How long will an unattended power plant run?

Factual Questions
1

Watching the new Dawn of the Dead remake over the weekend a question occurred to me. If you were to take a typical modern power station and remove (or kill, or turn into zombies) the entire operating crew, how long would the unattended power station keep providing power to the grid?

I imagine it’ll have a lot to do with the type of power station. A coal, gas, or oil burning plant will run out of fuel if nothing else. What about a hydro or wind power plant - will they keep running indefinitely until some vital part breaks down? In a nuclear plant, how long is it likely to be until something critical breaks, and are the automatic controls in a nuclear plant smart enough to safely shut down the core before it melts down?

2

You know, as soon as I saw the thread title, I knew this question was somehow realted to zombies. It looks like I’m not the only one who is mentally preparing for a zombie hoard.

3

I used to work in a coal fired plant, so I can answer that one for you. Coal plants typically have several sources from which they can get their coal (trains, river barges, and trucks, for example) so that if say the truckers all go on strike, the plant can still run. The coal from all of these sources is stored in big piles, usually sorted by the type of coal (there’s a big difference in sulphur content, for example). Once you get the coal into the plant, it’s all pretty much automated from there, but the trick is you have to get the coal into the plant in the first place. Where I worked, this was done by a guy on a bulldozer, who went merrily around the coal piles and pushed stuff onto the conveyors. Without him being out there, the plant is going to shut down fairly quickly.

The coal goes into crushers, and from there conveyors take it into the boilers. Once it has been burned, the ash is taken by conveyors out into silos where it cools and eventually is removed by trucks. At the first sign of trouble (probably when the crushers run out of coal to process) the automated systems will probably trip the generators. I’d be surprised if the plant would be up for more than a day.

4

Oh, one more thing. Most plants on the eastern side of the US are coal fired plants. Gas and other plants don’t add up to much. There are very few nuclear plants, but the nuclear plants typically have two or three times the power output of a single coal fired plant. Once the coal plants go down, the nuclear plants won’t be able to handle the load and you’ll end up with a cascade type failure like what we saw in the blackout last summer.

5

If you were talking about the relatively small place I worked (15MW electricity+15MW heat extraction CHPS power plant) then it could work for quite some time.

Usually any size power station is connected to the grid, and a large amount of the economic viability is tied to the price per unit of energy that the grid needs to keep consumers supplied - the greater the demand the higher the price, generally speaking(apologies to Californians :slight_smile: )

The result is that power stations are often only partly run for particular parts of a day and there is usually not much need for them to run continuously for extended periods of perhaps several weeks.

This means that the fuel feed system need not be designed to operate unattended which would be costly for the kind of machinery needed to ensure fully automatic operation.

At the place I worked, we oftentimes did not run connected to the grid distribution system, and the grid price of power was nearly always significantly more than we could produce for ourselves, especially as we were able to utilise the heat byproduct which makes it much more economic compared to traditional coal fired stations which had no use for the surplus heat(in most cases).

The result was that we could run for long periods without supervision, our engines run on natural gas, with a squirt of diesel fuel required for the bang.

Our only limit would either be the amount of diesel in the tanks, which were pretty large, several hundred tons in each of them, or maybe the amount of lubricatiing oil required.

These engines use up lots of lubricating oil, and they lose it literally by the ton.

I don’t remember the rate of usage, but once a certain oil level was reached then the engines would shut down automatically. We would never actually let this happen except as part of a engine safety shutdown excercise when we would simulate low oil levels by diddling around with the oil level switch actuator arm(float switch to you!)

Such a plant could run for a week with no trouble my guess is probably for some time longer than that, most of the time we would shut down in the night when the grid price of electricity tends to fall below our break even price.

6

I can’t say much about civilian nuclear power, but I can assure you that in a typical Navy steam plant (conventional or nuclear), there are plenty of parameters that are not automatically maintained. In cases where a specific operating point is desired (e.g. a specific pressure or temperature), it is often easier to allow it to slowly increase/decrease over time and make an adjustment every once in a while rather than attempt to get the valves and such set “just so” so that everything is in harmony.
In addition, there are several odd tanks that need to have stuff added to them from time to time.

