CALCULATION ANALYSIS OF SIMULTANEOUSLY OCCURRING BEYOND DESIGN BASIS ACCIDENTS AT POWER GENERATING UNITS № 3 AND 4 OF THE BNPP

The paper presents the results of a computational analysis of simultaneously occurring beyond design basis accidents at power generating units No. 3 (BN-600) and No. 4 (BN-800) of the BNPP. Safety analysis for operating power generating units at the same time occurring beyond design basis accidents is carried out in accordance with the requirements of NP-001-15. Computational studies were performed with the SOCRAT-BN, ANSYS, ORIGEN2, and VIBROS 2.2 codes. There are considered beyond design basis accidents caused by seismic impact with intensity of 7 points on MSK-64 scale (exceeding the maximum allowed earthquake (MAE) for the site of power unit No. 3 and the corresponding MAE for the site of power unit No. 4). As a result of seismic impact at all the power generating units of the BNPP, a loss of system power supply occurs, which, together with additional failures of the main equipment, leads to beyond design basis accidents. The paper presents the results of computational studies of beyond design basis accidents in terms of reactor plant, assembly cooling pond and holding pond and radiation effects assessment. The results of a computation analysis of the beyond design basis accident showed that the release of radioactivity occurs only for the BN-600 reactor facility (where are breaking of the fuel elements cladding). At the same time, the predicted radiation doses for the first years after the accident are lower than the NRB-99/2009 criteria for making a decision on the evacuation and resettlement of inhabitants.