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Nuclear Waste: Energy Department Adequately Prepared for Water Movement, Engineer Says By Mike Nartker When the Energy Department first evaluated sites for the planned nuclear waste repository, U.S. Geological Service experts said the most important factor was “water, water and oh yeah, water,” Patrick Rowe, an Energy design engineer on the Yucca Mountain project, said. There will be five radionuclides in storage that could be carried by water seeping through the mountain down into the water table, located about 1,000 feet from where the waste canisters would be stored: uranium, plutonium, radioactive iodine, americium and technetium. While these radionuclides could contaminate local groundwater if they leached into the water table, it would be physically impossible for them to do so unless they were carried by water moving through the mountain, Rowe said. “The mountain’s natural features present a formidable line against the movement of radionuclides,” according to an Energy Office of Civilian Radioactive Waste Management release. Yucca Mountain is located in the Amargosa Desert, a brown and arid stretch of land in Nevada that is one of the driest places in the United States. On average, Yucca Mountain receives about seven inches of precipitation per year. Testing conducted in an alcove located near the mouth of a tunnel leading into the mountain determined how much of that precipitation would seep down into the mountain, Rowe said. By using a sprinkler system installed on the top of the mountain, covered to prevent evaporation, Yucca Mountain engineers determined only about a tenth would seep down to the level of the first alcove, about 100 feet from the top and far above where any waste canisters would be stored, he said. At a second alcove cut into the tunnel leading down to where the waste canisters would be stored, Energy Department engineers evaluated whether any water that seeped down to that level would travel through a geologic fault, Rowe said. He said the department determined that the fault would not carry water down into where the canisters would be stored. At about 800 feet down into the mountain, researchers installed heating elements into holes cut into the rock wall to simulate the heat that would be given off by the waste canisters (see GSN, Feb. 1). The heating elements, which reached a peak temperature of about 290 degrees during the four-year test, have now been shut down and will be monitored for an additional four years to determine the effect of the cooling of the rock on water movement, Rowe said. The heating elements were switched off “almost on the day [Energy Secretary] Spencer Abraham made his recommendation,” he said (see GSN, Feb. 15). The tests determined that, while there would be movement of the rock due to the heat, the water itself would be drawn away from the canisters, in effect creating “a buffer zone,” he said. Researchers also examined how the alternating layers of volcanic and nonvolcanic rock that make up Yucca Mountain would block the movement of water through the mountain. If any water were able to penetrate down into the “drifts,” or underground tunnels cut into Yucca Mountain where the waste canisters would be stored, it would then have to corrode through a thick titanium drip shield placed over the canisters, Rowe said. He added that if the water could corrode its way through the shield, it would then have to corrode its way through the storage canisters themselves. In that situation, most of what little water that would reach the spent-fuel itself would be evaporated by the heat generated by the waste before it could dissolve any radionuclides and carry them down into the water table, Rowe said. Water would then have to make its way through the floor of the storage tunnels and through a layer of zeolites – minerals that can either filter out radionuclides or slow down their process through the rock layer. Rowe was shocked at claims made by Yucca Mountain opponents that the mountain was in effect a sieve and water would easily flow through the mountain and carry radioactive contaminants into the ground water supply (see GSN, Feb. 6). “It doesn’t look like any sieve I’ve ever seen,” he said.
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