One of my civil engineering professors worked as a consultant on Yucca Mountain and the Swedish nuclear waste repository. I had the chance to talk to him about Yucca Mountain, and he was very critical of their approach. Yucca's design is intended to prevent contact between groundwater and the waste, and ensure the waste is always accessible. While it sounds like a good idea, it's hard to guarantee in practice and made the design very difficult to engineer.

The Swedish design is simpler - they simply bury the waste and backfill the chambers. Waste is always in contact with groundwater, but the site was chosen so that diffusion through the rock is slow enough that it will decay to stable elements long before leaving the site.