Looking For Better Ways to Determine Severe Weather Hazards

Thomas Nicholson
Senior Technical Advisor
Office of Nuclear Regulatory Research


The NRC staff evaluates flood hazards when we review applications for new nuclear facility sites. In addition, we re-examine flooding at operating nuclear power plants — a result of what we learned from the 2011 tsunami flooding at Fukushima Dai-ichi in Japan. These evaluations cover a range of flood events including extreme storms that produce intense local rainfall. The NRC works with other federal agencies to better understand events caused by severe weather as we develop ways to better evaluate possible flooding issues at these sites.

weatherBefore the Fukushima event, the NRC staff informed the Federal Subcommittee on Hydrology of the urgent need to update the National Weather Service’s reports for estimating extreme rainfall events. We use these reports as the basis for our flood design and protection studies. As a result, the subcommittee formed a task force and later the Extreme Storm Events Work Group. The work group is looking at the best practices being used to study extreme storms, and developing estimation procedures and guidance.

The Extreme Storm Events Work Group has an impressive membership. In addition to the NRC, it includes the National Weather Service, U.S. Army Corps of Engineers, U.S. Bureau of Reclamation, Federal Energy Regulatory Commission, Natural Resources Conservation Service, Tennessee Valley Authority, and the U.S. Geological Survey. The work group meets monthly to talk about ongoing activities and products federal agencies are developing to help monitor, model and publish rainfall estimates.

Based in large part on the group’s work, we held a three-day workshop last year on probabilistic flood hazard assessment. The workshop brought together more than 250 international experts and included presentations and panel discussions on extreme rainfall events, coastal storm surge flooding, river flooding, tidal waves, flood-induced dam and levee failures, and combined flood events.

More recently, the work group held a workshop at the National Weather Service to define needed extreme storm products for the nation. These products will greatly assist the federal agencies that are moving towards a risk-informed approach for assessing flooding hazards. NRC staff members are benefiting greatly by their interactions with their federal counterparts in the work group.

Nuclear power plants are built to withstand local extreme weather, but we are always learning how safety margins can be improved even more. By working with weather experts in other federal agencies, we can build on what they’re doing and our nuclear power plants will benefit from this collaboration. We can’t stop flooding from happening, but we can make sure the facilities we regulate are prepared to deal with it safely.

Author: Moderator

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

11 thoughts on “Looking For Better Ways to Determine Severe Weather Hazards”

  1. The last thing anyone needs is another NPP risk analysis, especially of external events like severe weather or earthquakes. This might have made sense when I did it back in the 80’s, but now we have decades of operating experience and thousands of reactor-years to rely upon, and a much better understanding that ALARA really is no basis for regulation or any rational risk assessment.
    No further analysis is required: nuclear power is far and away safer than any alternative, and there is no point to figuring out how many angels can dance on the head of a pin.

    Please do not burden the industry with any more superfluous regulation, especially when you can get away with practically anything if you are fracking, burning coal, or forming gigantic piles of toxic metals into PV panels. The evidence is irrefutable. Any event that causes core damage, be it weather, earthquake or terrorism, would be far worse than any consequences from core damage.

  2. If the NRC is satisfied with flooding protective measures at nuclear power plants why are the flooding analysis results for the Fort Calhoun Nuclear Station being kept from the public? The NRC has had several closed meetings with the plant. Makes one question the honesty of the NRC.

  3. The NRC says, “We can’t stop flooding from happening, but we can make sure the. facilities we regulate are prepared to deal with it safely.”
    Excellent words. But what about the secrecy surrounding the Fort Calhoun Station’s flood hazards analysis. The results must be bad for the NRC to have closed meetings only with the licensee. So much for regulatory transparency!

  4. 🙂 right on, yet, the problem remains, what kind of Order requirements will prevent a tragedy like Fukushima, in a similar natural disaster? And perhaps that’s an unanswerable question, yet we must try, mustn’t we?

  5. The singular focus on flooding instead of all severe weather events and how the nuclear operators and the regulator reacts to these events is not reassuring the public that nuclear power is safe nor reliable. In tornado events where off-site power is destroyed nuclear reactors can not produce power and must be placed either in standby or shutdown while relying on generator power to cool the reactor and cooling pool system.

    Give us reassurances that the NRC is doing their job. You should be looking at not only flooding but how a severe storm such as a category 4-5 Hurricane with flooding and tornadoes effect the different reactor systems and how human factors enter into a compounded disaster scenario. Particularly with the GE Mark 1 system, since the sheet metal attached to steel beam secondary containment is defective, it does not provide adequate overhead protection for the cooling pools nor controls in the event of a direct strike by overhead missiles generated by high winds in extreme hurricane or tornado events.

