4
$\begingroup$

Here is the question: "Following an immediate, irreversible collapse of the power grid and the medium-term (few decades) disappearance of humanity, would would happen to nuclear power plants?"

An alternate question is the same as the question above, but the power plant's staff don't disappear.

For the plant itself, assume it's this one: Prairie Island Nuclear Plant in Minnesota. This may seem extremely specific, but it's relevant if you know the context.

The context isn't necessary, but if you want to know it, here it is:

All humans and human-created structures on mainland continents disappear. All islands are spared from this fate (being defined as separated from the mainland by a natural body of water, so inland islands count). That's why the power plant is so specific.

Improve this question
$\endgroup$
11
  • $\begingroup$ To Ash's point about spent fuel: does a 14-foot tube of manufactured alloy, which contains multiple pellets of painstakingly refined material, count as a "human-created structure" for purposes of your apocalypse? If yes, then it seems safe to assume that all the nuclear material on the mainland, spent or otherwise, would disappear along with our gymnasia, aquaria, planetaria, et cetera. $\endgroup$
    – Tom
    Commented Jun 1 at 21:56
  • $\begingroup$ @Tom It looks like nothing in the plant counts as a human-created structure, since it's on an island. Otherwise, I would wonder what happens when something disappears: does it magically vanish, or get broken so it doesn't work? Radioactive materials would still be very dangerous if disassembled. $\endgroup$
    – Michael Foster
    Commented Jun 2 at 1:15
  • 1
    $\begingroup$ @MichaelFoster I'm asking whether the spent nuclear fuel in the affected areas would disappear along with the containment structures that house the spent fuel. Because it appears to be the case that a nuclear fuel rod is actually a device in its own right. A fuel rod is less like post-consumer motor oil and more like an iPod. If all the vending machines in Oregon disappear, I'd expect fuel rods in OR to disappear too. But it's OP's apocalypse, so I'm asking. Apologies if my first comment was unclear. $\endgroup$
    – Tom
    Commented Jun 2 at 1:30
  • 1
    $\begingroup$ Spent nuclear would absolutely disappear $\endgroup$
    – Baudshaw
    Commented Jun 2 at 2:27
  • $\begingroup$ What does "disappear" mean, then? If they simply vanish, does the earth have slightly less mass? If not, where do the radioactive atoms go? $\endgroup$
    – Michael Foster
    Commented Jun 2 at 13:25

3 Answers 3

Reset to default
7
$\begingroup$

Most power plants, nuclear and otherwise, are going to automatically go into shutdown once the grid stops drawing power. The biggest issue at nuclear plants is then one of the spent fuel, which if you've removing the structures it's stored in is going to immediately combust on contact with the air and kill everything for miles around, unless it is removed with them.

Prairie Island still being staffed will be safe from this immediate issue so it's all about keeping the pool topped off, and component failure in the pumps that move coolant around the site is the biggest threat.

Edit because AlexP makes a good point; if Prairie Island is allowed to go into full shutdown then the coolant pumps will be reliant on backup generators with finite fuel reserves, when that runs out the pool starts to dry out and then starts to burn.

Improve this answer
$\endgroup$
8
  • $\begingroup$ This may be far-fetched, but how long can a power plant last shut down? If there’s nobody around, will it eventually become inoperable? $\endgroup$
    – Baudshaw
    Commented Jun 1 at 23:45
  • 3
    $\begingroup$ @Baudshaw: Until the fuel runs out for the emergency diesel generators running the cooling pumps. After that, you don't want to be around. $\endgroup$
    – AlexP
    Commented Jun 2 at 0:09
  • $\begingroup$ And that diesel fuel will last for only 7 days before it runs out and... meltdown $\endgroup$
    – SurpriseDog
    Commented Jun 2 at 0:55
  • 1
    $\begingroup$ @SurpriseDog The reactor itself should be in cold shutdown by the time the diesel runs dry so the core should be safe from anything that doesn't rupture the contaminant vessel. The spent fuel pool on the other hand will boil down to the top of the rods in the space of a few hours and since spent fuel is Pyrophoric the pool will then explode into flames. In theory staff on site can keep the plant online to keep the pumps running but I'd be pouring cement and then Lead as fast as possible. $\endgroup$
    – Ash
    Commented Jun 2 at 3:00
  • 1
    $\begingroup$ @user51614 For backup purposes, solar+batteries is most likely treated identically to batteries. You can't rely on solar to be working on any given day, so they would not design a failsafe system that is dependent on it. Backups are typically a more predictable source of energy. $\endgroup$
    – Cort Ammon
    Commented Jun 5 at 5:49
2
$\begingroup$

