Richland, WA

Columbia Generating Station, Seismic Probabilistic Risk Assessment


After the Fukushima Daiichi accident, the U.S. Nuclear Regulatory Commission (NRC) issued 10 CFR 50.54(f), a letter requiring licensees to perform a re-evaluation of seismic hazard and take further actions if it exceeds their design basis. In response to this letter, Columbia Generating Station (CGS) performed a seismic probabilistic risk assessment (SPRA) of their facility.

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

Project Summary



Completion Date


Repair & Rehabilitation
Advanced Analysis
Energy Northwest
Specialized Capabilities

Key team members

Philip Hashimoto
Philip Hashimoto
Senior Principal
Mohamed Talaat
Mohamed Talaat
Senior Project Manager