External Hazard & Risk Assessment: Earthquakes, Floods, Explosions & Earth Movement

The March 2011 Tōhoku Earthquake in Japan has renewed focus on flood and seismic risks to our nation’s nuclear power plants. The NRC, based on lessons in their Near Term Task Force report 1, have required that all plants review their seismic and flood risk hazards using state-of-the-art knowledge of these external events. In addition, a joint EPRI / NRC team has comprehensively updated the seismic source characterization in Central and Eastern U.S. (CEUS), and EPRI has updated their ground motion models using the latest geological information and attenuation data. As a result, some plants are now faced with reassessing seismic risks to their structures, systems and components.

Exponent engineers can assist the industry to meet these upcoming challenges by providing high-level engineering consultation:

  • Development of fragility curves for the seismic, wind or flood risk assessment of plant structures and structural components. Calculations are made using the using state-of-the-art material models and software tools, perhaps incorporating shake table testing.
  • Flood Hazard Assessments using the latest hydrodynamic models (e.g., RMA-2 and ADCIRC) and the most current bathymetric and on-shore topographic data, historical tidal information, and meteorological data.
  • Peer reviews and confirmatory analyses of complex engineering calculations by others in preparation for NRC reviews and audits.
  • Geotechnical analysis of the effects of ground shaking on slopes and retaining walls.
  • Engineering evaluation of expected levee performance.

Exponent is pleased to offer these services in the context of our firm’s broader experience with the nuclear power industry, for whom we have provided guidance in addressing the most complex engineering and scientific problems.

Storm Surge Analysis Capabilities for the Nuclear Industry

Storm surge is a phenomenon where ocean water surface elevations rise as a result of high winds and decreases in atmospheric pressure during tropical storms and hurricanes. Storm surge can cause significant flooding in coastal areas, and may overwhelm existing flood protection infrastructure (e.g., seawalls, dikes and levees, breakwaters, groins, jetties and piers, bulkheads, sills, and perched beaches) with significant implications for coastal communities. Nuclear power plants located along the Gulf of Mexico and the Atlantic coastlines are at great risk during large tropical storm events because of the threat posed by high water levels associated with storm surge.

Exponent is experienced in performing assessments in coastal areas to evaluate the risks posed by storm surge to nuclear power plants. Exponent personnel apply the best available data and techniques to develop statistically-based predictions of storm surge. Various computer programs are employed to conduct a full analysis of coastal storm surge including planetary boundary layer (PBL) models, hydrodynamic models (e.g., RMA-2 and ADCIRC), the Empirical Simulation Technique (EST), and other models.

Exponent uses the most current bathymetric and on-shore topographic data, historical tidal information, and meteorological data when estimating storm surge levels at a site. Examples include the use of high resolution topographic data acquired using Light Detection And Ranging, or LiDAR, an optical remote sensing technology that measures the distance to, or other properties of, a target by illuminating the target with light using pulses from a laser. Integration of LiDAR data and field inspection observations are often important in performing such studies. The images on this page show an example of a topographic grid produced using LiDAR data at the South Texas Project Electric Generating Station, and the storm surge levels produced by a Category 5 storm impacting the site using ADCIRC. Exponent has appeared before the NRC on behalf of nuclear power plant operators to present such results to verify the safety of a site when subject to extreme environmental impacts like storm surge.

1 Recommendations for Enhancing Reactor Safety in the 21st Century - The Near-Term Task Force Review of Insights from the Fukushima Dai-Ichi Accident

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