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Scenario: Deadly virus wiped out 80 - 90% world population and it did it pretty quickly (in 2 months)

Although it is plausible that among these 10 - 20% of survivors will be people who actually know how to run nuclear power plant, it's safe to assume that they will have different tasks to solve now.

Now, I did read several apocalypse scenario questions here. And it seems that it is wide consensus, that should the nuclear power plants remain unattended for longer period of time, they will simply overheat and cause major damage to their surroundings.

I know that power plants are mainly run by computers. Also, the nuclear power plants have several backup power on and off-site to provide emergency power to help cool down.

So, In case of no natural disaster, will unattended nuclear power plant cause any damage to its surroundings?

Please try validate your claims by references.

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    $\begingroup$ Is there something stopping the nuclear operators from shutting down the plants before everyone dies? Two months is a long enough time for that. $\endgroup$
    – Lacklub
    Commented Mar 14, 2016 at 12:34
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    $\begingroup$ @Jim2B is exactly right. Nuclear fuel is made from low-enriched uranium, which, in normal operations in a power plant, is fissioning as fast as it can already. Atomic bombs require high-enriched uranium, (or more commonly, plutonium,) and even then they need extremely precise explosive triggers to set them off. This means it's quite impossible for a nuclear reactor to turn into a mushroom cloud. They can have other types of accidents, of course, but an atomic explosion is not one of them. $\endgroup$
    – Mason Wheeler
    Commented Mar 14, 2016 at 17:35
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    $\begingroup$ It's never the fuel in the reactor that you need to worry about, it's the highly radioactive stuff in post-processing baths that will heat up and mess up your day... $\endgroup$
    – user3652621
    Commented Mar 14, 2016 at 18:24
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    $\begingroup$ Thorium salt reactors literally can't melt down if designed and built properly, but the idea got mothballed after initial proof-of-concept by anti-nuke hysteria, ironically enough. Some reactors would probably leak due to exigencies... Whether those are caused by idiots trying to exploit them improperly, subtle defects, or disasters. That wouldn't do as much damage as you might think, though. Scale, you see. $\endgroup$
    – The Nate
    Commented Mar 14, 2016 at 19:55
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    $\begingroup$ @Lacklub: you can shut down the chain reaction, but you cannot shut down the ongoing decay of the fission products; without cooling, those will cause a meltdown which can start the chain reaction again. $\endgroup$
    – Michael Borgwardt
    Commented Mar 15, 2016 at 13:03

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No, probably.

Here's why:

Nuclear power plants will be unlikely to go into a meltdown scenario in the event of operators' absence. After several days, most will shut themselves down if they have not received maintenance. However it is plausible that a lack of operators combined with some hitherto undiagnosed problem with the cooling cycle or systems could begin a series of events that lead to a meltdown.

Nuclear power plants are already some of the most failure-redundant systems we have. Such events as mass strikes, earthquakes, power surges are all planned for as a matter of course. A properly-designed nuclear plant would be much less likely to explode without human contact than some other things in cities such as

  • Gas works
  • Coal/Gas power plants
  • Sewage treatment centers
  • Oil refineries

Even if there is a runaway heating without humans present, there are several redundant cooling systems that can replace each other. Computers can dump the control rods if a large meltdown starts to occur, and even if the core burns though the container, it will be caught in a 'core-catcher'—a structure designed to stop radiation from escaping in the event of an accident.

However, in the unlikely case that damage does occur, what can we expect? Well. A nuclear reactor will not go off like an atomic bomb, because the fuel is not in a pressure container. The most likely scenario is that a runaway reaction would cause the fuel to melt through the bottom of its container like a thermite charge, and drop onto the floor slowly sizzling away down into the concrete below. large fires would be set in the immediate vicinity by the intense heat, and localised explosions would throw radioactive debris around, which could be moved several hundred kilometers by the winds to affect a long but thin area with radioactivity. However, this would mostly be unnoticeable apart from in the nearest few km.

