A REVIEW OF THE AVAILABLE INFORMATION ON THE TRIGGERING STAGE OF A STEAM EXPLOSION

This article reviews the available experimental data and modeling work on the triggering stage of a steam explosion. The importance of the t riggering stage and the various different means of triggering an explo sion are discussed. The extant modeling work is then reviewed, and it is concluded that no validated model exists. Data are reviewed from ex periments designed to investigate triggering and the triggering behavi or observed in medium-scale experiments using prototypic melts is exam ined. An attempt is then made to draw these data together and to come to some conclusions on the likely use of triggering arguments in steam explosion assessments. As an example, the use made of triggering argu ments in the Sizewell B steam explosion assessment is presented. The m ain conclusions are that the data available do not support the hypothe ses that early triggering is virtually certain and that triggering at high pressure is impossible. The available data do, however, suggest t hat triggering becomes more difficult with increased pressure and easi er with increased water subcooling. Experimental results show that eve n a small increase in pressure from 0.1 to 0.5 MPa can inhibit spontan eous triggering. It is concluded that the available data and modeling do not justify making strong claims using triggering arguments in stea m explosion assessments. They do, however, allow modest claims for the lack of an effective trigger and allow the relative likelihood of tri ggering during the various stages of the melt-water interaction to be estimated.