Columbia Generating Station exceeds the Nuclear Regulatory Commission's robust seismic design requirements, and is capable of withstanding a massive earthquake.
A team of local and international experts in the field of seismology, geology, and ground motion modeling, managed by the Pacific Northwest National Laboratory, have been conducting field research and studying the most recent seismic information at Columbia and the surrounding region. As this work progresses, multiple inspections by the independent Nuclear Regulatory Commission continue to support the conclusion that Columbia is designed, constructed and operated safely.
Design & Construction …
The NRC requires that the design of U.S. nuclear energy facilities take into account the most severe natural phenomena historically reported or expected for the site and surrounding area. Additional, significant safety margin is then added into a nuclear facility’s design. This safety margin not only ensures the survivability of the facility following a natural event that exceeds historical data, but it also ensures the reactor can safely be shut down and cooled, using any number of reactor cooling options.
Columbia’s built-in safety margin began with preparation of the new construction site in the 1970s. The soil at the site was removed to a depth of 65 feet and replaced with structural backfill soil – soil specially engineered based on composition and gradation, and then compacted to meet stringent density requirements. Because this backfill is very dense, it is not subject to liquefaction, or the process by which water-saturated sediments transform into a liquid-like substance during an earthquake. It is liquefaction that undermines the foundations of a structure during a seismic event, and can cause serious damage.
Additionally, should an earthquake result in the loss of offsite power, Columbia has three giant diesel generators that will continue to power important plant functions, plus a fourth, smaller mobile diesel generator. Columbia also has large installed battery systems which can power equipment directly. All this equipment is regularly tested and stringently maintained.
Fukushima Comparisons ...
The Fukushima plants safely survived the March 11, 2011 earthquake, an event well beyond the seismic design requirement of those facilities. Control rods were automatically inserted into the reactors, and emergency generators came online as designed to power electronics and coolant systems. However, the facilities were not designed to withstand the effects of the tsunami that followed the earthquake. The independent NRC stated very strongly in the wake of the Fukushima disaster that U.S. nuclear plants are safe.
Nevertheless, across the U.S. nuclear industry, seismic measures were re-inspected.
Seismic Inspections ...
The NRC, an independent regulatory body, has on-site, full-time inspectors at each of America’s nuclear energy facilities.
Originally licensed to rigorous NRC standards, the NRC closely re-assessed Columbia’s current seismic capabilities before renewing the facility’s operating license in 2012.
Shortly after events at Fukushima, Columbia engineers with structural and safety equipment expertise performed seismic inspections on more than 130 nuclear safety systems and related components and supporting structures. Although the inspections did not reveal any degraded or nonconforming conditions with regard to current seismic license requirements, minor ways were discovered to further improve safety margins. For instance, batteries for starting diesel engine-driven fire pumps were not strapped down to battery holder platforms, and the holder platforms were not bolted to the ground. The batteries were immediately strapped to the platforms, and the platforms bolted down. NRC inspectors followed with independent walk downs of the facility and inspection reviews.
The industry continues to work with the NRC to implement some of the most stringent safety measures in the world, and Columbia is committed to pursuing the most reliable solutions that have proven science-based safety results.
Seismic Instrumentation ...
Traditionally, large earthquakes are preceded by increased seismic activity. Columbia has three accelerometers that record seismic motion.
These sensors are monitored from the plant’s control room, and set to begin recording when vibrations from a seismic event produce even mild ground motion accelerations of 0.01g (gravitational force). The seismic motion detectors are linked to two control room alarms:
If any of the seismic monitors detect Columbia’s minimum detectable ground motion set point of 0.01g, then Columbia control room operators initiate appropriate, procedural emergency action plans. Should the facility require shutdown, all structures, systems and components related to plant safety are designed to ensure safe shutdown while withstanding the effects of an earthquake.
Current Seismic Study Efforts … The most rigorous analysis to date
The Pacific Northwest National Laboratory is currently managing a seismic analysis study of South Central Washington state focused on the Columbia Generating Station and four other key locations in the Columbia Basin.
This PNNL study is the most rigorous to date, involves local and international experts in the field of seismology, geology, and ground motion modeling, and utilizes critical review panels and challenge teams. Energy Northwest is a funding partner and co-sponsor of the study, although the study is being performed by independent seismic experts from around the world with PNNL managing the project.
Development and challenge teams ensure the study results are backed by a review of the most up to date information available. The study team is using the Senior Seismic Hazard Analysis Committee Level 3 process from US Nuclear Regulatory Commission Regulation 2117 and Contractor Technical Report 6372.
Energy Northwest has a responsibility to provide the results of that study to the NRC by March of 2015.