I'm trying to understand the nuclear waste problem, and I've read enough to know that even the 10,000 years that the Waste Isolation Pilot Plant is licensed for is far too short to eliminate the risk posed by spent nuclear fuel.
This table on Wikipedia gives some good numbers on the biggest problem isotopes. It shows that up to 7% of the fission products are Caesium-135, which has a has a half life of 2.3 million years and high bioavailability.
It gives numbers on the decay energy of the isotopes (269 KeV for 135Cs), but I'm not sure how to convert that to something familiar like Sieverts.
Here's a specific question: How radioactive is spent nuclear fuel from a PWR after 10,000 years, as a percentage of the initial (let's say 30 year old) radioactivity? To resolve any ambiguity, let's use Sieverts to compare. How about in 1 million years? How long until it only emits, say, twice the normal background radiation?
I also know that there are a lot of other factors influencing how dangerous the waste actually is, like how mobile the elements are in the environment and their bioavailability. I'm interested in any mitigating factors like that for the major contributors to the radioactivity at different points in the future.