It's going to depend on details about the safety systems at the plant. I'm no expert on nuclear plant engineering so I'll yield if someone who is chimes in here. But in the US, at least, nuclear plants have built in safety system so that they will automatically shut down if anything dangerous happens.

If the staff were all killed in the plague that wiped out humanity or whatever, then odds are SOMETHING would go wrong before too long, as there's nobody maintaining all the complex systems, and the power plant would shut down.

If the staff were still there, they could probably keep it running for a while. Until they ran out of spare parts and supplies. How long would that take? Depends on their stocks. A few months would be plausible. 100 years? Probably not.

In the US, politicians have been arguing what to do about nuclear waste for decades, so in the meantime nuclear plants have to store their waste on site. So if the staff are still around, adding some spent fuel rods to the repository would probably not be a big deal.

Improve this answer
$\endgroup$
3
  • $\begingroup$ US nuclear plants will shutdown as soon as the grid collapses, they are built that way as a saftey precausion. $\endgroup$
    – John
    Commented Jun 2 at 16:53
  • $\begingroup$ Suppose the plant does shut down, but the operators know what's going on and wish to bring the plant up again. I'm curious how difficult it'd be to defeat/trick the safeguards such that the plant can be bootstrapped from the diesel generators, then keep itself powered. I know some deadtime is required for short-lived decay products/poisons to themselves decay, but would it be possible to bring back up before generator fuel ran out? $\endgroup$
    – user51614
    Commented Jun 2 at 19:48
  • $\begingroup$ @user51614 That’s not just dependent on the generator fuel supply, but also the amount of power required for what amounts to a cold start. Circumventing the safeguards is easy enough though if you can get the required supplies, you just need to make an absurdly large electric heating element that can draw enough power to keep things above the minimum operational threshold (plus a bit extra as a safety margin). $\endgroup$
    – Austin Hemmelgarn
    Commented Jun 2 at 21:56
-2
$\begingroup$

No need to wonder, we have a real world example. Fukushima is what happens when a nuclear plant is cut off from all power.

Improve this answer
$\endgroup$
12
  • $\begingroup$ No thats what happens when a poorly build massively outdated plant is cut off at the same time its hit with a magnitude 9 earthquake. There is a reason no one builds reactors like that anymore. $\endgroup$
    – John
    Commented Jun 6 at 0:31
  • $\begingroup$ @John The main damage was because the cooling failed. The reactor will still produce 3% power when the cooling is lost. $\endgroup$
    – Loren Pechtel
    Commented Jun 6 at 1:41
  • $\begingroup$ @LorenPechtel Saying that the main damage was "because the cooling failed" makes it sound like the main damage was from a meltdown; rather, it was explosions caused by a buildup of hydrogen gas, which comes from the high temperatures and contact with steam and the zirconium cladding that holds the fuel. The reason I make the distinction is that, since the Three Mile Island incident, the NRC requires US power plants to have systems in place to mitigate any buildup of hydrogen that might come from a loss of cooling accident. $\endgroup$
    – Amocito
    Commented Jun 6 at 11:58
  • $\begingroup$ @Amocito And those systems will work without power?? $\endgroup$
    – Loren Pechtel
    Commented Jun 6 at 14:19
  • $\begingroup$ I mean, yes. Just a passive catalyst bed and a battery that can produce a spark would be a significant improvement. $\endgroup$
    – Amocito
    Commented Jun 6 at 17:23

Not the answer you're looking for? Browse other questions tagged .