The Supercritical Water Reactor (SCWR) is one of the six types of nuclear reactors proposed by the Generation IV International Forum (GIF), based on the technology of light-water reactors. SCWRs are designed to remove heat from the core using the natural circulation system, which is usually done by active pumps. This will make the reactors safer. Since conditions in quasi-critical regions are complicated for fluid like water, and the results of experiments and analyzes indicate discontinuities or extreme changes in the various physical properties of water, in this study, generally speaking, by describing the circulation system in supercritical conditions, the types of instabilities that occur in the system are investigated. Also, attempts were made to calculate the instabilities as much as possible for operating conditions. In reality, the problem is much more complicated, and this thesis briefly examines the quality of a natural circulation system. Ultimately, the Ledinegg instability areas were found, but their precise positions were not predicted in the stability map. This thesis focuses on the natural circulation system of the supercritical water reactor.
