Addressing the Unpredictable Through Mitigation Strategies

Lauren Gibson
Project Manager
Japan Lessons-Learned Directorate

The Fukushima accident reminded us how important prior planning is when it comes to safely handling extreme events at a nuclear reactor. We continue to conclude U.S. plants can survive many scenarios, such as loss of offsite power or flooding. After Fukushima, however, we’re requiring plants to have strategies for dealing with the long-term loss of normal safety systems.  Instead of figuring out which events might happen, we’re focusing on significantly improving the plants’ flexibility and diversity in responding to extreme natural phenomena (such as severe flooding, earthquakes, extreme temperatures, etc.).

mitigation_strategies_infographic_r4The plants’ strategies must protect or restore key safety functions indefinitely in the case of an accident. The strategies focus on keeping the core cool, preserving the containment’s barrier that prevents or controls radiation releases, and cooling the spent fuel pool. Plants with more than one reactor must be able to do this for every reactor on site at the same time.

Ideally, plants would have everything for their strategies on site. The strategies must protect the plant indefinitely, however, so plants may need to bring in additional equipment or resources.  The order reflects this by having three phases with different requirements.

The first phase begins with the accident or event.  At this point, the plants will use installed equipment, such as steam-driven pumps or battery-powered systems, to protect or restore safety functions. The plants must be able to shift to the second phase before the installed equipment is exhausted.

The strategies’ second phase uses portable equipment that’s stored onsite, such as additional pumps or generators. This equipment is stored near the reactors and reasonably protected from severe weather or earthquakes. The phase two resources are brought to the reactors and connected to maintain the safety functions. During this phase, plants would also be able to transfer fuel from onsite tanks to the places were it’s needed to run generators and other equipment. Plants have to ensure the third phase can take over before the portable equipment runs out of supplies.

The final phase starts when outside help arrives. The nuclear energy industry is setting up two response centers to provide additional equipment and other resources to any U.S. reactor within 24 hours. One center is in Memphis, Tenn., and the other is in Phoenix, Ariz.

The plants have all submitted a plan for what they intend to do and use in each of these phases. The plans must also explain how the plants will have everything in place by the end of 2016.  We’ve been reviewing those plans and we’re at the point of issuing interim staff evaluations, which let the licensee know whether we think they are on the right track. The NRC will inspect the plants throughout this process to ensure the strategies will get the job done. Our website’s Japan Lessons Learned section has more information about the mitigation strategy requirements and related guidance.

Note: The graphic is now available on our Flickr site.

Author: Moderator

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

15 thoughts on “Addressing the Unpredictable Through Mitigation Strategies”

  1. So far as I could ascertain, no regulatory agency worldwide is dealing with the effects of a severe electromagnetic pulse (EMP event). Former CIA director Wolsey has been holding hearings about this, amongst others. We only narrowly escaped such an event quite recently when solar eruptions passed earth by a wide enough margin not to cause interference. However, they are expected to hit every 150 to 200 years and the last one that set telegraph poles on fire happened in the first half of the nineteenth century. Apart from natural causes, EMPs can be caused (and have been experimented with in the Cold War) by nuclear devices exploded in orbit. This is the tool of choice e.g. for nations who cannot afford direct attacks via interballistic missiles or which have too few warheads to take on an opponent such as the US or Russia. North Korea comes to mind, which has but few warheads, but has the ability to launch them into space. Now I understand you cannot openly talk about EMP hardening of infrastructure and utilities, as this is likely classified information. However, as far as I can understand, it actually is public knowledge that no such countermeasures exist?!

  2. Thank you Scott. We had discussions yesterday at the Watts Bar Inspection meeting concerning NRC oversight of the Regional Response Centers. I hope the NRC will inspect all contracts relating to the stocking, preventive maintenance and shipping of equipment to nuclear facilities in the case of a disaster.

  3. We could have been clearer in our original response. The NRC has had more than a year of extensive discussion with the industry regarding the creation and stocking of the response centers. The NRC continues that discussion and the agency will inspect and oversee the centers, since they are part of responding to events at U.S. nuclear power plants. The NRC has no authority to volunteer potential non-nuclear uses of the material in the response centers, which is the collective property of the nuclear power plant owners. FEMA is the national agency that deals with large scale, non-nuclear events – FEMA’s website has more information on its roles and responsibilities —

    Scott Burnell

  4. Wait a minute, you can’t have it both ways. either the nuclear industry has response centers or they do not. You say in the article about the response centers: “The nuclear energy industry is setting up two response centers to provide additional equipment and other resources to any U.S. reactor within 24 hours. One center is in Memphis, Tenn., and the other is in Phoenix, Ariz.” Here you pass the buck and say you have no control over the regional response centers: “The regional response centers are privately owned facilities and the NRC only has jurisdiction over events at nuclear power plants. FEMA is in the best position to discuss national response resources.” Do you know what is in the regional response centers since you have no control over them? Is FEMA in the best position to know what is needed to support nuclear facilities during an extended disaster? Does the NRC participate in the inspection of these centers?

