Ho Nieh, director of the Nuclear Regulatory Commission’s Reactor Regulation program, plans to retire Jan. 30, he said Friday.

Nieh announced his decision in a letter to Commission staff. He is leaving for “personal reasons,” NRC spokesman David Castelveter, wrote in an email on Friday.

As director of the Reactor Regulation program, Nieh oversaw reactor decommissioning funding, licensing and rulemaking and emergency preparedness, among other responsibilities.

Nieh first joined the NRC in 1997 as a resident inspector, according to his bio. Prior to his most recent stint at the Commission, Nieh worked at the International Atomic Energy Agency as a communications advisor in the Department of Nuclear Safety and Security.

It was not immediately clear who would succeed Nieh.