Purex nuclear site
The Purex (Plutonium Uranium Extraction Plant) separations facility at the Hanford Works is seen in an undated aerial photo. DOE/Handout via REUTERS

A tunnel collapse at a nuclear site in Washington state has led to evacuations but no release of radiation, authorities have said.

The collapse occured at the Hanford Nuclear Reservation, a site half the size of Rhode Island, the Associated Press reported. Though no workers were in the tunnels at the time, nearby personel was evacuated and others were told to stay inside.

More from IBTimes UK

Around 9,000 people work at Hanford.

The tunnel was part of the PUREX facility, formerly somewhere American nuclear weapons were made. Hanford previously refined plutonium for nuclear weapons but it is now a despoitory for nuclear waste.

Hanford began in World War II and procuded the plutonium used in the atomic bomb dropped on Nagasaki in Japan.

Inside the tunnel were rail cars with radioactive waste but no radiation release had been detected. Most of the 56 million gallons of radioactive waste held at the facility is in underground tanks.

The full scope of the collapse was not immediately understood, with officials saying that it may have been larger than first thought.

The US Department of Energy, which oversees the country's nuclear facilities, told CBS that construction by nearby road crews may have been the cause of the collapse.