Safety is and always be a core value for PG&E and the Diablo Canyon Power Plant. That's why seismic, tsunami and flooding safety was at the forefront in the design of the facility.
It's also why PG&E maintains a Long Term Seismic Program (LTSP) for Diablo Canyon. The LTSP is a unique program in the U.S. commercial nuclear power plant industry. It is comprised of a geosciences team of professionals who partner with independent seismic experts on an ongoing basis to evaluate regional geology and global seismic and tsunami events to ensure the facility remains safe.
Because of the LTSP and decades of industry-leading research, the seismic region around Diablo Canyon is among the most studied and understood areas in the nation.
New and extensive scientific re-evaluations performed at the direction of the Nuclear Regulatory Commission (NRC) continue to show that Diablo Canyon can safely withstand earthquakes, tsunamis and flooding that could potentially occur in the region.
This updated seismic evaluation provides additional confirmation the plant is designed to withstand the ground motions, or shaking, from earthquakes.
PG&E's flooding hazard re-evaluation determined that the plant's key safety systems and components continue to be safe from tsunamis, including those generated from underwater landslides and earthquakes.
As part of its response to the Fukushima event in Japan in 2011, the NRC directed all U.S. commercial nuclear power plants to perform a reassessment of the potential seismic and flooding hazards to their facilities.
The seismic hazard analysis was performed using an NRC-mandated process known as the Senior Seismic Hazard Analysis Committee, or SSHAC. Under the SSHAC process, existing and new seismic information was peer-reviewed and publically evaluated by leading third-party, independent seismic experts.
The flooding hazard re-evaluation involved the use of the latest NRC guidance and methodologies and independent expertise to determine the maximum potential waves and rainfall that could impact Diablo Canyon. It also examined the plant's ability to withstand storm flooding.
The updated seismic assessment represents a more extensive evaluation of the seismic hazard than previously performed. Prior evaluations determined the ground shaking from an earthquake on a particular fault in the region, based on historical records and geological evidence, and then compared this information against structures, systems and components at the facility to ensure they could withstand seismic ground shaking.
Using the NRC's SSHAC process, independent seismic experts publically re-evaluated existing and new seismic information, including data acquired during the advanced seismic studies recently performed near Diablo Canyon, to re-evaluate how earthquakes could potentially impact the facility.
This process included examining the probability of earthquakes occurring on individual and multiple geologic faults. The result is a more thorough assessment of the seismic hazard, providing additional confirmation that the plant is seismically safe.
PG&E's flooding and tsunami hazard update involved the use of the latest NRC guidance and methodologies to determine the maximum potential waves and rainfall that could impact Diablo Canyon.
The re-evaluation, utilizing independent expertise, determined that the plant's key safety systems and components continue to be safe from tsunamis, including those generated from underwater landslides and earthquakes.
The plant's design is also deemed appropriate to withstand expected storm flooding. In addition, measures were identified and implemented to address a rare, theoretical event of excessive rainfall and a quick build-up of water in some plant locations that greatly exceeds any known precipitation event recorded in the site's history.
The NRC has the ultimate regulatory authority when dealing with nuclear and seismic safety for operating nuclear power plants in the United States.
The NRC will review the seismic re-evaluation in order to provide guidance on how and when PG&E should perform an additional risk evaluation that examines the probability of earthquakes potentially damaging plant safety equipment. The same evaluation is being asked of other U.S. commercial nuclear power facilities. The NRC will also review the flooding re-evaluation to determine if additional actions might be required.
Even after the NRC's review, PG&E's industry-leading work in the area of seismic and tsunami safety will not cease. The utility's commitment to safe operations and protecting public health and safety will continue to be reflected in its ongoing study and evaluation of the seismic characteristics and tsunami potential of the region surrounding Diablo Canyon.
As part of its response to the Fukushima event in Japan in 2011, the NRC directed all U.S. commercial nuclear power plants to perform updated assessments of the seismic and flooding hazards for their facilities. Plants located in the eastern and Central U.S. completed such analyses and provided them to the NRC in 2014. Western plants, including Diablo Canyon, were directed to complete and submit their assessments by March 2015.