A 2004 report by the academy suggested that fresh spent fuel, which is radioactively hotter, be spread among older, cooler assemblies in the spent fuel pool. "You're buying yourself time, basically," says Crowley. "The cooler ones can act as a thermal buffer."
First Energy, which runs two nuclear power stations in Ohio and one in Pennsylvania, was able to reconfigure the spent fuel rods in its pools to make more room. Still, the company is now running out of space, says spokesman Todd Schneider. Ohio has 1,136 tons of spent fuel in pools and 37 tons in dry casks.
The casks in the U.S. are kept outdoors, generally on concrete pads, but industry officials insist they are safe. Unlike the pools, the casks don't need electricity; they are cooled by air circulation.
One cask model, selling for $1.5 million, places spent fuel inside a stainless steel canister, which is placed inside an "overpack" -- an outside shell composed of a layer of carbon steel, 27 inches of concrete and another layer of carbon steel. When in place, the system stands 20 feet tall and weighs 150,000 pounds, said Joy Russell, a spokeswoman for manufacturer Holtec International of Florida.
Russell said engineers have designed the system to withstand a crash from an F-16 fighter jet and survive the resulting jet fuel fire.
Plant operators in some states have moved aggressively to dry cask storage. Virginia has 1,533 tons of nuclear waste in dry storage and 1,105 tons in spent fuel pools. Maryland has 844 tons in dry storage and 588 tons in spent fuel pools.
Utilities in Texas, though, have not. There are 2,178 tons kept in spent fuel pools at reactor sites there, and zero in dry casks. In New York, 3,345 tons are in spent fuel pools while only 454 tons are in dry storage.
No cask is totally invulnerable, but the academy report found that radioactive releases from casks would be relatively low.
"If you attacked a fuel cask and managed to put a hole in it, anything that came out, the consequences would be very local," Crowley said.
Casks can be licensed for 20 years, with renewals, said Carrie Phillips, a spokeswoman for the Atlanta-based Southern Co., which has a dozen such casks at its two-reactor Joseph M. Farley plant near Columbia, Ala. She said officials have "every expectation" the casks could last "in excess of 100 years by design."
But not the needed tens of thousands of years. For long-term storage, the government had looked to Yucca Mountain. It was designed to hold 77,160 tons -- 69,444 tons designated for commercial waste and 7,716 for military waste. That means the current inventory already exceeds Yucca's original planned capacity.
A 1982 law gave the federal government responsibility for the long-term storage of nuclear waste and promised to start accepting waste in 1998. After 20 years of study, Congress passed a law in 2002 to build a nuclear waste repository deep in Yucca Mountain.
The federal government spent $9 billion developing the project, but the Obama administration has cut funding and recalled the license application to build it. Nevadans have fiercely opposed Yucca Mountain, though a collection of state governments and others are taking legal action to reverse the decision.
Despite his Yucca Mountain decision, President Barack Obama wants to expand nuclear power. He created a commission last year to come up with a long-term nuclear waste plan. Initial findings are expected this summer, with a final plan expected in January.
"They are 13 years late," says Terry Pickens, Director of Nuclear Policy at Xcel Energy, the Minneapolis-based utility that operates three reactors in Minnesota. Xcel is building steel-and-concrete cask containers to hold old waste on site, and suing the government periodically to pay for them. "We would like them to get done with what they said they would get done."
Some countries -- such as France, Japan, Russia and the United Kingdom -- reprocess their spent fuel into new nuclear fuel to help reduce the amount of waste.
The remaining waste is solidified into a glass. It needs to be stored in a long-term waste repository, but reprocessing reduces the volume of waste by three-quarters.
Because reprocessing isolates plutonium, which can be used to make a nuclear weapon, Presidents Gerald Ford and Jimmy Carter put a stop to it in the U.S. The ban was later overturned, but the country still does not reprocess.
France produces 1,300 tons of nuclear waste per year, and reprocesses 940 tons. Still, fuel is only reprocessed once and then it, too, needs to be stored. France is expecting that engineers will eventually succeed in building a new type of nuclear reactor called a fast reactor that will use the waste it can't reprocess as fuel.
"They've kicked the can down the road," says Frank von Hippel, a director of the Program on Science and Global Security at Princeton University.
Other countries, such as Germany, store spent fuel in casks. Finland is building a repository it says will store waste safely for 100,000 years.
Even though there is no long-term storage in the U.S., utility customers and taxpayers have been paying for it -- twice.
Customers have paid $24 billion into a fund Congress established in 1982 to pay for such storage. The charge -- a penny for every 10 kilowatt-hours -- would typically add up to about $11 a year for a household that received all its electricity from nuclear plants.
Users pay as taxpayers, too -- for dry storage. Utilities that have run out of storage space in pools successfully sued the federal government for breach of contract, because it failed to keep to the 1998 deadline to establish long-term storage. By law, the money for dry casks cannot come from the nuclear waste fund, and must come from the federal budget.