The Tennessee Valley Authority has shut down its undamaged Browns Ferry nuclear power plant in northern Alabama, cooling its reactors after power transmission lines into the plant were knocked out by severe storms in the state.

All 3 units are offline at this point, said a TVA spokesman on Thursday. It has nothing to do with damage at the plant and has to do with the transmission lines.

The spokesman said power from diesel backup generators and a 161 kilovolt transmission line into the plant were operational and the three reactors at the plant were coooled to below 212 degrees. Power is needed to keep reactors cooled. The reactors' temperature level would be maintained until the reactors needed to be brought back online, he said.

He said TVA was working to restore work on the lines. No power generation is currently needed because the transmission lines are currently down, he said.

On Wednesday afternoon TVA declared an 'unusual event,' the lowest of four emergency levels used by the Nuclear Regulatory commission to classify emergencies.

TVA Chief Operating Officer Bill McCollum said Wednesday that all systems at the plant functioned as designed and normal procedures were being used to cool down the plant.

The plant's units combine to give it 3,274 megawatts of power.

The Brownsferry plant has the same design and age as the Fukushima Daiichi plant in Japan, which was damaged when a tsunami in the aftermath of a 9.0 magnitude earthquake knocked out power and water damaged emergency backup units.

Browns Ferry's nuclear reactors are of the Mark 1 type by General Electric, similar to those at Fukushima.

Preston D. Swafford, TVA's chief nuclear officer said on a March 26 tour of that plant that Browns Ferry was ready for a one-in-a-million-year flood, or however many zeroes you want to go out, according to the New York Times.

TVA - which serves 155 local power companies - said Wednesday that the weather had caused serious damage to the utility's transmission system in Alabama, Tennessee, Kentucky and Mississippi, reporting that 78 large transmission lines remain out of service as of 6 a.m. EDT., although 12 have been restored.