Work to fill a Hanford nuclear waste tunnel that partially collapsed started, and then stopped, overnight Tuesday after some of the dirt used to initially stabilize the tunnel began to cave into it.
The minor cave-in early Wednesday morning was around a box where workers were injecting grout, a concrete-like material, into the tunnel.
No radiological readings above those anticipated were detected, and none of the workers were at risk, according to the Department of Energy.
A PUREX plant tunnel holding eight rail cars loaded with highly radioactively contaminated equipment was discovered partially collapsed on May 9. A sand and soil mixture was poured into the 20-by-20-foot hole the next day.
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Plans were made to next fill the tunnel with a concrete-like mixture to further stabilize it. That required some of the fill placed in the hole to be removed, creating an area to insert a trench box equipped with pipes for the grouting work.
Dirt began to fall into the tunnel around the edges of the trench box after 15 truckloads of grout were injected into the tunnel early Wednesday morning.
Hanford officials knew some additional dirt fall was possible as grouting began, and had a soil and sand mixture and equipment staged to be used if needed.
More fill mixture had been added around the trench box by 11 a.m. Wednesday.
Hanford leaders continue to discuss how to address the issue, but DOE said in a statement that it expects grouting to resume soon.
An estimated 650 truckloads are expected to be required to fill the nearly 360-foot-long tunnel.
DOE still expects to have the tunnel grouted on schedule by the end of the year.
“There is no question about the difficulty of the work, but we will work safely and methodically to fill up the tunnel,” said Doug Shoop, manager of the DOE Hanford Richland Operations Office.
Sen. Maria Cantwell, D-Wash., said she had been informed of the issue.
“I have been in touch with labor leaders, and in contact with the Department of Energy and contractors at the site,” she said. “Worker safety must be our number one priority, and I will continue to monitor this situation to ensure worker and environmental safety in the area.”
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