True, but it is still question of the half-life (i.e. plutonium)
> Obsessing over what could happen if somebody digs it up after 10000 years is not anchored in reality.
It is a reasonable concern, because we have never before in our history produced such toxic waste that lives so long. I don't know about you, but I do hope that Homo sapiens will survive next 10k years.
> True, but it is still question of the half-life (i.e. plutonium)
To expand my statement, yes, spent fuel is a mix of different isotopes, some stable, and others unstable with different half-lives. The point being, if something is super-radioactive, then by definition it has a short half-life. And conversely, if something has a long half-live, it's per definition not as radioactive has something with a short half-life.
Thus, after 10k years, what is left is not that radioactive (to be more specific, after 10k years with a once-through cycle, spent fuel will have a radio-toxicity about 20 times that of natural uranium ore. Now, I'm not suggesting you should grind it into dust and sprinkle on your cheerios in the morning. But it's not any kind of civilization-ending toxicity either.
The idea that a future civilization will have the know-how to mine stuff 1 km underground, but somehow they have no clue about chemical or radio-toxicity just seems so absurd to me.
> It is a reasonable concern, because we have never before in our history produced such toxic waste that lives so long.
Citation needed. My guess would be that we have produced an unfortunately large amount of toxic waste, but the vast vast majority of that is not radioactive, and will thus never decay. Dig it up a million years from now, and it will be as toxic as it is today. The incredible energy density of nuclear fuel means that, in the end, the amount of nuclear waste is very small.
> I don't know about you, but I do hope that Homo sapiens will survive next 10k years.
I hope so too. In my mind, however, climate change, biodiversity loss, topsoil loss etc. rate far far higher as risk factors than a comparatively small amount of nuclear waste. In fact, by not deploying nuclear due to risks associated with nuclear waste, we significantly reduce our chances of dealing effectively with climate change, a much higher risk.
Meanwhile, "According to a recent model study the total anthropogenic mercury released into the ocean is estimated to be around 80,000 to 45,000 metric tons" [1]. We have spewed so much mercury that people are advised to eat less tuna because they have too much mercury.
And mercury is not radioactive. In other words, 24,000 years later, there will be 100% of the same mercury there is now! (Granted, some of them might have been removed from the ecosystem and deposited deep underground... I mean, just like how plutonium is stored right now.)
[1] https://en.wikipedia.org/wiki/Mercury_pollution_in_the_ocean
Even if there's an all-out nuclear war or runaway global warming, I think it's overwhelmingly likely that a sizable population will remain to safeguard our scientific knowledge. Instead of stone age, we'll probably end up with the situation in Alita: Battle Angel. In that case, I would be more worried about rogue groups digging up dangerous stuff on purpose than about anybody 20K years in the future.
Besides, we can read Egyptian hieroglyphs pretty well, and the Egyptians weren't even trying to create a writing system to last millennia. Armed with a much better understanding of linguistics and anthropology, I'm sure we can do a better job with our warnings signs.