July 2011

Answer:

Although the Nuclear Regulatory Commission (NRC) would allow used fuel with as little as one year of cooling to be moved from the used fuel storage pool into dry storage, there currently are no NRC-licensed dry storage casks that could handle used fuel cooled for only one year. Since the heat generating rate of used fuel decreases very rapidly (exponentially) as the cooling time of the used fuel assemblies increases, designing and using dry cask storage systems is far easier and safer for used fuel that has been cooled longer in the used fuel storage pool. The shortest cooling time for used fuel assemblies in dry storage systems licensed by the NRC is three years and is only approved for a few cask designs; for the majority of NRC-licensed systems, the minimum cooling time is five years. In practice, most used fuel loaded into dry storage casks is cooled for seven or more years.

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There has been discussion in the media about the possibility of a “zirconium cladding fire”; however, this term is not completely accurate. In the extremely unlikely event that the cladding could reach the very high temperatures necessary to initiate (1,700 ˚F), then the zirconium cladding in a water or air environment would undergo a rapid and self-sustaining heat generating (exothermic) oxidation reaction. This oxidation reaction could look similar to a fireworks sparkler, thus it has colloquially been called a “zirconium fire.” Nuclear fuel is maintained well below these temperatures. For more information, the 2006 National Academy of Sciences report “Safety and Security of Commercial Spent Nuclear Fuel Storage” provides an accurate description of this phenomenon.
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Plant Status

  • Tokyo Electric Power Co. expects to meet its self-imposed July 19 deadline to stabilize reactor cooling and mitigate radiation at the Fukushima Daiichi nuclear energy facility. That work includes injecting inert nitrogen gas into the reactor 3 containment vessel, which started today. The nitrogen is intended to help prevent a potential explosion of built-up hydrogen. TEPCO has been injecting nitrogen into reactors 1 and 2 since April 7 and June 28 respectively. The next major milestone in the plan for Fukushima recovery includes cold shutdowns for reactors 1-3, which are expected to take place in the next three to six months.
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NEI has posted a new backgrounder to its website:

  • U.S. Industry Taking Steps to Learn Lessons from Japan, Enhance Safety at America’s Nuclear Energy Facilities
    The nuclear energy industry will continue to work with the Nuclear Regulatory Commission as it considers forthcoming recommendations of an agency task force on new procedures and regulations in light of the accident at Fukushima Daiichi.  We have undertaken significant work in the past 90 days to examine our facilities and take the steps necessary to enhance safety.  We will continue to work with the Nuclear Regulatory Commission to understand any potential gaps in safety and fill those gaps.
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See the main fact sheet Web page for all of NEI’s backgrounders on the Fukushima nuclear energy situation and the U.S. nuclear industry’s response.

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