The second of two storage tunnels for radioactive waste from the PUREX Plant at the Hanford Site in Washington state has been stabilized.
Contractor CH2M Hill Plateau Remediation Co. completed work on April 26. “The tunnel has been filled with grout, and we’ve significantly reduced the risk of contaminating Hanford workers, the public, or the environment,” Brian Vance, Department of Energy manager for the Hanford Site, said in a press release.
Grouting began in October 2018, with the project 90 percent complete in early April. The concrete-like material was topped off in recent weeks, filling any remaining voids in the tunnel. In total, roughly 4,000 truckloads, or 40,000 cubic yards of grout, were placed in the tunnel, which is about 1,700 feet long and stores 28 railcars loaded with failed and obsolete equipment contaminated with highly radioactive waste.
“It took a lot of preparation and day-to-day attention to ensure we could make, move, and place thousands of trucks of grout safely while assuring the potential for a radiological release was minimized,” said Ty Blackford, president of CH2M Hill Plateau Remediation. Workers practiced and tested equipment for grouting the tunnel before starting work. They also were able to determine the optimal grout mixture that would flow through after being added from risers every 100 feet along the tunnel’s length.
Concerns were raised about the second PUREX Plant tunnel, constructed in 1964, after the plant’s first tunnel, built in 1956, partially collapsed in May 2017. Hanford workers were ordered to take cover for hours until officials determined that no radioactive material had been released. The collapse of a section of the tunnel shut down work at Hanford for two days.
A June 2017 structural assessment determined the second tunnel was also at risk of collapse. But concerns increased in spring 2018 when a video inspection of the interior of the tunnel showed corrosion of bolts and weld plates.
The first tunnel, which holds eight railcars with waste from the former plutonium-extraction plant, was filled with grout under emergency conditions by November 2017.
Grouting was recommended in late 2017 for the second tunnel as an interim step after an independent panel of experts considered options. The panel concluded that grouting would prevent a collapse, while not precluding future remediation of the waste in the tunnel.
Although mayors in four communities near Hanford called for the Washington state Department of Ecology to curtail a public comment process on the tunnel to allow grouting to begin in summer 2018, the state refused. It did, however, read comments as they were submitted and gave the Department of Energy approval to begin grouting immediately after the comment period ended.
“We approved this action, but not before insisting that the pubic have a chance to comment on the proposal,” Ecology said in a statement this week. “Opponents raised legitimate concerns, but in the end those concerns did not outweigh the potential environmental and safety threats that could have been posed had the tunnel collapsed and exposed its highly radioactive contents.”
Some people were concerned that if the waste in the tunnel were grouted, no further action would be taken to clean up the waste.
Ecology said its next step will be to work with the Energy Department to determine the ultimate disposition of the contents of both PUREX tunnels. Discussions have not begun on final remediation of either tunnel, but grouting “means the risk to people and the environment is significantly reduced while those decisions are made,” said Joe Franco, Energy Department deputy manager for the Richland Operations Office.
