Simulation of Thermohydrodynamic Processes during an SBO Accident with the Externally Cooled Vessel of a VVER-I Integral Small Modular Reactor

The development of small modular reactors (SMRs) attracts increasingly growing interest both in Russia and abroad in connection with the trend toward decreasing of greenhouse gas emissions and diversification of energy sources. Small nuclear power plants (SNPPs) could occupy their niche in the field of electricity production in remote regions, in which there is no demand for large power capacity. It is exactly for this reason that great attention is presently paid to the development of SMRs and SNPPs as a whole. Given that there is no demand for large capacity NPPs, and with more stringent requirements for safety systems based on fully passive principles of their operation, and also in view of the fact that there has been no assessment of decreasing the prime cost of electricity in putting the SNPP equipment in mass scale manufacture, the problem of their development is becoming increasingly more relevant. The article presents the results of calculations of thermohydrodynamic processes in the new integral modular small capacity reactor plant (RP) with natural coolant circulation called VVER-I as applied to a beyond design basis accident involving the power unit long-term blackout. For the VVER-I RP, all safety systems relating to defense-in-depth levels two and three are based on the passive principle of their operation, also with the use of natural circulation, without the need of power supply and operator’s intervention for quite a long period of time. The calculations were carried out using the KORSAR/GP computer code certified for analyzing the safety of NPPs with VVERs. The possibility of reliable decay heat removal from the core in the natural circulation mode with the reactor pressure vessel externally cooled with water has been confirmed. The passive safety systems incorporated in the design ensure reliable heat removal from the core under the conditions of all NPP power supply sources lost for a long period of time without intervention of the operational personnel. The study results can be used in elaborating new designs of VVER type RPs with natural coolant circulation, including those with passive safety systems.