Evaluation of the innovative steam generators passive heat removal system efficiency for VVER-1200 power units in beyond design basis accidents conditions

This paper presents the results of the independent assessment of the steam generators passive heat removal system (PHRS) efficiency for the NPP unit with VVER-1200 reactor (V-491) during beyond design basis accidents. In SEC NRS the calculation full-scale model of the water-type passive heat removal system through a steam generator was developed and was implemented into VVER -1200 reactor (V-491) calculation model. All models were developed using the best-estimated code ATHLET 3.1A (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. 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 unit total blackout. The report contains a brief description of the PHRS and its calculation model, as well as the results of independent calculation analyzes of the beyond design basis accidents, confirming of the PHRS efficiency. This paper demonstrates the possibility of technical and scientific 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 GSR part 4 and GSG-13. (author)