Workers at the Hanford Site in southeast Washington have completed the filling a second waste storage tunnel with engineered grout, significantly reducing the risk of a collapse and possible release of radioactive materials, the Department of Energy said on Monday.
The contractor, CH2M HILL Plateau Remediation Company (CHPRC) began grouting Tunnel 2 next to the Plutonium Uranium Extraction (PUREX) Facility in October 2018. The project was prompted by the May 2017 partial collapse of another storage tunnel (Tunnel 1) on the site that was the first to be filled. The partial collapse caused a two-day shut down of work at the Hanford Site.
Crews placed the last truckload of grout into Tunnel 2 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,” said Brian Vance, DOE’s Manager for the Hanford Site. “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 determined to be the best choice for stabilizing this tunnel by the Department’s independent panel of experts because it provides the highest level of stability and protection and does not preclude future remedial actions.
Joe Franco, DOE Deputy Manager for the Richland Operations Office said completion of the grouting is not the final outcome of the radioactive materials in the two tunnels. “Even though the tunnel is full of grout, this does not preclude future remedial actions or limit final closure decisions,” Franco said.
“It just means the risk to people and the environment is significantly reduced while those decisions are made.”
Filling the tunnel took approximately 4,000 truckloads of grout – 40,000 cubic yards.
Cameras in the tunnel ensured the grout flowed the length of the tunnel and around the contaminated equipment inside. The grout was injected in several lifts, or layers, and each lift was allowed to set before the next began.
After Tunnel 1 collapsed, an engineering evaluation of Tunnel 2 showed it also was at high risk of doing the same. CHPRC and subcontractor Intermech, Inc., developed mock-ups of grout placement to enhance lessons learned from successfully stabilizing Tunnel 1 and to train the workforce to ensure a safe, deliberate approach to reducing this significant risk in Tunnel 2.
A number of safety controls ensured employee and environmental safety during grout placement, including 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 to ensure reliable delivery of grout while decreasing traffic impacts.
Hanford crews will continue to monitor the tunnel until the full mission is complete, the DOE statement said.
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