Seismic assessment of 'early built' nuclear power plants - A challenge for the regulator

The older Canadian multi unit nuclear power plants were designed at a time when seismic standards were not in place for such facilities. Seismic loading was applied, in accordance with the National Building Code of Canada, as a uniform lateral load equal to a percentage of gravity. In order to assess the seismic capacity of the early built plants, the Canadian Nuclear Safety Commission (CNSC) settled on Seismic Margin Assessment (SMA) as accepted methodology for evaluating the seismic capacity of components above the Design Basis Earthquake (DBE). This paper focuses on the history and implementation of this methodology. (author)