Efficacy analysis of hydrogen mitigation measures of CANDU containment under LOCA scenario

Abstract

Mitigation of hydrogen risk has been a critical objective to assure ultimate safety of the nuclear power plant (NPP). Since the CANDU containment showed potential vulnerability over hydrogen explosion during severe accident, efficacy of hydrogen mitigation measures equipped in the current CANDU NPP need to be investigated thoroughly. Herein we report the effect of mitigation measures such as spray, igniter, passive autocatalytic recombiner (PAR), local air cooler (LAC), and filtered containment venting system (FCVS) on the hydrogen behavior using MELCOR 2.1 code. Wolsong Unit 1 was selected for target NPP and Loss of Coolant Accident (LOCA) was assumed as a plausible severe accident scenario. The analysis showed that the hydrogen concentration in the lower region of the containment was higher in the unmitigated base case. The application of FCVS with other safety measures successfully prevented the containment failure. Expected safety function of the FCVS was to filter out the fission products but substantial amount of oxygen was also vented out. This leads to the oxygen starvation in the containment and prevention of the containment failure in the long run.