Lisa Gordon-Hagerty resigned as administrator of the NNSA, a semi-autonomous branch of the department.
William Bookless is now serving as NNSA’s acting administrator, it said. He had been serving as NNSA’s principal deputy administrator for the last year-and-a-half.
Gordon-Hagerty became the first woman to serve as administrator when she took up her post in early 2018.
NNSA oversees the development and maintenance of nuclear weapons, but not the delivery systems, which are managed by the Department of Defense.
DefenseNews was first to report Gordon-Hagerty’s resignation. The news outlet said she had clashed over her budget with Energy Secretary Dan Brouillette.
Gordon-Hagerty had proposed a record budget of nearly $20 billion for fiscal year 2021 to help pay for modernization of the nuclear weapons stockpile, which is expected to cost more than $1.2 trillion over 30 years.
Brouillette had backed a budget of $17.5 billion proposed by the Office of Management and Budget, a White House office. President Donald Trump later sided with Gordon-Hagerty for a budget of nearly $20 billion. Reporting by Timothy Gardner in Washington; Editing by Leslie Adler, Matthew Lewis and Tom Brown