A section of an underground storage tunnel in a plutonium uranium extraction (PUREX) plant collapsed at the Hanford Nuclear Reservation on Tuesday, prompting authorities to declare emergency at the Washington state site.
Officials were alerted of a cave-in of a 20 feet section of a tunnel that is hundreds of feet long. Located next to the PUREX in the centre of the Hanford site, it is used to store contaminated materials, Xinhua reported.
The Hanford site is about 230 kilometres southeast of Seattle and is generally regarded as the most contaminated nuclear site in America.
Located to the east of the PUREX facility, the tunnels were used since the 1950s to store contaminated equipment.
The collapse was discovered during a routine surveillance of the area by workers.
Workers at the facility were sheltered as a precaution while authorities said there was no indication of a release of contamination for the time being. There were no reports of injuries.