Analysis of Hydrogen Behavior in a PWR Containment Vesselunder Spray Operations

摘要

When a containment vessel (CV) of PWR is overpressured by steam and hydrogen generated in therncore and transported to the CV during severe accidents, the vessel is immediately depressurized by a CVrnspray system through steam condensation. Then relative concentration of hydrogen becomes higher, andrna chance of hydrogen burn or detonation with a concern of damage to the vessel with extremities mayrnoccur. Another concern is locally high concentration of hydrogen driven by density difference. Therefore,rnit is one of safety concerns to examine the effects of CV spray and such associated synergetic events, asrnsteam condensation, depressurization and hydrogen stratification or mixing driven by possiblerncirculation flow with the CV.rnThe present paper deals with three-dimensional analysis of thermal hydrodynamics in the vesselrnunder spray operations performed by INSPAT/CV, which can analyze the performance of droplets andrnmulti-components gases and has been developed at INS/NUPEC.rnIn the analysis, the hydrogen behavior was calculated for various conditions of spray operationrnunder conservative assumptions of localized hydrogen accumulation at the top of the vessel. Asrnregarding spray operations, droplets flow rates and spray patterns from four spray rings at differentrnvertical locations were varied as parameters. The analysis results showed that spray droplets induced arncirculation flow in the vessel with a downward flow near the wall sides induced by falling droplets, and arnupward flow around the center of vessel. This circulation flow rapidly diffused and mixed hydrogenrnaccumulated locally at the top, and homogenized hydrogen concentration in the vessel. Regarding a lowrnflow rate operation of CV spray, a possible operation mode for accident management (AM) wasrnsimulated. It was found that even a 1/10 of normal flow rate only from the lowest spray ring was stillrneffective for hydrogen diffusion and mixing.