Nuclear watchdog groups on Thursday demanded a thorough accounting of a fire at a national lab in South Carolina, noting the surrounding site contains nuclear material and U.S. officials are ramping up efforts to build a core nuclear weapon component there.

The U.S. Department of Energy said the fire at the Savannah River National Laboratory on Wednesday did not release any radiological material or expose employees to radiological contamination. There is no risk to the public or the environment, the agency added in a brief email statement on Thursday.

The fire prompted the declaration of a “site area emergency,” restrictions on rail, boat and air traffic, the closure of barricades to incoming traffic and the sheltering of employees, according to a news release from the Savannah River Site Emergency Response Organization.…