I understand that nuclear bombs don't have lasting radiation effects on the area that they're dropped. Examples of this are Nagasaki and Hiroshima, where less than a century after an atomic bomb was dropped, both cities are thriving.

However, nuclear reactor meltdowns are a different story. Apparently, a 30km radius around Chernobyl will not be safe for humans for another 20,000 years. I imagine that a worldwide nuclear war would affect many of these reactors and that the radiation from these would cause a pretty terrible environment for many years to come. There are currently 433 nuclear reactors in the world:

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If the majority of these were hit by atomic bombs in a world wide nuclear war, how would the radiation affect the entire world? Would there be any areas safe from radiation? How long would it be before the earth was safe to live on again? Would there be any adverse affects of the radiation?

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    $\begingroup$ The answer to this depends mightily on what the definition of "destroyed" is. They design these reactors to break down gracefully, so the effect could be "none at all." Or you might overpower all of those safety features, in which case the effect could be epic. $\endgroup$ – Cort Ammon Dec 19 '16 at 19:22
  • $\begingroup$ @CortAmmon The Fukushima Daiichi disaster was instigated by a tsunami and has the same level of classification as the Chernobyl event. I was wondering what would happen if all of the nuclear reactors underwent this level of destruction. $\endgroup$ – Faulkner Dec 19 '16 at 19:29
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    $\begingroup$ You significantly changed the question which you originally asked, to the point where my posted answer no longer has anything to do with it. This is not done on SE. If you've changed your mind about what you wish to ask, simply ask a second questions, don't waste people's time and effort by rendering their answers irrelevant/flawed. $\endgroup$ – AndreiROM Dec 19 '16 at 19:45
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    $\begingroup$ Please do not chameleon questions. If you have another question, ask it separately. $\endgroup$ – Mołot Dec 19 '16 at 19:46
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    $\begingroup$ @Faulkner - no big deal. It's just SE etiquette. I guess I snapped a bit, because of the circumstances of how I found out about it (another user telling me that I'm off topic). $\endgroup$ – AndreiROM Dec 19 '16 at 19:56

It certainly is possible for a large enough nuclear war/event to cause the Earth to enter a Nuclear Winter. This would most certainly affect every corner of the globe, and lead to massive die-offs.

Understand that this has less to do with whether the nuclear reactors are all hit/destroyed, than with the actual amount of destruction that a nuclear war would inflict even without causing some reactors to fail catastrophically. The destruction which those failing reactors would cause would be rather localized. However, they would release a much higher amount of radioactive waste into the atmosphere than a relatively "clean" nuclear weapon.

The weather system would then probably move those radiation clouds around quite unpredictably, running a very good chance of wiping out most land-dwelling species, Homo Sapiens among them.

And so, a bunch of nukes going off would be quite sufficient to kill the vast majority of us as it is. 400+ of them would most likely wipe surface dwelling life off the planet. And exploding nuclear reactors would probably release exponentially more radioactive waste into the atmosphere, making it that much more likely for all of us to die gruesome deaths.

Would any place be safe? In the event of a nuclear winter, the entire globe would be affected. That would be dangerous in and of itself, additionally, that much radiation would stay up in the air for a very long time, and would eventually make its way to pretty much every corner of the planet. Might some places be very minimally affected? It would depend entirely on the weather patterns, but I think it's safe to say that no place would be safe in the long run.

How long would it be before the earth was safe to live on again? Safe for who? For the radiation to fade to current levels it would probably take tens of thousands of years in the areas hit by the nukes/where reactors failed. The nuclear winter itself would probably fade sooner, but might still last hundreds of years (maybe longer, who knows?). Either way, there's a good chance that humanity would not survive it all, except maybe off-planet, somewhere.

Would there be any adverse affects of the radiation? Of course. A majority of surface dwelling species would die off. Horrible mutations would likely become common place for those unlikely to survive the initial cataclysm. Over time the Earth would be reclaimed by other species, but not a for a long time.

  • $\begingroup$ OP specified destruction of nuclear reactors (presumably ones for electricity production), which is not the same thing as a nuclear war. Your answer may or may not apply, but at the very least, you should elaborate on how reasoning about the effects of nuclear war is relevant to the OP's scenario. $\endgroup$ – a CVn Dec 19 '16 at 19:31
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    $\begingroup$ @MichaelKjörling - well, the OP went and fundamentally changes his/her question, so yes, my answer is now off-subject. $\endgroup$ – AndreiROM Dec 19 '16 at 19:44
  • $\begingroup$ Mołot fixed that by rolling back to the original revision. $\endgroup$ – a CVn Dec 19 '16 at 19:49
  • $\begingroup$ @MichaelKjörling - I had just finished answering the revised question :-P $\endgroup$ – AndreiROM Dec 19 '16 at 19:50
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    $\begingroup$ OK, guys, just go and post revised question and answer separately and I'll upvote both. Deal? $\endgroup$ – Mołot Dec 19 '16 at 20:01

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