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 Mad Doc Grotsnik wrote:

 Tyran wrote:
A nuclear winter requires a nuclear exchange, so unlikely, and even the worse nuclear meltdowns like Chernobyl should be cleaned up after tends of thousands of years (radioactive material does disintegrate after all).

It may take a million years, but the idea that the planet cannot fully recover is anthropocentric arrogance. It recovered from superplumes and asteroid impacts, either which make our biggest nukes look like harmless toys.

Although yes there will be some evidence left in the shape the biodiversity takes after us. In that aspect we will have an enduring influence.

So, on that?

I was around for Chernobyl all going at a bit wrong. And I’ve since learned wind direction was a serious concern for Western European countries due to nasty bad dust.

If we look at a worst case scenario? And every nuclear power station has a meltdown? What’s the impact? I ask because I genuinely don’t know the difference between a nuclear weapon being used and a nuclear power station going horribly wrong.

Chernobyl was a conventional explosion caused by the core overheating. It is generally not possible for nuclear powerstations to cause a nuclear explosion, it's usually the result of stuff flash-boiling due to the enormeous amounts of heat a overheating core produces. Mind, that is still plenty destructive - and the larger problem is that contrary to nuclear weapons, it does not use up most of the fuel (you want your bombs to be efficient, as procuring the fissible material is expensive) but scatters it over relatively large areas where it will keep merrily radiating away for centuries to millenia. Fortunately, most nuclear plants are of a type where that extreme type of failure can't really happen - even in the Chernobyl plant, it was only possible by a combination of unrecognized-at-the-time design failures and the reactor crew running an experiment wildly outside of safe operating parameters on purpose. People learned a bit after the event, and nowadays most reactors just go in a safe failure mode where you basically have the fuel rods sitting around forever, radiating for as long as their lifetime is; they're still dangerous, but mostly only if disturbed - as long as no geological process or extreme weather event breaches the containment, they're essentially safely locked away for eternity. They may no longer be recoverable safely after some time, but that does not need concern us in your scenario.

Also there aren't that many reactors. Even assuming somehow they all meltdown, their impact will be on the US west coast, Europe, and the pacific coast of Asia (China* and Japan) because those are the places that have nuclear reactors.

Meanwhile Latin America, Africa, Australia and central Asia pretty much have no reactors.

*Chinese reactors in particular are very new and should be meltdown proof.

The difference on the climate between a meltdown and a nuclear weapon exchange is down to how many aerosols/dust get pushed up into the stratosphere. A meltdown is a Alston’s to a terrible fire. There will be smoke plumes and they will be radioactive but they should be kept in the lower atmosphere.

Nuclear weapons pulverise dust and the explosion pushes it up where it stays and blocks the incoming sunlight, hence nuclear winters.

Volcanoes do the same thing with dust, ash and sulphur dioxide.

 Skinnereal wrote:
That's a point. What happens to the satelites when there's no-one to steer them into the sun when spent, or degrade their orbits when decaying? There'll be stuff falling from space for quite some years.

Huh?

No one is sending the satellites into the Sun. In fact, due to enormous energy differences needed, sending anything into the Sun is in fact much harder to do than sending stuff to the outer Solar system. Getting to Pluto of all things is easier. Where did that came from?

And yes, stuff will be falling, but first, it will take dozens if not hundreds of years, second, mass of satellite fall will be insignificant next to just space dust that will fall in the same period, never mind actual asteroids and such, sooo...

 ThePaintingOwl wrote:
a new disease that wipes out 90% of humanity would by definition not be able to have a substantial resistant population to spread it

Thanks to morons who screech about face masks, vaccines, and other protective measures, it doesn't need to. I am strangely sure next pandemic will be a problem not due to whatever is causing it, but thanks to imbeciles who will ruin all measures to contain it. Especially now that they were ""vindicated"" with just some 10+ million people dying, no big deal, eh?

Something like MERS, with 20% mortality as opposed to COVID 2%, can easily wipe out half of humanity or more with repeated infections and if it reaches the chain reaction stage, it just might, and the fact the dumbass minority that helped it breach the dam so to speak is likely to die first is not really a consolation...

 Tyran wrote:
A nuclear winter requires a nuclear exchange, so unlikely, and even the worse nuclear meltdowns like Chernobyl should be cleaned up after tends of thousands of years (radioactive material does disintegrate after all).

Try 20 years. You can literally now sit on melted reactor core in Chernobyl. Well, if security lets you, but there are photos of people who did. Yes, 'nukular' scares are dumb/wildly exaggerated

 Mad Doc Grotsnik wrote:
I was around for Chernobyl all going at a bit wrong. And I’ve since learned wind direction was a serious concern for Western European countries due to nasty bad dust.

If we look at a worst case scenario? And every nuclear power station has a meltdown? What’s the impact? I ask because I genuinely don’t know the difference between a nuclear weapon being used and a nuclear power station going horribly wrong.

Nuclear meltdown generally produces two kinds of threats - small dose of really radioactive elements, larger of mildly radioactive ones, and secondary contamination.

The really radioactive ones will kill you in horrible ways, but they burn out in months if not weeks. Their short half life means that after a decade they are no longer big threat, after two, you can literally sit on them without danger. Your own skin stops the residual radiation, never mind something like a coat.

The mildly radioactive ones are funnily enough bigger problem, because they stay active for longer, decades or in some case centuries. All they do, though, is give you slightly higher cancer risk, if that. There are spots in Iran or Bohemia where natural ground radioactivity is similar and people lived there just fine for millennia. Hell, eating a banana will give you similar dose of radiation. A plane trip will be actually much more dangerous, because thanks to thin air above space radiation gives you a much bigger dose.

Now, for secondary contamination, stuff that becomes irradiated due to dispersion of radioactive elements, you might want to wear protective NBC clothing going to really bad spots like Red Forest in Chernobyl. These are rare, though, and after a few years cease to be a problem, as long as you have common sense to not eat anything growing there or ingest dust particles or something (again, even t-shirt will protect you there). Also, they tend to be discernible even without Geiger counters due to abnormal plants so even typical low tech civilization should be able to avoid these. All in all, I am not saying a meltdown won't be a problem, but it will be limited, and it won't last very long.

In fact, I'd be more afraid of 'meltdowns' of chemical plants because these can produce contamination that unlike radioactive elements will stay in the soil/water forever and won't clean itself up with time, and these can kill in even more horrible, slow acting ways that won't be obvious at first. I could give some examples later, but suffice to say, I'd rather try my chances with most of radioactive threats before coming close to some of the chemical spills we can produce.

 Mad Doc Grotsnik wrote:
or get back on their idiot feet as a technological species.

If they even want to.

With the proposed alien colony ship in orbit, I’d reckon there’d be some drive to get up there and have a good old nose about.

I've got a enough dry brush to send them smoke signals.