Source(s)

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    $\begingroup$ Decent answer, but see Fukushima. While the circumstances differ (natural disaster vs. lack of manpower), part of the problem was that much of the redundancy was defeated by concurrent failures with local infrastructure (plausible in a manpower scenario as well). Also, the effects from just that one incident have been felt globally (certainly far more than "the nearest few km"!), so you might want to consider revising the impact portion of your answer. Finally, atomic bombs are certainly not pressure containers, either! :-) $\endgroup$
    – type_outcast
    Commented Mar 14, 2016 at 12:12
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    $\begingroup$ In terms of atomic bomb being a pressure container the idea is to keep the fuel together long enough to get a sizable explosion rather than just a small explosion that throws the fuel away in all directions. As a rebuttal to your statement of distance of effects, I would ask do you have any mention of severe life-threatening radiation more than a few km from an accident? Even in fields around fukishima there was few effects other than higher than usual radiation levels in milk, but in a pinch that milk wouldn't kill you, just make you slightly more vulnerable to cancer. $\endgroup$
    – Rugnir
    Commented Mar 14, 2016 at 12:34
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    $\begingroup$ As far as the 'atomic bomb' thing goes, it's not just pressure - weapons-grade fuel is much, much more pure than the stuff used in nuclear power plants, and an atomic bomb is actually a very carefully designed piece of equipment that will fail to explode if it has even a little damage - even weapons-grade fuel does not explode easily. Put simply, a nuclear power plant will not explode like a bomb, ever. The worst thing it can do is leak into the groundwater (which is what happened at Fukushima). $\endgroup$
    – IndigoFenix
    Commented Mar 14, 2016 at 12:45
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    $\begingroup$ @Lacklub makes an important distinction as well; whenever you hear of explosions associated with nuclear reactors, it's always in reference to comparatively minor, conventional (non-nuclear) explosions caused by secondary fires, steam pressure, etc. Your answer is correct in that a nuclear reactor is never going to blow up like a nuclear bomb. $\endgroup$
    – type_outcast
    Commented Mar 14, 2016 at 13:34
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    $\begingroup$ @type_outcast: Incorrect to say that effects from Fukushima have been felt globally, at least if you discount mass hysteria produced by news media, which of course wouldn't exist in an apocalypse scenario. Even with Chernobyl, beyond those few kilometers it's hard to tease out effects from background data without sophisticated statistical analysis. $\endgroup$
    – jamesqf
    Commented Mar 14, 2016 at 18:27
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Short-term, it's probably safer if they don't shutdown. When the generator no longer produces electric power, the cooling of the residual nuclear reactions depends on power coming from the grid - if the grid is down, the cooling fails and when the backup generators run out of fuel, you may get a steam explosion. This doesn't necessarily mean a release of radiation, and it definitely doesn't mean a nuclear explosion (that's just popular pseudoscience - nuclear power plants simply can't "go nuke").

However, in your scenario, most people are already dead. That means that even for those places that will get affected by a radiation release, the remaining people are going to have plenty of space to live on. Don't forget that the more area you "poison", the lower the radioactivity at any given place - worst case scenario, the site of the plant itself and its nearby surroundings might be dangerous, but most land already has plenty of natural sources of radioactivity that are stronger. Just avoid possibly contaminated water (which may be tricky, since you need a lot of water to run a power plant, so they tend to be close to big-ish rivers), and you'll be mostly fine. Life is actually quite resistant to radioactivity - you may get an overall increase in occurence of cancer and similar issues for a while, but nothing too major. I mean, we're talking relatively to 80-90% people outright dying basically overnight - you should really concern yourself with all the dead bodies everywhere, rather than a bit of nuclear fallout, maybe.

But let me stress again that there's not going to be a nuclear explosion. There will be very little to no direct damage to the surroundings. All we're talking about here is a (potential) release of radiation and radioactive substances. It's actually very hard to make a nuclear bomb - and nuclear power plant designers have pretty much the opposite design goals.

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The short of it, YES.

Both the radiation and poisonousness of the materials encased in these facilities will long survive their containers and especially the cooling systems.

Today maintenance is a big cost factor sometimes requiring these facilities to shut-down for a while. If you dive into incidence records even so there are many many small problems per year.

Left unattended either in a 'safe' state or not will make for a poisoned area later on always. I expect few real blow-ups. I expect all of them to poison both the immediate environment and pretty far downwind and downstream while the containment structure degrades much much faster than the important nuclear degradation times, both for power plants and weapon systems.

Not to forget an entire ubiquitous industry carrying poisonous corrosive substances in truly BIG containers.

