What would happen to nuclear missiles left to rot post-apocalypse?

Question

A sudden cataclysm takes place. The human race is all but wiped away. And the nukes in their bunkers and silos are left to rot for 800 years before anyone finds a record of them. What has happened to them in that time?

Answer 1

Assuming that there was no interaction with human scavengers for the entire period of oblivion:

• The active material inside the core will have been altered, because of natural decay. Since nuclear powers felt the need to detonate some nuke to test the importance of this decay only after a few decades from the manufacturing of the warhead, I guess the problem is not negligible.
• The primary conventional explosive, where used, might have degraded to the point of not being properly functional anymore. Maybe not to the point of not exploding anymore, but surely to the point of not assuring the correct timing.
• The electronic controlling the device will probably be gone, due to oxidation, diffusion and radiation damage accumulated over 800 years.
• The casing of the warhead will also have undergone oxidation and weathering
• The propellant for the missile would have also long be gone, due to its instability

Answer 2

Even when still having critical mass, humans can't move or detonate it.

The mechanics require repair

These bombs will be in bad shape, after 800 years. Its metal parts will be a mix of preserved amounts of certain metals and a pile of rust. Fission bombs work mechanically: two parts of the bomb are to be merged, to reach critical mass. The merge requires explosive force, which is to be applied very accurately. The working of a fission bomb depends on valves and bearings with a very small friction. After 800 years, the parts cannot be clashed together anymore and with enough force.

Worst case..

A bomb could yield a dangerous situation and the place should be properly sealed after discovery. Now.. suppose the folks that find it have bad intent and have the basic means to repair mechanic. They are terrorists that want to deploy the bomb to do maximum harm, the condition of the weapon itself is not the only problem. Nuclear devices are heavy equipment and complicated stuff.

No knowledge will be the main issue

The repair will fail. If it has taken 800 years to essentially rediscover the bombs, there will be no record, no manual, no calibration procedures, no working missile.. a nuclear device weighing tons is not easily moved from a damaged silo.. and all knowledge to deploy the weapon will be lost.

Now suppose these terrorists can move the bomb from its silo, isolate the nuclear war head and drop it somewhere.. it will have become a "dirty bomb". It can render large areas uninhabitable for many years.. but there will be no nuclear explosion of any kind. Just a lot of mess.

Repair attempts, you'll always miss things

Now suppose.. see DarrelHofman's comment, there's an operation manual. Nice to have some extra info.. but a manual for direct deploy is in fact useless.. before deploy can happen, the repairs AND checkups need to be done. The device is in bad shape, after 800 years.

Electricity has to be switched on, sensors have to work.. timers, servo lock initiators.. when it was in use, the launch procedure provided all that, but the silo and missile are gone, you found a nuclear warhead. The repair document sais something like

connect A8-J7 to junction AB of the MSE-564 and repeat measurement for each barrel

No living soul knows what MSE-564 is supposed to measure. The other instruments and the drawings got lost. So you can't realign the cylinders properly, even if you have polished them again or whatever repair you did, you can't reproduce e.g. the cryo-shrink to mount the cylinder.

Answer 3

Material science of decay

Electronics

Within a few years, the batteries would fail. This isn't just lighting -- without that little CMOS battery, your computer loses its ability to keep track of time. After ten years, rebooting computer systems might become impossible.

Digital data storage will decay over a couple of decades. Hard drives and tapes will become riddled with errors caused by tiny electromagnetic fluctuation in the environment. CDs will de-laminate due to temperature shifts. They do have M-drive disks that can store information for millennia, so those should be fine, but the hardware to read them would fail long before that.

Electronic components are usually soldered together, which results in an unstable crystalline structure. The normal shifting of this structure over time can result in loss of connectivity between soldered components, even for periods of a couple of decades. This is why reflow soldering exists.

Chemistry

There are a lot of compounds that we build things out of that, all by themselves, fall apart over time. Pretty much anything with stored chemical energy is like this. This is why a canned food looses its nutritional value, even if perfectly stored. Explosives, batteries, and even some metals will just fall apart on its own over periods of years. Gasoline in gas tanks actually goes bad after about six months of sitting around.

Humidity

If the missile silo is in a really dry area, then you might be able to prevent ground water from getting in, but almost any deep underground facility has pumps that keep it dry. With no power, the space will become humid, and everything will start to oxidize. Thin steel will be reduced to rust, electrical components will fall apart, and electronics will desolder. Aluminum will be good for a long time, but bolts holding it together would suffer. If you have ground water running through your facility, it'll be a total loss.

Even in low humidity environments, the steel stairways probably wouldn't survive.

Cement

You won't find scientific analysis of how long cement would last because (a) we haven't been studying it for long enough, and (b) what research is available is geared towards identifying the service life, which is 50-100 years.

Cement keeps its structural strength for a long time, but it isn't chemically inert. When they did the Biosphere experiments, they discovered that the cement was actually leeching carbon out of the air, limiting the growth of their food plants. Over a couple hundred years, it will loose structural strength, and concrete supports will collapse. Over eight hundred, you would be lucky to squeeze your way in.

Studies on Roman concrete is a great narrative for explaining why missile silo concrete wouldn't survive the centuries. The industry is looking into Roman concrete for more applications, but there is no technological overlap between it and missile silos.

Answer 4

You wont have much left other than a pile of radioactive dust.

Not only will these nukes not last 800 years, they will not last 8 years. Most modern nukes use Tritium which has a 7 year half life. Without routine maintenance, Tritium will typically degrade enough to make a nuke non-functional within 2-3 years. Even those nukes that don't use tritium have all sorts of other parts that can not last long in the presence of the bomb's radioactive core.

As for what is left over... after 800 years, most of the missile will likely be completely rusted, evaporated, and decomposed away unless your bunker is in a particularly arid region. Even if you your bunker started off air tight, any rubber seals meant to keep it that way will likely decompose enough to fail within the 1st 50-150 years at which point the bunker will start to slowly collect rain water. Since there is nowhere for water to flow out, it will become a sump meaning that water will flow in with trace amounts of salts that will build up as the water evaporates; so, within a few more decades, it could become a rather corrosive salt water environment, being able to even break down the aluminum, titanium, and copper components of the missle over these time periods.

Even the Uranium or Plutonium core will likely have rusted down to dust, but that said, most nukes use either PU-239 which has a halflife of about 24,000 years or U-235 which has a half life of 700 million years; so, the rust you are left with will still be very dangerously radioactive.

So, after 800 years, depending on the type of concreate the bunker is made with, it may or may not still be mostly intact. Significant mineral deposits containing both the salts and silicates washed in from outside, and the decomposed remains of missiles, computers, etc. will likely line the lower walls and floors. There may or may not be significant flooding at the exact time you enter the bunker, but there will be evidence of a history of the bunker being flooded a repeatedly... and if you have a gigger counter, it will certainly be going off.