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Storms in US cause loss of external power at three nuclear reactors.

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

(Credit: Wikipedia/NRC)

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.”)

For full coverage of the Fukushima disaster, go to Nature’s news special. For a selection of our coverage in Japanese, see Nature Asia Pacific.

Comments

  1. Report this comment

    Steve said:

    15 minutes without offsite power requires unusual event notification. this does not mean the plant was without any power for 15 minutes. perhaps unit one is the unit that had a diesel out for maintenance and is therefore cooling down slower.

  2. Report this comment

    sb32511 said:

    geo, you are mistaken, just like your post at CBSNews, in that all power was never lost. The criteria for declaring the Unusual Event is the loss of off-site power for more than 15 minutes. The emergency diesels kicked in as designed to continue providing power after the loss of off-site power. No temperature or pressure excursions happened. As an FYI, the plants are designed to cope with the complete loss of A/C power, which did not happen here.

  3. Report this comment

    Ernest said:

    How on earth does a power plant not have electricity? If the external electric source goes out – and the equipment is undamaged – can’t they run off of internally generated electricity? This just seems absurd.

  4. Report this comment

    sb32511 said:

    The minimum power level at which a plant can operate is somewhere like 20x more than what it would consume. They just can’t operate at that low of power output.

  5. Report this comment

    Steve said:

    when the transmission lines cant accept the generated electricity from the station, the generator trips to protect itself and the main transformer, then the turbine trips to protect itself, then if reactor power is higher than about 50%, the reactor trips to protect itself. after the turbine trips power transfers from onsite supply to offsite, if it is available, otherwise the diesels carry the safety loads.

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    Scott said:

    The longest track and possibly most violent (exceptionally long and wide swaths of EF5 damage) tornado of the 27-28 April 2011 outbreak tracked about 5 miles to the east and south of Browns Ferry. It hit Tanner, producing high-end EF4 to near EF5 damage in that town, which was hit by an F5 in the 1974 Super Outbreak and another F5 a half hour later.

    Also, on 16 April 2011, a tornado touched down in the switchyard of the Surry Nuclear Power Plant in Virginia, which also cut its power, caused a reactor trip, and required an Unusual Event declaration. http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2011/20110420en.html#en46761

    In both cases, it seems that emergency shutdown and diesel generator backup worked as designed with no serious complications. As Fukushima Daichi demonstrates, a reactor building itself can be initially intact and a plant still be in a very serious situation. Other tornadoes passed through or near US nuclear plants causing emergencies in the past.

  7. Report this comment

    Garry Morgan said:

    The large majority of nuclear power plants cannot operate without incoming power. It is incoming power which is utilized to supply power to the coolant systems of the reactor and spent fuel cooling pools during normal operation. Once off site power is lost, the reactor must be scrammed and the emergency power generators provide power to the various cooling system pumps and spent fuel pools. If the diesel generators are lost then the backup batteries must be relied on to provide power to cool the reactor and spent fuel pools. Lose the battery backup – a Fukushima type event occurs. The Browns Ferry Alabama Nuclear Plant is of the same type as the Fukushima plant.

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