The United States has accumulated more than forty thousand tons of spent nuclear fuel and high-level radioactive wastes from commercial, research, and defense activities with an estimated two thousand tons added every year. The materials are currently stored in thirty-nine states at 131 temporary above-ground facilities, requiring constant monitoring and maintenance. Worldwide, scientific consensus holds that deep geologic disposal, with robust engineered barriers, can best contain and isolate these materials from the accessible environment. The Nuclear Waste Policy Act of 1982 established this approach as U.S. policy. If ultimately licensed by the Nuclear Regulatory Commission, Yucca Mountain, in southern Nevada, could become the first U.S. geologic repository for such materials. The Department of Energy (DOE) plans to open the proposed repository by 2010 if a license is granted.
Between about fifteen and twelve million years ago, large volcanic eruptions deposited hot ash that solidified into the rock composing Yucca Mountain. The proposed repository would be built about one thousand feet underground and, on average, about one thousand feet above the water table in rock that has remained undisturbed for millions of years. For about two thousand feet under the mountain's surface the rock is very dry, or unsatu-rated, meaning its pore spaces are not completely filled with water.
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