The Devil’s Scenario – near miss at Fukushima is a warning for U.S.

[ The most likely event to trigger a loss of power long enough to cause a spent fuel pool zirconium fire meltdown and release of radioactive particles into the atmosphere is a nuclear or natural geomagnetic storm electromagnetic pulse (see Dr. Pry’s testimony at the U.S. House of Representatives on May 13, 2015 at a hearing titled “The EMP Threat:  the state of preparedness against the threat of an electromagnetic pulse (EMP) event”.  The EMP Commission estimates a nationwide blackout lasting one year could kill up to 9 of 10 Americans through starvation, disease, and societal collapse.

Dr. Pry states that “Seven days after the commencement of blackout, emergency generators at nuclear reactors would run out of fuel. The reactors and nuclear fuel rods in cooling ponds would meltdown and catch fire, as happened in the nuclear disaster at Fukushima, Japan. The 104 U.S. nuclear reactors, located mostly among the populous eastern half of the United States, could cover vast swaths of the nation with dangerous plumes of radioactivity“.

Alice Friedemann  author of “When Trucks Stop Running: Energy and the Future of Transportation, 2015, Springer]

Stone, R. May 27, 2016. Near miss at Fukushima is a warning for U.S. Science  Vol. 352, Issue 6289, pp. 1039-1040 

Japan’s chief cabinet secretary called it “the devil’s scenario.” Two weeks after the 11 March 2011 earthquake and tsunami devastated the Fukushima Daiichi Nuclear Power Plant, causing three nuclear reactors to melt down and release radioactive plumes, officials were bracing for even worse. They feared that spent fuel stored in pools in the reactor halls would catch fire and send radioactive smoke across a much wider swath of eastern Japan, including Tokyo.

Thanks to a lucky break detailed in a report released last week by the U.S. National Academies of Sciences, Engineering, and Medicine, Japan dodged that bullet. But the report warns that spent fuel accumulating at U.S. nuclear plants is also vulnerable. The near calamity “should serve as a wake-up call for the industry,” says Joseph Shepherd, a mechanical engineer at the California Institute of Technology in Pasadena who chaired the academies committee that produced the report.

A major spent fuel fire at a U.S. nuclear plant “could dwarf the horrific consequences of the Fukushima accident,” says Edwin Lyman, a physicist at the Union of Concerned Scientists, a nonprofit in Washington, D.C., who was not on the panel. Unpublished modeling from one panel member presents chilling scenarios for a hypothetical spent fuel fire at the Peach Bottom nuclear power plant in Pennsylvania. “We’re talking about trillion-dollar consequences,” says Frank von Hippel, a nuclear security expert at Princeton University, who led the modeling.

After spent fuel is removed from a reactor core, the radioactive fission products continue to decay, generating heat. All nuclear power plants store the fuel in deep pools for at least 4 years while it cools. To keep it safe, the academies panel recommends that the U.S. Nuclear Regulatory Commission (NRC) and plant operators beef up systems for monitoring the pools and topping up water in case a facility is damaged. The panel also says plants should be ready to tighten security after a disaster. “Disruptions create opportunities for malevolent acts,” Shepherd says.

At Fukushima, the earthquake and tsunami cut power to pumps that circulated coolant through the reactors and cooled the water in the spent fuel pools. The pump failures led to the meltdowns; in the pools, located in all six of Fukushima’s reactor halls, they allowed water temperatures to rise dangerously. Of preeminent concern were the pools in reactor units 1 through 4: Explosions had heavily damaged three of those buildings in the days after the tsunami.

The “devil’s scenario” nearly played out in Unit 4, where the reactor was shut down for maintenance. The entire reactor core—all 548 fuel assemblies—was resting in the Unit 4 pool along with another 783 assemblies, shedding vast amounts of heat. When an explosion blew off Unit 4’s roof on 15 March, operators assumed the cause was hydrogen—and they feared it had come from fuel in the pool that had been exposed to air.