Examples? Cooling system problems caused both Three Mile Island and Chernobyl. Achilles heel, as heat will keep coming and to stop it from building you need the facility in working order. Fukushima is another example of the bad stuff surviving where the structure goes down. (Luckily) no examples of long unattended facilities. Yet.

Better carry a good, up-to-date map.

References:
https://en.wikipedia.org/wiki/List_of_nuclear_power_accidents_by_country
https://en.wikipedia.org/wiki/Three_Mile_Island_accident
http://www.nei.org/master-document-folder/backgrounders/fact-sheets/chernobyl-accident-and-its-consequences
https://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster
https://en.wikipedia.org/wiki/Kyshtym_disaster

http://www.forbes.com/sites/realspin/2014/02/27/the-dangerous-degradation-of-the-u-s-nuclear-arsenal/#3cc993be2104

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  • $\begingroup$ It's tricky, yeah. There's a lot of different things that can happen - everything might be contained (especially for certain designs), or there might be a steam explosion with or without a release of radioactivity. Some designs will also release pressure (and heat) long before a catastrophic failure, so leaking radioactivity to the surrounding environment as slowly as possible. Depending on what happens, everything might be contained on premises, or within a small area around the plant, or leak into water sources, or a more global (and less intense) release as in Chernobyl. $\endgroup$
    – Luaan
    Commented Mar 14, 2016 at 13:33
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    $\begingroup$ I down-voted this because — I am sorry to say — this is essentially a rehash of anti-nuclear fear mongering and does not reflect the scenarios that OP mentioned. Fukushima and TMI where sudden, unexpected losses of power where they failed to keep the core covered during the critical first week. That caused a meltdown which caused the fuel elements to fail. OP said - specifically - that this downfall will take place over at least two months and leave as much as 20% of the population. That is plenty of time and people to safe the plants and get them into so called "Cold Shutdown". $\endgroup$
    – MichaelK
    Commented Mar 14, 2016 at 18:54
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    $\begingroup$ You can look at Wikipedia's page on nuclear meltdowns for more information as well. I'm confident some reactors would go into meltdown globally, but I think it's a bit of a stretch to say they would always contaminate the environment. Today's reactors are engineered pretty well to meltdown "safely". Even in the event of the entire reactor crew being the first plague victims, the odds of major local devastation aren't that high. $\endgroup$
    – MichaelS
    Commented Mar 15, 2016 at 2:56
  • $\begingroup$ "poisonousness"... Try "toxicity." $\endgroup$
    – jpmc26
    Commented Mar 15, 2016 at 4:44
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    $\begingroup$ Very incorrect on the "poisonousness". Wildlife around Chernobyl is in reasonably good health. Radiation levels in the Fukushima exclusion zone are lower than natural background radiation in many areas of the world. Three Mile Island produced no additional risk of cancer to anyone in the area, to the limits of measurement. As far as poisonous substances go, you need to be very much more concerned about oil in all its forms, or any chemical plant dealing with chlorine. $\endgroup$
    – Graham
    Commented Mar 15, 2016 at 14:08
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Short-term will be fine if the automatic shutdown systems work. The very long-term is more of a problem. The reactors will have the usual pre-reprocessing mix of fuel and toxic waste products, wrapped in zirconium tubes, inside a steel vessel filled with coolant (usually water), in a steel and concrete structure.

All those materials are durable, but they are not forever. The weather always wins in the end, possibly hundreds of years in the future. And when it does things will start to leak slowly into the water table.

This is why waste reprocessing plans include treatments like "vitrification": enclosing it in glass. Because it remains potentially dangerous for tens of thousands of years. The design of the Waste Isolation Pilot Plant is interesting here, especially their PDF on how to design warning signs to last a hundred centuries: http://www.wipp.energy.gov/picsprog/articles/wipp%20exhibit%20message%20to%2012,000%20a_d.htm

