WASHINGTON -- The state of Nevada plans today to unveil a report that argues the true cost of a Yucca Mountain nuclear waste repository "vastly exceeds" that of leaving radioactive waste at reactor sites for the foreseeable future.

In the latest move to raise questions about the Yucca site, 100 miles northwest of Las Vegas, state officials commissioned an economic analysis they said shows more savings the longer spent fuel is kept on site.

"The cost savings of storage relative to constructing Yucca increase the longer the repository is delayed," a summary states. Over 200 years, it would be cheaper by $24.1 billion to store waste at reactors than to build the Nevada repository, the study concludes.

The study assumes that by then alternatives to Yucca Mountain will have been discovered or developed, making the Nevada site unnecessary.

The Energy Department was forwarded a copy of the report Wednesday but had no comment.

The study, performed by Nevada technical consultant Michael Thorne, applies a "discount rate" accounting principle to DOE-estimated costs to build the repository versus keeping waste on site. The principle holds that a dollar spent today is worth more than a dollar spent tomorrow.

Bob Loux, director of the Nevada Agency for Nuclear Projects, said the White House budget office requires agencies to incorporate such discount rates into long-term projects, but he said the Energy Department for some reason did not do that for Yucca Mountain.

DOE in 2002 estimated a Yucca Mountain repository will cost $58 billion to build and operate while dry cask storage would cost $4 million per reactor per year, multiplied by 103 active plants, more costly in the long run, according to the report.

"DOE did a faulty analysis that illustrated reactor storage was vastly more expensive than Yucca Mountain, but when you apply the discount rates that they were required to do the numbers come out differently," Loux said.

"I would say take these same assumptions and run them through OMB or GAO or CBO and they will show these numbers are not cooked in any way," said Loux, referring to government financial agencies.

Brian O'Connell, an executive who monitors Yucca Mountain financial matters, said the analysis could prove helpful to explore long-term repository costs, an area where there still is much uncertainty.

"It is the first such calculation I have seen using discount cost methodology," said O'Connell, nuclear waste manager for the National Association of Regulatory Utility Commissioners.

O'Connell added that cost is only one among several reasons the government and industry have advanced for building a repository.