IRIS is a modular light water reactor with an integral primary system con­figuration designed by an international group of 20 organizations from nine countries led by Westinghouse. ARIS has a simplified compact design where the primary vessel houses steam generators, pressurizer and pumps; a novel safety approach; and an optimized refueling cycle with intervals of at least four years. Due to its integral configuration, in IRIS a variety of accidents are by design either eliminated or their consequences and/or probability of occurring are greatly reduced. This provides a superb defense in depth which may allow IRIS to support a claim of no need for an emergency response zone.