I have a question about nuclear weapons. Anyone here know much about them?
My question is this: What happens to them if the human race were to pretty much disappear tomorrow? Do the computer systems that run them just wind down and the missiles are then forever locked away in silos or bunkers or wherever they keep them? Is there any way for missiles to launch themselves without human interaction providing access codes or turning keys or whatever it is they have to do to give the final "Go?" (And outside of our country, do you figure all other nuclear-armed nations have similar safeguards in place?)
The reason I ask is that I had this weird thought the other night (it's always the middle of the night when these things come to you, right? 
) that if we suffered a massive pandemic that decimated the population, there would be no one left to watch over all these complex things we have made. And wouldn't it be ironic if we disappeared and the planet started to heal from our treatment of it, only to suffer further damage from us as things like nuclear warheads went off long after we were gone?
= new reply since forum marked as read
continue to impact the environment somehow. I can just imagine what the ocean will look like if it rises and starts swallowing up nuclear and industrial sites. 
On the other hand, it should give you an idea of how long a high-tech device will be usable if it isn't maintained.
(This isn't Beneath the Planet of the Apes.)
If humans vanish or we destroy ourselves then the earth's natural environment will rapidly recover.
In less than a million years it will almost be like we were never here. Nothing left of us but some peculiar fossils and a few tons of space trash.
Plutonium and nuclear waste is a big deal to people because people don't like cancers and birth defects. But nature doesn't care. If one creature doesn't thrive in an environment contaminated with our nuclear waste, then some other creature will.
If we can't protect this environment our species evolved within for ethical reasons, then we ought to be protecting it for selfish reasons.
Since we seem to be too stupid to do either we are likely to be short-timers on this planet. Most species go extinct. Looking around it seems humans won't last. Maybe our descendants will look like this, and they won't cause so much trouble:
wikipedia
What goes around come around.
To have a nuclear explosion you need to have something like 98% U-235 or 98% pure plutonium. U-235 breaks down into U-238, which does NOT go super critical (unless enhanced with Neutrons to become Plutonium). What is the "Super Critical" Percentage is Classified but we know it takes about 25 pounds of Uranium or 12 pounds of Plutonium to go "Super Critical". In 1946 the US issued a book on its Nuclear research. The book is part of the Classification of Nuclear weapons technology. The book gave out a lot of information the Scientists on the Manhattan Project thought other scientists should know, but kept what they thought was needed to make an actual nuclear device secret. Thus we know the Weight of the Hiroshima And Nagasaki Bombs, but NOT the percentage of U-235 in the Hiroshima bomb or the percentage of Plutonium in the Nagasaki bomb.
Anything less then whatever is the Super Critical mass percentage, you do NOT have enough Uranium or Plutonium to go "Super critical" (i.e. what we call the Nuclear bomb "exploding"
. It is estimated that given the nature of Uranium and Plutonium (i.e. being radioactive, they are constantly breaking down into other elements), it takes no more then 5-10 years for the percentage of U-235 and Plutonium to drop below what is needed to go "Super Critical". Some indication is that it may be less time (i.e. 2 years) but the exact percentage is classified (The decay rate is NOT, for that is well known, the issue is what is the point when the AMOUNT of Uranium or Plutonium falls below what is needed to go Super-Critical).
If the Nuclear device is on a Rocket, if it is a liquid fuel rockets (As were the First ICBMs, the Atlas also used in the Mercury Launches and the Titan IIs, also used in the Gemini project) then within about a month enough Hydrogen would have leaked out to make the rocket useless. Liquid Hydrogen leaks at the rate of 1% per day from any container, not from leaks, but right through the walls of the Container. Hydrogen is the smallest atom, when liquidlified it is even smaller. Thus the Hydrogen atoms and easily squeeze through the atoms of any container, thus the 1% per day leakage rate.
