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Reactor Shutdown Darkens South Florida
grassy_knoll asks, "So how fragile is the electrical grid, and just what technical problems could shut down five reactors?" "Five reactors at a nuclear power plant in Florida had gone down on Tuesday and two were now back online amid a massive power outage in the southern state, CNN reported. The report on the Turkey Point nuclear plant came as four million people had lost electricity in Miami and elsewhere in Florida, with traffic signals out and major delays on roads, authorities and media said."
Here is FPL's page on the Turkey Point reactor: About Turkey Point. Their site also has a News Releases page, which I'll be watching for updates whenever they get their PR department in gear.
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Uh.. Turkey Point has *2* reactors and 3 major fossil fuel generators (As well as several generators under 5 MWs).
Yup, just east of Panama City, Florida.
http://en.wikipedia.org/wiki/Springfield,_Florida
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God is everything science has yet to explain.
The power outage -- ie, some serious switch failures -- triggered the reactor shutdown. Nuclear reactors are great at supplying base load power but if all of a sudden the grid goes offline, they have nowhere to send that power and have to shut themselves down. (Power reactors don't do well with highly dynamic loads.)
It was not, as some posters seem to have misread even the summary, that the reactors went down first and caused the outage. Mind, once the reactors are down it takes longer to bring the whole grid back up, so in that sense it's contributory.
-- Alastair
Did anybody seem to notice that while yes, the nuclear plants shut down, so did the coal plants. Neither of of the plants had problems. It was a problem with the substation.http://money.cnn.com/news/newsfeeds/articles/djf500/200802261723DOWJONESDJONLINE000845_FORTUNE5.htm
Agreed. I found the NRC press release in about 2 seconds by simply going to their website. Perhaps people should 2 seconds of research before they begin jumping to conclusions about things.
http://www.nrc.gov/reading-rm/doc-collections/news/2008/08-037.html
I agree, using the word nuclear in this article was not necessary. The only 'story' about the nuclear plant is the safety system activated, disconnected them from the grid, and scrammed the reactor (shut it down), which just results in less electricity to go around when the grid reconnected. Nuclear reactors take a while to start up, and some models get poisoned quickly if they are shut down and can't be restarted for several days.
(NPR is running a story on it right now):
These plants were designed to shut down in case of a fall in the power reaching them from *other sources* (because they need, e.g., to run cooling pumps for a safe shutdown and can't count on their own power). I'm not sure why the outside power browned out, but it did, so these plants did what they were designed to do.
What would it take to trigger the automatic release of the control rods? An earth tremor above a pre-set limit, insufficient input of cooling water from rivers (or water that's too hot or too impure), a controller hitting the wrong switch, a software glitch, a glitch in a clock crystal screwing with timing calculations, a loose connector, a chip in an old-style spring-based socket catapulting itself into the air (which they had a nasty habit of doing), erronious control signals from other power stations, a downed power line on any segment with single points of failure, etc.
Of these, the vast majority apply to any power station - one line down not too long ago caused a blackout that covered three States and half of Canada. One line down between the east and west coasts about 14-15 years ago shut down large parts of the northwest USA for a couple of weeks. Cascading failures are inherent in the meta-stable mashup of networks that form the power grid. Too many SPFs, too little redundancy, too many communication glitches, too few contingency plans.
Personally, I think the grid needs to be massively redesigned, with far better (and more intelligent) signalling, far more redundancy at all levels and a huge upgrade on software and hardware (NT4 and Windows 3.11 are not acceptable to me for mission-critical systems - they're tried and tested, but they're not reliable and they're not secure).
Of course, this won't happen, massive cascading faults will continue to be reported on a regular basis, and people will continue to be surprised when they occur. Preventative maintenance on the scale needed to cure the system as a system is so expensive (even though it's one-off), the distributed costs of regular blackouts on even a gigantic scale look cheaper on the balace sheet, so an inefficient, decrepid, flawed power grid becomes the preferred option.
