Unscheduled Shutdown at Limerick Nuclear Plant
NRC: Electrical fault in transformer was impetus for manual shutdown; plant operator says 'no threat' to public safety
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Last updated 9:48 p.m. Wednesday
The Unit 1 nuclear reactor at Exelon's Limerick Generating Station was shut down at 8:15 a.m. Wednesday following an electrical fault in a transformer, the Nuclear Regulatory Commission said in a statement sent to area media outlets.
The reactor was manually shut down from the power station's control room following the fault, according to the NRC.
"The NRC is closely monitoring the shutdown, with our Resident Inspectors assigned to the plant gathering information from the control room and sharing it with NRC staff. There do not appear to be any complications at this point. We will want to know more about Exelon’s root cause evaluation of what caused the event and about any and all corrective action," NRC spokesperson Neil Sheehan said.
The NRC has two inspectors permanently assigned to the facility.
Sheehan said Exelon had declared an "Unusual Event," which is the lowest of four levels of emergency classification used by the NRC.
An "electrical disturbance caused a loss of power to generator cooling equipment" at the plant, Exelon Nuclear spokesperson Dana Melia said in a statement.
"There is no threat to the health and safety of the public associated with this event," Melia said.
The company said the Unit 1 plant will remain offline until repairs, testing, and inspections are complete. The generating station's other power plant, Unit 2, continued to operate at full power.
Melia denied reports that there had been an explosion at the plant.
"It wasn't an explosion," Melia said, instead referring to the fault as an "electrical flash-out," comparable to a circuit breaker being tripped.
Sheehan said the failed transformer was in the building that also houses the plant's control room.
"The 13-kv (kilovolt) transformer that failed was located in the plant’s control structure, not the turbine building. The control structure in where the control room is housed but it usually also is location of electrical switchgear rooms, battery rooms and other equipment rooms. There was no impact on the control room from this event," Sheehan said via e-mail.
"There can be a loud noise when an electrical transformer experiences a failure. That may be what [the reports] are referring to," Sheehan said.
The plant, which is in the process of applying for license extensions that would keep it operating until 2049, experienced three unscheduled shutdowns between February and June of 2011.
John M. Baxter
1:22 pm on Wednesday, July 18, 2012
The original generators at Limerick had both hydrogen cooling of their rotors and isolated water cooling circuit cooling of their stators. Probably several pumps involved in doing the cooling. Too bad somethng failed on the hottest day of the year! That unit produces something like 1,200 MW these days which is well over 1.5 million horsepower. It's a triumph of engineering that we still have power!
Aric
2:27 pm on Wednesday, July 18, 2012
Digging around it appears a transformer exploded inside the "protected zone" of Unit 1.
http://enenews.com/explosion-inside-a-protected-area-at-u-s-reactor-says-local-official-no-impact-on-public-health-nrc
Tom Bartman
7:09 pm on Wednesday, July 18, 2012
Most likely a fault from a winding inside the transformer. Ideally, the systems monitoring the transformer would protect from this but with old technology (electromechanical relays), things like this happen. Since today's new technology is not rated for nuclear applications, we're stuck with old technology for protection and control. Regardless, the event was handled well and everything went as planned.
Aric
8:42 pm on Wednesday, July 18, 2012
Much as I hate Nuclear power, what really gets me is all the people getting bent out of shape in West Norriton Township about not being told why there was a helicopter with a searchlight out last night, yet it's crickets here in the article about Unit 1 of the local Nuclear Reactor going offline because of an explosion this morning. As if the guy who's running from cops in Only is more a danger than a possible nuclear meltdown 15 miles away.... (joking, kinda.)
Tom Bartman
11:17 pm on Wednesday, July 18, 2012
Aric - why do you hate nuclear power?
Aric
11:27 pm on Wednesday, July 18, 2012
@Tom- It's not so much that I hate it, as realize it's a contraption Rube Goldberg would fantasize about. Seriously.... the whole process revolves around creating poisons that will be around hundreds of thousands of years, to boil water, to make electricity, to run your air conditioning, to make up for the fact that we forgot how build self-cooling houses over the past hundred years.
But that's not my point... my point is that people in WNT are all up in arms because the police didn't tell them about a guy who hit a cop in Olney, yet are oblivious to the fact that we hit stage 1 of 4 stages of Nuclear Emergency 15 miles up the road. Which is the greater danger to your home and family? They guy who's fled through a half dozen jurisdictions and has every cop in the area looking for them, or the nuclear power plant up the road that just had an unscheduled shutdown? Having done more than a little research into TMI, I'm going with the latter.
Aric
11:30 pm on Wednesday, July 18, 2012
Don't get me wrong, I agree this is not really anything to worry about re: Limerick. Middle (end? I hope...) of a heat wave, not surprising a transformer let go. Yet people are overreacting to the thought that a single person might be hiding in their back yard, when there's a potential for much worse up the river that never makes the news.
Stephen Eickhoff
3:30 pm on Friday, July 20, 2012
Self-cooling houses? The closest we had to those in PA were the stone colonials the 17th and 18th century German and Dutch settlers built... and those required that you build them on top of a spring. Most people wouldn't really like having running water in their basement. Unless you want to live in a cave, a "self-cooling" house would still require energy to run a geothermally-coupled heat pump.
Aric
4:18 pm on Friday, July 20, 2012
Perhaps I should have been clearer, Stephen... What I meant by "self cooling" is designed-in architectural features to deal with the heat passively, like high ceilings, transoms over the windows to allow air flow, chimneys to draw the heat up and out while replacing the air with cooler air from the north side of the building, ceiling fans, etc. Our 1905 Dutch Colonial does ok in this regard, and we end up only running the A/C on the hottest days (maybe 2 weeks total). The 1859 Colonial I'm restoring (with its 19" thick stone walls) can pretty much go all summer with the inside never going above 80 if you manage the windows properly at night. Chances of doing that with new construction? Basically nil.
Tom Bartman
11:09 am on Thursday, July 19, 2012
I agree. What happened seems to be what is known as an arc-flash which occurs when transformer insulation fails. It is nothing new. The downstream relays see the fault and trip offline. It worked as planned. There is also misconception about how the power grid works. Our power comes from the grid of many many generation plants. When one goes offline, electricity still finds where load is needed.
Tom Bartman
6:09 pm on Thursday, July 19, 2012
The reactor will be offline for 'weeks to months'