being developed for the simulation of fuel-coolant interactions. The reactor cavity with a venting tunnel is modeled based on 3D cylindrical coordinate. A parametric study was performed varying the location of the melt release, the break size, the melt temperature, the cavity water subcooling, the coolant water level, the triggering time and position for explosion calculations. The main purpose of the study was to establish the influence of the varied parameters on the fuel-coolant interaction behavior, to determine the most challenging cases and to estimate the expected pressure loadings on the cavity walls. The results indicate with the increase of break size and melt temperature, pressure loading of cavity wall increases. When the explosion is triggered earlier, pressure loading of cavity wall increases. The effect of trigger position on the pressure loading is not obvious. When the melt release angle in the bottom of vessel is 45°, the pressure loading of cavity wall reaches the maximum value. The most dangerous case shows the pressure loading is above the capacity of a typical reactor cavity wall.
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