2011 Complete Guide to Spent Nuclear Fuel Pool Risks at Nuclear Power Plants: NRC Reports on Spent Fuel Rods, Zircaloy Fires, Mitigation Measures, Crisis at Japan's TEPCO Fukushima Power Plant

The crisis at the TEPCO Fukushima Daiichi Nuclear Power Station in Japan following the great earthquake and tsunami of March 11, 2011 has raised important issues about the safety of spent nuclear fuel rod storage, especially those located at the top of boiling water reactor (BWR) units. At press time, there is continuing concern about the status of the spent nuclear fuel pools located above the reactors in several units of the Fukushima Daiichi Power Station in Japan ravaged by the March 11, 2011 earthquake and tsunami. Heroic efforts are underway to spray the pools with water to prevent the emission of large amounts of radiation. This new compendium includes a brief overview of the handling and security of spent nuclear fuels and three major studies for the Nuclear Regulatory Commission (NRC) which deal with the hazards of reactor spent fuel pools. The first report, by the Sandia Laboratories, specifically addresses the type of situation faced by TEPCO at Fukushima with boiling water reactors (BWR). The second report, by the Brookhaven National Laboratory, characterizes the radiological risks posed by storage of spent reactor fuel at commercial reactors. Excerpts from a third report discuss possible mitigation options for pool accidents. Finally, we reproduce a report by the GAO about the safety of spent nuclear fuel.

A 1989 Brookhaven National Laboratory report dismissed suggestions for additional safety measures in a cost/benefit analysis. Measures which might be useful in a situation such as the Fukushima disaster, including inventory reduction, seismic-proof water systems, and covering the pool with solid materials after an accident, are discussed.

Allen Benjamin and others, writing in the Sandia report, state: "Analysis of spent fuel heatup following a hypothetical accident involving drainage of the storage pool is presented. Computations based upon a new computer code called SFUEL have been performed to assess the effect of decay time, fuel element design, storage rack design, packing density, room ventilation, drainage level, and other variables on the heatup characteristics of the spent fuel and to predict the conditions under which clad failure will occur. It has been found that the likelihood of clad failure due to rupture or melting following a complete drainage is extremely dependent on the storage configuration and the spent fuel decay period, and that the minimum prerequisite decay time to preclude clad failure may vary from less than 10 days for some storage configurations to several years for others."

The report discusses emergency aspects of pool water loss relevant to the Japanese situation. "An alternative way to maintain coolability, at least on a temporary basis, would be to provide an emergency water spray of sufficient intensity to remove the decay heat by its latent heat of vaporization. The water supply could be available from onsite hydrants, from onsite storage tanks, from remote portable storage tanks, or, preferably, from a combination of onsite and remote sources in order to reduce the risk of unavailability. Facility personnel would presumably be available to set up fire hoses and initiate the spray in the event of a complete power failure, and the spray would be continued until the source of the leak could be repaired."

The abstract for the BNL report reads: "This investigation provides an assessment of the likelihood and consequences of a severe accident in a spent fuel storage pool - the complete draining of the pool. Potential mechanisms and conditions for failure of the spent fuel, and the subsequent release of the fission products, are identified. Two older PWR and BWR spent fuel storage pool designs are considered based on a preliminary screening study which tried to identify vulnerabilities. Internal and external events and accidents are assessed.

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