CFD studies of hydrogen distribution in 220 MWe PHWR containment

Abstract

In this study, containment hydrogen distribution for 220 MWe PHWR containment for LOCA + LOSECCS + LOSMOD accident scenario has been carried out. A full 3D structured mesh for the entire containment including internal structures and wall thickness has been generated. The simulation model in CFD code FLUENT (ANSYS 16) for this mesh is generated and wall condensation model have been invoked to CFD code FLUENT through the user defined functions. The simulation has been divided into three phases, LOCA phase (0–100 s), hydrogen release phase before OPRD rupture (100–1500 s) and moderator boil-off phase beyond 1500 s. The analysis was performed up to 36000 s. It is found that significant amount of steam gets condensed which leads to strong change in the species mixing and distribution in containment. At the end of third phase of hydrogen release at 36000 s, a single uniform concentration of 5.6 % hydrogen is formed in the containment. At this moment, almost entire containment falls under deflagration zone. The uniform concentration of hydrogen in the containment ruled out the possibility of stratified layer formation in the containment at this stage of time. The present investigation reveal that in early stage of simulation, convection is predominantly affecting the hydrogen distribution while in late stage diffusion is governing the hydrogen distribution pattern in the containment.