DEVELOPING A LOGIC-TREE FOR UPDATING THE PROBABILISTIC SEISMIC HAZARD ASSESSMENT FOR THE ANGRA DOS REIS NUCLEAR POWER PLANT SITE IN BRAZIL

摘要

The seismic design loads for the existing reactors of the Angra dos Reis nuclear power plant in the state of Rio de Janeiro, SE Brazil, were defined using deterministic seismic hazard analysis. In the 1990s, work began to update the seismic hazard assessment for the site using a probabilistic approach, and characterizing the ground motions in terms of PGA. Following the accident at the Fukushima Daiichi power plant in March 2011, a project was initiated to re-evaluate the site hazard in accordance with modern practices. The new PSHA will characterize the ground motions in terms of response spectral ordinates rather than only PGA, so that uniform hazard spectra can be developed for the site. The most important development is that the hazard assessment is to be conducted within the SSHAC framework (as a Level 1 study) and will develop a logic-tree to capture the epistemic uncertainties in both the seismic source and ground-motion characterization models. In accordance with the SSHAC process, the first stage of the project is to update the geological and seismological databases for SE Brazil, with a particular focus on the earthquake catalog, for evaluation by a Technical Integrator team. The proposed procedure for the study is then to develop a relatively simple initial model that will allow extensive hazard sensitivity calculations to be performed in order to focus the efforts of the team on those elements contributing most strongly to the hazard and/or to the overall uncertainty.