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It was due to a distribution line that failed. For those not familiar with how nuclear reactors work, two of the fission products of concern are I-135 and Xe-135. I-135 will decay into Xe-135 and Xe-135 is a very strong neutron poison (absorbs neutrons). During normal operations Xe-135 is produced from fission or I-135 decay and it is removed by neutron absorption of Xe-135 or by beta decay of Xe-135. If you are operating at high power and have a significant amount of Xe-135 in the core and you suddenly drop power the neutron flux that is removing a significant fraction of your Xe-135 from neutron absorption is gone. But the I-135 in the core still remains and more than compensate the reduction of Xe-135 from direct fission. The result is a Xe-135 spike that will overwhelm certain types of reactors forcing a shutdown and a waiting period for the Xe-135 to decay. For those familiar with the Chernobyl disaster, the reason that the control rods in that core were fully withdrawn was because they were trying to compensate for a xenon transient (since they were operating at high power before they dropped to low power for the test). The Turkey Point reactors don't suffer from the flaws that the RBMKs had, but they will still be shutdown due to xenon transients.
Actually, I believe they shutdown due to a safety issue. When they lose grid power for powering water cooling pumps etc, their standard response is to shutdown for safety reasons. Yes I know, a power generating plant that gets power off the grid, but consider if the plant is unable to drive a turbine to power its own pumps, where does it get the power from? Okay backup generators, but they can also fail. From what I hear the current dropped enough from the grid to cause them to need to shutdown the reactors. This is a good safety thing. The bad thing is the issues on the grid that caused this and other sites to shutdown generation.
And now, we return you to regular scheduled blackout... if this were an actual emergency, you would of killed the person sitting next to you.
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What I've heard on the radio so far (in Tallahassee, FL) is that the nuclear reactors have their coolant pumps connected to the grid so if the reactor ever had to be shut down the coolant would continue to flow, avoiding a meltdown. There was apparently a problem with the substation supplying (backup) power to the coolant pumps, and as a precaution the entire reactor shut down automatically.
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More information Here (pg 34) and here
The electrical grid is a really tricky system. You've got generators putting in energy at a bunch of points. And the whole thing is AC, which means that, if you look at any particular point, you see the voltage (and current) going in a sine wave. If you drive the system at the correct phase, you're supplying power; if you're slow by 1/120 second, you're turning twice your capacity into waste heat, and you start blowing up substations. Furthermore, since electricity moves at a finite speed along the wires, you can't just have a really good clock and have everybody agree; the difference in phase you need depends on the distance between the power plants along the wires. The solution is to have the power plant measure the phase of the lines they're on, and generate with a matching phase.
Now, if something goes wrong somewhere down the lines, the power plant may not be able to get a good read of the phase. At that point, you just shut down the power plant, shut down the substations (so there isn't customer load on the lines), get the switching stations fixed, start the power plant up again in phase, and reconnect the customers. It's only if the switching stations are really destroyed that they'd actually run a power plant for local customers disconnected from the national grid, and they'd have to shut it down again in order to rejoin the grid.
What happened today is actually how it's supposed to work in case of an equipment failure: a regional blackout, some time to repair the malfunctioning equipment or swap in replacements, and then restoring power. When the grid doesn't handle the failure correctly, power lines melt down and power company manholes and buildings blow up and service isn't restored for days to some customers.
A substation. Not the reactor. Then the reactor went offline because of the undervoltage condition caused by that power outage. Neutron-absorbers in the fuel had *nothing* to do with this.
It isn't that hard. You watch the phasing meters and tweak the generator speed until it's in phase with the grid, then close the breakers.
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The backup generators have backups. All critical systems have at least double redundancy, that's why nuke plants are so darn expensive to build.
Neutron-absorbers have something to do with minimum down times for nuke plants.
I'd have to guess the reactors generators were over-voltage due to lack of load and that triggered the shutdown. I can't imagine they ran the reactors control systems off the Miami substation.
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Long before then we will run out of money to pay to OPEC and China.
I prefer the "u" in honour as it seems to be missing these days.
Most everything's been covered here, but I'll put my two cents in as a Nuclear Engineer (albeit in PA). Nuclear power plants run all safety systems on offsite power. This is a perfectly understandable setup, because if something goes wrong and we need to scram the reactor, the safety systems need to keep running. At my plant, we have two completely separate backup diesel generators to supply power in the event of loss of offsite power, but shutdown is nevertheless the automatic response, both because the diesels won't run forever and because a sudden loss of load messes with a very delicate balance of turbine power, reactor power, and load. Nuclear power is a popular black sheep for these kinds of events because people are afraid of it, and the news media profits from sensationalist broadcasting. Whatever garners the greatest response, they'll run with it. As for the grid as a whole, it is not a Florida problem. The same issue came up with that massive northeast blackout in what was it, 2003? The whole system is ancient, but it's too expensive to completely overhaul it, not to mention people wouldn't stand for the loss of power as systems were replaced and/or updated. In terms of power distribution, there's a delicate balance as plants come on and offline and demand goes up and down. Any significant transients (like this undervoltage line) just causes a complete mess. This is a problem that's only going to get worse as power demands continue to rise, especially if we don't build enough plants to keep a healthy amount of excess capacity.
