What are fuel rods?
They’re the source of the fission reaction that makes nuclear plants work. Fuel rods are long metal tubes filled with uranium that’s been formed into pellets. When these rods are placed inside the reactor, nuclear fission occurs, generating heat. That in turn boils water and creates steam, which powers turbines and produces electricity. When the uranium fuel is used up, usually after about 18 months, the spent rods are generally moved to deep pools of circulating water to cool down for about 10 years, though they remain dangerously radioactive for about 10,000 years.

How do the Japanese store their spent fuel rods?
The same way we do in the U.S. When the earthquake and tsunami knocked out the cooling systems at the multiple nuclear reactors at the Fukushima Daiichi plant, it wasn’t just the reactors that were affected. Several spent-fuel-rod pools also lost electric power, shutting down pumps. Water in the cooling pools stopped circulating and began to boil off or leak out. As the water level fell, the spent fuel rods were exposed, and their temperatures soared. Several began to melt down, releasing extremely high levels of radiation into the air.

Could that happen in the U.S.?
It’s within the realm of possibility. The U.S. has 104 operating nuclear plants, and most store all the spent fuel rods they’ve ever used right on-site. All told, there are 71,900 tons of spent fuel rods at U.S. nuke plants—the vast majority of them sitting in pools that today are mostly full, according to a recent state-by-state tally by the Associated Press. “The spent-fuel pools are currently holding, on the average, four times more than their designs intended,” said Robert Alvarez, of the Institute for Policy Studies. U.S. officials insist they have stricter safety standards for the pools than Japan does. But former Nuclear Regulatory Commission member Peter Bradford said, “The phrase ‘it can’t happen here’ is an invitation to disaster.”

Is there a threat of terrorism?
There’s little doubt of that. The National Academy of Sciences warned Congress in 2006 that if terrorists flew a plane into the pools, or bombed the pools after crashing through a plant’s security perimeter, they could expose the fuel rods, causing “the release of large quantities of radioactive materials to the environment.” David Lochbaum, head of the nuclear-safety program for the Union of Concerned Scientists, told a congressional hearing last week that while nuclear fuel inside reactors is protected by multiple thick layers of metal and concrete shielding, spent-fuel pools are typically covered with sheet-metal roofs, “like that in a Sears storage shed.” Pete Stockton, a former security expert with the Department of Energy, warns that if fuel rods were exposed and melted down near a populated area, the resulting radiation would force a massive evacuation. The Indian Point plant 35 miles north of Manhattan, for example, could “take out New York City,” Stockton said.

Is there a better way of storing rods?
One possibility is to seal them in aboveground “dry casks” made of concrete and steel, as Germany does. Casks are already in use across the U.S., though on a limited basis due to the cost and the absence of regulations compelling utilities to use them. Enclosing all spent fuel rods in casks would cost between $5 billion and $10 billion, experts estimate. The nuclear industry has strongly resisted taking on that cost.
Why not bury the rods under a remote mountain?
That was actually the plan until two years ago. In the 1980s, the federal government launched a plan to bury spent fuel in nickel-alloy chambers 1,000 feet below the surface of Nevada’s Yucca Mountain. George W. Bush green-lighted the Yucca Mountain repository in 2002, and nuclear utilities have levied more than $20 billion in charges to pay for its construction. But opponents, led by now-Senate Majority Leader Harry Reid of Nevada, argued that waste could eventually leak into the water table 1,000 feet below the repository, and worried Yucca Mountain would become a terrorist target. “Leave it on-site where it is,” Reid argued in 2009. “Saves the country billions and billions of dollars.” Last year President Barack Obama, delivering on a campaign promise that helped him win Nevada in 2008, called off the stalled project and named a “blue-ribbon commission” to come up with something else.

How urgent is the situation?
Fairly urgent. The NRC predicts that at the rate we’re discarding rods—about 2,000 tons a year—we’ll run out of existing storage space by 2015. The Japanese crisis has sparked a new debate about fuel-rod storage in Congress, with some congressmen pushing for a reconsideration of Yucca Mountain. During hearings last week, William Levis, chief operating officer of a New Jersey–based nuclear plant, said the industry keeps storing fuel rods in pools next to nuke plants because the government has provided no better alternative. “It’s really our lack of a national strategy of what we’re going to do with it,” he said.

The Scandinavian solution
Sweden and Finland are no longer merely talking about the possibility of storing spent fuel rods underground—an approach known as “deep storage.” They’ve approved, and begun work on, their own Yucca Mountains. Sweden has chosen a site at Forsmark, and work on an underground nuclear storage facility is expected to be completed in about a decade. Finland has already begun blasting a network of tunnels for a deep storage cavern called Onkalo, which it hopes to have up and running in 2020. Among other cutting-edge innovations, these sites will line the storage shafts with bentonite, which, when exposed to water, swells, sealing off the spent fuel rods, and protecting them from earthquakes and underground water flows. The group spearheading the construction says that sealing fuel rods inside corrosion-resistant copper canisters, bedrock, and bentonite guarantees safe burial for 100,000 years. “We are going to be the ones who set the standard for final disposal,” a spokesman said.