    Flooding as a result of a hurricane along with tornadoes occurring in a singular event is a real world high risk disaster scenario and the public has a right to know how you as our regulator will insure nuclear operators are prepared for such a disaster and how they will react. Skewered risk analysis for such events does not facilitate reliability of human nor engineering systems.

    The public should never be willing to accept skewered risk analysis and a lack of planning for extreme weather events. This includes evacuation plans for compounded disaster events.

    NRC State-of-the-Art Reactor Consequence Analyses (SOARCA) project to develop best estimates of the offsite radiological health consequences for potential severe reactor accidents is currently not realistic and uses skewered data and risk analysis. There is no reason the SOARCA project could not be a worthwhile project if it supported safety instead of operator profits. The applicability of SOARCA to real world extreme weather events would enhance safety if it was applied properly.

    Here’s the bottom line – Either the NRC provides a regulatory framework where human safety is first and foremost in your mission or all civilian nuclear reactors should be shuttered. It is not your mission to place any support for operator profits over human safety. Your doing so equates to a Human Reliability failure as our regulator. The allowance of political influence to degrade your mission is likewise a Human Reliability failure.

    Weather is truly amazing, more amazing is how humans interact with or to weather, engineering, risk analysis, politics and the massive machine we call a nuclear reactor. Safety first ladies and gentleman of the NRC, not reactor operator profits.

  6. Let’s not forget that with the warming climate, the assumption of stationarity, that new floods will be like old floods, will weaken as climate change proceeds.

    Also, with sea-level rise, surge flooding will get worse. (Sandy’s surge flooding of New York City would have been less severe if the local sea level hadn’t been rising.) The operators of all coastal plants should be reevaluating their surge-protection plans in light of rising sea levels.

  7. The NRC’s efforts to learn from Fukushima include an Order to all operating U.S. nuclear power plants to have “mitigating strategies” (https://public-blog.nrc-gateway.gov/2014/04/02/addressing-the-unpredictable-through-mitigation-strategies/) in place to keep key safety functions going if an event knocks out installed emergency equipment. The NRC is inspecting plants as they put resources and procedures in place for those strategies, and to this point we’re satisfied the plants will be able to meet the Order’s requirements.

    The 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.

    NRC Moderator

  8. Testing for extreme tornado weather interactions with the GE Mark 1 Nuclear Reactor system is lacking, and the 1968 base study is an example of bad science, bad analogies and out dated – inaccurate results.

    The Nov. 1968 APED-5696 “Tornado Protection for the Spent Fuel Storage Pool” disclaimer, in part, states: “…Makes no warranty expressed or implied with respect to the accuracy, completeness, or usefulness of the information contained in this report…”

    The use of a shop-vac to demonstrate how a tornado works is not and has never been realistic. The faulty assumptions made in this report are not supportive of the facts regarding an EF5 Tornado striking the unsafe sheet metal secondary containment structure over the cooling pools of the GE Mark 1 nuclear reactors.

    GE Mark 1 Nuclear Reactor 1968 “Tornado Protection for the Spent Fuel Storage Pool” is seriously lacking and should be replaced with a modern day study utilizing ACCURATE computerized risk models based on modern computerized data from EF5 Tornado events which would include twin tornadoes and multiple overhead direct strikes with overhead missiles to the fuel pools structure instead of “shop-vac – East Coast Cadillac – West Coast Volkswagen” unrealistic hypothesis.

    Luck has been favorable; relying on luck instead of science and engineering is not a wise choice. If an EF5 tornado strikes a GE Mark 1 Nuclear Reactor’s secondary containment’s, spent fuel pool sheet metal structure, the probability of a serious disaster is greatly increased.

    Strengthening the defective GE Mark 1’s overhead containment has not been accomplished. An example of placing reactor operator profits before human safety; a failure of regulator and corporate-management reliability concerning nuclear materials, systems and processes.

  9. RE: “We can’t stop flooding from happening, but we can make sure the facilities we regulate are prepared to deal with it safely.”

    Planning for future events is always a good thing but that said, nobody can hope to outplay Nature!

    Fukushima proved that Nature can destroy any land based nuclear reactor, any place anytime 24/7 so the NRC statement “the facilities we regulate are prepared to deal with it safely” is nothing but bravado…

  10. This is all encouraging and preemptive in nature, i guess my next question is this, what if, like fukushima, all those precautions fail, what plans do we have that are different than what have and still are failing in fukushima? How would we work to contain that same situation at, say, Diablo Canyon which work is any different than what is being done in Japan right now, today? Would we be able to contain Diablo Canyon in a similar meltdown any better than the Japanese?

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