An assessment of steam-explosion-induced containment failure

Abstract

A variety of probabilistic models to quantify the likelihood of steam explosion induced (..cap alpha..-mode) containment failure from core melt accidents in commercial light water reactors have been proposed in the past. In many respects, these models and associated mechanistic considerations were complimentary. Based on this and taking into account recent research efforts in this area, we perceived a need to consolidate a common approach. A new probabilistic framework is proposed for this purpose. Quantification of all inputs required by this framework is carried out for the case of low pressure core melt scenario in a pressurized water reactor. In particular, this quantification is based on detailed mechanistic considerations of premixing and energy partitions during the early expansion and later impact phases of the explosion. Key findings of these studies are: (1) premixing of large corium pours is limited by strong coolant depletion phenomena; (2) explosions which may be energetic enough to be considered challenging to the upper head vessel integrity would also fail the lower head, thus substantially reducing the upward-directed mechanical energy release; and (3) upper vessel head loading is dominated by a solid-solid impact (i.e., core support plate and associated structures impacting the upper head), which producesmore » a highly concentrated, in time, impulse. The results of the probabilistic combination of these inputs provide additional support to the generally prevalent expectation that steam explosions do not pose a significant threat to the containment. To fully appreciate the qualitative limitations on this result the complete study must be carefully considered. 79 refs., 85 figs., 14 tabs.« less