CAMBRIDGE, Mass. — The earthquake that shook the Nevada desert this month wasn't much by seismic standards, but with luck it rattled some nerves in Congress.
The magnitude-4.4 temblor's epicenter was a mere 12.5 miles southeast of Yucca Mountain, the site where the Bush administration proposes constructing a national nuclear waste repository. The proposal has already been approved by the House of Representatives, and a Senate vote is pending. As a geologist who has spent the last six years studying the proposal, I hope that the earthquake has made some senators rethink their votes.
The state of Nevada is strongly opposed, as one might expect, to a nuclear waste repository in its backyard. The other 49 states are pleased that they weren't chosen for the facility. But a decision that could affect environmental health for the next 10,000 years deserves to be treated as more than just another NIMBY case.
The government has a problem --more than 70,000 metric tons of high-level radioactive waste. No one would dispute the need to secure that material. The question is whether burying it in the Nevada desert 90 miles from Las Vegas would meet standards set by the Environmental Protection Agency to ensure that hazardous radiation would not leak from the site for 10,000 years.
Though research on Yucca Mountain has been going on for years, few scientists outside government agencies have had a chance to review this work, much of it in groundbreaking areas of earth science. The Yucca Mountain Project was created by geologists at the Massachusetts Institute of Technology and the University of Michigan in an effort to ensure independent and unbiased scientific review of the planning for the repository, but that has not been easy.
The science itself is both fascinating and challenging. For starters, it's difficult to project what the Earth will be like in 10,000 years--a short period in geological time, but a long one when you are trying to predict relatively small changes in the Earth system. Currently, the climate seems to be warming, which could mean that in 100 years today's dry location might not be so dry.
Then there is the issue of whether it is better to store nuclear waste above or below the water table. The U.S. is planning to bury its waste above; every other industrialized nation is planning to bury it below or in a salt formation. Sweden and Finland have made their choices because spent nuclear fuel "rusts" when exposed to air but not to water. In a dry location like Nevada, waste will deteriorate more rapidly if the canisters in which it is buried corrode, and the radioactivity would then have nothing to contain it. The United States is betting on a new corrosion-resistant composite out of which its canisters will be constructed.
The U.S. Department of Energy's plan is to bury the waste in tunnels constructed 1,000 feet below ground and 1,000 feet above the water table. The waste will be placed in the canisters, and the tunnels, after 100 to 300 years, will be permanently sealed.
Yucca Mountain was picked, in part, because it is an arid, unpopulated area already owned by the federal government, which used it as a nuclear test site from the 1950s to the early 1990s. The original theory was that, if canisters deteriorated, there would be little water in the dry ground to carry the radioactive waste to other areas. But that theory has already been thrown into doubt.
Chlorine-36, a radioactive isotope created during nuclear weapons tests over the Pacific Ocean in the 1950s, has recently been found 1,000 feet below ground at Yucca Mountain. In just 50 years, that material traveled in the atmosphere to Nevada, was delivered as rain at Yucca Mountain and traveled at least 1,000 feet below the surface--the level where the nuclear waste would be stored. Such rapid movement was completely unexpected and required a revision of models of water flow in the area.
Scientists are only beginning to understand how water moves at Yucca Mountain, but it is already clear that buried radioactive material may travel more quickly than the Department of Energy (DOE) expected. Earthquakes, like the one this month and another with a magnitude of 5.6 in 1992, further complicate the situation.
The federal government's reaction to the complex geology is to focus more heavily on the canisters in which waste will be buried, reasoning that the longer the canisters last, the longer it will take for waste to be exposed to the elements.
The U.S. plans to bury its waste in canisters made of Alloy 22--a new composite metal containing nickel, chromium and molybdenum--and then lined on the inside with stainless steel. Alloy 22 is resistant to corrosion from water, but it is a man-made substance that has existed for only about 20 years. The DOE has only about two years of data on the effects of corrosion on it. Using such limited data, the government is predicting the life expectancy of the canisters 10,000 years into the future.