Year: 2001
Type: conference-paper
Abstract: When a containment vessel (CV) of PWR is overpressured by steam and hydrogen generated in the core and transported to the CV during severe accidents, the vessel is immediately depressurized by a CV spray system through steam condensation.Then relative concentration of hydrogen becomes higher, and a chance of hydrogen burn or detonation with a concern of damage to the vessel with extremities may occur.Another concern is locally high concentration of hydrogen driven by density difference.Therefore, it is one of safety concerns to examine the effects of CV spray and such associated synergetic events, as steam condensation, depressurization and hydrogen stratification or mixing driven by possible circulation flow with the CV.The present paper deals with three-dimensional analysis of thermal hydrodynamics in the vessel under spray operations performed by INSPAT/CV, which can analyze the performance of droplets and multi-components gases and has been developed at INS/NUPEC.In the analysis, the hydrogen behavior was calculated for various conditions of spray operation under conservative assumptions of localized hydrogen accumulation at the top of the vessel.As regarding spray operations, droplets flow rates and spray patterns from four spray rings at different vertical locations were varied as parameters.The analysis results showed that spray droplets induced a circulation flow in the vessel with a downward flow near the wall sides induced by falling droplets, and a upward flow around the center of vessel.This circulation flow rapidly diffused and mixed hydrogen accumulated locally at the top, and homogenized hydrogen concentration in the vessel.Regarding a low flow rate operation of CV spray, a possible operation mode for accident management (AM) was simulated.It was found that even a 1/10 of normal flow rate only from the lowest spray ring was still effective for hydrogen diffusion and mixing.
Authors: Osamu Kawabata, Takuji Nagayoshi, Mitsuhiro Kajimoto, Naoyuki Ishida, Nobuo Tanaka
Language: English
Subfield: Nuclear Energy and Engineering
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2563585773