Professor suggests studying safety of Yucca barriers

Monday, Nov. 20, 2000 | 11:58 a.m.

RENO -- A University of Michigan professor criticized the Nuclear Regulatory Commission's reliance on a complicated mathematical analysis to assess the safety of a proposed high-level nuclear waste repository at Yucca Mountain, saying it can be misleading.

Rodney Ewing, who has studied radioactive waste disposal for 20 years, suggested Thursday at the Geological Society of America meeting that he has a better approach.

Instead of relying on the Department of Energy's performance assessment approach, which is rooted in mathematical formulas that don't reflect actual conditions at the mountain 90 miles northwest of Las Vegas, Ewing suggested studying the safety of individual barriers that would be used in the repository.

Yucca Mountain is the only site being studied to dispose of the nation's 77,000 tons of spent nuclear fuel and highly radioactive defense wastes.

The DOE is charged with solving the nation's nuclear waste problem. The NRC would have to license a repository before it can operate.

By testing separately the canisters expected to keep highly radioactive wastes sealed away, the rock in which they are buried and the rate of ground water flow through the mountain, the DOE and the Nuclear Regulatory Commission, would have a more complete idea of how Yucca Mountain would work, he said.

"I'm asking -- not so much as a scientist, but as a member of the public -- why should I accept the results of an extremely complicated analysis for which there can be no verification?" Ewing said.

Licensing before the Nuclear Regulatory Commission could begin in 2002, and a repository at Yucca could open by 2010.

In 1998, Ewing noted, the DOE completed a site analysis and found no "show stoppers," no problems that would halt developing the site as a nuclear waste repository.

But Ewing said the DOE's analysis may not recognize a "show stopper" because of large uncertainties in its assessment.

"This is because the analysis involves thousands of variables, many of which are not based on experiments or actual observations, but rather are established by panels of experts," Ewing said.

Originally the DOE called for nuclear waste disposal from a "belt and suspenders" approach, Ewing said. That means a series of engineered and geologic barriers would prevent radiation from escaping into the environment. If one barrier failed, others would back it up.

But separate evaluations of each of the barriers is no longer the DOE's way, Ewing said. Hundreds of calculated results are combined to project a range of behaviors that may not work in thousands of years, he said.

"There is very limited, relevant experience in modeling geologic systems of this site and overextended periods of time," Ewing said. "One should not expect greater success with such a prediction than we have in other fields, such as predicting which presidential candidate gets the electoral votes from Florida."