Code validation and application of hydrogen mitigation by passive autocatalytic recombiner in small modular reactor

Abstract

Hazard of hydrogen fast deflagration or explosion could highly lead to an over-pressurization of nuclear reactor containment in case of severe accidents. In order to mitigate the hydrogen hazard, Passive Autocatalytic Recombiners (PARs) are wildly used in water-cooled reactor containment via the hydrogen recombination with the oxygen. The Computational Fluid Dynamics (CFD) code GASFLOW-MPI, which provides the hydrogen concentration details for calculating the recombination rate, is appropriate to analyze PARs performance aiming at the prevention or mitigation of hydrogen risk. The validation of the PARs model implemented in GASFLOW-MPI against THAI-HR experiment is comprehensively carried out. The comparisons indicate good agreements between the predictions and the experimental data, which increase the confidence of using GASFLOW-MPI in a full-scale rector containment. Thereafter, the validated code is used to analyze the severe accident in a water-cooled Small Modular Reactor (SMR), specifically with regard to the hydrogen distribution, the risk posed by hydrogen, the mitigation by PARs and the H2 combustion under accidental ignitions. The analysis methodology is improved according to the GASFLOW-MPI features, and the simulation results indicate that: 1. Hydrogen distribution is fairly uniform that reduces the limit for the PARs installation since the hydrogen recombination efficiencies of the installed PARs are similar, 2. PARs (8 units) mitigate the hydrogen risk well in the long-term phase, but a supplementary combustion analysis is needed, since the potential of flame acceleration exists in the intermediate short time period.