An event of water coolant ingress into vacuum vessel is one of the most important events leading to severe consequences in nuclear fusion reactors. The ingress of coolant to the vacuum vessel could appear due to coolant pipe rupture of in-vessel components. Vacuum vessel could not withstand the high pressure inside. Pressure increase in vacuum vessel is due to water evaporation because of pressure difference and water contact with high temperature plasma facing components. If pressure in vacuum vessel is too high — safety valve opens and the steam containing activated dust will be transferred form the vacuum vessel to the environment. Therefore, it is important to understand the thermo hydraulic processes in vacuum vessel during the ingress of coolant event (ICE).
There are few experimental investigations performed, modeling of ICE. In this article ingress of coolant event in vacuum vessel was modeled using RELAP5 code. RELAP5 is a “best estimate” system code suitable for the thermo-hydraulic analysis of all transients and postulated accidents in nuclear fission, light water reactor systems, including both large and small-break loss-of-coolant accidents as well as the full range of operational transients. The use of RELAP5 code for the accident analysis in nuclear fusion reactors allows to perform integral analysis of thermal-hydraulic processes in the cooling system and vacuum vessel. The comparisons of calculation results and experimental data showed that with some limitations the RELAP5 program could be used for the analysis of the thermal hydraulic processes in the vacuum vessel during ICE.