WASHINGTON -- It's a nightmare that scientists say could happen.
Terrorists penetrate a nuclear power plant but ignore the concrete-protected reactor. They're really after the pool of water containing hundreds of used fuel rods.
Explosive charges lead to an uncontrollable fire, sending radiation into the air.
A National Academy of Sciences report released Wednesday concludes such an event could happen. It also says the Nuclear Regulatory Commission and nuclear industry have not done enough to understand the vulnerability.
It's "a critical national security issue," said the academy's president, Bruce Alberts, after the release of a report subject to haggling with regulators over how much of it should remain secret.
The scientific experts found many of the fuel storage pools at nuclear power plants in 31 states may be vulnerable and that regulators should conduct a fresh examination of each plant.
In the meantime, plant operators promptly should reconfigure used fuel rods in the storage pools to lower decay-heat intensity and install spray devices to reduce the risk of a fire should a storage facility be attacked, the scientists said.
Congress sought the study because of the heightened concerns that terrorists might seek to target nuclear power plants.
At 68 plants, including some already shut down, in 31 states, thousands of used reactor fuel rods are in deep water pools. Dry, concrete casks hold a smaller number of these rods.
Much more highly radioactive fuel is stored in pools than is in the more protected reactors -- 103 in total -- at these sites.
Some scientists and nuclear watchdog groups long have contended that these pools pose a much greater danger to a catastrophic attack than do the reactors themselves.
Some plants where pools are all or partially underground present less of a problem. Others, including a series of boiling-water reactors where pools are more exposed, represent greater concern, said Bob Alvarez, a former Energy Department official who has argued for increased protection of used reactor fuel at nuclear plants.
The experts' report "pretty well legitimizes what we've been saying," Alvarez said in an interview.
The scientific panel said reinforced concrete storage pools -- 25 feet to 45 feet deep, with water circulating to keep the fuel assemblies from overheating -- could tempt terrorists.
The report said an aircraft or high explosive attack could cause water to drain from the pools and expose the fuel rods, unleashing an uncontrollable fire and large amounts of radiation.
Nuclear regulators said they would give the report's recommendations "serious consideration." But the NRC has disputed many findings and suggestions from the experts.
After the classified document was provided to members of Congress last month, the NRC's chairman told lawmakers in a letter that some of the panel's assessments about plants' vulnerabilities were "unreasonable" and that certain conclusions "lacked sound technical basis."
"Today, spent fuel is better protected than ever," Nils Diaz wrote.
The NRC said it believes the potential for large releases of radiation from such a fire "to be extremely low." Still, the agency has advised reactor operations to consider refiguring the pools' fuel rods -- pairing new ones with older ones to reduce the heat.
Kevin Crowley, the scientific panel's staff director, said the classified version of the report includes "some attack scenarios well within the means of terrorists" that could result in a catastrophic fire of spent fuel.
Nuclear safety advocates said the report recognizes, for the first time, the vulnerability of spent fuel.
David Lochbaum, a nuclear industry watchdog for the Union of Concerned Scientists, said the study makes clear that regulators have not acted aggressively enough.
"Three years after 9/11, our hope would have been more of that homework had been done," Lochbaum said.
The industry says its system of storing the fuel is safe and protected. But in response to the report, the industry said it was "assessing the potential to augment" safety systems for spent fuel facilities.
Marvin Fertel, a senior executive at the Nuclear Energy Institute, the industry's trade group, said a computer analysis the industry commissioned in 2002 showed that fuel pool structures would withstand, without a significant loss of water, the impact of an aircraft crash.
But the study said the pools vary among plants and reactor designs, and that some are more vulnerable than others.
The panel said dry cask storage provides better protection. It also said significant numbers of used fuel rods always will have to be stay in pools for as long as five years before they adequately cool. At least one-quarter of the power plants now have some of their spent fuel in dry casks.
The panel said the government should look into more widespread use of dry cask storage as part of its detailed assessment of risks.
The academy is a private organization chartered by Congress to advise the government of scientific matters.
On the Net:
National Academy of Sciences: http://national-academies.org
Nuclear Energy Institute: www.nei.org
Nuclear Regulatory Commission: www.nrc.gov