Helium-air stratification experiment in SPARC test facility

To plan on mitigating the hydrogen risk during a severe accident, we should consider the hydrogen behavior affected by thermal-hydraulic conditions in a containment building. A large-scale experimental facility is necessary for simulatin complex phenomena including convenction, diffusion, and condensation. The Korea Atomic Energy Research Institute (KAERI) constructed a large-sized test facility, called SPARC (SPray-Aerosol_recombiner-Combustion). First, we conducted a simple test case to observe the erosion of the stratification layer of a helium-air mixture using an air-vertical jet. Helium-air stratification and mixing were observed in a SPARC vessel with a 3.4 m diameter and 9.5 m height. The stratification layer was eroded continuously, and the volume concentration of helium reduced in order of height. Finally, the volume concentration of helium measured from the bottom to the top of the SPARC vessel became less than 3% after 6,255 s from injecting a vertical jet, i.e., the stratification layer was fully mixed. In the future, it will be necessary to compare this test with previous studies on the stratification and mixing of a light gas in different-scaled test facilities. We are going to visualize the erosion process using Particle Image Velocimetry (PIV) to observe the flow field near a stratification layer. These results can be useful to validate a computer code for estimating the hydrogen risk during a severe accident. In addition, we have plans to observe the hydrogen behavior, such as stratification, mixing, combustion, and mitigation by operating of Passive Autocatalytic Recombiner (PAR) in the SPARC test facility to understand the complex phenomena in a containment, as well as a code validation.