Yucca Mountain critic picked to head Nuclear Regulatory Commission WASHINGTON - Stirring the lingering debate over storing nuclear waste at Yucca Mountain in Nevada, President Obama tapped Yucca critic Allison Macfarlane as the new chairwoman of the Nuclear Regulatory Commission. The nomination of Macfarlane, an associate professor at George Mason University in Virginia who has written extensively on Yucca Mountain, is sure to be a lightning rod in the Senate, setting up a confirmation showdown. Republicans in Congress continue to lead the fight against Obama's decision to halt development of the nation's nuclear dump 90 miles north of Las Vegas. If confirmed, Macfarlane would replace embattled Chairman Gregory Jaczko, who announced this week he would step down after a congressional investigation into claims that he had an overbearing management style. Jaczko was among the panel's chief opponents of Yucca Mountain, and in choosing Macfarlane, who has raised scientific concerns about the viability of storing waste in Nevada, the White House gave nod to the continued importance of the issue for the crucial campaign swing state of Nevada - and its senior senator, Majority Leader Harry Reid. "I am confident that like her predecessor, Dr. Allison Macfarlane will make preserving the safety and security of American citizens her top priority as chair of the Nuclear Regulatory Commission," Reid said in a statement. Jaczko had previously been a top aide to Reid in fighting the waste repository. A confirmation stalemate in the Senate could threaten the function of the five-member panel that oversees nuclear energy development, as Republicans have been pressing to grant Commissioner Kristine Svinicki another term when hers expires June 30. Svinicki, a nuclear engineer, had previously worked as a Senate Armed Services Committee staff member for Sen. John McCain of Arizona, the committee's top Republican, who at one point had been a strong supporter of Yucca Mountain. Sen. Mitch McConnell of Kentucky, the GOP leader, said this week that Svinicki deserved a "speedy re-confirmation." But on Thursday, Reid said he had "grave concerns" over Svinicki's record, and suggested moving the two nominations together - a potential compromise - "to ensure that we have a fully functioning NRC." Macfarlane, a geologist, has been an associate professor of environmental science at the university since 2006. She was picked for a federal commission that studied alternatives for nuclear waste storage and previously worked as a research associate at Massachusetts Institute of Technology. The Union of Concerned Scientists, a nuclear watchdog group, welcomed Macfarlane's nomination, and said it expected she would advocate for enhancing nuclear power safety and security. Neela Banerjee in the Washington bureau contributed to this report.