Solid Fuel Missiles (Such as the Minuteman missiles) do NOT have the problem of hydrogen leaking, thus can last forever, in theory. In these weapons the limitation is thus the ability of the warhead to go super critical (i.e. explode) AND the ability to keep rodents out of them so that enough material is left to actually fire the system. In affect after 5-10 years of neglect even these would be useless.
Now, Nuclear power plants do NOT need "Weapons Grade" nuclear material (Whatever that is, I suspect 98% or more Uranium or Plutonium), the uranium they use tend to be in the 20% grade level. Enough to go "Super-critical" to make power and even cause a nuclear meltdown, as in Chernobyl and Fukushima. Many of the writers above, get hung up on Nuclear Power, which your question does NOT ask about, and ignore Nuclear Weapons, which is what your question is about. I hope I have done the opposite ignore Nuclear power plants and concentrated on Nuclear bombs.
In simple terms, the Nuclear devices will NOT be capable of exploding within 5-10 years of neglect. Some missiles will no longer work after 30 days, but most (the Solid fuel Missiles) will outlast the ability of the warhead to go boom. I have ignore the electrical power needed to launch such missiles, no power no launch, but most such power is very secure and would outlast the warheads (underground bunkers with backup automatic generators, would run till out of fuel 30-60 days after the generators start to generate i.e. after all other electrical power is shut off). \
Side note: Most the Uranium and Plutonium in these missiles (or hangers if you include the bombs kept for use on planes) will still be highly radioactive, but not enough to do any damage i.e not enough nuclear material IN THE WARHEADS to cause a melt down. The material will just sit there until the missile collapse under them to do age, then sit where ever they may fall till the material decay to non-radioactive materials. These weapon grade levels of Uranium and Plutonium are in terms of mass way less then in a nuclear power plant. In a plant you can have enough nuclear material to cause a chain reaction (go Super Critical) but NOT at the pace to cause what we would call a "Boom". Instead you could have enough at one spot to go super-critical and then fall to the center of the earth, for there would be nothing to stop it.
According to some recent research, the reason the Earth is Volcanic is that when the earth was formed Uranium, being the heaviest element, fell to the extreme center and then form a natural nuclear reactor (Thus the background radiation all over the world). This natural nuclear reactor produced so much heat that it has kept the surrounding iron liquid so that we have a molten core, which permits the continents of "move" and Volcanoes to exist. Just pointing out Nuclear power will exist for millions of years to come, will this center runs out of Uranium and cools down (and the Continents stop moving and the earth dies). Uranium is not bad in itself, but bad if used incorrectly or carelessly. The nature of Nuclear weapons is that unless someone uses them within a few years of making them OR rebuild them to keep them active, they will naturally become useless as weapons within less then 10 years. The Actual nuclear material can still kill people for thousands of years, but not enough to go super critical and melt to the center of the earth, unlike Nuclear plants when that can happen given the serve volume of Nuclear material used in such plants.
"The reactor was now only producing around 5 percent of the minimum initial power level established as safe for the test.[23]
3 Control-room personnel consequently made the decision to restore power by extracting the majority of the reactor control rods to their upper limits.[26] Several minutes elapsed between their extraction and the point that the power output began to increase and subsequently stabilize at 160–200 MW (thermal), a much smaller value than the planned 700 MW. The rapid reduction in the power during the initial shutdown, and the subsequent operation at a level of less than 200 MW led to increased poisoning of the reactor core by the accumulation of xenon-135.[27][28] This restricted any further rise of reactor power, and made it necessary to extract additional control rods from the reactor core in order to counteract the poisoning."
Perhaps not a return to full power, but to increase power, regardless.
Increasing coolant flow actually contributed to the excursion. They ended up bringing all of the coolant close to the temp where it flashes over to steam.
The entire reactor configuration at the time was outside the bounds of the design limits, AND the parameters of the test. Operator error.
They wanted the reactor at 700mw thermal, not 30mw thermal. That is when the xenon poisoning occurred. Loss of coolant really cannot be considered any more than half responsible for the excursion, mechanically.
