Earlier quoted context omitted.
> We are talking about time frames that are many times longer than the existence of modern humans as a species. No, we absolutely are not. "Long half-life" = "less radioactive". By definition. Do you know what the half life of CO2 is? Infinity.
The half life of Plutonium is ~24k years. That's way beyond a time frame we have any grip on. Then its still very, very dangerous. Uranium (nuclear fuel) has a half life of 200k - 4.4 million years. Then its half as dangerous. CO2 has a half life of ~ 10 years in our atmosphere btw.
Nuclear fuel itself isn't radioactively dangerous, it's dangerous because it's a heavy metal (like lead).
After nuclear fuel is reacted, it produces a bunch of nuclear decay products. Some of these decay products have a half-life of 10s of years, which are the problems: they're short enough to be dangerously radioactive, but long enough that they need to be handled carefully for a long time. But not for 10s of thousands of years.