By Scott DiSavino
NEW YORK (Reuters) - The second-biggest nuclear power plant in the United States may be down for weeks after killer thunderstorms and tornadoes in Alabama knocked out power and automatically shut down the plant, avoiding a nuclear disaster, officials said on Thursday.
The backup power systems at the Browns Ferry nuclear plant in Alabama shut as designed on Wednesday, preventing a partial meltdown like the disaster last month in Japan that was also caused by a natural disaster.
In the wake of the Fukushima nuclear power plant accident, even relatively routine outages at the U.S. nuclear fleet are drawing greater scrutiny.
The three-reactor 3,274-megawatt Alabama plant, located along the Tennessee River about 170 miles north of the Alabama state capital of Montgomery, can power up to 2.6 million homes.
Its units are similar in design to those crippled by the earthquake and tsunami that hit the Fukushima plant.
"The systems at Browns Ferry did exactly what they were supposed to. This is not comparable to Fukushima because it wasn't the result of damage to the plant, rather the lines leaving the plant were cut," said Scott Brooks, spokesman at the U.S. Nuclear Regulatory Commission (NRC).
When Browns Ferry lost offsite power, the reactors automatically shut and emergency backup diesel generators kicked in to cool the nuclear fuel.
In Japan, the reactors also automatically shut when the plant lost offsite power due to the earthquake and the backup generators kicked in to cool the fuel, but at Fukushima, the diesel generators were wiped out by the tsunami, allowing the fuel to overheat and ultimately release radiation.
"The (Browns Ferry) reactors will remain shut until we have restored the reliability of the transmission system," said Ray Golden, spokesman for the Tennessee Valley Authority (TVA), which owns and operates the Alabama plant.
DAYS TO FIX LINES
The repairs to the U.S. reactor's transmission lines would take days and could possibly take weeks, Golden said, but the plant itself was undamaged.
"The plant can't produce power if that power doesn't have any place to go. So the system shut down automatically. TVA is in the process of restoring power as quickly as possible," the NRC's Brooks said.
The NRC is monitoring the plant amid heightened concern about the ability of nuclear plants to withstand natural disasters.
The tornadoes and thunderstorms left a trail of destruction across seven southern U.S. states on Wednesday, killing at least 220 people in southern states, officials said.
The storm knocked out power to about 300,000 homes and businesses, primarily in the northern parts of Alabama and Mississippi, TVA's Golden said.
In addition to the Browns Ferry nuclear power plant, the Tennessee Valley Authority operates several other facilities and provides power to about 150 municipal utilities, which distribute electricity to some 9 million people in seven states.
The federally-owned power generator said its two nuclear power plants in Tennessee -- 1,123 MW Watts Bar and 2,274 MWSequoyah -- were largely unaffected by the storm. Sequoyah continues to provide power to customers and Watts Bar was already shut for scheduled maintenance when the storm hit.
As of 6 a.m. EDT, the Tennessee Valley Authority had restored 12 large transmission lines but still had another 78 out of service, said another TVA spokesman, Scott Brooks.
ALL REACTORS COOL
By Thursday afternoon, the NRC said the TVA had cooled all three units at Browns Ferry to a safe temperature so that the water around the reactor's core will not boil away -- as happened at Japan's Fukushima.
Ken Clark, another spokesman at the NRC, said seven of the eight diesel generators at Browns Ferry were operating to keep the reactors cool and the plant also had some offsite power via the small 161 kilovolt Athens line. He noted that line was not big enough to allow the reactors to restart.
"No point in restarting the reactors until the main offsite power lines are restored because there would be no where to send the power," Clark said.
Clark said the plant had batteries to backup the diesel generators but could run on the diesels "indefinitely" since there was nothing blocking the pathways into the plant to replenish the diesel fuel.
(Reporting by Scott DiSavino; Editing by Marguerita Choy)