Assessment of Passive Autocatalytic Recombiners (PARs) under Severe Accident Conditions for ACP1000 NPP

This paper presents an evaluation of ACP1000 Passive Autocatalytic Recombiners (PARs) through the use of MELCOR-1.8.5. A comprehensive model of ACP1000 Containment (CMT) was created, dividing the primary equipment compartments into sub-compartments, resulting in a total of 37 control volumes, 80 flow paths, and 124 heat structures. The MELCOR simulations extended up to 100,000 s to establish steady-state parameters. The study considered the most severe accident, Large Break Loss of Coolant (LB-LOCA), and also incorporated the ACP1000 Containment Spray System (CSP). For the assessment of ACP1000 PARs, the empirical relation for the recombination of hydrogen by PARs, as provided in the ACP1000 design document, was modeled using the Control Function (CF) Package of MELCOR. Both CMT models, with and without CSP, were integrated with the PARs model, and an analysis was conducted for each case. The results of this modeling approach demonstrated that ACP1000 PARs are sufficiently capable of removing hydrogen from CMT, thereby avoiding deflagration and detonation of hydrogen.