[doikor]

After a few years the fuel is cool enough to passively cool. At that point you just bury it underground.

The facility (Onkalo) does not need any maintenance once it has been filled up and closed as you just fill the whole thing making access to it very very hard as it is 520m under ground so a couple kilometers of tunnel to dig through to get to it. (clay sediment at the bottom where the vessels are and concrete for the pathway up)

As I said the 3.5 billion is the projected total lifetime costs of the permanent storage site Onkalo. So that is the total cost (to the best of our ability to estimate for it)