The batteries that back up power at most U.S. nuclear plants are required to last about as long as the average cellphone battery -- four hours.
The Nuclear Regulatory Commission says that's enough. The agency's critics say it's not. And those critics are pointing to the Fukushima Daiichi plant in Japan, which is teetering on the brink of meltdown because it lost power.
"Most of our plants have far less than what the Japanese had," said David Lochbaum, a nuclear engineer with the Union of Concerned Scientists who has long criticized U.S. nuclear protections as inadequate. "So, we're more vulnerable to a situation where we lose primary power and the backup."
U.S. regulators also allow plants to operate without backup power for the controls monitoring spent nuclear fuel. These ponds often do not have containment, and in the United States they contain more of the highly radioactive material than in Japan.
NRC says it has adequate safeguards in place for battery backup and spent-fuel pools.
"All U.S. plants have in place additional resources and procedures to deal with situations where significant portions of the plant have been rendered inoperable," NRC spokesman Scott Burnell said. "The NRC has inspected those arrangements and the agency finds them capable of continuing to protect the public after severe events."
And industry officials say U.S. plants have layers of safety backups not reflected by rules about power blackouts. There are multiple sources of power from offsite facilities, extra generators and equipment that can be shared with other plants in crisis. In addition, plants have prepared for specific catastrophes that go beyond their overall safety requirements, such as a plane crash.
"There's layer upon layer of protection," said Alex Marion, vice president of nuclear operations for the Nuclear Energy Institute, the nuclear industry's policy arm.
Of the country's 104 reactors, 11 are required to have eight hours of battery backup. But Marion said most plants have eight hours of backup even though they might be required to have only four.
As an island nation on the Pacific Ocean's "Ring of Fire," a zone of active volcanoes, Japan appears particularly vulnerable to the earthquake-tsunami combination that killed thousands and crippled the Fukushima Daiichi plant. The earthquake cut off-site power to the plant, and the tsunami flooded its generators. That constitutes what nuclear experts call "station blackout." Eight hours of backup power proved woefully inadequate.
But there are different threats that could cause similar problems with reactors in the United States, according to groups that act as watchdogs to the nuclear industry and NRC's regulatory approach.
"Many of our reactors are in situations where earthquakes or hurricanes in the Gulf or ice storms in the Northeast or a tree in Cleveland can cause an extensive blackout that puts us in a very similar situation," Lochbaum said.
"So, I think battery capacity and ... what we do when the batteries go dim may be an area that we need to shore up, so that our plants aren't as vulnerable as Japan was."
For example, a 1998 tornado knocked out power to the Davis-Besse plant near Toledo, Ohio, for more than a day. An NRC analysis of the event said that the outage brought the plant perilously close to meltdown.
Battery backup requirements, NRC's Burnell said, are evaluated on a site- and design-specific basis. Plants must convince NRC that their individual approaches meet federal requirements.
"The NRC continues to conclude that existing battery backups at every plant are sufficient and acceptable for that plant's situation," Burnell said.
Concerns about spent-fuel pools
Since NRC began monitoring nuclear plants' emergency backup capacity, the number, duration and severity of power outages has steadily decreased.
Still, regulators were alarmed by a blackout that hit the northeastern United States in 2003, cutting power to nine reactors and prompting a wide-ranging review by NRC.
And in 1992, Hurricane Andrew caused the Turkey Point Nuclear Reactor near Miami to lose access to the grid for more than six days.
Station blackout at a nuclear facility can account for as much as 88 percent of the chance of reactor core damage in a year, according to NRC records. The average, though, for U.S. plants is about 23 percent.
A 2005 NRC report shows there were 24 "loss of offsite power" events between 1997 and 2004, including the nine in the Northeast blackout.
Some nuclear critics say the situation is even more dangerous with spent fuel -- uranium-bearing rods that no longer produce enough energy to sustain a nuclear reaction in the reactor.
In the United States, most spent fuel remains on site at nuclear plants because the country has not developed a facility to store it.
The United States has 71,862 tons of the waste, according to a recent analysis by the Associated Press (Greenwire, March 23).
Three-quarters of that waste is stored in water-filled cooling pools like those at the Japanese plant, stored outside the thick concrete containment barriers that block the release of radioactive material in an accident. The rest is encased in "dry casks" constructed of steel and thick concrete.
"The spent-fuel pools are currently holding, on the average, four times more than their designs intended," said Robert Alvarez of the left-leaning Institute for Policy Studies.
By contrast, Japan reprocesses spent nuclear fuel, turning much of it into new fuel.
Spent-fuel pools, NRC's Burnell said, must be built to withstand the strongest earthquake at their site and are therefore as robust as any structures at a reactor.
"These factors preclude the need for specific containment structures for the pools," he said.
The Union of Concerned Scientists' Lochbaum says the federal government should require spent fuel rods to be stored in dry casks. He said it could take a terrorist attack or other catastrophe to expose the danger of keeping so much spent fuel at the plants to get policymakers to act.
"Why don't we do it now," he said, "and skip the step where a bunch of Americans get killed?"