Safety characteristics of the super LWR design concept

The supercritical water cooled reactor (SCWR) is recognized as one of the Generation IV reactor concepts. The Super LWR is a thermal reactor version of the SCWR that is now being promoted and developed at the University of Tokyo. This paper describes safety design principle and a series of safety analyses for Super LWR to present the safety characteristics of this reactor concept. Safety of the Super LWR is characterized by the design features such as a once-through cooling system, supercritical-pressure operation and a coolant flow scheme with downward-flow water rods. The safety characteristics are investigated with the analyses of abnormal transients, accidents and anticipated transient without scram (ATWS). The good safety performance of the Super LWR well appears under ATWS conditions. Besides the above good responses against loss-of-flow and pressurization, the Super LWR has self-controllability of the reactor power against flow abnormalities and reactivity insertion due to the coolant density and Doppler feedbacks. All the ATWS events satisfy the same criteria as those of the accidents with margin and settle to a high-temperature stable condition without any alternative action even for a high rating core. It is an outstanding safety advantage of the Super LWR