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Keeping Proper Track of Spent Fuel Pool Conditions

Lauren Gibson
Project Manager
Japan Lessons-Learned Directorate
 

While “spent fuel pool #4” at Fukushima Daiichi did keep its contents safe during the March 2011 accident, no one could confirm that during the accident. The plant’s staff and other experts, including the NRC, simply didn’t have enough information to know what was going on in the pool. Why not? There was no reliable way to measure the pool’s water level.

SFP_instrKnowing the water level is important because if the pool had boiled dry, it would have damaged the fuel and added to the accident’s radiation release. The Japanese plant’s staff did the right thing in assuming the worst and making many attempts to add water to the pool. They even dropped water from helicopters. If they had known the pools were OK, however, they would have been able to focus on addressing the real problem: the damaged reactors.

This experience led the NRC to order U.S. nuclear power plants to add instrumentation to their spent fuel pools. That way, if an accident occurs at a U.S. reactor, plant staff will be able to tell when the spent fuel pool needed attention. Spent fuel pool instrumentation will help plant staff properly prioritize their accident response and keep the public safe.

U.S. reactors already monitor a small fraction of the water level in the spent fuel pool. However, this system may not work if power is lost, as it was at Fukushima, and can’t provide advance warning of low water levels.

The NRC’s order requires U.S. reactors to be able to tell whether water is at or above certain important levels. The highest level means enough water is available for the normal cooling system to work. The second level marks the level of water needed to protect someone standing next to the pool from the fuel’s radiation. The lowest level is still enough to cover the fuel, but the plant staff should begin adding more water to the pool.

Of course, water may be added—and most likely would be—prior to reaching this point. The order also requires that plant staff must be able to read these levels from somewhere away from the pool, such as in the control room.

U.S. reactors must install the new instruments no later than two refueling cycles after they submit their plan to the NRC or by the end of 2016, whichever comes first. All U.S. plants submitted their instrumentation plans in February 2013. We’ve been reviewing the plans and we recently issued interim staff evaluations. These documents give the plants feedback so they can continue on the right track for implementing the order.

The evaluations also ask plants for additional information we need to complete our review. While the agency’s final approval is yet to come, the interim evaluations give plants the confidence to order equipment and move forward with installing the instruments. We’ll provide the plants a final staff evaluation when we can conclude that they’ll comply with the order by the deadline by following their plan. We’ll continue inspecting plants to confirm they’ve finished complying with the order.

Our website’s Japan Lessons Learned section has a page with more information about the order and related guidance.

11 responses to “Keeping Proper Track of Spent Fuel Pool Conditions

  1. A Green Road (@AGreenRoad) December 30, 2013 at 10:30 am

    Spent Fuel Pool Risks At Nuclear Power Plants and High Burnup Plutonium Fuel Storage Problems; via @AGreenRoad
    http://agreenroad.blogspot.com/2013/12/spent-fuel-pool-risks-at-nuclear-power.html

  2. devolpi December 28, 2013 at 7:51 pm

    Although the NRC order requiring reliable spent-fuel-pool instrumentation was based on Fukushima accident uncertainties, the lessons-learned apply more tangibly to reactor water-level realities.

    After the Fukushima accident, responders were without means to determine reactor water level. Operators of Unit 2 lost ability to cool fuel after about 70 hours. Paraphrasing the NRC spent-fuel-monitoring order 2012-0067, lack of reactor water-level information contributed to poor understanding of potential radiation releases and adversely impacted prioritization of emergency response actions. Confusion was aggravated because reactor water-level instrumentation was (and still is) not available.

    Additional safety improvements could be made in light of Fukushima, improving capability of nuclear plants to mitigate beyond-design-basis accidents. Such augmentation would be consistent with a preventive defense-in-depth strategy. They would also reduce potential financial risk and public apprehension.

    Appropriate regulatory and industry response to the Fukushima accident should require reactor water-level instrumentation consisting of fixed independent high-energy gamma-radiation detectors mounted outside the reactor vessel (ex-vessel).

    Such ex-vessel instruments would provide autonomous and redundant measurements of reactor water level and density at all times, irrespective of power level. These independent instruments, installed within the biological shield — external to the reactor pressure vessel – would be qualified for temperature, humidity, and radiation levels consistent with extended reactor operation.

    Trained personnel would be able to monitor water level from the control room, or from external locations. The information display would continuously indicate reactor water level.

    A half-century of published experimental and intellectual technical base exists for autonomous gamma-ray water-level monitoring, derived in part from the TMI-2 loss-of-coolant billion-dollar accident which might very well have been prevented if such ex-vessel instrumentation had been in place.

