ICONE15-10649 INVESTIGATION OF LIMITATIONS TO STEAM EXPLOSION STRENGTH DUE TO WATER DEPLETION

Abstract

Steam explosions might occur during an accident with core melting in light water reactors (LWR) as a consequence of an interaction of molten core material with water inside the reactor pressure vessel (RPV) or in the cavity. The physics of steam explosions mainly involve two stages - the premixing and the explosion phase. Analytical tools to model and simulate the premixing (IKEMIX code) and explosion phase (IDEMO code) are being developed at IKE Stuttgart. A major limitation of obtaining strong steam explosion is identified to be a high void in the mixture i.e. water depletion during the premixing phase of steam explosion. Previous calculations done (with IKEMIX) in the frame of the SERENA project showed an overestimation of void production. A significant decrease of void concentration in the mixture has been obtained by reducing interfacial friction between water and vapour. Calculations with the improved models for the experiment FARO L-28 showed good agreement with the experimental data. Reactor calculations were performed for an assumed in-vessel case in saturated conditions by varying different parameters (such as melt diameter, the flow rate, the water level, the possible lateral extension of the mixture and the trigger time) in order to find the most critical conditions which would lead to a strong steam explosion despite limitations due to high void. It appears that limitations to strong steam explosions due to water depletion and, in addition, due to partial jet breakup, strongly reduce the damaging potential of steam explosion, at least in saturated conditions, much more than it has been assumed earlier.