The Energy Department (search) left out risk factors related to potential airplane crashes and hazards at the Yucca Mountain (search) nuclear waste dump in planning for the project, nuclear regulatory staff told the agency in a memo released Thursday.

The department undercounted the number of Air Force (search) plane crashes at the site in Nevada during the 1990s, and discounted the possibility of impacts from jettisoned ordnance, birds hitting planes and cruise missile testing at the Nevada Test Site (search), said the memo by Nuclear Regulatory Commission (search) staff.

The Energy Department also made an unsupported assumption that airplanes that malfunction outside the no-fly zone would never enter the no-fly zone and crash into the dump, the memo said.

The memo relates to aircraft failures and problems, as opposed to potential terrorist attacks, at the proposed dump site 90 miles northwest of Las Vegas. It was written as part of the consultation between the Energy Department and the Nuclear Regulatory Commission as the department prepares to submit a license application to the NRC to operate the dump.

An accompanying cover letter says that the NRC has concluded its review of aircraft hazard issues at Yucca Mountain, but that the issues outlined in the memo remain unresolved.

"DOE should note that it may need to address some or all of these items in a potential (license application), depending on the final aircraft hazard analysis approach used," says the letter signed by Lawrence E. Kokajko, deputy director of the division of high-level waste repository safety at the NRC's Office of Nuclear Material Safety and Safeguards (search).

An Energy Department spokesman, Craig Stevens, emphasized that the NRC had closed its review of the issue.

"This letter shows that we are one step closer to meeting the needs and concerns of the NRC," Stevens said. "After fully reviewing this letter the department will work with the NRC and provide them with enough information to fully allay their concerns."

Yucca Mountain is planned as an underground repository for 77,000 tons of the nation's nuclear waste. Delays have pushed back the planned license application date to next spring at earliest.