XV — 1. Introduction

IRIS is a pressurized water reactor that utilizes an integral reactor coolant system layout. The IRIS reactor vessel houses not only the nuclear fuel and control rods, but also all the major reactor coolant system components including pumps, steam generators, pressurizer, control rod drive mechanisms and neutron reflector. The IRIS integral vessel is larger than a traditional PWR pressure vessel, but the size of the IRIS containment is a fraction of the size of corresponding loop reactors, resulting in a significant reduction in the overall size of the reactor plant. IRIS has been primarily focused on achieving design with innovative safety characteristics. The first line of defence in IRIS is to eliminate event initiators that could potentially lead to core damage. In IRIS, this concept is implemented through the ‘safety-by-design’ ™ IRIS philosophy, which can be simply described as ‘design the plant in such a way as to eliminate accidents from occurring, rather than coping with their consequences.’