Tuesday, March 26, 2013

Fission Stories #133: Mayflies, and Squirrels, and Rats, …

Fission Stories #133: Mayflies, and Squirrels, and Rats, …:
Fukushima Daiichi recently received worldwide media attention when another power outage once again interrupted cooling of the water in the Unit4 spent fuel pool for several hours. The culprits in 2011 were an earthquake that knocked out the normal supply of electricity to the cooling system and a tsunami that disabled the backup power source. This time, a rat was the culprit. It chewed through the insulation on an electrical cable, exposing wires that shorted out and stopped the cooling system. It was also the rat’s final meal as the event also electrocuted the guilty party.
It was not the first time that wildlife mixed it up with nuclear power plants. On December 29, 2012, a pelican started an emergency diesel generator for the Unit 2 reactor at the Surry nuclear plant in Virginia. The pelican contacted an overheard power cable causing a short that de-energized one of the connections between the plant and its offsite electrical power grid. One of the emergency diesel generators automatically started in response to indications that electrical voltage inside the plant were decreasing. Both reactors at Surry were operating at 100 percent power at the time and continued operating throughout the power disruption.
Another bird caused the Fermi Unit 2 reactor in Michigan to automatically shut down on September 14, 2012, after it landed in the switchyard containing electrical cables connecting the plant to its offsite electrical power grid.
The operators manually shut down the Unit 1 reactor at the St. Lucie nuclear plant in Florida on August 22, 2011, after a squad flotilla bunch of jellyfish blocked the screens at the intake station, significantly reducing the flow of cooling water to the plant.
The perators manually shut down the Unit 2 reactor at the Diablo Canyon nuclear plant in California on October 21, 2008, after a bunch of jellyfish blocked the screens at the intake station, significantly reducing the flow of cooling water to the plant.
A snake slithering onto an overhead power cable on August 1, 2007, at the Hatch nuclear plant in Georgia caused a short that caught the wooden pole holding the cable on fire. The operators reduced the power level of the Unit 2 reactor about ten percent because the snake stopped the flow of electricity to some of the cooling towers. Workers declared an Unusual Event, the least severe of the NRC’s four emergency classifications, due to the fire that burned for over 10 minutes.
The operators manually shut down the Unit 2 reactor at the Point Beach nuclear plant in Wisconsin after “a large number of small forage fish” blocked the screens at the intake structure, significantly reducing the flow of cooling water to the plant.
The reactor at the Wolf Creek nuclear plant in Kansas automatically shut down from 100 percent power on September 4, 2000, after a squirrel caused an electrical short in the main power transformer.
The operators manually shut down the Unit 1 reactor at the St. Lucie nuclear plant in Florida on September 18, September 20, and September 22, 1993, after a bunch of jellyfish blocked the screens at the intake station, significantly reducing the flow of cooling water to the plant.
The LaCrosse nuclear plant in Wisconsin was disconnected from its offsite electrical power grid on July 16, 1984, when mayflies caused a power transformer to short out. Two emergency diesel generators automatically started to provide power to essential equipment at the plant.

Our Takeaway

When a single rat (make that an individual rat–its marital status is uncertain) can accidentally interrupt cooling of a spent fuel pool for hours, a lone squirrel and an individual bird can inadvertently knock out power supplies to a nuclear plant, and teams of jellyfish and forage fish can unintentionally disrupt cooling water flow to a nuclear plant to the extent that the plant must be shut down, one wonders about the havoc that an individual saboteur or a team of bad guys might be able to cause by malicious intent. Could well-trained and heavily armed attackers cause more devastation than a furry little squirrel or a pesky rat?
But on the other hand, nuclear power plant security seems adequate–no nuclear plant has ever been stolen. Watch out for an army of ants!

“Fission Stories” is a weekly feature by Dave Lochbaum. For more information on nuclear power safety, see the nuclear safety section of UCS’s website and our interactive map, the Nuclear Power Information Tracker.
Figure source: vetmed.duhs.duke.edu/GuidelinesforRatAnesthesia.html