The shoring of a waste storage tunnel at the Dept. of Energy’s Hanford Nuclear Waste Site in southeast Washington proved successful and wraps the response to a May 2017 partial collapse of an adjoining tunnel.
In 2017, Tunnel 1 next to the Plutonium Uranium Extraction Facility (PUREX) partially collapsed, causing an emergency response and shut down of work at the Hanford site for two days. An engineering evaluation of Tunnel 2 next door showed it also had a high risk of collapse, leading to contractor CH2M Hill Plateau Remediation Company (CHPRC) beginning the grouting of Tunnel 2 in October 2018.
“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, DOE’s manager for the Hanford site, said in a statement. “The team did an excellent job performing this work safely, reducing a potential risk on the site.”
Tunnel 2 contains 28 railcars with contaminated processing equipment and materials generated during Hanford’s weapons production era. Grouting was chosen as the best choice for stabilizing the tunnel by an independent panel of experts because it provides the highest level of stability and protection and does not limit future remedial solutions.
“Even though the tunnel is full of grout, this does not preclude future remedial actions or limit final closure decisions,” Joe Ranco, DOE deputy manager for the Richland Operations Office, said in a statement. “It just means the risk to people and the environment is significantly reduced while those decisions are made.”
It took approximately 4,000 truckloads and 40,000 cu yds of grout to stabilize the tunnel. Cameras in the tunnel ensured the grout flowed the length of the tunnel and around the contaminated equipment inside. Injected in several lifts, or layers, the grout was allowed to set before the next lift began.
“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,” Ty Blackford, president and CEO of CHPRC, said in a statement.
During the process, CHPRC and subcontractor Intemech Inc. developed mock-ups of grout placement to enhance lessons learned from stabilizing Tunnel 1 and to train the workforce for a safe, deliberate approach to Tunnel 2. Continuous monitoring and detection systems to alert workers to potential chemical or radiological exposure conditions, lights and cameras installed in the tunnel to allow crews to remotely monitor grout placement and progress and on-site batching of the grout provided safety and efficiency enhancements during the project.
The tunnel, five times longer than Tunnel 1, required 26,000-man hours and 7,000 miles driven between the on-site batch plant and tunnel. Crews used 1,300 deliveries to the batch plant to complete the grouting project.
Follow Tim Newcomb on Twitter at @tdnewcomb.