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  • $\begingroup$ Agreed. We can quibble about how long it will take, but ultimately weathering (chemical and physical) will eat through all the protective systems and expose the core to the environment. It may be that the really "hot stuff" elements will have decayed by then but it will emit a higher level of radiation than background. You can handle the pure metal (Pu or U) without special precautions but Plutonium Oxide (the chemical) is highly toxic in small doses. Then again, very few reactors will have Pu in them (unless they are breeder reactors making the stuff). $\endgroup$
    – Jim2B
    Commented Mar 14, 2016 at 17:48
  • $\begingroup$ No... no no no no... the trope that plutonium is very toxic is nonsense. It falls on the same level as lead. Botulin — you know the stuff people inject into their faces as Boox? — is more than 1000 times as toxic. $\endgroup$
    – MichaelK
    Commented Mar 14, 2016 at 18:47
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    $\begingroup$ I down-voted this as well because that claim "It gets into the water-table and then it gets everywhere" is pretty much anti-nuclear nonsense. The time it will take for the plants to deteriorate that much is measured in centuries, if not millennia. That means the main contamination concerns - Cs-137 and Sr-90 - will have decayed to insignificance. What you are left with then are the actinides.... uranium, americium and plutonium. They have the fun chemical qualities of 1) being next to unsoluable in water and 2) having a fantastic affinity for dirt and rock. They will stay on the site. $\endgroup$
    – MichaelK
    Commented Mar 14, 2016 at 19:06
  • $\begingroup$ Eventually, the layers of concrete surrounding the core will erode. Eventually that shielding, now expised, will weather and errode. Eventually the waste will cease to be radioactive. Eventually, the wind will grind down the mountains we know. Eventually, new mountains will rise. Eventually the sun will die out. How long do these events take, though? You need to check yourself in your relative time scales. $\endgroup$
    – The Nate
    Commented Mar 14, 2016 at 19:45
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    $\begingroup$ I have checked myself into the relative time scales in this issue. Maybe you should too. The three major contamination concerns are I-131, Cs-137 and Sr-90. I-131 is gone in much less than 10 years. I can show you the math for it if you like. Cs-137 and Sr-90 both have a half-life of ~30 years. Which means that in 300 years the inventory is down to 1/1000 of the original. And then there is the matter of actually dispersing them. The actinides are so low in intensity and so immobile in the environment that they are of little concern in this apocalyptic scenario. Other things matter more. $\endgroup$
    – MichaelK
    Commented Mar 14, 2016 at 20:26
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In short: no.

EDIT 2: And the reason for this is how you phrase the question: "should the nuclear power plants remain unattended for longer period of time, they will simply overheat and cause major damage to their surroundings".

That(!) — the boldfaced part — does not happen, even in the very unlikely case of meltdowns. Not even in the worst case scenario of Chernobyl did we see that. Chernobyl is currently an unintentional wildlife preserve. Nature and wildlife are doing just fine, save for one part, known as the "Red Forest" where the fallout was so heavy it actually killed the vegetation. That however is a shining exception to the rule. The rest of the area — and Fukushima even more so — remain undamaged.

Then we can start to ponder what "damaged" actually means. "Damaged" as in "destroyed", "disfigured", "dysfunctional" or "disturbed"... no, that does not happen. But "damaged" as in "uninhabitable" or "economically unusable", that is different matter since humans are quick to abandon such areas.

However even with that definition you are going to have much bigger problems elsewhere. Chemical plants, refineries, oil wells, waste facilities and waste dumps, and — which is particularly alarming — dams of all sorts.... hydro power dams, tailings dams, coal ash dams and water regulation dams in particular. And the breakdown of clean water and sewage facilities is going to take a much higher toll on us.

And this is still while assuming that catastrophic failures do happen at under-staffed/abandoned nuclear power plants... a scenario which I am about to explain why it is not very likely at all.

The long answer: A nuclear power-plant can be shut down in seconds. Literally so. The issue then is residual decay and the heat that creates. And here is where it gets a bit curious and most people misunderstand.

Used nuclear fuel is not in a steady state where it remains at the same, let us call it "danger level", all the time and then - after a set time - click, it is suddenly turned off and stops being dangerous. Anti-nuclear campaigners aside, this is not how it works. Spent nuclear fuel starts off at insanely dangerous when you have just closed the reactor, to "worrisome" within a week, "handle with care" within a year, to "let's wrap this up and put it away" within 50 years... and then the rest of the time is pretty much just us being unnecessarily paranoid.

Spent nuclear fuel is like the embers of a recently extinguished campfire. At the beginning everything is crazy hot. But the hotter something is, the faster it cools off. So in the beginning, the activity of the fuel is intense. But the isotopes that cause this intense heat decay the fastest and therefore disappear quickly. The more time passes, only the less and less intense isotopes remain.