Confirmation was impossible because the power loss on 11 March had disabled the pool’s water level indicators. (Analysts now concur that the hydrogen had come not from exposed spent fuel, but from the melted reactor core in the adjacent Unit 3.) Concerns abated after a helicopter overflight on 16 March captured video of sunlight glinting off water in the pool. But the crisis was actually worsening: The water was evaporating away because of the hot fuel. As the level fell perilously close to the top of the fuel assemblies, something “fortuitous” happened, Shepherd says. As part of routine maintenance, workers had flooded Unit 4’s reactor well, where the core normally sits. Separating the well and the spent fuel pool is a gate through which fuel assemblies are transferred. The gate leaked, allowing water from the well to partly refill the pool.

Without that leakage, the panel’s modeling predicts that the tops of the fuel assemblies would have been exposed by early April 2011, and the odds of the assemblies’ zirconium cladding catching fire would have skyrocketed. Only good fortune and makeshift measures to pump water into all the spent fuel pools averted that disaster, the academies panel notes.

A similar scenario could play out at a U.S. nuclear plant if a pool lost water via evaporation or leakage. At most plants, spent fuel is densely packed in pools, heightening the fire risk. NRC has estimated that a major fire at the Peach Bottom nuclear plant’s pool would displace 3.46 million people from 31,000 square kilometers of contaminated land, an area larger than New Jersey. But Von Hippel and others think that NRC has grossly underestimated the scale and societal costs of such a fire.

nightmare scenario pennsylvania contamination cs-137

Figure 1 nightmare scenarios.  Models of a hypothetical spent fuel fire at a pennsylvania nuclear plant.  Depending on weather the Cs-137 plume displaces up to 41 million people (1 July) and contaminates up to 274,000 square kilometers (1 October)

NRC used a program called MACCS2 for modeling the dispersal and deposition of radioactivity from a Peach Bottom fire. Princeton’s Michael Schoeppner and Von Hippel instead used HYSPLIT, a program able to craft more sophisticated scenarios based on historical weather data for the whole region.

In their simulations, the Princeton duo focused on Cs-137, a radioisotope with a 30-year half-life that has made large tracts around Chernobyl and Fukushima uninhabitable. They assumed a release of 1600 petabecquerels, which is the average amount of Cs-137 that NRC estimates would be released from a fire at a densely packed pool, and approximately 100 times the Cs-137 spewed at Fukushima. They simulated such a release on the first day of each month in 2015.

The contamination from such a fire on U.S. soil “would be an unprecedented peacetime catastrophe,” the Princeton researchers conclude in a paper to be submitted to the journal Science & Global Security. For a fire on 1 January 2015, with the winds blowing due east, the radioactive plume would sweep over Philadelphia, Pennsylvania, and nearby cities (Figure 1 nightmare scenarios). For a fire on 1 July 2015, shifting winds would deposit Cs-137 over much of the mid-Atlantic. Averaged over 12 monthly calculations, the area of heavy contamination—exceeding 1 megabecquerel per square meter, the level that would trigger a relocation—is 101,000 square kilometers. That’s more than three times NRC’s estimate and would force the relocation of 18.1 million people on average, about five times NRC’s estimates.

NRC’s first look at the academies report “did not identify any safety or security issues that would require immediate action,” says spokesperson Scott Burnell in Washington, D.C. The agency has long mulled whether to compel the nuclear industry to move most of the cooled spent fuel in densely packed pools to concrete containers called dry casks, which would reduce the consequences and likelihood of a spent fuel fire. As recently as 2013, NRC concluded that the projected benefits do not justify the roughly $4 billion cost of a wholesale transfer. But the benefits of expedited transfer to dry casks are fivefold greater than NRC has calculated, the academies found. “NRC’s policies have underplayed the risk of a spent fuel fire,” Lyman says.

The academies panel recommends that NRC “assess the risks and potential benefits of expedited transfer.” Burnell says that NRC’s technical staff “will take an in-depth look” at the issue and report to NRC commissioners later this year.

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One Response to The Devil’s Scenario – near miss at Fukushima is a warning for U.S.

  1. Rice Farmer says:

    This is why nuclear power plants are all ticking time bombs. Although terrorism is usually cited as a risk, that is only a possibility, while it is virtually assured that NPPs will lose offsite power (and run out of generator fuel) after the financial system collapses. Just like everything else — including food production — power plants and power grids depend on financing, and when the money stops flowing, so will the electricity. Even though financial collapse is by far the most likely trigger of nuclear disaster, no one will see it coming.