US President Barack Obama on Thursday nominated a new chairman of the Nuclear Regulatory Commission, after the former head Gregory Jaczko resigned after months of personnel controversy.

Obama picked Allison Macfarlane, an academic expert on nuclear power who is currently a professor at George Mason University, to serve in the post, subject to Senate confirmation.

Jaczko, who had a high-profile public role in assessing the US response to last year's nuclear disaster at Fukushima following Japan's devastating earthquake and tsunami, said earlier this week that he would step down.

He said his departure had nothing to do with personnel issues and allegations that he bullied senior female members of his staff.

It was unclear whether Jaczko will leave before his term is up next year.

In February, Jaczko was the sole commissioner to oppose the approval of the first new US reactors in decades, saying he was concerned safety issues needed to be addressed in the wake of the Fukushima disaster.

Regardless, commissioners voted 4-1 to approve the construction of two 1,100 megawatt Westinghouse-Toshiba reactors at a facility in Vogtle, Georgia.

On Monday, Jaczko said: "This is the right time to pass along the public safety torch to a new chairman who will keep a strong focus on carrying out the vital mission of the Nuclear Regulatory Commission."

Jaczko said he will step down once his successor is confirmed.

Senate Democratic Majority leader Harry Reid called on Republican senators to join him to quickly confirm Macfarlane.

He proposed also moving on the nomination of Kristine Svinicki, who Republicans want to back for a second term on the commission, after her nomination was held up by Democrats over her clashes with Jaczko.