I'm in Miami and experienced the horrific even (playing tennis for 45 minutes because I could not log into wow). I spoke to my bud in FPL (ze power company) and he told me that a massive transmission cable went down by aligator alley (I75 stretch that crosses the everglades). This created some load issues and a plant (non nuke) had to shut down to protect itself. This in turn routed more power to the rest of the grid creating the same effect we saw in California and in the NE in the past. Turkey Point, the nuke, was merely one of the plants that shut down to protect itself. Only reason we are talking about that one and not the others is that talking about nuclear power is sexy.
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"the large and rapid build-up of additional Xenon reactivity load following a reactor trip can cause an extended (approximately 40 hours) reactor shutdown"
http://www.nuceng.ca/ep6p3/class/Module3D_XenonJun21.pdf
The fundamental thing that is missing is the amount of power being generated.
You have to cool the steam down somehow, normally it looses energy by turning the generators but if that is not the case the energy needs to go somewhere.
The steam is normally re-condensed and then reused in a closed or semi closed loop depending on whether there are cooling towers. There is no way that the
cooling capacity would be able to dissipate the full load and hence the need to rapidly shut-down. This is the same for coal and gas plants as well.
The Xenon is what prevents you from starting the reactor once the grid problem has been fixed. Thus while the reactors had nothing to do with the cause of the shutdown, they can't simply be restarted the moment the problem is gone, you have to wait for several hours or even a day. The time period depends a bit on the precise reactor type, and some can be safely restarted without waiting for Xenon to decay. I don't know about the specific reactors in question, so I can't tell if this was an issue or not.
This is the same for coal and gas plants as well.
This is the key point that the idiot with the +5 mods above is missing.
This shutdown has nothing to do with neutron poisoning, and everything to do with load loss, the same as any conventional power plant. Negative reactivity from 135Xe typically doesn't prevent restart for an hour or so, and as the news is reporting the reactors are running again they must have had then back on line fairly quickly.
And yes, I am a nuclear physicist, and my undergraduate education as an engineer included reactor design.
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LOL! I live in the Orlando area and we got the power back on after approx 40 min.. Slight chaos outside to say the least, people lose all their common sense when the traffic lights go out and start doing all kinds of smart things. Quite a few crumpled cars in the closest intersection.
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First off, There are not 5 nuclear reactors at turkey point. there are 5 units. units 1 and 2 are oil and natural gas(fossil) units 3 and 4 are nuclear and unit 5 is a gas turbine unit. The shutdown of the reactors DID NOT cause the blackout contrary to what the slashdot summary says. A failed switch and fire at an electrical substation outside Miami(read: not at the power plant) caused the grid to go into an imbalanced state at which time the plant experianced a loop(loss of offsite power) and did what they are supposed to do. There was no place for the power to go, so they shutdown to stop making it. All the power plants did what they were supposed to do. The fossils were presumably shut down. I'll find out more when I get to work. great, now i'm gonna be late.
Oh Crap, I'm an optimist.....
The AC had his facts in order. Even your quote backs him up. "The initiating event was a malfunctioning disconnect switch." The reactor shutdown was an (expected) response to the initiating event.
Fission products in the fuel have everything to do with why the plant was shut down. Operating nuclear plants run at a significant percentage of their capacity for reasons of economy. A sudden loss of load (as in the disconnect opening) results in the rapid rise in primary coolant temperature due to noplace for the energy to be dissipated. This will result in a reactor shutdown shortly after the load is lost (either by overtemperature or by turbine overspeed trip).
Heck, a sudden loss of turbine load can cause the turbine to overspeed, causing a turbine trip which in turn causes an automatic scram. Since every good discussion needs a car analogy, imagine driving up a steep hill and then knocking the transmission into neutral while keeping the accelerator mashed. RPM goes up, eh?
