(An) analysis of the effect of the controlled containment venting on the containment response for postulated severe accidents

Abstract

A filtered vented containment system (FVCS) has been considered at a risk reduction measure for postulated severe accidents at nuclear power plants. In general, the risk analysis includes analyses of accident sequences, containment event trees(or containment response), radiological source terms and off-site damage. This study focused on the effects of the controlled containment venting on the containmeent response for postulated severe accidents. The various methodolgies along with input data used in the containment response analysis for Zion and the results were reviewed and further utilized in this study. For application of these methodologies to YGN 1\&2, plant-specific input data and associated plant-specific features were identified and some of them were considered in the course of calculation and analysis. As the results, it was found that overpressure failure seems to be the most dominant cause for overall risk from YGN 1\&2 and the late venting is very effective to reduce the conditional probability of late overpressure failure for most plant damage states (groups of accident sequences), whileas the early venting has little effect on the conditional probability of early containment failure. Finally, sensitivity for a group of uncertainty issues was examined, which showed that the statistical results of the containment response analysis are very sensitive to Issue 3 (Magnitude of pressure loadings at vessel breach due to direct heating and steam spike), Issue 4 (Magnitude of hydrogen burn pressure at vessel breach), and Issue 5 (Containment failure pressure).