Nuclear reactor in Connecticut shut down due to excessive seawater temperatures


37-year old nuclear reactor, Unit 2 of The Milestone Nuclear Power Station in Connecticut, was shut down on Sunday, August 12, 2012 as seawater used in cooling the reactor soared to 76.7 degrees Fahrenheit (24.83 degrees Celsius). 880-megawatt reactor was shut down by Dominion Power who operates the facility. Under the reactor’s safety rules, the cooling water can be no higher than 75 degrees Fahrenheit.

“Temperatures this summer are the warmest we’ve had since operations began here at Millstone,’’ said a spokesman for Dominion, Ken Holt.

Unit 2 of Millstone Power Station has occasionally shut for maintenance or other issues, but in its history it has never gone down because of excessively warm water, Holt said on Monday. Dominion does not have an estimate of when the unit will restart, he added.

The plant’s first reactor, now retired, began operation in 1970. The plant’s third reactor was still running on Monday, but engineers were watching temperature trends carefully out of concern that it, too, might have to shut down.

The water from the sound is piped into the plant to absorb heat from pumps and other pieces of equipment. As the sound’s temperature inched upward this summer, Dominion Power received permission from the Nuclear Regulatory Commission to measure it at three locations instead of one and to calculate the average in the hope that it would be lower. That did not help on Sunday.

And higher water temperatures could lie ahead. The sound’s temperature usually does not peak until late August.

Eventually, engineers could change reactor’s intake pipe so it draws water from further below the surface, where temperatures are lower, Mr. Holt said. They could also sharpen their pencils and try to determine whether the plant can operate safely with cooling water above 75 degrees, but neither is a short-term project.

The Millstone Nuclear Power Station is the only nuclear power generation site in Connecticut. It is located at a former quarry (from which it takes its name) in Waterford. Of the three reactors built here, units two and three are still operating at a combined output rating of 2020 MWe.

Some of the previously recorded events on Millstone Nuclear Power Plant

April 17, 2005 – Millstone plant safely shut down without incident when a circuit board monitoring a steam pressure line short-circuited, which caused the board to malfunction and indicate an unsafe drop in pressure in the reactor’s steam system, when in reality there was no drop in steam pressure. The cause was attributed to “tin whiskers”. In response to this event, Millstone implemented a procedure to inspect for these whiskers at every refueling outage, or 18 months. David Lochbaum, a nuclear engineer with the Union of Concerned Scientists, while remaining critical of the processes leading to the discovery of the whiskers, praised Millstone for its handling of the situation.

February 26, 1996 – a leaking valve forced the shutdown of units 1 and 2. Multiple equipment failures were found.

July 7, 2009 – Millstone Unit 2 Reactor Trip and Shutdown Greater Than 72 Hours.

September, 2009 – Unit 2 shut down when an electrical storm caused power fluctuations. When workers tried to restart the unit, they discovered a small leak in the reactor coolant pump.

December 21, 2009 – Millstone Unit 3 Reactor Trip and Shutdown Greater Than 72 Hours.

September 9, 2011 – The Nuclear Regulatory Commission said Connecticut’s Millstone nuclear power plant shut down one of its two reactors to stop a water leak. Neil Sheehan, a spokesman for the federal agency, said yesterday the reactor in southeast Connecticut was shut down Saturday because the leak exceeded the plant’s specifications. He said there is no estimate when the reactor will return to service. The federal agency monitored the shutdown and plans to follow repair work to make sure it is done safely. When fully in service, Millstone generates nearly 2,100 megawatts, which it says is enough electricity to power 500,000 homes.

Extended Operating License of Unit 2 Expires July 31, 2035.

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