

Depends on the reactor type. I know the CANDU reactors that Canada uses are very difficult to meltdown since they use unenriched uranium fuel, and if the deuterium moderator disappears due to a missile strike or something, the reaction just fizzles instead of running away.
If you are burying the waste, you’d be using a mine that is below the impermeable bedrock layer. There would be no leeching at all.
And using the most expensive project on the planet as your reference is disingenuous as best. Most other projects cost less than a third of that.
Additionally, almost no one is ever suggesting that nuclear is a 100% replacement. Most people suggest nuclear baseload with renewables+battery for peaks.