You would probably have some alarm condition within the first day – perhaps something as simple as high salinity in the feedwater or as nasty as loss of lube oil to the main engines. Some of these conditions will automatically shut down the plant.

On the nuclear side, all should be OK for as long as the steam plant runs. Once the steam plant shuts down, you’re in deep doodoo. There may be no electricity available to run the reactor coolant pumps, and I’m not certain in the backup generator can come on line without human intervention. There may be breakers (huge breakers) that need to be thrown for the coolant pumps to switch over to the diesel generator.
Assuming the worst, no electricity available, the plant would most certainly shut down immediately. Indeed, as the control rods are maintained in their position by electromagnets, when power is cut they will slam down into the core.

Once the reactor shut down, there would probably be some unpleasant event caused by decay heat. Much of the fairly random crap that is created in nuclear fission is itself unstable and decays over time creating an amount of heat equal to a significant fraction of the operating power at time of shutdown. If you don’t remove this heat, you know what will happen.

The “Reactor Fill” system exists to keep the reactor cool at all costs, but I’m not certain how well this would perform with no living souls in the plant.

7

There is some variation in coal plant operations. I’ve been to about half of all the plants in the US, perhaps 2/3; it’s hard to tell.

Typically, once the coal is conveyed into the plants, the coal is stored in bunkers, which are large silos which sit near the top of the building. These, depending on their size and the unit output, hold about 8-24 hours of coal in them when filled. So in theory, one might expect from 8-24 hours of operation.

The problem is that coal plants are not steady-state closed-loop devices. All except the very most modern ones require relatively constant operator input to maintain load. I’ve spent woman-weeks in control rooms, and have seen some plants essentially require an operator response every 2-3 minutes all day long. The best one I was ever at could go perhaps 2-4 hours between required operator input, but it definitely is an outlier.

I’ll hazard most coal plants would die within 4-8 hours, through one shutdown mechanism or another.

In the US, coal accounts for roughly 55% of net generation as of this year. Gas perhaps 22% (no reference nearby right now).

Natural gas turbines can run for days with no operator input, potentially a week or more, although they rarely do and always have operators present. Gas boilers can do the same, but typically they need tweaking of the valves and controls in the steam side, so they might have problems in a day or two. However, there are not many gas boiler plants.

There are almost no oil power plants in the US; they are more common elsewhere.

I won’t speak for nuclear plants.

8

This thread might be useful to ya…

I’m the last man on Earth…how long till the power grid fails?

9

I get my electricity from Hoover Dam. Are there any reliable estimates on how long that sort of power plant would last if everybody turned into zombies?

10

I worked in the petrochemical industry for many years. Operated and later was responsible for many large gas fired turbines, steam turbines, large combustion engines… none of that equipment consumed lubricating oil.
Engines, turbines require lubricating oil… this oil is circulated with a pump at the lubrication oil reservoir through filters, coolers and then to the bearings of the equipment and then back to the oil reservoir. If there is “usage” it would indicate a problem with the equipments bearings, seals or a leak which is very** abnormal and uncommon. **

All large equipment have low oil pressure shutdown protection… the low reservoir level alarms are for warning, not shutdown.

11

The reason these particular engines use plenty of oil, is that on such large units there is a constant leakage from pipeworks, past rocker box covers and the like.

When you have five of them running then this loss seems to be significant but as a percentage of lub oil circulating it is very small.

When that oil leaks out, it ends up in the collection tray and due to all the contaminants, it is no longer fit as lubrication oil.

This is collected, stored in a tank, and periodically the tank is emptied into a tanker which take it away and recycles it.

Actually there are two level switches in the lub oil tanks, one as a waring which allows an operator time to transfer more oil inot the tank from the much larger reservoir tanks, or in extremis oil can be moved from the tank of one generator to another.
The other float switch is a shutdown, and yes there are also lub oil pressure warnings and shutdowns too.

