Fukushima Lessons: Updating Earthquake Hazards at U.S. Nuclear Plants

Scott Burnell
Public Affairs Officer

The NRC is examining new earthquake-related information from U.S. nuclear power plants, and we’re making that information available over the next week or so. We’d like to summarize how we got here and what the next steps are.

seismicgraphicNuclear power plant designs set a basic standard for reactors to completely and safely shut down after an earthquake, based on site-specific information. Plant construction methods and other design factors add to a reactor’s capacity to safely withstand stronger motions than what the basic design describes.

The end of March marked an important milestone for our post-Fukushima activities. We received 60 reports from central and eastern U.S. nuclear power facilities updating the seismic hazard at their individual reactors. The NRC staff is making these reports available through its normal process. The NRC will post each plant’s report on the agency website’s Japan Lessons-Learned Activities page.

We will require the same updates of the three western power plants (Palo Verde in Arizona, Columbia Generating Station in Washington, and Diablo Canyon in California), but delayed by one year because of the more complex geology in that region of the country. Each western plant is individually looking at the seismic sources and local ground motion characteristics that could affect it. This Senior Seismic Hazard Analysis Committee process will inform the overall seismic hazard reassessment that the western plants are completing.

Our staff will spend the next month going over the submissions carefully, checking for errors, before confirming which plants will be required to do more extensive analysis of their ability to respond safely to a significant earthquake event.

These reports mark the first step in a comprehensive process to keep safety at U.S. plants up-to-date with the latest understanding from the earth sciences on the processes that create earthquakes in the U.S.  In 2012, the Department of Energy, Electric Power Research Institute and the NRC joined forces to update the “seismic source model” for the central and eastern U.S. This was based on a new understanding of what creates earthquakes on the North American tectonic plate, with a focus on the New Madrid fault zone near St. Louis, the Charleston fault zone near Charleston, S.C., and other updated information.

The data on seismic sources will be used in conjunction with a ground motion model for the central and eastern U.S. as well as data from individual plants on the localized geology, topography, soil cover, and other data to create a picture of the “ground motion response spectra” for each plant. This new ground motion response spectrum at each plant will be compared with that developed in the past to see if the new data suggests the plant could see higher ground motions than previously thought. If that is the case, the plant will be considered to have “screened in” to further detailed seismic hazard analysis.

Those plants that “screen in” will be required to do a seismic “probabilistic risk assessment” or a seismic “margin analysis” to evaluate in detail how the existing plant structures and systems would respond to the shaking from the range of earthquakes that could affect the plant based on our current understanding of seismic sources. This assessment is extensive, involving experts from a variety of fields, and will require at least 3 years to complete. Once these assessments are complete, the NRC will decide if significant upgrades to plant equipment, systems, and structures are required.

In the meantime, to ensure that the plant is safe, the NRC requires that by the end 2014, plants have reported the interim actions they will take to ensure the safety of the plants before the assessment is complete. Such measures could include re-enforcing existing safety-significant equipment or adding equipment.

It’s important to remember that significant earthquakes at central and eastern U.S. plants are unlikely. But it is our job to ensure that these plants are ready for all that nature might throw at them. And it is our job to keep up with the changes in the science to ensure that plants are as safe as they can be.

Author: Moderator

Public Affairs Officer for the U.S. Nuclear Regulatory Commission

21 thoughts on “Fukushima Lessons: Updating Earthquake Hazards at U.S. Nuclear Plants”

  1. I can not get a straight answer regarding which nuclear power plants will be required to do new site specific site characterization in order to meet NRC requirements. The new NRC GMRS report (where is the site profile data required for these calculations? Have these data been compared to to existing data used in SPID assumptions?) indicates that there are several Group 1 sites where the NRC GMRS exceeds the SSE and/or existing GMRS. It is reasonable to assume that the Group 1 sites would be required to perform new site specific surveys (especially shear wave profiles) and perform new site response models. The procedures prescribed in the SPID are not an adequate substitute for site specific data when computing site response spectra (where is the NRC review of existing data used to support SPID assumptions?). Basic site response modeling clearly shows the disproportionate impact that low velocity layers near the surface have on amplifying ground motion. There is no way these layers will be detected and accounted for in the SPID process and it is unlikely that these layers were properly identified in the original surveys. The SPID relies heavily on references that have nothing to do with east coast and central US geology. For example, the statistical model of Toro (1998) is based on CA sites. Also note that Toro, 1998 is not publicly available. Other statistical models cited in the SPID are likewise terrible substitutes for site specific data, such as the correlation of topography with shear wave velocity which was never intended for non CA use. The range of shear wave models and uncertainties are useless until they are compared with actual data. The large uncertainties (0.35 to 0.5) are larger by a factor of 3 compared to uncertainties from modern site characterization for site response models which are generally on the order of 0.15. THE LARGER UNCERTAINTY IN THE SPID WILL IRRATIONALLY REDUCE THE SPECTRAL PEAKS!!!!

