Direct containment heating: Surtsey test results and models

Direct containment heating is one of the processes that can lead to containment rupture early in a severe reactor accident. The origins and the current understanding of this process are surveyed. Three issues arise in connection with direct containment heating threats to containment integrity posed by transfer of energy to the containment atmosphere from dispersed core debris or the generation of hydrogen by reactions of core debris with steam, and the formation of radioactive aerosols available for release from the plant should containment integrity be lost. The two threats to containment integrity have different characteristics. Energy exchange between core debris and the atmosphere depends on the long range dispersal of the debris and can be affected by interactions of the debris with structures and co-dispersed water. Hydrogen generation is dependent on the detailed flows of debris and steam within and near the reactor cavity. Results of four experiments in the Surtsey test facility to explore energy exchange with the atmosphere are presented. These experiments suggest single particle models of direct heating over-predict the threat to containment integrity and that debris/structure interactions can enhance heating of the containment atmosphere. Results of tests to establish the low pressure cut-off to direct heating are reported