WASHINGTON - The Yucca Mountain chief engineer on Wednesday defended the Energy Department's level of design for the radioactive waste site, saying the project does not need to map "the last nut or bolt" in order to show whether it is safe.

Critics have seized on comments by DOE officials that designs for the proposed Nevada repository for used nuclear fuel will be 35 to 40 percent complete when DOE applies for a construction license next summer.

Nevada Attorney General Catherine Cortez Masto has asked the Senate environment committee to prevent DOE from filing an application "that does not contain final designs for all the proposed Yucca Mountain facilities."

Speaking to a Nuclear Regulatory Commission advisory board on Wednesday, DOE official Paul Harrington said the department is forming blueprints to a level where the repository's safety can be judged, and it would not add anything to go farther at this time.

Harrington, director of the Office of Chief Engineer on the Nevada project, said DOE has not detailed "all the warehouses, the administration building, the parking lots, the heavy equipment maintenance facility, but 100 percent design represents that."

Many parts of the site and the details of how they might be built "have no bearing on identification of what the facility is or what its operating basis for a safety case is," Harrington said in response to a question on the matter.

NRC officials also have expressed surprise at DOE's comments about Yucca blueprints, and have asked for an explanation. Harrington said officials from the agencies will discuss the issue at a management meeting next month.

Cortez Masto asked Sen. Barbara Boxer, D-Calif., to take action on the design matter.

Boxer, the chairwoman of the Senate Environment and Public Works Committee, has not said how she plans to respond.