WASHINGTON — Thousands of shipments of highly radioactive nuclear waste can be conducted safely, a panel of scientists concluded Thursday, although they warned that significant radiation might be released if a shipment becomes engulfed in a lengthy and intense fire.

The report by a panel of the National Academy of Sciences is expected to carry considerable weight as the government moves toward developing a central repository in Nevada for used commercial reactor fuel and defense waste now kept in 39 states.

The group examined the risk from possible accidents as nuclear shipments crisscross the country, but said it did not assess security risks to such shipments because it could not gain access to classified information.

It called for a further examination of security issues, including a shipment's potential vulnerability to terrorist attacks. It also said that the group doing the investigation should be independent of any governmental or industry conflicts. Such information should be made public to the extent possible, the scientists said.

The Energy Department is preparing a transportation plan to ship some 70,000 tons of nuclear waste from around the country to a proposed central repository at Yucca Mountain in Nevada, if the facility gets a license from the Nuclear Regulatory Commission.

The department said that would require 4,300 shipments -- about three-fourths by rail and the rest over highways -- over 24 years. Nevada officials, who strongly oppose the Yucca project, have said there could be as many as 50,000 shipments with wastes going through at least 43 states.

The study by a special panel of the Academy's National Research Council concludes there are "no fundamental technical barriers to the safe transport of spent nuclear fuel and high-level radioactive waste in the United States."

"The radiological risks ... are well understood and are generally low," the report continued, noting that during 40 years of making such shipments there has never been a significant release of radioactive material.

But the scientists warned of "social and institutional challenges" -- from possible property value decline and loss of tourist business along transport routes to public anxiety over such shipments -- that would have to be overcome as the number of shipments increase.

The panel concluded the robust canisters in which the waste will be kept have been shown to withstand virtually all conceivable transport accidents. But it warned that a significant radiation release could occur "in extreme accidents involving very-long duration, fully engulfing fires."

"While the likelihood of such extreme accidents appears to be very small, their occurrence cannot be ruled out," said the scientists. They called on the NRC to further analyze the impact of such an event on various waste package designs and said any transportation plan should try to minimize the likelihood of such an accident.

The panel also urged the government to ship as much of the waste by rail on dedicated trains, as opposed to trucks. The Energy Department has said that it prefers rail over highway transport.

While some sensitive information such as the times or routes of a specific shipment may have to be kept secret, the panel urged the government to share with the public as much information as possible including general information on possible routes, what material is being shipped and the broad timeframe of shipments.

The 16-member Research Council panel was chaired by Neal Lane, a professor of physics at Rice University, and included representatives from academia and various consulting organizations.

The government's plan for opening the proposed Yucca Mountain facility has been delayed and the facility now may not open until 2015, or even later. The Energy Department has yet to send an application for a license to the Nuclear Regulatory Commission.

Energy Secretary Samuel Bodman has said the administration remains committed to building the Nevada facility and last week asked Congress for $544 million for the project for the next fiscal year, including money to develop a transportation plan.

But some in Congress, including Sen. Harry Reid, the Senate's Democratic leader from Nevada, has argued that the waste should remain in aboveground storage at current reactor sites to avoid transportation concerns.

Source: Associated Press