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Seismic safety


The conclusion of all the conducted surveys, as confirmed also by IAEA experts, is that the nuclear power plant location falls in a homogeneous block. This block is structurally uniform and is characterized by a very quiet tectonic structure. No data have been found to indicate availability of faults with horizontal amplitude (strike-slip faults) in the Belene NPP area. The earth faults located in the subregional zone are older than 650 000 years, they lack manifestations in the quaternary cover layer and do not belong to the capable faults category.

The analysis of the seismic conditions in the area around the Belene NPP site shows that it falls within the seismically most tranquil part of the Central Balkans, characterized by absence of historic and current seismicity, with magnitude M≥4.0. The strongest earthquake registered in the years after 1976 (a period of reliable instrumental monitoring) had a magnitude of M=3.6 and occurred 150 km away from the Belene NPP site. 

The Belene NPP local zone (30 km) has a seismic activity lower than the average for the stable part of the Misia platform. There are no data of any earthquakes with a magnitude of M > 2.5 throughout the period of instrumental monitoring, 1976 - 2003.

The heaviest earthquake on the Belene NPP site, rated level 7 according to the MSK-64 scale, was generated by the strongest earthquakes in the Vrancha seismic zone. The other seismic sources located within 320 km around the Belene NPP site (Gorna Oryahovitsa, Shabla, etc.) have had a registered impact on the Belene site of level 6 according to MSK-64 scale.

The analysis of the Belene NPP seismic hazard points to an anticipated absolute acceleration of 0.24g for the safe shutdown earthquake (with a recurrence period of 10000 years). Thus, the Belene NPP design has to ensure plant safety for this level of earthquake impact while implementing a conservative approach for evaluation of its seismic capacity.

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