Hydrogen hazard mitigation in small modular reactor during SBO severe accident using GASFLOW-MPI

Abstract

Hydrogen combustion or explosion will lead to over-pressurization of the reactor containment in case of severe accident caused by Station BlackOut (SBO) in an Small Modular Reactor (SMR). In order to mitigate the hydrogen hazard, ignitors as well as recombiners have been typically used in the reactor containment via the hydrogen deliberately burned or recombined catalytically with the oxygen in air. Computational Fluid Dynamics (CFD) tool GASFLOW-MPI, which provides the details of the 3D flow field and hydrogen distribution, is appropriate to analyze hydrogen mitigation system performance. Analysis of mitigation system performance is to evaluate the efficiency of the mitigation of hydrogen hazard in reactor containment. The objective of this paper is to apply the GASFLOW-MPI code to analyze the SBO severe accident in SMR, specifically with regard to analysis of the hydrogen distribution, the risk posed by hydrogen and the mitigation by deliberate ignition and the Passive Autocatalytic Recombiner (PAR). The relevant analysis is presented according to the GASFLOW-MPI features, and indicates that: 1. The hydrogen with/without mitigation distributes well during accident scenario. 2. The ignitor reduces hydrogen accumulation significantly, and 8 units of PARs can mitigate the hydrogen risk in the long-term phase. 3. Both installed mitigation systems (8 PARs and 6 ignitors) can prevent the flame acceleration and local detonation. 4. Utilization of PARs could be better than ignitors in SMR containment, since the passive mitigation with PARs can avoid the failure situations such as the ignitors’ electricity supply cut-off, etc. 5. GASFLOW-MPI provides the possibility of a CFD simulation to a long-time accident scenario in SMR containment.