Three Mile Island Shuts Down After Pump Failure 247
SchrodingerZ writes "The nuclear power station on Three Mile Island in Pennsylvania shut down abruptly this afternoon. Its shutdown was caused when one of four coolant pumps for a reactor failed to work. 'The Unit 1 reactor shut off automatically about 2:20 p.m., the plant's owner, Exelon Corporation, reported. There is no danger to the public, but the release of steam in the process created "a loud noise heard by nearby residents," the company said.' If radiation was released into the environment, it is so low that it thus far has not been detected. The plant is a 825-megawatt pressurized water reactor, supplying power to around 800,000 homes, thought there has been no loss of electrical service. Three Mile Island was the site of a partial nuclear meltdown in 1979. The Unit 2 reactor has not been reactivated since."
Re:No redundancy (Score:5, Informative)
They ARE there for redundancy. For safety reasons, a reactor must not be operated without adequate redundancy. So, one of the redundant pumps failed and the system shut down in an orderly manner. That is necessary since it takes just a wee bit longer to swap in a cold spare pump than it does for a disk in a RAID.
It would be technically possible to run the reactor on 3 pumps but safety would be compromised.
The best way to know a pump will run is to have it running. That's why they keep all 4 running under normal conditions.
Re:And, cue shitstorm.. (Score:3, Informative)
Um, no. This is how these things are supposed to fail.
Re:No redundancy (Score:1, Informative)
Reactors run with 'inoperable' components all the time. Primary Reactor Coolant Pumps [frbiz.com] aren't one of them. They circulate core coolant in high volumes and they literally cost a fortune. When a PRCP trips you SCRAM, cool the core and figure out the problem. No fucking around. When you've figured it out the chairman of the NRC and the CEO of your power company is briefed.
There are four on that particular reactor, btw. All four must be 100% for the reactor to be allowed to operate.
I would love to be there once during a SCRAM. When a PORV on a B&W PWR lifts at full power the noise is heard for miles. A primal howl of super heated steam blowing out of the reactor. Every mope in earshot gets reminded of exactly what it is that makes that air conditioner spin.
The valve in question is that same one that stuck open leading to a Loss Of Coolant Accident in '79. It can only be actuated like 40 times. Nuclear reactors defy everyday experience; it's best if you don't indulge too much guesswork.
Re:And, cue shitstorm.. (Score:5, Informative)
Of course it's not graceful but a shutdown as a result of equipment failure never is. Steam venting isn't graceful, but then neither is a SCRAM.
I work in the process industry and the only time a shutdown is ever graceful is through carefully planned and usually long duration operator actions. Even then some processes they just get it down to a stage where there will be minimal damage and then hit the trip button and hope nothing breaks.
The key thing here is what shutdown the process was a safety system which prevented a hazardous event from occurring, rather than hazardous event occurring and causing the shutdown. Compared to that this event really can be considered quite graceful.
Re:And, cue shitstorm.. (Score:4, Informative)
"Three Mile Island is still shutdown Thursday night. Around 220 Thursday afternoon, people who live near the nuclear power plant heard a loud noise, saw steam and then the plant automatically shut down.
This is the second time that this has happened in the past month."
http://www.whptv.com/news/local/story/UPDATE-3-Thursdays-TMI-shutdown-is-the-second-in/_Z1vYirDt0ybASp0FZhmUw.cspx [whptv.com]
"The Nuclear Regulatory Commission said Thursday that it was satisfied with Exelon’s repairs following a reactor shut-down at Three Mile Island on Aug. 22.
The NRC said a small leak in the reactor coolant system was caused by “micro-cracks” in a diaphragm in a pressurized heater bundle within the containment barrier. The cracked diaphragm was made of alloy 600; it was replaced with one made of stainless steel, and the unit was powered back up."
No doubt the saga will continue.
Re:And, cue shitstorm.. (Score:5, Informative)
This is a very accurate reply with one exception. Generally, the condenser can't support the steam output of the steam generators (they're normally rated around 10-25% of full load). Most plants in the US will steam dump to atmosphere because it's easier and doesn't put unnecessary strain on the equipment.
Plus, dumping to atmosphere has the added benefit is that the whole plant staff knows immediately that they are staying late.
Source: I am an I&C engineer that has worked on many US and European units.
Re:And, cue shitstorm.. (Score:5, Informative)
"Basically, when you add the costs of decomissioning and waste storage, they become pretty expensive. For the tax payer, of course."
Actually no. US and most other Western power reactor operators pay into funds for decommissioning their reactors and also for waste disposal on a kWhr basis. The US rate for waste disposal is 0.25 cents/kWhr which goes to the US government as it is in charge of all high-level nuclear waste since it is seen as a security risk. The current fund total is about 36 billion dollars IIRC. It's the taxpayer that has to deal with coal-slurry lagoons, mercury and other nasties in the exhaust stack, the buildup of CO2 in the atmosphere etc. Legislative attempts to cut down such releases under the EPA and such are a "war on coal" according to, surprise suprise, the coal-mining and coal-burning industry.
As for nuclear power costs in the US, fuel costs are about 0.5 cents/kWhr and operations (running the plant, refurbishing the generators, landscaping the area etc.) are about a cent/kWhr. The killer cost is construction which is all up-front and expensive. It means that once a nuclear power station is up and running it starts paying off the 30 or 40 year financial instrument it took to build it and the owners really want to keep it running 24/7/365 to pay the capital and interest accruing.
Re:And, cue shitstorm.. (Score:5, Informative)
It's called spinning reserve. Mostly turbines running at idle and hydro units that are river flow limited on generation anyhow. The hydro units in particular are not wasting any energy waiting to be called on. That said they are limited on ramp rate as putting a 'wall of water' down most rivers is not allowed (for good reasons; dangerous, erosive. Also strands fish when it stops). The exception there is when one reservoir cascades directly into another, those can more or less ramp as fast as the equipment will allow (which is pretty fast).
Also note: the system just lets the voltage drop (browns out) while the 'ready reserve' units spin up. 120 VAC is purely nominal. Talk to someone that designs 120VAC power supplies. They should function down to about 95V IIRC. This is by design.
Also also note: most transmission areas are both importing and exporting at any given time. They can always just cut their exports and shift a part of the issue to their neighbors. Increasing imports isn't likely to happen in the middle of the day. The lines were likely running at max capacity to begin with.