Water Hammer Caused by Rapid Gas Production in a Severe Accident in a Light Water Reactor(<Special Issue>Experimental Mechanics in Heat and Fluid Flow)

We investigated the water hammer caused by striking of water mass pushed up by a rapidly growing bubble and its scale effects using two cylindrical model containment vessels of 1.0 and 0.428m diameters. We also closely observed the movement of water mass and the growing bubble in the vessels. In these experiments, rapid bubble growth was simulated by injecting high-pressure air into a water pool. It was clarified that the water mass was pushed up without any air penetration until the water level reached a certain elevation. On the basis of all data, experimental correlations for estimating the height and striking velocity of the water mass with coherency were proposed, and the water hammer pressure for exerting large forces on the structures was quantitatively evaluated.