By Roberta Rampton and Ayesha Rascoe
WASHINGTON (Reuters) - One day after deadly tornadoes knocked out power to nuclear reactors in Alabama, the head of the U.S. nuclear safety regulator expressed concern whether backup batteries at sites across the United States have the staying power in a prolonged emergency.
The commission on Thursday was examining whether the 104 U.S. nuclear plants have enough emergency power in place to ensure that safety systems can keep running in extreme blackouts, like when an earthquake and tsunami shut down power to the Fukushima plant in Japan in March.
Senior staff at the Nuclear Regulatory Commission explained that plants have a series of strategies including diesel generators, emergency fuel supplies, back-up batteries and battery rechargers to keep plants going when power gets knocked out.
But commissioners questioned whether enough attention was being paid to the lifespan of batteries used in worst-case scenarios, which are designed to last at least four hours to give plants enough time to get longer-lasting back-ups in place.
"We have lots of examples where it takes longer than four hours to restore offsite power," said NRC Chairman Gregory Jaczko.
"Four hours doesn't seem to be a reasonable time to restore offsite power if you lost the diesel (generators) immediately," he said during the briefing with staff.
PLANT HIT BY TORNADOES
Violent storms in the south on Wednesday that knocked out power to the 3,274 megawatt Browns Ferry nuclear plant in Alabama were a reminder of the importance of the NRC's regulations about power loss, Jaczko said.
Tennessee Valley Authority, which operates the plant, said its reactions could be shut down for days and possibly weeks under the power transmission system in the region is restored.
Jackzo said the reactors' backup systems performed well.
"All of the available diesel generators started and loaded, and ultimately, the core cooling systems are operating normally. In addition, the spent fuel cooling is currently in service. All these plants are stable," Jaczko said.
FOCUS ON BATTERIES
The NRC is examining its rules and regulations in the wake of Japan's nuclear disaster, including rules designed to ensure ensure U.S. plants can withstand blackouts.
NRC rules require the batteries last at least four hours, which is at least twice the estimated amount of time required by plants to get generators restarted.
"To a layperson, when they come to you and say, 'Is it really only four hours that nuclear power plants have to cope with some sort of event of a long duration?' What do you say, if you were talking to a family member?" asked Kristine Svinicki, a Republican NRC commissioner, to senior staff.
An official with the NRC's office of nuclear reactor regulation said the four-hour coping time is the maximum time a plant can plan to rely on battery power.
"We have a high expectation that you restore either offsite power, or one of your emergency diesels, or an alternate (alternating current) power source" within that timeframe, Pat Hiland said.
JAPAN STILL NOT STABLE
The NRC's executive director for operations told commissioners Japanese officials are making progress on addressing safety and environmental issues at the Fukushima plant, but said the situation is not yet stable.
"I would say that the situation has definitely improved, but we're still in the accident mitigation phase," said Bill Borchardt.
"There's still many unanswered questions regarding the status of various pieces of equipment, the reactor vessel integrity, spent fuel pool," he said.
An NRC task force is slated to deliver a report on the safety of U.S. plants this summer, with a more detailed report expected in six months.
(Editing by Russell Blinch and Marguerita Choy)