SPOKANE (AP) — Workers have placed a protective cover over a partially-collapsed tunnel filled with radioactive waste on the Hanford Nuclear Reservation.

The U.S. Department of Energy said workers finished installing the cover over the weekend at the former plutonium production site near Richland, Washington.

The waste is left over from production of plutonium for nuclear weapons, and the aging tunnel partially collapsed on May 9, prompting evacuation of nearby workers.

The Energy Department has said no workers were injured and no airborne radiation escaped into the environment as a result of the incident.

The hole left by the partial collapse was immediately filled with more than 50 truckloads of soil. The agency said the cover will provide additional protection while work continues to find a permanent fix for the tunnel collapse.