Scientists huddled in Las Vegas last week to discuss what could happen hundreds or thousands of years after dust settles on Yucca Mountain's nuclear waste containers.

While there is still much work to do, consultants to federal agencies found that corrosion on waste containers stemming from dust and water infiltrating the volcanic-rock ridge won't be significant for tens of thousands to hundreds of thousands of years.

State consultants, however, who examined 2,000-year-old mud brick ovens and 3,500-year-old tunnel deposits in Egypt's harsh desert environment say there's not enough accurate data for computer models to make such predictions. In essence, scientists for Nevada contend their federal counterparts are making too many assumptions on how ideal conditions are going to be.

"What we have is garbage going in ... and garbage going out," said Maury Morgenstein, geologist and president of Geosciences Management Institute Inc., a Nevada contractor, referring to the data on which the government is basing its conclusions.

To make predictions on how the planned repository, 100 miles northwest of Las Vegas, will perform in the future in light of NRC guidelines, the scientists are attempting to answer a number of questions.

Will ingredients in the dust such as salts of chloride, nitrate, sodium and potassium, mix with water vapor to form substances in sufficient amount that corrode the metal-alloy shell surrounding the steel-encased packages of deadly, used nuclear fuel?

What role will heat generated by the decaying waste play in the process and will nitrate, for example, slow down the corrosion rate?

The answers will weigh in the NRC's review of the repository's design when the Department of Energy submits a license application that's expected before June 30, 2008.

Lietai Yang, a senior research engineer for the Center for Nuclear Waste Regulatory Analyses in San Antonio, said his team's work shows the potential for dust mixtures corroding the protective, nickel-chromium Alloy-22 shell around the disposal containers could be higher than once thought above 320 degrees Fahrenheit. That temperature for the waste container will occur first about a century after the repository is loaded, the doors are shut and the ventilation fans are turned off.

The temperature will continue to rise for another few centuries then drop back to 320 degrees with dust corrosion occurring during that period of several hundred years, followed by brine corrosion up to several thousand years.

In the dust phase, the corrosion rate is 10 times higher than it is as a vapor, Yang said.

John Walton, a civil engineering professor at the University of Texas-El Paso and consultant to Nye County, noted that the dust samples that scientists are studying might not be representative of those in the future.

His conclusion: "The corrosion environment is dynamic, periodic and poorly understood."

After showing slides of a trip to El Hibeth, Egypt, Morgenstein said, "I don't think the question is what does dust look like now, the question really is what will dust look like in the future?"

Chris Kouts, director of the Office of Waste Management for the Department of Energy's civilian radioactive waste branch in Washington, said vendors soon will be asked to submit designs for the waste-package system and canisters that will be sealed at reactor sites with spent fuel assemblies inside them.