WASHINGTON - The Energy Department predicts up to 60 uncontrolled nuclear reactions would take place inside nuclear waste casks stored at power plant sites should the casks corrode, according to a department study obtained by Nevada officials.

After a review of the documents, state officials say they believe the same thing would happen at the planned Yucca Mountain nuclear waste dump, 90 miles northwest of Las Vegas.

The state wants the Nuclear Waste Technical Review Board, an independent board set up by Congress to review the potential dump, to look into the matter.

"We were amazed to learn, after finally obtaining some of the pertinent documents from the Department of Energy through the Freedom of Information Act, that DOE's own studies anticipate that, if the repository operates as is now planned, up to 60 nuclear criticalities may plausibly occur inside the mountain, and that (the) conditional probability of occurrence may be greater than one in 1,000 per year," Bob Loux, executive director of the state's Agency for Nuclear Projects wrote to board Chairman Michael Corradini.

Criticalities are uncontrolled nuclear reactions that could occur if water - or other liquids - got inside the casks. It could start a mininuclear reaction inside the casks and cause a steam explosion, said Washington attorney Joe Egan, who represents the state on Yucca matters.

The issue of water seepage at Yucca Mountain has been a critical point of debate over the planned nuclear waste repository. Scientists are still studying how water moves through the mountain. With or without water, the casks are eventually expected to corrode over a period of thousands of years.

State officials expressed surprise that the report wasn't disclosed as part of the Yucca Mountain debate.

They say Energy officials have said that the issue won't affect Yucca Mountain and state officials say this study shows that it does.

But Allen Benson, a Yucca Mountain project spokesman in Nevada, said the documents the state received do not relate to Yucca Mountain but are from a 4-year-old report looking at on-site waste storage facilities at nuclear power plants.

Benson said the department was glad Loux sent the letter to the board since it can now choose to review the matter, but that on-site storage and storage inside Yucca "are two different things."

Benson said that since the report shows that criticalities can take place inside above-ground storage containers at the 103 nuclear power plants throughout the country, especially if water gets in them, it makes even more sense to store the waste in Yucca, which is in the desert.

But state officials say the fact that the Energy Department acknowledges in this report that criticality is an issue is a huge threat.

Egan and Nevada Attorney General Brian Sandoval filed petitions with the U.S. Court Appeals for the District of Columbia Circuit, asking the court to include the FOIA documents in the court record. The state's major court arguments on the site will take place there on Jan. 14.

Loux said the department only predicated an "extremely low probability of occurrence" of such reactions in the Final Environmental Impact Statement issued last year. He quotes the document's specific text to that effect in his letter to Corradini.

State officials had Michael Thorne, a criticality expert, review the report and found that an expected 60 chain reaction events would occur throughout the lifetime of the repository since the department anticipates the waste packages will degrade over time.

"A criticality occurring in the repository could severely compromise the entire facility, vastly increasing radionuclide releases and making waste packages irretrievable," Loux wrote.

The department documents do not have a timeline for the events to occur, according to the letter.

"These are not nuclear explosions," Egan said. "We are not trying to scare anyone ... we are not saying this is going to happen, but DOE's own analysis notes it was a nonspeculative scenario."

But if the casks were to burst, the radioactive material would go with it. "It's literally a dirty bomb, a conventional explosion with radioactive materials," Egan said.

"Their maximum accident scenario in transport is $18 billion in clean-up (costs) and 44 early fatalities, and that's with a small puff of radiation not an explosion - they call it a "violent event" which is a euphemism for explosion," Egan said.