Influence of Relief Valves Operation in ITER Vacuum Vessel Pressure Suppression System during Hydrogen and Dust Explosion Accident

Safety is regarded as one of the highest priorities in nuclear industries. Several safety systems and alternative methods for generating electricity were studied after the Fukushima nuclear accident, including nuclear fusion reactor. ITER, an international nuclear fusion research project, holds no exception in safety since it may cause radiological risk to the public. ITER presented Accident Analysis Report(AAR) which demonstrated safety analysis for design basis accidents and beyond design basis accidents(BDBA) that could occur in the fusion reactor. Safety analysis of hydrogen and dust explosion in ITER vacuum vessel accident was performed using MELCOR code. The rapid pressurization of the VV induced confinement barrier rupture creating a penetration line into the port cell and NBI cell. The accident transient was similar with the results presented in ITER AAR. However, at accident situations such as the Fukushima accident where external power supply is blocked, the accident consequences may vary from the AAR results since less safety systems are under operation. Therefore, simulation with larger relief valve flow area was conducted as a comparative study. As a result, larger relief flow area condition guaranteed bigger pressure relief which lead to less radioactive material release into the environment. For future study in nuclear fusion research, various options for current safety system conditions must be evaluated to assure safety at any accident scenarios.