The U.S. agency that last week raised alarm over the condition of spent fuel ponds at the earthquake- and tsunami-damaged Fukushima nuclear power plant in Japan said in a meeting this morning that the situation at the plant has nearly been stabilized. The Nuclear Regulatory Commission (NRC) also suggested no changes to guard against such damage to spent fuel pools at power plants in the U.S.

Last week, the head of the NRC said that damage to pools for storing and cooling spent nuclear fuel at the Japanese facility had allowed water to drain, exposing the fuel. That condition would eventually cause the fuel to overheat, generating explosive hydrogen, and releasing large amounts of radiation into the air. Workers at the plant in Japan have struggled to get water to these pools; high radiation levels have kept them from approaching the plant; and a lack of power and damage to the plant’s cooling systems prevented them from using the plant’s built-in safety systems. They’ve resorted to dropping water from helicopters that have been equipped with lead plates to shield against radiation, and spraying the pools from a distance with high-power water cannons.

This morning, William Borchardt, executive director of operations at the NRC, blamed radiation releases at the Japanese plant on the spent fuel pools, not the reactors themselves. But he said that the agency believes the the situation at the pools “has stabilized,” after a “concerted effort” to get water into them. “The fact that offsite power is close to being available for use by plant equipment is perhaps the first optimistic sign that things could be turning around,” he said. With power restored, cooling systems at the plant could be used, but it’s not clear yet whether those cooling systems were damaged by the earthquake and tsunami.

Spent fuel cooling pools at power plants in the U.S. contain too much spent nuclear fuel, according to some researchers, who say that if water were to be lost from these pools, the results could be worse than Chernobyl, the worst nuclear reactor accident in history. They say that the amount of dangerous material in the pools is greater than what was contained in the damaged reactor at Chernobyl, and so more radioactive material could be released. A paper published in 2003 outlined the potential problem, pointing in particular to the danger posed by terrorist attacks. The researchers suggested that to reduce the risk, rules be changed to require power plant operators to more quickly move fuel out of the pools and into dry cask storage, which relies on air cooling rather than water. “We suggested a relatively inexpensive solution,” says Allison Macfarlane, a professor of environmental science at George Mason University, and one of the authors of the paper. It would cost billions of dollars, she says, but that’s cheaper than losing multi-billion nuclear reactors, as is happening in Japan. After a review, the NRC decided not to implement the proposed changes. “It is still a problem in the U.S.,” Macfarlane says.

The NRC has not responded to requests for comment. But at this morning’s meeting the agency briefly raised the issue of the ponds in the U.S. “It’s a very simple problem. All you have to do is keep water in the pool,” Borchardt said. After the 9-11 terrorist attack, the agency required that power plants have backup plans, such as extra generators, to respond to problems like those seen in Japan. He said that the NRC task force that is trying to draw lessons from Japan needs to look at whether the backup plans, “really would work under that scenario.”

William Ostendorff, one of the NRC’s commissioners, raised the question of the spent fuel pools at the meeting. Compared to the discussions on emergency core cooling systems, he said, “we don’t spend a lot of time as a commission talking about that.”