Supercritical water-cooled reactors (SCWRs) are recognized as a Generation IV reactor concept. The Super LWR is a
pressure-vessel type thermal spectrum SCWR with downward-flow water rods and is currently under study at the University
of Tokyo. This pa...
Supercritical water-cooled reactors (SCWRs) are recognized as a Generation IV reactor concept. The Super LWR is a
pressure-vessel type thermal spectrum SCWR with downward-flow water rods and is currently under study at the University
of Tokyo. This paper reviews Super LWR safety. The fundamental requirement for the Super LWR, which has a oncethrough
coolant cycle, is the core coolant flow rate rather than the coolant inventory. Key safety characteristics of the Super
LWR inhere in the design features and have been identified through a series of safety analyses. Although loss-of-flow is the
most important abnormality, fuel rod heat-up is mitigated by the “heat sink” and “water source” effects of the water rods.
Response of the reactor power against pressurization events is mild due to a small change in the average coolant density and
flow stagnation of the once-through coolant cycle. These mild responses against transients and also reactivity feedbacks
provide good inherent safety against anticipated-transient-without-scram (ATWS) events without alternative actions.
Initiation of an automatic depressurization system provides effective heat removal from the fuel rods. An “in-vessel
accumulator” effect of the reactor vessel top dome enhances the fuel rod cooling. This effect enlarges the safety margin for
large LOCA.