A quote from Blade Runner captures the essence of this:

"The light that burns twice as bright burns half as long"

The critical time where you need to keep actively cooling the fuel elements — in order that the residual heat will not melt them — is about one week. After that you need to keep them soaked but they will not boil away the water.

Within a month you can open up the reactor, take out the fuel elements and put them in the storage pool. Natural circulation is more than enough to keep the fuel elements nice and snug and safe to be around, as long as you top up the pool. Not because the water keeps them from melting but because water is an excellent radiation shield.

So with your scenario of 2 months until the apocalypse and 10-20% of the population remaning, nuclear power plants will have plenty of time to safe their fuel. If the worse comes to happen and some plants are left without the resources to safe them this thoroughly, they only need to keep the pumps going for a week, then leave it filled with water. The reactor pressure vessel and the containment will handle the rest.

In the long run we are then left with sites of spent fuel elements in pools, dry storage on the surface or in reactor vessels. Does that present radiation hazards?

Not really no. Sure there may be some local contamination from damaged fuel elements, but unless someone deliberately goes in there and starts lifting elements out of the pools and try to break them, the fuel cladding, the pools, the reactor vessels and containment buildings will keep the nasties — I-131, Cs-137 and Sr-90 in particular — inside. That is after all why they are there.

Sure... the "Irradiated Wasteland" trope is very popular and an effective plot generator. But if you are going for "reality check" here, then it will not happen with your scenario. If you desperately want to use it, the downfall will have to be much faster.

And — again — then your problems will be much larger elsewhere.

EDIT: In a pre-Fukushima scenario, then the disaster scenario where nuclear plants blow up left and right might have been slightly credible. Post-Fukushima however it becomes outright nonsense. Not only has Fukushima set the baseline for what a nuclear plant must be able to handle — a sudden and catastrophic loss of both cooling and emergency cooling — but other measures to mitigate the damage done by a meltdown have also been put into effect. Two of them are especially noteworthy...

  • Hydrogen re-combiners. Noted already during the Three Mile Island accident, accumulation of hydrogen in the containment is a major issue. That may end up exploding, as it did(!) during both TMI and Fukushima. The solution to this is to install passive hydrogen re-combiners. These are catalyzers in the ceiling that makes hydrogen combine with oxygen — in a non-explosive manner — and become water again.

  • Release filters/scrubbers. The other issue identified by TMI was the need to be able to vent containments in a controlled manner. This is actually rather simple to achieve, using scrubber pools and stone filters, which can absorb up to 99.9% of the substances of most concern.

Some counties had already after TMI started employing these countermeasures. Here is an example from Sweden, the Barsebäck Nuclear Power Plant. The cylindrical structure to the left of the two reactor blocks is the release filter, known as FILTRA.

enter image description here

So — again — the issue will not be with nuclear power plants because they are, compared to the rest of our civilization, ridiculously well prepared for disaster compared to some other problem areas.

A final note: as someone both invested in the debate on nuclear power and nuclear technology in fiction, I personally feel that it is long past due that we got over tripe such as The China Syndrome, or the TV series "24"...

"Eeep! Terrorists stole the McGuffin that controls all our nuclear power-plants and caused all 104 of them to start melting down, and we can't stop it unless we get the thingie back! Oh noes!! It happened in a few sites, and everyone around them are now dead!!!"

...because this trope is as silly and unrealistic as to assume a light drizzle over New York causes the city to disappear under six feet of water within a few hours. Nuclear tech in fiction has been assigned magical properties of the blackest sort for the past 60 years, and it is time we got over it and stopped using nuclear as a lazy plot-generating device in apocalyptic/dystopian fiction.

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    $\begingroup$ Side-note: The Blade Runner quote is from an ancient Chinese text, the Tao Te Ching, written by Lao Tzu somewhere around 6th century BC. If you're into that kind of thing. $\endgroup$
    – MichaelS
    Commented Mar 15, 2016 at 3:48
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    $\begingroup$ A nuclear power plant can not be shut down in seconds. It's power output can be reduced from say 1000MW to 50MW, but these 50MW still need cooling for years. $\endgroup$
    – Martin Schröder
    Commented Mar 16, 2016 at 0:06
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    $\begingroup$ @Martin Schröder: You are wrong. Read through the post. $\endgroup$
    – MichaelK
    Commented Mar 16, 2016 at 5:12
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Yes, they will

The critical event is loss of electrical power. After this event, diesel generators will start up (hopefully! there were examples of failure ...) and an automatic shutdown will be performed.

