超临界水反应炉（英语：Supercritical water reactor，缩写：SCWR）是一种第四代反应炉设计，使用超临界水作为工作流体。超临界水反应炉也是一种轻水反应炉（LWR），但是工作流体运作于较高的温度与压力，采取类似沸水反应炉（BWR）的单次循环和类似压水反应炉（PWR）的单一相态运转机制。BWR、PWR与超临界蒸气锅炉皆是已实证过的技术。由于SCWR具有较高的热效率与简单的设计结构，成为倍受关注的新式核反应炉系统。

The supercritical water reactor (SCWR) is a Generation IV reactor concept that operates at supercritical pressure with a direct once-through cycle like a supercritical boiler. It uses light water as the working fluid. The reactor inlet coolant is high density water. It is heated in the core and becomes supercritical water above the thermodynamic critical point of water (374C, 22.1MPa)(referring to the critical point of water, not the critical mass of the nuclear fuel). The water is always in a single fluid state at supercritical pressure. SCWRs resemble light water reactors (LWRs), but it is different from a boiling water reactor (BWR) operating at subcritical-pressure with steam-water separation and recirculation of the coolant. The BWR, pressurized water reactor (PWR) and supercritical steam generator are all proven technologies. The SCWR is a promising advanced nuclear system because of its high thermal efficiency (~45% vs. ~33% for current LWRs) and simpler design, and is being investigated by 32 organizations in 13 countries.