100,000 not so much. All kinds of things can go wrong. It is expected for instance that as Yucca Mountain cools down water will infiltrate. Uranium is water soluble so some will migrate in the direction of Death Valley. Uranium is toxic the same way lead and mercury are and that is more dangerous than the radiotoxicity of uranium.
A "once through" repository will contain valuable plutonium and uranium. People might want to drill into it 10,000 years from now because they want to use it as a power source or to make nuclear explosives. For that matter we could change our minds and decide we want to recycle the waste in Yucca Mountain after all so we have to be able to retrieve the waste in the first 100 years.
A waste repository used for fission products can use highly secure but difficult to reverse approaches such as encapsulation in a salt dome or burial in areas at sea where sedimentation is taking place where waste would get deeper and deeper year after year and be blocked from migration by the tendency of ions to get trapped in clay.
With larger timescales, my understanding is that the mountain itself might disrupt the cube + drums, opening Pandora’s box.
Perhaps an actual geologist can weigh in and correct me.