However: The ongoing nuclear decay in the fuel will demand further cooling. The diesel for the generators is limited (typically, for one day of operation). When the generators stop because of lack of fuel the nuclear power station will start to destroy itself.

Fukushima is an example of exactly this scenario: Power outage, diesel generators destroyed by the tsunami, self-destruction of the nuclear power plants. The human operator teams present at the site weren't able to stop it, because they could not restore the cooling in time.

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  • $\begingroup$ Your scenario hinges on the assumption that when the outbreak occurs — which OP says happens over 2 months from the start to having 10-20% survivors — electrical power suddenly and unexpectedly goes away. How did you come up with this Non Sequiteur? Also you assume that the generators cannot keep running until Cold Shutdown has been achieved. Where does that assumption come from? Essentially you are saying that there will be a sudden power loss and that no nuclear power station can deal with it. Those are some extremely pessimistic assumptions. $\endgroup$
    – MichaelK
    Commented Mar 15, 2016 at 15:03
  • $\begingroup$ @Michael Karnerfors: When some virus is killing 80% or more of the total population, the survivors will probably have different thoughts and plights (think of burying the dead a caring for the ill ones) than keeping the electrical network up and running and fuelling the diesel generators of the Nuclear power plants. It is only realistic that electrical power suddenly (maybe not unexpectedly) goes away. A nuclear power station can deal with power loss, but only for a certain time (a few days in the best case). $\endgroup$
    – Sir Cornflakes
    Commented Mar 15, 2016 at 15:10
  • $\begingroup$ Before Fukushima your scenario could have had some credibility. After Fukushima however, I am sorry but your scenario is outright unrealistic. Not only has emergency cooling been heavily scrutinized across the world, but mitigation measures for when a meltdown do(!) occur — such as hydrogen re-combiners and release filters — have also started to be utilized to much greater extents. Fukushima was a instant event that knocked out both cooling and emergency cooling in one stroke, which has set the baseline for post-Fukushima nuclear power. OP's scenario is not instant, but gradual. $\endgroup$
    – MichaelK
    Commented Mar 15, 2016 at 15:24
  • $\begingroup$ @Michael Karnerfors: Sorry, but your arguments may hold water for Nuclear Power stations desinged and built after the Fukushima accident. But most of the Nuclear Power stations all over the world are decades old and later mitigations don't bring them to a state that they can control themselves for approximately one month (which would be probably sufficient for a safe shutdown, but we don't have an actual demonstration that nothing goes wrong. Some passive systems at Fukushima did not work as designed.). $\endgroup$
    – Sir Cornflakes
    Commented Mar 15, 2016 at 15:34
  • $\begingroup$ Well I guess you better get on the horn then and inform all the nuclear regulatory authorities around the world — and their counterparts in the nuclear industry — that what they have been doing for the past five years is completely inadequate... for the sole reason that such an assumption makes for a convenient plot-generating device in a fictional world. I am sorry if this comes off as harsh but the trope of "My Nuclear Is Going Critical! The World IS DOOMED!!!" is ridiculous and totally over-used both in fiction and the public discourse since the 1970's. Get over it already. $\endgroup$
    – MichaelK
    Commented Mar 15, 2016 at 15:44
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Yes, the landscape is scattered with nuclear debris.

Most nuclear power plant designs will fail spectacularly with long lasting effect on the surrounding area.

The notion that nuclear reactors can run for extended periods of time without human intervention is simply not founded in reality.

Keeping a nuclear reaction from becoming critical is a feat within itself. It's balancing act of maintaining a state that is less than critical.

It will fail within a few months to a few years working under the assumption that it is not getting it's cooling water replenished which is entirely plausible.

Most nuclear power plants in the United States require are light water reactors or pressurized water reactors and require the circulation of water in order to stay within a 'steady state' of operational limits. The two failure scenarios that come into play under an unattended state both involve overheating and a change of state to critical. Other incidents occur on the timeline to critical such as hydrogen explosions but these events are essentially ancillary and aren't central to root cause.

Background

There are two types of nuclear reactors that can suffer from water related failure.

