All three reactors at the Browns Ferry nuclear power plant in Alabama are in automatic shutdown after external power was cut to the plant. The powerful storms and tornadoes that swept the region yesterday, killing more than 250 people, downed much of the local transmission network, causing large blackouts. The Tennessee Valley Authority, which operates the plant, said in a statement today that: “Wednesday will go down in history as one of the worst outbreaks of tornadoes in a single day in American history.”
<img alt=“BrownsFerry” src="http://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Browns_ferry_NPP.jpg/754px-Browns_ferry_NPP.jpg " width=“300” " />
The Browns Ferry plant
According to an incident report submitted to the US Nuclear Regulatory Commission last night, an emergency was declared at the plant following a loss of external power at 16:35 CDT. Backup diesel generators kicked into action to keep the reactors’ cooling systems operational, and although some power has been restored to the plant since, the backup generators will continue to operate until full power is restored, according to updates on the TVA website. The reactors at Browns Ferry are of a similar design to those at Fukushima-Daichii.
Nuclear power plants have multiple incoming power lines, so that if one or more should fail external power remains available. A total loss of external power at a nuclear power plant, as seems to have happened at the Browns Ferry nuclear power plant, is “not very common”, says George Felgate, managing director of the World Association of Nuclear Operators (WANO)
Although the backup systems appear to have worked well on this occasion, the incident, coming on the heels of the Fukushima disaster, again highlights the threat to nuclear power plants from extreme natural hazards
– one has to ask how the Browns Ferry plant might have otherwise fared had it taken a direct hit from a tornado like the one which hit nearby Tuscaloosa yesterday – see on the BBC’s website for one of the several stupefying videos of that mile-wide tornado.
Relatively few people live in the immediate vicinity of the Browns Ferry plant, according to the map I published last week in Nature estimating the sizes of populations around nuclear power plants – 170,000 people within 30 kms (red circle in screenshot below), and 950,000 within 75kms (green circle). Some 16 million live within 300 kms, which includes the cities of Atlanta, Nashville and Memphis. The Sequoyah and Watts Bar nuclear power plants, located just to the North East — see screenshot — have not reported major problems following the storms.
<img alt=“BrownsFerry.jpg” src=“http://blogs.nature.com/news/thegreatbeyond/BrownsFerry.jpg” width=“550” " />
Update 19:00 CEST
TVA has just reported that:
"Units 3 and 2 at TVA’s Browns Ferry Nuclear Plant achieved “cold shutdown” Thursday at 2:43 a.m. CDT and 5:45 a.m. CDT, respectively. “Cold shutdown” is achieved when the reactor coolant system temperature is cooled to 212 degrees Fahrenheit or less. Unit 1 is being cooled."
(They are probably there for reactor units 3 & 2, though the update may have it’s definition slightly off — according to the US NRC, cold shutdown, is “the term used to define a reactor coolant system at atmospheric pressure and at a temperature below 200 degrees Fahrenheit following a reactor cooldown.”)