  2. Nuclear engineer here.

    Each plant has an “Operating Basis Earthquake” (OBE) and “Safe Shutdown Earthquake” (SSE). The plant is allowed to continue operating up to and including the OBE. Above the OBE, a plant must shut down and inspect for damage. The SSE is the plant’s “Design Level” for post earthquake safe shutdown, and must maintain integrity of its seismically qualified systems up to that level.

  3. The licensee must consider all sources of flood waters in their evaluation. We are not able to comment on the Corps’ protections.
    We’ve referred your questions to JLD_Public.Resource@nrc.gov for further discussion.

    Scott Burnell

  4. The staff continues to process the reports and we expect the rest of the reports will be posted in the next week or so.

    Scott Burnell

  5. Thanks for the clarification. So for a nuclear plant on the Missouri River, other sources of floodwaters would perhaps be other streams and tributaries feeding the Missouri River? If that is so wouldn’t that even add to the flood projection consequences postulated by the Corps if an upstream dam failed?
    I will post elsewhere if I have other than a seismic concern in the future.
    Thanks for your patience.

  6. By flooding sources I meant sources of flood waters, not information.

    Since this blog post discusses seismic evaluations, further questions or comments about flooding are more appropriately directed to JLD_Public.Resource@nrc.gov or to the blog’s Open Forum.

    Scott Burnell

  7. I see that the seismic hazard reports for only a handful of the plants have been uploaded. When can we expect all of the reports top be available on ADAMS?

  8. Thanks once again for the response. You mentioned other sources of information on flooding. What would be examples of these other sources. I would think however that there is no more definitive source on flooding than the Army Corps of Engineers.

  9. The Army Corps of Engineers has followed its normal procedures for determining what parts of its analysis are publicly available. Other government agencies would work directly with the Corps to obtain that information, if necessary.

    Fort Calhoun will perform its flooding re-evaluation based not only on the Corps’ information but also other flooding sources.

    The NRC will review Fort Calhoun’s re-evaluation and ensure the plant responds accordingly.

    Scott Burnell

  10. I appreciate the prompt response Mr Moderator.

    You mentioned that an affected nuke plant would have time to take action in the event of a catastrophic upstream dam failure. If you think a few hours is a lot of time then I suppose you are right. I think in that time though it would be a lot like rearranging the chairs on the Titanic. The nagging issue with nukes is that you have to remove decay heat for months to prevent nuke fuel from overheating. Gross flooding renders all efforts to keep fuel covered and cooled utterly impossible. In a couple of hours the plant could be shutdown and cooled down but there would be no way to maintain it without any AC or DC power. Can you even fathom the destructive power of a nearly 5-story wall of water descending on not only the plant itself but the entire Missouri River valley?

    I received an April 4, 2014, copy of the non-safeguards version of what the Army Corps of Engineers sent the Fort Calhoun Nuclear Station relative to what they found if an upstream dam failed on the Missouri River. Pardon my pun but it must be pretty “damming” info to be withheld from the public record. As I understand the data provided it would give the flood elevation at select river miles downstream of a failed dam. Those river miles would include those at the reactor site itself. Now that this information is officially on the docket, will the NRC take appropriate action to protect the public if the projected flood elevations exceed that for which the plant is currently designed (1014 feet)?
    Also will the NRC share this info with other parties who have a real need to know? Some of these parties would be FEMA, and local, county, and state emergency preparedness groups?

    Lastly, you mentioned that the Corps has noted no problems with the soundness of these very old upstream earthen dams. Of that I have no doubt whatsoever. However, we both know that is not the issue. The issue is a severe earthquake causing catastrophic dam failure. Or an act of terrorism using a large IED or a suitcase nuke that utterly destroys the dam.
    I hope the data provided by the Corps supposes total, complete, instantaneous dam destruction.

  11. There is no evidence of any “tsunami” or sudden flooding scenario that would prevent Fort Calhoun from taking appropriate actions to protect the public prior to a flood’s arrival. As we’ve noted previously, the NRC reviews all information plants submit to us and performs its own confirmatory analysis when warranted. We will do so when Fort Calhoun submits its flooding reanalysis. That review would tease out any biases or unjustified methods of analysis. The Army Corps of Engineers continues to monitor the dams upstream from Fort Calhoun and has yet to suggest any near-term remediation is needed for those dams.

    Scott Burnell

  12. I went to the link you provided on flood analyses required of nuclear plants downstream from dams. These dams are not designed to withstand an earthquake of near the magnitude that nuclear plants are designed to withstand. More disturbing is the fact that these dams have no measures in place to protect them from terrorist attack. Dam failure would result in a tsunami event for downstream nuclear plants equivalent to Fukushima. I can understand then why the NRC has put a gag order on any information relating to dam failure flooding analyses. What is also very disturbing to me is that in one case the NRC calculated that an upstream dam failure would result in a tsunami wave 46-feet high at the Fort Calhoun Nuclear Station. Yet the NRC has taken no action to address this terrible threat to the plant and the public. The NRC is obviously hoping that the owner of the plant will evaluate this problem away. Furthermore, how can the owner of a plant be expected to do a thorough and unbiased flooding analysis when their huge investment in the plant is at risk?