Failure Scenario - Lack of Water

Both water cooled reactor types suffer cataclysmic failure due to a lack of water. Some reactors can be more robust than others depending on the design. Many reactors derive their cooling water directly from their environment using ocean, lake or river water. These reactors are prone to having their water intake ducts clogged with debris thereby restricting the flow of cooling water to their segregated cooling systems. A lack of human intervention in these reactor types can lead to failure.

Cooling towers are used with reactors that are not in close proximity to ocean, river and lake water. Palo Verde Nuclear Power Plant in Arizona is one such example as was Three Mile Island.

In the event of an overheating reactor in the United States the Federal Government only requires a 30 day supply of cooling water. This cooling water, called a UHS (Ultimate Heat Sink) is a finite source and dissipates over time due to a number of reasons including evaporation, steam release and lack of re-circulation of primary cooling circuits due to radiation (the water for cooling is used one time only, in some cases, due to the amount of radiation contamination of the water)

As the water supply for cooling dwindles and water pressure decreases enough for flow rates to diminish beyond preset thresholds, the reactor undergoes an automatic shutdown called a SCRAM. A SCRAM event does not require electricity. Neutron absorbing control rods are held in place by electromagnets above the fissile pile and upon loss of electricity the electromagnets lose their magnetism and the rods are dropped into place bringing fission to a near halt in the core. These systems are automated and do not require human intervention, however, the continued decay heat of the fissile material continues to create issues with cooling and with a finite water supply, eventually, the reaction pile becomes exposed to air which cannot cool the fissile rods due to simple lack of density.

At this point water changes it's state to a gas and becomes steam. The heat increases further and more steam and pressure buildup in the chamber. Water becomes superheated and takes on properties and attributes more akin to an organic solvent. The pressure is so high within the chamber that it eventually prevents the water from boiling. This superheated water's hydrogen bonds are eventually broken and the chamber becomes filled with superheated highly pressurized hydrogen which eventually explodes due to combustion or the failure of the reactor pressure vessel to contain the extremely high pressures. This failure has been made famous by the hydrogen explosion at the Fukushima Daiichi reactor containment vessels in Japan due to the tsunami which did not damage the reactors, it damaged generators that prevented the circulation of water for the cooling systems.

The loss of integrity to the reaction chamber is the penultimate step to the catastrophe, all systems are essentially destroyed and now the fissile material can become molten and eventually melt through any concrete casements that require cooling features in order to prevent the molten nuclear pile from actually melting through it. Once this molten pile of nuclear material hit's moisture an explosion can occur sending nuclear debris into the atmosphere and contaminating the surround landscape with fallout. Mind you, this isn't a nuclear explosion it's just an explosion....but you see what the problem is here, it's called a meltdown.

Conclusion

Water inlets that use water from the environment (rivers, lakes, oceans) for secondary cooling systems require regular maintenance to prevent debris from clogging their inlets.

US located closed loop cooling reactors require only 30 days of backup cooling water.

Manual events such as steam or pressure release to prevent containment vessel explosions won't be occurring. There are disaster prevention events that require human intervention. See this IAEA root cause analysis document and salivate over it's plethora of manual events and whether staff followed procedure and a logical decision tree before, during and after a disaster.

I will close this scenario with, there's nuclear waste all over the place.

Other Failure Scenarios

There are hundreds of nuclear reactors across the world. Educational and research reactors are sprinkled across the topography of nations. Some are mercury and graphite cooled. Others use molten salts and even molten sodium. Fast reactors requires considerable human intervention and are used primarily in naval ship propulsion and in some cases the production of electricity in Russia. There are a plethora of scenarios where these reactor types can go bad in their own unique and beautiful ways.

All in all in this scenario that I put forth is feared. There are many other failure points that I have failed to mention. The list is too long and nuanced. With the framework you have presented.

Here is the official US Government Nuclear Reactor Regulation Response Plan to Pandemic Notice the emphasis on staff and staff skills and manning the facility to prevent failure. With all the dead engineers it will be difficult to staff these facilities, chaos will ensue attempting to man the reactors as they slowly begin to fail one by one.

So to answer your question again.

Yes, the landscape is scattered with nuclear debris.

