The Update of the Seismic Probabilistic Site Hazard Assessment for Loviisa NPP in Finland

Abstract eng:
The Loviisa Nuclear Power Plant obtained an extended operation license for the period of 2007 -2027 in July 2007. One of the conditions set in the safety assessment document that accompanied the license extension approval was the requirement to update the seismic probabilistic risk assessment of the plant dated from 1991. This paper outlines the update of the seismic site hazard assessment of the said work. The purpose of the present work is the update of estimation of seismic hazard in the site of the Loviisa nuclear power plant in Finland. Because there are no registered strong motion acceleration recordings of earthquakes in Finland, the earthquake recordings from Saguenay and Newcastle regions from Canada and Australia were taken as sources of initial data because of their geological and tectonic similarity to Nordic countries. The code basis for the ground motion estimation in probabilistic seismic hazard studies stipulates the median spectra for mean return period of 100 000 years. The decision tree approach is used in the treatment of uncertainties in this study. The most important task in the update of the hazard analysis was the uncertainty quantification in the form of discrete distribution of the hazard at site. The actual hazard analysis carried out with the aid of Fortran Computer Program for Seismic Risk Analysis SEISRISK III developed by USGS and with the aid of the computer program EZ-FRISK developed by Riskengineering Inc. The resulting raw site hazard depicting the distribution of the seismic hazard was given in the form 32 curves equipped with appropriate weights. The end result of the analysis was given in the form of median, mean, 95% - fractile and 5% - fractile curves for horizontal peak ground acceleration amplitudes of 0.001g, 0.005g, 0.01g, 0.05g, 0.07g, 0.1g, 0.2g, 0.3g and 0.4g and for corresponding non-exceedance probabilities.

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