I have it from a colleague that the rocks there are severely fractured. Some of that might be from coring (which sometimes induces fractures), but the images I saw showed what looked like joint sets--structurally related fracturing from deformation of the rocks. That would be tolerable in the present climate with some safeguards, but in the event the climate becomes wetter, the probability of leaching significant amounts of active and toxic material increases substantially. Not the sort of repository to keep something the estimated 10,000 years the specs were calling for, considering at this latitude, for instance, we have gone from ice sheet to prairie.
Climate does change, whether we humans drive that or not.
So far, none of the proposed permanent repository methods is without a serious flaw, which is why 'spent' fuel rods continue to sit in ponds all over.
Reprocessing that material would cut down on the problem, but IIRC, that was done away with by treaty during the Carter years.