Yucca Mountain: Putting A Limit On Risk

Yucca Mountain has unique characteristics that make it arguably the best location to store hazardous waste, chiefly a water table so low that it is possible to store steel canisters of waste 1000 feet below ground and 1000 feet above the water table. Two questions form the current debate: how dry will the site remain, and what is the risk from earthquakes?

Seismic hazard assessments usually look at the risk over 500 to 1000 years. The Nuclear Regulatory Agency is requiring a much more cautious evaluation that exams what would happen with odds as low as 1 in 10,000 over 10,000 years, which would be equivalent to something that happens only once every 100 million years. Scientists study the past to help predict the future, but Yucca Mountain was formed only 10 million years ago, limiting the value of the historical record.

While the relative stability of the area is clear, some seismic hazard evaluations assessed potential movement at rates larger than experienced anywhere on earth. Researchers turned their attention instead to quantifying the maximum possible movement from any earthquake at Yucca Mountain, given its unique geological composition. Was there a limit to ground motion?

D. J. Andrews and colleagues at USGS looked at the worst-case scenario to find that the ground can move a maximum of 3.6 meters per second, which is near the most intense ground motion ever recorded anywhere, but is within the range of feasible engineering mitigation.

Andrews, et al., used a numerical method to calculate ground motion related to stress changes at the source of an earthquake and throughout the surrounding area to establish physical limits on extreme ground motion.

The authors suggest this new finding adds significantly to the body of evidence that supports a long-term stable seismic environment for Yucca Mountain and provides an opportunity to shift discussion to the large question of the comparable merits of available options for hazardous waste storage.

The full research article was recently published in the Bulletin of the Seismological Society of America. D. J. Andrews, Thomas C. Hanks, and John W. Whitney work at the U.S. Geological Survey -- Menlo Park.