Jaczko, a physicist, is a former Reid science policy adviser who helped the Nevadan fight the Yucca project before joining the NRC in 2005.

At the same time, 34 Bush nominees were approved. Among them was Kristine Svinicki to the NRC. Svinicki, a nuclear engineer and a professional staffer to several senators including Larry Craig, R-Idaho, was the choice of Republicans to fill a term that will expire in June 2012.

Svinicki and Jaczko were confirmed in tandem in a deal to maintain political balance on the NRC, which regulates nuclear power plants and the management of nuclear waste and nuclear materials.

The confirmations bring the NRC's membership to four, with one remaining vacancy.

According to reports in trade publications, Reid has urged Bush to fill the final vacancy with Allison Macfarlane, an associate professor of environmental science at George Mason University who also has expressed skepticism about the suitability of the Yucca Mountain site for nuclear waste disposal.

While Reid has declined to confirm reports that Macfarlane is his preference, nuclear industry lobbyists have said the White House is resisting the nominee.

"Macfarlane is being left at the altar," one lobbyist said Friday.

Contact Stephens Washington Bureau Chief Steve Tetreault at stetreault@stephensmedia.com or (202) 783-1760.