Simulation of fluid-structure interaction between a drywell penetration and a high energy line break in a BWR

To evaluate the structural integrity of the full pressure steel containment vessel at a piping penetration during a high energy line break (HELB) in a boiling water reactor (BWR) nuclear plant, a computer simulation using RELAP5/FORCE, ADLPIPE and WERCO computer softwares was performed for the fluid-structure interaction considering actual fluid conditions, geometry and system characteristics. The objective of this study is to check the stress field in the drywell penetration assembly to make sure that applicable code requirements are satisfied. The worst condition was found to be the case for the condensate portion of the emergency condensate system (ECS) where mixtures of saturated water and saturated steam discharge at the break location and accelerate inside the penetration assembly. Furthermore, the operating sequence for the system dictates that fluid sources from both ends of the pipe break have to be considered, which consequently increases the blowdown loads. It was ascertained that an effective way to limit the blowdown forces at the penetration is the installation of a flow limiter inside the drywell, specifically, right at the end of the annulus between 10'' process line and 24'' penetration sleeve