The Environmental Protection Agency expects to finalize a radiation safety standard by the end of this year for the planned Yucca Mountain repository, one that protects Nevadans from decaying nuclear waste for 1 million years, a public health officer said Monday.

But the officer, Capt. Ray Clark of the U.S. Public Health Service and team leader for Yucca Mountain standards, declined to say what confidence level he would have in such a standard based on climate changes and corrosion of metal waste containers projected so far out in the distant future.

That task of determining confidence will be left to the Nuclear Regulatory Commission, the agency that must review a license application from the Energy Department for the Yucca Mountain Project.

Asked if dose calculations to the public would be meaningful beyond 500,000 years, Clark said, "We have qualms about that. That's why we first proposed 10,000 years" for radiation safety standards for the Yucca Mountain site, 100 miles northwest of Las Vegas.

"However, at this time we feel we need to go out to 1 million years," he told colleagues gathered at a session of a nuclear waste conference at Texas Station attended by scientists from around the world.

The annual International High-Level Radioactive Waste Management Conference sponsored by the American Nuclear Society runs through Thursday and has 400 attendees representing 22 countries. The conference theme is "Global progress toward safe disposal."

Clark's presentation followed one by Bo Stromberg of the Swedish Nuclear Power Inspectorate who said a deep geologic repository in Sweden is undergoing layers of review to uncover any weakness with his country's effort to dispose of deadly, spent nuclear fuel.

Sweden's review of investigations at a proposed disposal site is taking place this year with a license application due before regulators and an environmental court in 2008.

Similarly, the U.S. effort by the Energy Department to submit a license application to the Nuclear Regulatory Commission for a Yucca Mountain repository will be ready for review in 2008 or four years later than had been planned, according to Energy Secretary Samuel Bodman.

In July 2004, the U.S. Court of Appeals for the District of Columbia Circuit invalidated the EPA's 10,000-year standard, ruling it would not cover peak dose periods of up to 1 million years as it should based on recommendations of a National Academy of Sciences panel.

Then in August 2005, to satisfy the court's ruling, the EPA proposed a two-tiered standard with one set of limits for the first 10,000 years of repository operation and a second set for succeeding years, out to 1 million years. The radiation dose limits were set at 15 millirem and 350 millirem per year, respectively, above natural background radiation.

A millirem is a small amount of energy that produces the same biological effect as a similar unit of absorbed dose from ordinary X-rays. For comparison, a chest X-ray exposes a patient to 10 millirem while a mammogram results in a 30 millirem exposure.

Nevada officials have criticized the proposed two-tiered standard, saying the EPA has backpedaled from its previous stance that a 150 millirem dose is unacceptable.