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:And, cue shitstorm.. (Score:3, Interesting)
Also, if one wishes to scare greenies half to death: http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2012/ [nrc.gov]
Re:Three Mile Island is STILL open?!?!?! (Score:5, Interesting)
Why not? You might be surprised to hear that the Chernobyl power station operated until 2000, 16 years after the well known incident.
Fukishima may not do so well. Losing a single reactor, as the US and USSR did, may be seen as bad luck. Losing three of them is an embarassment.
Re:And, cue shitstorm.. (Score:5, Interesting)
It doesn't sound like a graceful shutdown. We'll have to wait for the NRC event report tomorrow. A reactor cooling pump trip would typically initiate a reactor protection trip (scram). The steam generators would cool the primary by sending steam to the condenser steam dumps. Instead there was a loud noise which indicates that steam was being vented to the atmosphere via the atmospheric steam dumps. This implies that the main steam stops (isolation valves to the turbines) shut. Potential causes for that would be excessive cooldown (an interlock), loss of the condenser vacuum, or a secondary equipment fault. None of these is normal.
I'm guessing that it was probably an electrical fault. A reactor cooling pump trip and secondary pumps could be powered from the same electrical buses since they are not considered safeguards equipment. The other possibility is that the operators didn't control the cooldown properly, or there was an I&C fault that tripped an interlock for the main steam isolation valves.
Disclaimer: I'm familiar with Westinghouse PWRs, but not the Babcock & Wilcox PWRs. So take what I say with a grain of salt.
Re:And, cue shitstorm.. (Score:5, Interesting)
Oh for fucks sake. There are event classifications if shit goes really wrong. Since they didn't even declare an Unusual Event (lowest of four classifications), things are under control. It appears that there may have been complications during the trip, but there is no emergency. And for your information, if there is an emergency the plant has to declare it within 15 minutes and inform state and local authorities within another 15 minutes. The people who make these decisions are licensed by the NRC and can be held personally responsible. They are also legally protected from any type of retaliation for taking action based on safety concerns. They aren't going to cover it up for three reasons: 1) their families live nearby, 2) the legal ramifications are severe, and 3) they could easily get another job at any other plant in the country (~2000 workers of their level of training in an industry that wants 3000 or 4000).
Re:And, cue shitstorm.. (Score:5, Interesting)
A "graceful" emergency shutdown of a large thermal power station unit is actually bloody noisy as the steam goes into the blow down vessel/s.
Also any water that touches the turbines doesn't actually go into the reactor, it goes through heat exchangers where the working fluid of the reactor is on the other side.
Disclaimer: I'm familiar with the turbine side (fairly universal amoong all thermal power stations of the same size) but in my case the boilers were all coal fired. There are many similarities to the point where one of my co-workers was a Russian turbine engineer with a lot of nuke experience (and some scary stories).
Re:Three Mile Island is STILL open?!?!?! (Score:3, Interesting)
Re:And, cue shitstorm.. (Score:5, Interesting)
ozmanjursi didn't post any fact and yes I dispute their claims. The nuclear industry in the US has proven to be safe, they promptly report even minor incidents, and to the best of my knowledge have never lied about conditions at their plants or the scope of an event. What happened in other countries has no bearing on what happens in the US until there is evidence to the contrary.
As osmifra points out, the fossil fuel power supply industry (mining up through the power plants themselves) do have a long history of raping the natural resources, not providing safe working conditions for their workers (miners), being horrible polluters, and having massive lobbying arms to make sure that any regulations that do get passed to curb these things have no teeth to actually stop them. Nuclear power, on the other hand, is very tightly regulated (see lobbying power of the fossil power as a big part of that) and does none of those things.
Re:And, cue shitstorm.. (Score:2, Interesting)
This would be news if we read that... A coolant pumps failed and the reactor safey system did not respond as it should have.
Let's put this in perspective.
As a reactor operator, I have personally caused an automatic rapid reactor shutdown (called a reactor SCRAM in US Navy nucelar power terms) myself from an invalid coolant pump combination [note 1].
I'm not sure what TMI uses for setpoints but in general...
A reactor safety system compares running coolant pumps to measured power output. For a given pump combination, you can run at a certain power level. When the Power:Flow ratio exceeds a setpoint, the protection system will immediately take action. If a pump fails and you are above your power limit for the new lower setpoint... bam, protection system kicks in. No harm, no foul. That's what it does and it did it.
Getting off topic but my story anyway..
Note 1
In my case, the pump did not fail, I failed. I am not the only one that has done this and it happens a lot. We were running some test drills that put the plant into an abnormal but perfectly acceptable coolant pump combination (one pump in each loop running in fast). This was after we had lost a turbine generator. Everything was fine until we started losing the other turbine generator which was not planned. In the protection system we had, when you change a coolant pumps speed, you go through a condition for a fraction of a second where the pump is considered "off" by the protection system and it actually is because it's wired to prevent both fast and slow speed windings from being powered at the same time. It compared power:flow and it scrammed. I shifted pumps too fast based on the conditions I had seen and what I expected to happen next. In my mind I assumed we were about to have a complete loss of flow if I did nothing as that other electrical turbine went away. Frequency was starting to flucuate and I took action. At the same time, they were restoring vaccuum to that turbine and it never actually went away. Maybe my unloading gave it enouhg time to reocver, maybe not. The whole situation from doing good and stable to the shit hitting the fan and a total reactor shutdown was about 10 seconds. Given the overall situation of events, nothing happened to me even though I technically caused the protective action because I may have potentially saved a worse condition of no flow which would have taken a much longer time to recover from if I did nothing.
Re:And, cue shitstorm.. (Score:2, Interesting)
The NRC Event Report:
As far as your note on condenser steam dumps, it is true they aren't rated at full load. For a reactor trip that isn't a problem since only decay heat (6% at the time of trip and decreasing afterwards) is need to be removed. In a trip the condenser steam dumps would reduce the reactor coolant system temperature to the shutdown band. This report really doesn't explain the loud noise. Why there would be a venting of steam for a turbine bypass valve failure is unknown. If they wanted to isolate it they could have shut the main steam stops. But they claim they are cooling via condenser steam dumps. As far as NRC event reports, this one is unimpressive and doesn't explain what it needed to do. I expect there will be a followup report clarifying to the NRC what operator actions were taken and how they vented steam.
Been there.