Researchers believe that caves containing prehistoric paintings, such as those found in southern France, provide excellent natural analogues for the flow of water in the unsaturated zone 1 that would host a repository at Yucca Mountain. The paintings in these caves were made with oxides of iron and small amounts of manganese, as well as clay, charcoal, and silica. None of these materials would survive long in the presence of abundant water. Yet many such features have survived in areas far more humid, and with more than three times the rainfall, than Yucca Mountain. Those paintings survived because the water tended to flow around caves and tunnels not into them, in part because of the size of the openings.
Water is more likely to flow around and away from small openings than from large ones.
Most of the caves identified as natural analogues have as large or larger a cross-sectional area than that proposed for the repository at Yucca Mountain. Seepage into such a facility, therefore, is expected to be minimal. In a repository, waste packages would help protect the waste from water for thousands of years. And although we can't do experiments for such long periods, there are some analogues that support this conclusion. If a waste package fails, relatively small numbers of particles would escape.