Preliminary Analysis of Hydrogen Behavior Using GASFLOW-MPI in the OPR1000 Containment Under a Severe Accident Condition

Abstract

Hydrogen can be generated by the oxidation of fuel claddings with steam at a high temperature in a nuclear reactor. When the generated hydrogen is discharged from the reactor vessel into the containment, the integrity of the containment can be challenged by the high pressure and shock wave resulting from a hydrogen explosion similar to those during the Fukushima accident and the TMI accident. Thus, an investigation of the hydrogen behavior is required in order to assess the threat of a hydrogen explosion. The objective of this research is to conduct a preliminary 3D computational fluid dynamics (CFD) analysis to examine the hydrogen behavior in the containment. To achieve this objective, GASFLOW-MPI, a computational fluid dynamics tool, was selected given that it is specialized for analysis of hydrogen behavior in nuclear power plants. A large-break loss-of-coolant accident (LBLOCA) scenario was selected for the assessment. A guillotine break was assumed at a cold leg for the LBLOCA. The boundary condition, specifically the guillotine break, and the initial conditions were set based on calculation results from MAAP 5.03. Mitigation measures, including a spray system, passive autocatalytic recombiners (PARs), and hydrogen ignitors installed in the containment of a NPP were considered in the assessment. In this case, the mitigation measure models inserted by GASFLOW-MPI were used. Specifically, the Korean PAR was modeled by GASFLOW-MPI for the PAR installed in the OPR1000. The results of the preliminary analysis show that GASFLOW-MPI has the capacity to assess hydrogen behavior. The operation of the spray system increased the hydrogen volume fraction and halved the steam volume fraction compared to when it did not operate due to condensation.