• Eight hours in Japan's Fukushima Dai-ichi
• Four hours at local TVA plants
As the plume of radiation touches the U.S. Pacific coast from Japan's crippled and leaking nuclear reactors, nuclear officials here confirmed that battery-powered backups for most American reactors' cooling systems-including three local ones-provide only half the eight-hour safety net Japan had.
"The primary problem this plant [Fukushima] faced was the loss of power and the loss of backup power - having batteries that lasted eight hours and then having the clock run out," said Dave Lochbaum, director of the nuclear safety program at the Union for Concerned Scientists.
"In this country, most of our reactors are only designed with battery [backup] capacity for four hours, so we're more vulnerable for a situation where we lose primary power and the backup generators," said Lochbaum, a nuclear engineer who has worked both for TVA at Browns Ferry Nuclear Plant and for the U.S. Nuclear Regulatory Agency.
NRC spokesman Roger Hannah confirmed that federal regulations require only a four-hour battery backup to help cool reactor cores and spent fuel stored in pools. The power is necessary to keep cooling water circulating around the rods of uranium if both electric power and diesel generator backup power fail.
TVA spokesman Ray Golden confirmed that the utility's battery backups at is Sequoyah plant in Soddy-Daisy, Watts Bar in Spring City, Tenn., and Browns Ferry in Athens, Ala., are rated to last only four hours.
"It's possible they may last longer than that," he said, adding that the plants' diesel generator backups have a seven-day fuel supply.
Golden said the generators and batteries are routinely tested.
Just over a week ago, a 9.0 earthquake and tsunami threw reactors at the Fukushima Dai-ichi Nuclear Power Station into nuclear crisis. Americans living and working within 50 miles of the plant were ordered to evacuate.
On Friday, U.S. authorities confirmed that low levels of radiation had been detected in Sacramento, Calif. They said the very low detections of iodine-131 and cesium-137 - highly dangerous byproducts of reactor operation that in large amounts can cause cancer - would pose no danger to Californians' health.
Experts tracking the plume said it will continue to move eastward and could arrive in the New York region early this week.
TVA's Golden said contrasting the disaster in Japan with what could happen here is "is an apples and oranges comparison" because the region is unlikely to suffer a 9.0 earthquake and certainly not a tsunami.
But Lochbaum said the terrorist attacks of Sept. 11, 2001, taught America that kind of thinking is shortsighted.
"While most of our plants may not be vulnerable to the one-two punch of an earthquake and then a tsunami, many of our reactors are in a situation where earthquakes or hurricanes in the Gulf or ice storms in the Northeast can cause an extensive blackout that puts us in a very similar situation," he said.
After the terrorist attacks, the NRC required nuclear plant owners to stage more equipment at plant sites.
"One of things we learned from 9/11 was to be better prepared for tragedies than anyone in the area planned for," Lochbaum said.
NRC's Hannah said it's too soon to know whether NRC will change the battery backup rating requirement, but he's sure there will many "lessons learned" from the Japanese disaster.
But some utilities aren't waiting for NRC.
On Thursday, Atlanta-based Southern Co. said it supports President Barack Obama's call to the NRC for a safety review of all the country's nuclear power plants. Southern Co. operates six nuclear reactors in Georgia and Alabama.
Golden said TVA already is viewing the Japanese crisis as a game-changer and applying some of its lessons.
"We're watching this very closely, and we're right now - at each of our sites - taking any and all information from Japan and trying to see if it has application for our plants," he said.
"This will be just like Three Mile Island, and it will be a very important event in the industry. And it will bring about change," Golden said.