Evaluation of Performance and Safety Issues in FCVS with MELCOR code

Adoption of Filtered Containment Venting System (FCVS) installation in Pressurized Water Reactor (PWR) causes safety issues even though it has many beneficial features. Also, the effect of FCVS differs depending on operation strategies, type of Nuclear Power Plants (NPP) and accident scenarios, etc.. Therefore, many researchers studied about FCVS. Bracht et al. proposed an idea of hydrogen issue using Shapiro diagram in German nuclear power plants depending on the opening time of FCVS. Late venting could not avoid entering detonation region while early venting could avoid it. Y. S. Na et al. analyzed the thermal-hydraulic issue of FCVS using MELCOR computer code. He focused on the evaporation time of FCVS pool depending on diameter of venting/exhausting pipes. When the diameter of exhausting pipe is smaller, the pool exists for a long time so that the performance of FCVS can be kept. The performance and safety issue of FCVS were studied in this paper. The amount of fission products released to the environment decreases due to pool and filter in FCVS. However, when the valve which is connected with containment and FCVS is opened, the concentration of hydrogen in the FCVS increases rapidly compared with steam and air concentration. It takes about 12 minutes to avoid the detonation and flammability region. FCVS can prevent over-pressurization of containment and reduce the amount of radioactive material release to the environment. However, the risk of hydrogen explosion at instant time when FCVS is actuated may exist so that the further work related with safety issue of FCVS should be performed.