The Environmental Protection Agency (EPA) has proposed radiation limits out to a million years for Nevada's Yucca Mountain nuclear waste repository. Meeting the limits, announced yesterday, will be an important step for the Department of Energy (DOE) towards opening the Yucca project after nearly two decades on hold.
The repository site, which would store hundreds of thousands of tons of radioactive waste 300 meters below ground level, is located 160 kilometers northwest of Las Vegas, with few nearby communities. A series of court challenges by the state of Nevada and allied groups have blocked the project since Congress chose the site for the DOE project in 1987 (ScienceNOW, 23 February 1999).
EPA's proposal would require DOE to show that it could limit the release of radioactivity to future residents in the vicinity of Yucca Mountain. EPA had previously issued limits that applied only for the first 10,000 years of the life of the repository. But a federal court last year forced the agency to come up with a standard that follows a 1995 recommendation by the National Academies to extend the limits much further into the future. DOE, which says it can meet the standards, is expected to apply for a project permit next year at the earliest.
Under the new standard, DOE would have to show that, for 10,000 years, a hypothetical future resident of the area would receive only 15 millirem of radiation per year above the average 350 millirem per year that residents currently receive. (A chest x-ray delivers a dose of roughly 10 millirem.) DOE would face a more lenient standard for the later phase of the project: from 10,000 to one million years into the future, residents could be exposed to 350 millirem per year above the average, for a yearly total of 700 millirem. Residents of Denver, Colorado, receive that yearly level of background radiation right now, says Jeff Holmstead, EPA's assistant administrator for air and radiation. (At high altitude less atmosphere is available to protect from cosmic rays.)
Critics assaulted the new standards, pointing out that some long-term European standards for buried waste are much more stringent. Senator Harry Reid (D-NV) called EPA's proposal "voodoo science and arbitrary numbers" in a statement Tuesday. And Massachusetts Institute of Technology research associate Allison MacFarlane, a geologist, said that determining that a system could meet standards even to 10,000 years is "kind of ridiculous." John Ahearne, a physicist at Sigma Xi in Research Triangle Park, North Carolina, who served on the 1995 Academy panel, noted that estimating potential delivered dosage from the repository after 100,000 years is extremely difficult due to unknowns such as climate change, seismic shifts, and volcanism.