  13. Surely, the NRC do not mean what they say in the following sentence:
    “Nuclear power plant designs set a basic standard for reactors to completely and safely shut down after an earthquake, based on site-specific information.”

    If they do mean it, then they actually mean that a network of nuclear stations must all shut down after a postulated earthquake that exceeds a specified level. That is a terribly unsafe act.

    When we came to this question many years ago at Ontario Hydro, we found that such a mass shutdown would collapse the Ontario grid along with, most likely, that of the entire Northeast Power Pool.

    We engaged in a long discussion with the Canadian regulator on this matter, and they eventually agreed with our assessment. Therefore, no Canadian nuclear plant incorporates a seismic trip — nor should it, any time in the future.

    Interunit power connections at multi-unit stations plus suitable qualified emergency generators along with power setback and step back functions in the computer control systems of each unit give strong assurance that each nuclear site retains its capacity for “islanded” operation. Following a serious earthquake, these nuclear sites provide excellent “black start” capability for the NEPP grid.


  14. Excellent point about any earthquake leading to core damage is far worse than the core damage itself. However, as we all know, a NPP core damage accident by itself has a huge negative effect on people and the environment. A huge exclusion zone still exists at Chernobyl after 28 years. No telling how long a huge exclusion zone around Fukushima will have to be maintained. Tell me one more time that fossil fuel is worse than nuclear fuel? I want to be safe now and in the future and nuclear is nonsense. It is like playing Russian roulette with 5 bullets in a 6-shooter.

  15. The real “Lesson to be learned” is that towns and cities should be protected as well as reactors. After all, the reactors survived Richter 9 and no one at the plant died from the tsunami. 18,000 died because the towns had no tsunami protections. Let’s build 100-foot tall tsunami walls around all cities and towns along the coasts (starting with Los Angles) — after all, you can never be too safe!

  16. Let’s not forget the most important lesson here: any earthquake that leads to core damage is far worse than the core damage itself. Another lesson would be that if you shutter nuclear plants for fear of earthquakes, say in Bavaria of all places, the resulting environmental damage from fossil fuels will dwarf any risk from the NPP.

    IMO, Fukushima can be dismissed from considerations of NPP risk. PRA makes the assumption that the environment is safe and the NPP is a threat to the environment and those in it. That’s not what happened at Fukushima: if you were walking on the beach that day, you were dead; if you were in the plant, you had a good chance of survival. From a probabilistic standpoint, it makes no sense to worry about initiating events that are far worse than a slow release of fission products. Otherwise, you end up thinking like an anti-nuke and asking the NRC to figure out how many angels can dance on the head of a pin.

  17. I am glad the NRC is updating earthquake hazards at nuclear plants themselves. But what about the earthquake resistance of the dams that are upstream of many US nuclear plants? The failure of any such dam would result in tsunami-type event for downstream nuclear plants.

  18. It’s good that seismic standards are being reviewed, but it was the tsunami at Fukushima that did most if not all of the damage. What are you doing to review and, if necessary, upgrade countermeasures against tsunami and flooding risks?

  19. RE: “Our staff will spend the next month going over the submissions carefully, checking for errors, before confirming which plants will be required to do more extensive analysis of their ability to respond safely to a significant earthquake event.”

    And what happens if one or more of our Nuclear Power Plants suffer something a bit more stressful than a “significant earthquake event”?

    Think Fukushima or worse… :-0

    The NRC still fails to take into consideration the proven fact that Nature can destroy any land based nuclear reactor, any place anytime 24/7 just like it did at Fukushima and no engineering design work or NRC specifications can prevent that from happening.

    Fukushima proved that even though the probability of a meltdown was a 1 in 10,000 year or even a 1 in a 100,000 year event, not 1 but 3 meltdowns could occur almost on the same day! Probability dictates that an event is just as likely to happen today as it is sometime in the future, yet the NRC tends to always imply that if something does happen it will be far into the distant future, which is illogical at best and simply dangerous in the worst case. Using science to somehow imply that something is “safe” when it is not, is the worst thing those with scientific knowledge can do, because it makes nuclear scientists and engineers look like ” snake ☢il salesmen”.

    Think how the Japanese regulators felt both before and after Fukushima occurred. Now imagine the staff of the NRC in the exact same situation only they are at the “Before” position making claims about what will occur “after” a “significant earthquake event”.

    The USA cannot afford a nuclear accident and therefore it is up to the NRC to insure that there is Zero Tolerance when it comes to compliance with all safety regulations in order to thereby guarantee US that a nuclear accident will never happen for any reason, because Nature can strike at any time…

    Excerpts taken from https://public-blog.nrc-gateway.gov/2014/03/17/nrc-defines-risk-terms-in-a-new-glossary/comment-page-1/#comment-279123

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