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    $\begingroup$ The poster set the conditions that the apocalypse would happen over 2 months, with 10-20% surviving, not that everyone died within 2 minutes of the outbreak. Getting a reactor into so called "Cold Shutdown" takes at most 1 week, because the decay heat fades quickly. The 30 days of which you speak is ample margin to get into Cold Shutdown. After that there will not be meltdowns and hydrogen explosions. Your scenario is only ever viable if 1) people died instantly or 2) people figuratively stick their head in the sand and keep running the reactors at full speed, pretending as if all is well. $\endgroup$
    – MichaelK
    Commented Mar 15, 2016 at 8:48
  • $\begingroup$ This also suppose that there are no failsafe for unsupervised shutdown. $\endgroup$
    – MakorDal
    Commented Mar 15, 2016 at 14:49
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    $\begingroup$ This is incorrect in almost every way. The NRR Response Plan is for maintaining regular NRC operations (responding to license amendment requests from the plants, performing evaluations, etc) and has nothing to do with staffing of the plants. The cooling tower part is irrelevant because when the reactor is shutdown (which will happen automatically at some point) the cooling tower is not even used--it's just there to help extract more energy from steam and minimize impact on surface water temperature during operation. $\endgroup$
    – nvuono
    Commented Mar 15, 2016 at 20:01
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Damage, yes. Major damage, no.

We already have a perfect example of what will happen: Fukushima. That happened because the reactor was tripped and not getting any power to deal with the residual heat of the nuclear fuel.

The computer should be able to keep things running until something goes outside acceptable operating parameters. (This will inevitably happen as the fuel gets too contaminated with decay products even if nothing actually breaks.) The first reactors to fail will be ok--they will continue to draw power from the grid for cooling.

Eventually, however, too many will fail. One of the things that will cause a trip is the lack of two separate sources of power. As too many plants on the grid fail this will eventually cause a cascade that takes down every remaining nuclear plant. They'll fall back to local generators to keep the fuel cool--but eventually those run out of fuel. The rods boil their storage dry and you get a mess.

In practice the failure will happen pretty quickly as many of the external sources of power they rely on are fossil fueled--and those will shut down pretty quickly due to a lack of fuel.

All the safety improvements are based on buying enough time for the emergency crews to put things back together properly--if the emergency crews aren't coming they'll eventually fail.

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  • $\begingroup$ Fukushima is a bad example, because containment efforts started immediately and are ongoing five years later. Without human intervention, the failures of the cooling systems may have had much worse consequences in terms of radiation released. $\endgroup$
    – user2727
    Commented Apr 26, 2016 at 8:32
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Some misconceptions here. Most reactors would scram (automatic shutdown). But scram is not a fail safe. It's merely one safety measure. It's assumed humans step in and do the rest. The reason for this is time. It takes months if not years to bring a reactor that has been running back to a safe temperature. It's a full time management process, not a light bulb. That won't happen in a catastrophic situation so the core will start to heat up. Meltdown and breach of containment will occur within days followed by massive release of radiation. Some people talk about radiation like you can escape it being say 100kms away. No you can't. One reactor can spread deadly radiation over an enormous area. That's just one reactor! Seriously if people really knew how dangerous these things were there would be riots in the streets.

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    $\begingroup$ I am sorry but now you are speaking complete nonsense. Every year, LWRs are undergoing what is called "revision". It's like a yearly checkup where inspections, maintenance and — most importantly — defueling, refueling and rearranging the core is done. A quick revision is done in about a month. So by then the reactor has been turned off, gone into cold shutdown, been opened up, had its fuel elements manipulated (some of them moved to the storage pool), closed, then started up again. So you are making stuff up here, just because you want to portray nuclear power as evil black magic. Not cool. $\endgroup$
    – MichaelK
    Commented Apr 28, 2016 at 13:00
  • $\begingroup$ Having lived in europe during Chernobly, the guy has a point. And it wasn't the active rods in Fukishima, it was the cooling pools for the spent rods. The reactor did SCRAM. It wasn't the reactor that caused the explosion, it was the spent rods that were cooling down in the adjacent pool that caused the hydrogen buildup. $\endgroup$
    – James Aanderson
    Commented Dec 31, 2018 at 5:00
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The containment will be breached within hours, not hundreds of years. The decay heat will melt through the containment like it's butter. The containment is designed to contain the core under circumstances where it's being cooled. Nothing can contain that heat without active cooling. It's laughable what is being suggested here.

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