On the nuclear safety improvement by post-inerting small modular reactor with stainless steel cladding

•A simplified model is proposed for post-inerting SMR containment after a LOCA.•Hydrogen, oxygen and nitrogen volume fractions and containment pressure are predicted.•Code-to-code comparison shows that SMR model is in agreement with MELCOR model.•Stainless steel cladding improves safety margin in comparison with zirconium alloys.•Post-inertization with Passive Autocatalytic Recombiners controls effectively combustible gas. After Fukushima Daiichi accident, the replacement of zirconium-based fuel cladding in Light Water Reactors (LWR) became one of the main challenges of the nuclear industry. Austenitic steel–clad presents some safety advantages comparing to zirconium alloys, noticeably, higher activation energy and lower enthalpy of metal-water reaction. Thus, it produces a slower hydrogen release into the containment following a postulated accident. In this study, a Loss-of-Coolant Accident (LOCA) aggravated by the complete failure of the Emergency Core Cooling System (ECCS) is analyzed for a Small Modular Reactor (SMR). Post-accident injection of inert gas into the containment is used as one of the hydrogen control systems, to enhance safety margins during Severe Accidents (SA). The inertization system is successful in complementing Passive Autocatalytic Recombiners (PAR) to perform combustible gas control.