Design basis earthquake of the Ignalina Nuclear Power Plant

Eugenijus Uspuras Sliaupa S., Kacianauskas R., Markauskas D., Dundulis G., Uspuras E. Design basis earthquake of the Ignalina Nuclear Power Plant. Geologija. Vilnius. 2006. No. 54. P. 19–30. ISSN 1392–110X. Assessment of the seismic potential and related risk level of low seismicity areas is a highly complex problem. The Ignalina NPP, located in the East European Craton, was originally built for the lowest seismic risk conditions. Throughout two decades of operating the plant attempts were taken to reinforce the plant in the face of a possibly higher seismic risk. The seismic potential of the Baltic basin is seemingly underestimated, as evidenced by the recent Kaliningrad earthquakes (2004, M = 5.0). The Design Basis Earthquake was re-evaluated for the Ignalina NPP site. The deterministic approach was applied instead of probabilistic methods due to scarceness of seismic records. The Design Basis Earthquake of the site is estimated as ML = 5.6 (Io= 7.5) and the hypocentral depth of 10 km, based on the fact of presence of a neotectonically active large-scale shear zone close to the nuclear power plant. This tectonic feature is compatible to other fault zones identified within the radius of 150 km, which show historical earthquake activity. The free-field ground response spectra were calculated using the attenuation relationship derived from Japanese near-field seismic records. The site-specific amplification effects were taken into consideration. The estimated design peak ground acceleration is 0.166 g. It is higher than the minimum limit (0.1g) recommended by the IAEA guidelines for the SL-2 ground motion hazard level. The maximum spectral acceleration is defined within the frequency range 7–10 Hz. The in-structure response spectra were calculated for different levels of the Unit 2 Reactor Building. They differ considerably from previous estimates by a higher load in the high-frequency range, whereas much lower values are estimated for the low-frequency range.

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