After a major nuclear war/disaster, how much radiation would remain after ~300 years?

Question

The setting for my story is a post-post-apocalyptic Earth. There was a nuclear war (and several related nuclear disasters due to power plants being either targeted or neglected), and it's already been almost 300 years since that event.

A small portion of humanity stuck themselves down in bunkers for the better part of this time (kinda like in Fallout) and is only just beginning to re-emerge on the surface. Nature has reclaimed much, if not all, of the world and what's left of cities is pretty much unrecognizable from what they are today.

I was hoping to have minor conflict related to people having to deal with lingering radiation in certain areas, but googling has given me mixed information regarding how long that sort of stuff would actually last and none regarding what areas would be safer or more dangerous over time.

The question: Is is possible for radiation to linger in dangerous quantities after 275+ years? If so, what areas would be more dangerous after this amount of time? Are there any significant affects on the environment that this much lingering radiation would cause?

Nuclear winter is a thing that could have happened for a short period but not to such a degree that it would wipe out all life on the planet (the fallout would ideally be less smoke and ash and more radioactive debris getting as everywhere as it could in populous areas) since things need to be more or less "back to nature". I don't want the radiation to be something that everyone needs to worry about everywhere at all times, but something that should be a concern when going to specific places.

I am perfectly happy if such conditions are impossible to meet, but would appreciate clear answers as to why.

Please make a comment if I need to clarify anything and I'll do my best.

Answer 1

Bioweapons might be better for lasting trouble.

Nuclear war is a good way to wreck everything fast. But radioactivity fades, and especially outside with wind and water and life working on the particles, environmental contamination will be gone in decades or if not gone, diluted to harmless imperceptibility. The Chernobyl experience has demonstrated how fast environmental radioactivity can subside.

If you need lasting trouble from the war, and you are willing to stray into more purely fictional creations you could use bioweapons. They have advantages.

1: You can make them to fit your needs and no-one can wave a periodic table at you to say you are wrong or that it wont work.

2: Because they are biological, they might evolve with time. You could have the areas affected with the bioweapon have unusual carrier life forms (maybe even humans!) or other lasting blights representing the effect of the weapon.

Answer 2

Half life

Nuclear weapons and nuclear power plants use very different material for their nuclear reactions. A nuke needs stable material that can be pushed over the edge, using as much of the material as possible for maximum efficiency. Power plants use a material that can be less stable for ease of starting a reaction, and needs to more slowly react for a stable, longer reaction.

Taking this into account, it means an exploding nuke is radioactive and deadly, but all radioactivity quickly dissipates. As a metaphor, it's much like something warm that loses it's heat very quickly into it's environment. It warms the environment quickly, but afterwards the thing isn't warm any more and can't do much more. Any material that hasn't been used in the explosion is still stable, losing little radiation. So it's not very dangerous.

A power plant has material designed to give radiation and thus heat off over longer time. It isn't as dangerous as the immediate fallout of a nuke, but it's dangerous all the same. It will continue to decay in radioactive materials for long periods of time. As a real life example, lets examine the elephants foot.

The elephants foot is part of a nuclear core, left after the Chernobyl disaster. It got insanely hot, melted through it's protective case, sloshed through some pipes and eventually solidified in a weird form, vaguely resembling an elephants foot. It is still hot thanks to radioactive decay, very slowly melting through the floor. Although this melting isn't significant currently, nearly 35 years after the disaster. It is still giving off dangerous amounts of radiation, so they made a huge new structure over the old concrete they poured to seal it all in. It will still be radioactive and dangerous for humans in the area for 100 years and possibly more.

But the question is if it will still be dangerous after 275 years. It might still be radioactive and maybe not healthy to live in the area, but it might not be completely noticeable. Animals and plants in the area are actually flourishing. Most animals live out their lives fully before the radiation really takes effect. Without human interference, it is a small haven for them. It is likely you don't want to stand right next to any nuclear core even after so many years and probably a few more centuries to come, but it's effects will probably not be incredibly dangerous over larger area's.

So what kind of area's will be dangerous? Probably only the power plant and mostly the core area. But nuclear power plants after Chernobyl have been designed to cave in into itself at a melt-down, sealing any dangerous materials inside. The danger might be much, much lower than stated.