    It is not reassuring to know that the regulator does not control the stockpiling or inspection of emergency equipment and supplies at these private facilities for the nuclear industry. It would also seem prudent to inspect the contracts involved in the so called “regional response centers” to insure that they are actually valid contracts and that the contracts are actually being fulfilled.

  5. The regional response centers are privately owned facilities and the NRC only has jurisdiction over events at nuclear power plants. FEMA is in the best position to discuss national response resources.

    Scott Burnell

  6. The regional centers are expected to be fully operational this year. The centers’ proximity to major air freight facilities allows airlifting of major equipment to airfields near each operating nuclear power plant. Each plant’s strategies include appropriate measures to move equipment from the local airfield to the site.

    Scott Burnell

  7. Yes, we emailed it to you. It will also be available on Flickr shortly.


  8. As we noted in our Dec. 2012 press release on the topic ( ):

    “The NRC rulemaking process can appropriately handle further examination of the issues in [the] petition. The first step will be monitoring the progress of several Fukushima-related activities designed to enhance plants’ abilities to keep spent fuel pools safe. If the staff concludes these activities fall short of resolving the petition’s concerns, the agency will work to develop a technical basis for the petition’s suggested rule change. If such a basis cannot be established, the NRC will update the public on why the petition’s suggestions were not adopted.”

    Scott Burnell

  9. I do like the concept of regional response centers. I know they are designed to support a severe accident at any US nuclear plant site, but I wonder if at least some of the emergency equipment to be housed there could be used to support a non-nuclear disaster as well. I am thinking of emergency power generators and other electrical equipment like large batteries and inverters. Could these resources be listed and supplied to say FEMA so that they could consider them in the case of a natural disaster?

  10. NRC appears trapped in its own rhetoric, failing to heed some crucial lessons from nuclear accidents 35 years ago at TMI, and just a few years past at Fukushima. Rather than prevention, the Lessons-Learned Directorate focuses on mitigation strategies.

    Instead of forestalling a meltdown in the first place, the Directorate stresses responding to the consequences, such as: “handling extreme events at a nuclear reactor … keeping the core cool … preserving the containment’s barrier that prevents or controls radiation releases … and cooling the spent fuel pool.” All that is too late to prevent reactor self-destruction, followed by financial and public-relations havoc.

    Some major lessons that should have been learned from the TMI-2 accident were never implemented, and now three Fukushima meltdowns have accentuated these same shortcomings. The TMI accident occurred when operators lacked real-time independent indications of evolving loss of coolant. The TMI meltdown could have been prevented if autonomous ex-vessel water-level monitoring instrumentation had been installed.

    The Fukushima Task Force has been amply briefed on this capability, but continues to emphasize mitigation rather than prevention. The proposed water-level monitoring (high-energy gamma-ray technology) developed as a consequence of the TMI accident was published, even patented, long ago.

    As a result of the TMI-2 loss-of-coolant accident, NRC formally recognized as a high priority (NUREG-0933 [Dec. 2011]) – but never implemented — “Identification of and Recovery from Conditions Leading to Inadequate Core Cooling.” Similar lessons derivable from Fukushima are inexplicably relegated by the NRC Task Force to the bottom of its Tier 3 basement.

    –A. DeVolpi, PhD, retired nuclear-reactor safety specialist

  11. Does NRC planning take into consideration the events as outlined in these petitions petitions?

    “Potential interruption of active cooling for spent fuel pools due to geomagnetic disturbance and resulting long-term loss of outside power presents an unacceptable risk to public health and safety. Using the NRC-approved method of Probabilistic Risk Assessment (PRA), Petitioner has shown that spent fuel pools as currently designed and licensed do not meet NRC standards for safety. Amendment to the Code of Federal Regulations is required to rectify this situation.”

    Or, mitigating strategies as a result of a Carrington Event:

  12. Is there any way to get a higher resolution copy of the graphic attached to this blog?

  13. NRC-Planning for the Unthinkable
    I commend the NRC and the nuclear industry for considering accident scenarios that are beyond even the conservative design bases for nuclear power plants.
    The 3-phase accident response planning sounds very good. The first two phases must be handled with equipment that is on-site and ready to go. The last phase relies on equipment that is housed off-site in one of two response centers in the US. These centers are located in Memphis and Phoenix. Will these centers be operational by 2016 (the same timeframe for nuclear power plants to have their phase 2 equipment in place)? When considering severe earthquakes and Noah-type flooding, how will equipment stored in Memphis and Phoenix be moved to the affected nuclear plant site? As I understand it some of this equipment is quite large e.g. large diesel generators and battery banks. Will there be provisions for airlifting this equipment to the site? Again my thanks to the NRC and the nuclear industry for thinking about and planning for the unthinkable.

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