Workers completed filling a hole today (May 11) at Washington State's decommisioned Hanford Nuclear Reservation that was created by a tunnel collapse.

Around 8:30 a.m. on May 9, a 6-metre (20-foot) section of a 110-metre (360-foot) railcar tunnel, near the Plutonium Uranium Extraction Plant, collapsed. 

The 37-square-metre (400-square-foot) hole was located over a tunnel containing eight railcars containing contaminated equipment. The hole was near a connection to a longer tunnel containing 28 railcars with contaminated equipment. The tunnels were built in the 1950s and '60s out of wood and concrete, covered with about eight feet of soil, and sealed in the 1990s.

About 53 truckloads of soil (420.5 cubic metres or 550 cubic yards) were used to fill the hole.

The U.S. Energy Department stated that no one was injured in the incident and no radioactive material escaped. The department will conduct an investigation into what caused the collapse.

The site is located about 322 kilometres (200 miles) southeast of Seattle on the Columbia River.

The reactors at Hanford, established in 1943, produced plutonium for the U.S. defense program for over 40 years, including the plutonium that was in the atomic bomb dropped on Nagasaki, Japan, in 1945. Reactors were shut down during the 1960s, '70s, and '80s. Cleanup of the Hanford site began back in 1989 and is expected to continue until 2060.