Even inserting control rods doesn't drop power fast enough to prevent heating up. After shutdown the fission products in the core continue to decay, releasing significant amounts of heat which must be dissipated.
That's what I love about slashdot... folks argue with experts without having a background to do so.
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Nope, no can do. Your decision, Judge, is final. Mouse soberly; choose wisely,
U.S. power reactors generally do not have any problems starting up after a shutdown due to a buildup of poisons (neutron absorbers) in the reactor. Yes, xenon-135, a strong absorber, increases after shutdown, peaking about 10-15 hours after the scram. It decays to zero in about 72 hours. No, the xenon transient is not the reason why the plant owners don't start the reactors back up immediately. They evaluate the cause of the shutdown and the response of plant systems and make any necessary repairs before entering the startup mode. This typically takes somewhere between 12 and 72 hours. Then you go into your startup procedures. The best response I've seen got the reactor back online within 20 hours (near the peak of the xenon-135 transient) and at full power about 24 hours after that.
I should note that the ability to overcome the xenon transient is dependent on the geometry and neutron moderator configuration of the reactor. There probably are some reactors out there that would not be able to start up immediately. A link further down the page indicates that this is the case for heavy water-moderated CANDU reactors, which use natural unenriched uranium. The 20-hour startup I mentioned above occurred at a boiling water reactor.
Cool... we posted almost the same answer within minutes of each other. My experience is as a reactor engineer at a BWR. We scrammed at noon, I got sent home to sleep for a while, and then came back in at 6 PM for startup. (We knew exactly what caused the scram, some turbine EHC problem that was fixed easily.) We started pulling rods pretty soon after shift turnover, and went critical about 1:00 AM (7 hours, vs. 2 hours from a cold-clean core)... pretty much nailed the predicted critical condition, too. Heatup went by pretty quick because we were still at 475 degrees. We were synchronized to the grid (around 12% power) by about 5 AM, and up-shifted recirc pumps (25% power) by about 9 AM. I turned over to another guy at about 10:00. If I remember right, we hit 100% power by about 8 PM the next day, so the whole startup took about 50 hours.
According to various reports, the outage began with equipment failure and the loss of a distribution substation. Unlike major transmission links, distribution substations feed local loads and are not a part of the transmission system critical to the movement of power between alternate sources. The loss of a distribution system results only in the loss of loads, not generating or transmission capacity.
Two things may have happened here. Neither bode well for the system's condition.
It is possible that, following a fault at the distribution substation, the primary protection relays failed to operate. There are (or should be) backup relays. But these typically take longer to operate and allow the fault transient to push the system into an unstable condition. This is bad design. System stability should be maintained even if one station's protection fails.
It is also possible that, in spite of the proper design of primary and backup protection, the regional grid is being run too to its stability limits. A fault condition properly considered in the system design which should not have caused stability problems did so because the system was being run beyond prescribed limits.
Both of these possibilities suggest that, in spite of the big midwest outage we had several years ago, lessons have not been learned.
Have gnu, will travel.
These and other questions lead me to believe that IPoAC is entirely VAPOR and has most likely not even been successfully implemented in the real world.
Sorry to burst your belief bubble...
Yes, and still they fail. We had a somwhat interesting event at one of our sites in Sweden, Forsmark: When a fault in the outbound net triggered a shutdown in a similiar way, a power spike at the internal system forced all of the backup generators down, stopping power to the pumps. Fortunately, they were able to be restarted manually.
There is some debate about whether we had a risk of meltdown (our reactors *do* have some shielding if that would happend), but still the lack of safety culture was heavily critizised, and the event was classed as INES-2, and is regarded the most serious in Sweden.
The Forsmark plant was seen as a "flagship" plant for modernity and safety; hosting many demonstration tours and such. Stil there seem to be some "Oops" event beacuse of complexity ...
Actually, nuclear plants ARE dependant on grid power for operations. It may seem odd that a plant generating many megawatts to a gigawatt of power needs an external supply, but it's a matter of safety. Were the plant to run exclusively on it's own power, a single malfunction could leave it in a state where it has no power for coolant pumps yet the reactor is at full power. So, if grid power to the plant drops, the reactor shuts down immediatly as a precaution.
The Chernobyl plant was carrying out an experiment to see how well it could shut down using energy from the inertia of it's own steam turbines in the event of a secondary cooling failure with no grid power. That wasn't a direct cause of the disaster.