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Spent fuel: In the United States, 63 current and former nuclear reactor sites (including power plant complexes and government facilities) already have dry-cask storage facilities. Another 10 are applying to build them, and 11 haven’t yet announced plans to do so. But these casks are only keeping pace with newly generated waste. At most locations, liquid pools for holding and cooling fuel are still full of waste, and in many cases these pools are packed more densely than is the case at the stricken Fukushima reactors.

“If there is a loss-of-coolant accident, you are going to be in big trouble, especially with these high-density racks and the pools being heavily loaded—and even more so if there happens to be freshly discharged fuel in the pool,” says Allison Macfarlane, a geologist and associate professor of environmental science and policy at George Mason University, who was one of several coauthors of a 2003 report warning of the danger posed by dense reracking. “A lot of these pools are in upper stories at the power plant,” meaning breaches or cracks could let water run out. “If there is a loss of water, you can have a release of radioactivity much larger than Chernobyl, because there is a lot more fuel in the pool than in the core of the reactor.”

Last year, President Obama canceled plans to open the Yucca Mountain underground fuel repository 90 miles northwest of Las Vegas, and appointed a commission to come up with alternatives. The commission, due to issue its report in June, has not made any statements about Fukushima. Macfarlane, a commission member, says she could not discuss its possible suggestions. However, the body is scheduled to meet in a public session May 13 in Washington.

The 2003 report said that in the event of coolant loss in a densely packed pool, air cooling would not suffice. Temperatures could rise to 600 °C within an hour, causing the zirconium fuel cladding to rupture, and then increase to 900 °C, whereupon the cladding would burn, resulting in huge quantities of released radioactive material, the report said.

The report proposed immediate reversion to lower-density pool configurations, with more cooled fuel put in dry casks and moved to central sites. In looser-packed pools, the report said, airflow alone could be enough to prevent fire in the event of coolant loss. It said this could be done for no more than $7 billion nationally, which would work out to a wholesale electricity price increase of 0.06 cents per kilowatt-hour generated from the fuel.

These steps were not carried out. A subsequent National Research Council report also said the fire scenarios required more study, and suggested other measures while leaving dense configurations intact. “It appears to be feasible to reduce the likelihood of a zirconium cladding fire by rearranging spent fuel assemblies in the pool and making provision for water-spray systems that would be able to cool the fuel, even if the pool or overlying building were severely damaged,” the report said. Fuel rearranging and backup cooling of pools are being implemented, a Nuclear Regulatory Commission spokesman says.

If the U.S. government had followed through on its 1982 commitment to open a spent-fuel repository— and its subsequent contracts with utilities to begin removing the fuel in 1998—the pressure on U.S. spent fuel pools would have been relieved, Lester says.  “There were schedules that described how the DOE [Department of Energy] was going to move the fuel, and which fuel would be moved,” he says. “I think we can say, on the basis of all of that, that the pools would not be nearly as full as they are now.”

He says it was crucial to begin establishing central sites for dry-cask storage as part of a comprehensive plan for waste storage and disposal, which he says should not rule out Yucca Mountain.  “One possible use for the site is for temporary storage,” Lester says.

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Credits: Nuclear Regulatory Commission

Tagged: Energy, Japan, radiation, nuclear energy, spent fuel, Fukushima nuclear disaster

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