Evaluation of Efficiency of Passive Heat Removal System in VVER-1200 Under Beyond Design Basis Accidental Conditions

The paper presents the results of the steam generators passive heat removal system (PHRS) efficiency independent estimation for the NPP unit with a VVER-1200 reactor of the V-491 project during beyond design basis accidents. In SEC NRS the full-scale calculation model of the water-type passive heat removal system from a steam generator was developed and was implemented in the VVER - 1200 reactor (V-491) calculation model. All models were developed by using the best estimate code ATHLET (GRS, Germany). Since PHRS is an innovative safety system, the independent confirmation of its effectiveness in a wide range of emergency modes is especially important issue. PHRS is able to remove the heat from the reactor core due to the natural circulation of the coolant for a long period of time during beyond design basis accidents including the case of NPP station blackout. The paper contains a brief description of the PHRS and its calculation model, as well as the results of independent calculation analysis of the beyond design basis accidents, confirming the efficiency of PHRS. The paper demonstrates the possibility technical support organization of the Russian nuclear regulation authority (Rostechnadzor) to carry out its own independent scientific and technical assessments during licensing process of innovative reactor designs and this complies with the provisions of the IAEA Safety Standards Series Nos GSR Part 4 and GSG-13.