A seismic hazard update is currently being conducted for the Diablo Canyon Power Plant (DCPP) Site under the Senior Seismic Hazard Analysis Committee (SSHAC) Level 3 process. The SSHAC Level 3 process is a formal, structured procedure for developing Seismic Source Characterizations (SSC) and Ground Motion Characterizations (GMC), and has been identified in Nuclear Regulatory Commission regulatory guidance (RG 1.208) as an acceptable method for use in performing probabilistic seismic hazard analysis (PSHA) for nuclear sites.
The SSC and GMC for the DCPP site will involve complex assessments due to the location of the site within an active tectonic region of the United States. The seismic safety issues at DCPP will be subject to significant public and regulatory scrutiny. The SSHAC Level 3 update will re-examine parameters of the GMC and SSC in light of recent and ongoing studies with the objective of developing updated models that capture the center, body, and range (CBR) of the technically defensible interpretations (TDI).
Geosyntec's Scope of Services
Geosyntec was retained by Pacific Gas and Electric to serve as a member of the ground motion technical integration (GMTI) team. As part of the GMTI team, responsibilities include description of the potential ground motion experienced at the DCPP as a function of magnitude, style-of-faulting, source-to-site geometry, and site condition. The GMTI team will construct a model for input to PSHA and will provide complete and clear justifications of the technical bases for all elements of the model. The GMC logic tree model will incorporate results from numerical simulations into the available [Next Generation Attenuation Relationships for Western U.S. (NGA-West 2)] empirical ground motion prediction equations (GMPEs) and update the site-specific rock amplification from the current GMC logic tree.
The SSHAC Level 3 process began in August 2011 and will continue for up to 5 years. As a member of the GMTI, Geosyntec is intimately involved in the Pacific Earthquake Engineering Research (PEER) Center NGA-West 2 project. The new NGA-West 2 project addresses several important issues in earthquake engineering, including modeling of directivity and directionality; development of GMPEs for vertical ground motion; treatment of epistemic uncertainty; and evaluation of soil amplification factors in NGA models versus National Earthquake Hazards Reduction Program (NEHRP) site factors.