This paper describes the capability of an air cooling system (ACS) to remove decay heat from the core of an Advanced Boiling Water Reactor (ABWR). The motivation of the present research is the Fukushima Severe Accident (SA).The plant suffered damage due to the tsunami and entered a state of Station Blackout (SBO) during which (sea) water cooling was not available. To prevent this kind of situation, we propose a passive decay heat removal system (DHRS). The plant behavior during the SBO is calculated using the system code NETFLOW++ assuming an ABWR which has a steam-driven ACS. Two types of air coolers (ACs) are applied for the calculation model of an ABWR, i.e., a steam condensing air cooler (SCAC) of which the intake for the heat transfer tubes is provided in the steam region, and a single-phase type of which the intake is provided in the water region. Plant transients with ACS are calculated under conditions of forced circulation and also under conditions of natural convection. The results of the calculations indicate that the decay heat can be removed safely with a reasonably sized ACS if the heat transfer tubes are cooled with forced air circulation. However, the decay heat can be removed by air natural convection after safety relief valves are activated for a couple of days. The heat removal rate is evaluated as a function of air mass velocity at the inlet of heat transfer tube banks.
