Thomas P. D’Agostino, administrator of the National Nuclear Security Administration, announced Friday that he will retire.

In a statement, D’Agostino said he will retire Jan. 18, the end of President Barack Obama’s first term. He has been NNSA administrator and undersecretary for nuclear security for more than five years as well as deputy administrator for defense programs for two years.

“After more than 36 years of service … my wife Beth and I have decided the timing is right for me to leave federal service,” D’Agostino said in a statement. “This was a difficult decision for me as I am committed to serving our country, committed to the missions of the NNSA, the Environmental Management Organization, the Office of Legacy Management, and I am committed to you in carrying out this mission. However, I have an equally important commitment to my wife and family and I am a strong believer that organizations are healthier when leadership changes on a periodic basis.”

D’Agostino visited Aiken and the Savannah River Site several times in his tenure with the NNSA. His most recent public trip was for the opening of the Biomass Cogeneration Facility in March of this year.

At SRS, the NNSA operates tritium facilities to supply and process tritium, a radioactive form of hydrogen gas that is a vital component of nuclear weapons. The Tritium Extraction Facility at SRS is the only source of new tritium for the U.S. nuclear weapons stockpile.

NNSA also oversees the construction and operation of the Mixed Oxide Fuel Fabrication Facility, the Pit Disassembly and Conversion Facility and the Waste Solidification Building.

“From the reactor room on the U.S.S. Skipjack to the Roosevelt Room at the White House, Tom D’Agostino has proven himself to be a talented leader, a trusted adviser and a true confidant,” Energy Secretary Dr. Stephen Chu said. “Rising through the ranks of the U.S. Navy and then leading our nuclear security efforts here at the Department of Energy, Tom has devoted 36 years to serving and protecting the American people. He has done so with a sense of purpose that reminds us all why public service is a noble profession.”

A new undersecretary must be nominated by President Obama and approved by the Senate.

“Until the time when a fully confirmed administrator and undersecretary is in place, I ask that you give your full support to Neile Miller as she takes on the role of acting administrator and acting undersecretary for nuclear security,” D’Agostino said. Miller is the principal deputy administrator for the NNSA and the No. 2 in that organizations leadership hierarchy.

Under his watch, we have eliminated or secured hundreds of nuclear weapons worth of nuclear materials,” Chu said of D’Agostino’s work. “We have reduced the number of deployed warheads to the lowest level since the 1950s – an approximate reduction of 85 percent from the darkest days of the Cold War – while successfully maintaining the safety, security and effectiveness of a shrinking stockpile. Through EM (environmental management), we have permanently cleaned up 690 square miles of contaminated land – an area more than 30 times the size of Manhattan – and completed the cleanup of 22 transuranic waste sites across the nation, permanently eliminating an environmental risk at these sites and reducing the cost of monitoring and storing this waste.”