Columbia Generating Station, Seismic Probabilistic Risk Assessment

CGS has a one-unit boiling water reactor with a Mark II containment design. Essential safety and FLEX system components are located in several buildings and the yard. CGS is a deep soil site with significant soil-structure interaction (SSI) effects on building seismic responses. SGH performed the seismic fragility scope of the CGS SPRA and highlights of our work include the following:

• Performing seismic walkdowns and building an electronic database of results
• Selecting reference earthquake ground motion and acceleration time histories
• Generating probability distributions of in-structure responses by Latin hypercube sampling
• Developing thirty randomized finite element models for structures
• Selecting thirty representative soil profiles from 4,800 site simulations
• Simulating SSI/SSSI responses using efficient hybrid computational methods
• Developing novel methods for fragility evaluation to address unique conditions
• Efficiently estimating more than 1,000 CGS-specific representative fragilities for risk ranking and prioritization of detailed evaluations
• Developing a new approach for hybrid fragilities that improves on EPRI 1025287
• Evaluating failure modes from building impacts and separations
• Modeling partial correlation between major structure fragilities
• Evaluating and screening non-vibratory hazards and upstream dam breaches
• Supporting the CGS SPRA submittal to the USNRC