The supercritical water reactor (SCWR) is a reduced moderation water reactor concept that, due to the average speed of the neutrons that would cause the fission events within the fuel being faster than thermal neutrons,
it is more accurately termed an epithermal reactor than a thermal reactor.
It uses supercritical water as the working fluid.
SCWRs are basically light water reactors (LWR) operating at higher pressure and temperatures with a direct, once-through heat exchange cycle.
As most commonly envisioned, it would operate on a direct cycle,
much like a boiling water reactor (BWR), but since it uses supercritical water (not to be confused with critical mass) as the working fluid,
it would have only one water phase present, which makes the supercritical heat exchange method more similar to a pressurized water reactor (PWR).
It could operate at much higher temperatures than both current PWRs and BWRs.