RICHLAND (AP) — Workers at the Hanford Nuclear Reservation who questioned some unusual radiation readings are being credited with discovering the partial collapse of a waste storage tunnel last week.

That's according to Doug Shoop, manager of the Department of Energy's Richland Operations Office.

The Tri-City Herald reports the 400-square foot sinkhole atop the tunnel was discovered on Tuesday. It has since been filled in with more than 50 truckloads of soil.

The U.S. Department of Energy says no one was hurt in the incident.

Shoop says technicians were monitoring the area of the tunnel on Tuesday morning when they noticed that some radiation readings were higher than expected. Shoop says the readings were not at levels that would have harmed the workers.

Hanford for decades made plutonium for nuclear weapons.

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