When they first designed a granite repository, they made every mistake in the book. They wanted narrow tunnels, with the waste being set in boreholes. This design was tested at the play-school in Manitoba. Doesn't work for high stresses!
What you need is a large elliptical opening aligned with the stresses. Then place the waste within, in a suitable conductive matrix. Once everything is in place, jack the matrix up with some water. This will easily last a million years, and will be immune to glaciation. Unfortunately, we will never see this design.
So that's it for the series, now back to the reality of the depressing hearings. Have fun!