  3. richard123456columbia December 26, 2013 at 5:21 pm

    The report’s Enclosure 2 relates to one of several methods Browns Ferry could use to maintain spent fuel pool water levels after an explosion or large fire. Since explosions and large fires can be caused by hostile action, it’s appropriate to protect information on how a plant would respond to such an event.
    When one can drive a plane through the roof and smash into the fuel why would they need any other method.

  4. CaptD December 26, 2013 at 3:51 pm

    ” two refueling cycles after they submit their plan to the NRC or by the end of 2016, whichever comes first.” falls far short of what most would consider being proactive about nuclear safety and should a BIG problem occur before then, this ruling could prove to be the direct cause of a Trillion Dollar Eco-Disaster like Fukushima, “for want of a nail”…

  5. Nikohl Vandel December 26, 2013 at 1:30 pm

    Where the #NRC does itself no favors, “of course, water may be added -and most likely would be….” words like”may” and making assumptions of common sense of priorities, give economically intentioned corporations less than clear regulatory retirements, and they must first, because the nature of business and structure, make optional decisions based on the corporation’s bottom line in the moment, which may or may not be public health and safety. There should be no options for that which is required for security and safety. Water MUST be added. Mind your words and stay on mission.

  6. Jim Van Zandt December 26, 2013 at 12:25 pm

    How about rigging something simple involving a float, a pole, a flag, and some reference marks, that could be read from anywhere in sight of the pool, including a video camera that is probably in place for other reasons?

  7. badger777 December 26, 2013 at 12:13 pm

    Are you guys kidding me? Just because you have no solution to spent fuel storage, do you guys put your head in the sand and just ignore the spent fuel, which incidentally is the most dangerous thing on earth.

    This is just being done now? Water levels in SFP were not monitored from the get go, even 60 years ago? This is beyond belief. And NRC is allowing 2 fuel cycles to implement? Jesus, what would this take….a few days of work at most?

    And what is the water source? Fire hose from a fire truck? Is the future of humanity relying on the presence of a fire hose?

  8. Garry Morgan December 26, 2013 at 10:47 am

    No doubt Fukushima continues to be a disaster of worldwide implications, and is a great concern; but there are problems in the U.S. with the defective overhead cooling pools of the GE Mark 1 reactors such as in Browns Ferry Alabama.

    On December the 24th the NRC released a Fire Inspection report regarding Browns Ferry. Unfortunately you, the NRC, did not release the Fire Inspection report as it pertained to the cooling pools. There is a problem according to the NRC-there is a fire hazard identified in Enclosure 2 of that report. The NRC classified it as a protected document.

    It seems you care more about protecting the failures of nuclear power safety rather than telling the public the truth.

    How do you expect the public to trust the NRC when you inappropriately classify a fire inspection report concerning cooling pool hazards instead of releasing it to the public? What are you protecting – it sure is not public safety.

    • Moderator December 26, 2013 at 12:43 pm

      All U.S. spent fuel pools continue to safely and securely store their contents. The pools meet very strong design requirements for safely withstanding severe events. All of the Browns Ferry report’s issues (http://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber='ML13354B743‘ ) were of very low safety significance and the plant has already taken appropriate steps to address the report’s findings. The report’s Enclosure 2 relates to one of several methods Browns Ferry could use to maintain spent fuel pool water levels after an explosion or large fire. Since explosions and large fires can be caused by hostile action, it’s appropriate to protect information on how a plant would respond to such an event.

      Scott Burnell

      • Garry Morgan December 26, 2013 at 1:32 pm

        Your quote: “All U.S. spent fuel pools continue to safely and securely store their contents. The pools meet very strong design requirements for safely withstanding severe events.” That is not a true statement.

        The GE Mark1 cooling pools have no overhead reinforced containment above the cooling pool level other than a basic roof structure and sheet metal. The cooling pools of the GE Mark 1 are susceptible to natural disasters and human attack That is a design flaw which the NRC refuses to correct and deceives the public about. You can classify all you want, it will not change the obvious design flaws of the GE Mark 1 series of reactors relating to the cooling pools.

        The NRC has discouraged members of the public from discussing this obvious design flaw. Furthermore, the 1968 Tornado Safety report concerning the GE Mark 1 Cooling Pool Safety Report is seriously flawed. But yet the NRC accepts the report as scientific evidence, even though the disclaimer at the front of the report states the report may not be fact.

        The NRC has made no effort to undertake an updated, current scientific report concerning the cooling pool design flaws relating to tornado safety. The use of a shop vac as an example of a tornado’s force, coupled with the unbelievable hypothesis that materials falling into or a direct hit of the unreinforced overhead structure will not displace water in the cooling pool is ridiculous.

        It is my observation the NRC intentionally classifies some reports not for the protection of the public but for the protection of the nuclear industry and the failures of the NRC. Particularly as they relate to the defective GE Mark 1 reactors.

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