It is quite normal for there to be a constant leakage from these engines, ask anyone about Ruston diesels and they will confirm this.

12

[unrelated tangent]
It seems that a “main engine low lube oil” alarm was the most pressing situation one could encounter in my Navy days since that was the only one that merited its own effing loud siren in the engineroom. Even such necessities as radiation alarms or air particulate detectors (for airborne radioactivity) were handled by more mundane buzzers.
[/unrelated tangent]

From my steam plant experience, I’d say that loss of lube oil through leakage wouldn’t be a dominating factor – something else would bring the plant down first.

Oh yeah… I never stated in my other post how long I thought it would last. Grid effects aside, I’d give it a day. With outside interference (grid), probably only a couple of hours.

13

I also knew this was a zombie-related thread. Good to know that when there’s no more room in hell that I’ll have some like-minded company at the mall! (Monroeville for me, personally. :wink: )

Anyway, I was thinking that in a zombie type emergency that power stations might actually be a place that would still be manned, and possibly be turned into fortifications. Assuming that civil authorities had time to react, a power plant would be guarded and maintained to help in civil affairs (police, fire, military, etc.) and then just good old-fashioned survival. I could easily see state/local police along with army personnel going there first to make sure the plant and its operators were safe. As the disaster spread, the staff and its protectors might think they have a pretty good place to ride out the emergency in addition to whatever sense of civic duty they might have.

Of course, wanting to find friends and loved ones might encourage a lot of them to desert, and securing a food supply as well as an ongoing fuel source would also pose problems, but hey… We saw what four people did with some guns, a handful of trucks, a chopper and a lot of guts (pun intended) back in '78, didn’t we? People holed up in a power plant might inadvertantly provide power for the mallrats of the zombie apocalypse, no? Could anybody more knowledgeable about power plants speak to the usefullness of such an installation during this admittedly unlikely situation?

EZ

14

I think EZ touched on something that many, perhaps non Zombie fans forgot. Namely, that security at power-plants is pretty tight to begin with. I’m pretty sure that most, if not all, are surrounded by high fences topped with barbed-wire. In the event of a zombie insurrection, Police and Military would most definitely bolster said security, and likely ferry food in to the staff.

Which opens a completely different can of worms, about how easily society could fortify itself against zombies… That is to say, at least 40% of society would likely be able to lock itself in, and survive a considerable time.

15

If everybody turned into zombies then I would suspect that the demand for power would decrease dramatically whihc would produce an “overgen” situation, i.e. you have all these power plants pushing electricity onto the grid, yet no one is taking the power off. I would think it would not take long for the grid to trip and fail in that case

16

  1. I live in British Columbia, Canada. Here, our power is all hydroelectric (we export the excess south). I suspect that the dams could keep running until either the waterflow changed too much (reservior level change without associated gate opening/closing), or there was some sort of mechanical failure.

  2. Zombies, IIRC, are UNDEAD creatures that would continue to wander around under their own motive power. If you turned the crew complement of a power station into zombies, I suspect it wouldn’t be long until one of them interfered with something critical.

17

I can speak from extensive personal experience that power plant security, outside of nuclear facilities, still varies widely. The security levels I’ve seen just in the last year range from complete car sweeps and photo ID, coupled with continuous escort - to walk on up, chat with the guard, and walk on in. In fact, I do about that at power plants where I am known.

Some rural plants have limited fencing and barriers. One plant I went to, the operators took down a large section of fence to encourage the deer to graze on the property - so they could shoot them for food. :eek:

18

Please tell me this isn’t the Wolfcreek plant in Kansas.

19

Ditto, and since I just watched th original movie, I was going to ask this question.

20

Heh. No, it was two States away from here.

Someday, many years in the future, I’ll have to talk about the power plant in the middle of nowhere that was going to be used for a Militia Headquarters by the Staff when the “Black Helicopters” came to get them. At least, that’s what the staff told me when I was there and asking about the purpose of some odd “fortifications” that they had made. But now is not the time.