Workers at the US Hanford Site in southeast Washington state have finished filling a second waste storage tunnel with engineered grout, reducing the risk of a collapse and possible release of radioactive materials, the Department of Energy (DOE) said on 29 April.
DOE contractor CH2M HILL Plateau Remediation Company started grouting Tunnel 2, which is located next to the Plutonium Uranium Extraction Facility in October 2018. Crews placed the last truckload of grout on 26 April.
“The tunnel has been filled with grout, and we’ve significantly reduced the risk of contaminating Hanford workers, the public, or the environment,” noted Brian Vance, DOE’s manager for the Hanford site.
Tunnel 2 contains 28 railcars with contaminated processing equipment and materials generated during Hanford’s nuclear weapons production era. The decision to grout Tunnel 2 was made after the partial collapse of an adjacent waste storage Tunnel 1 in May 2017 caused an emergency response and shut down work at the Hanford Site for two days. An engineering evaluation of the second tunnel showed it too was at high risk of collapse.
CHPRC and subcontractor Intermech, developed mock-ups of grout placement to enhance lessons learned from successfully stabilising Tunnel 1 and to train the workforce. Grouting was determined to be the best choice for stabilising this tunnel by DOE's independent panel of experts because it provides the highest level of stability and protection and does not preclude future remedial actions. “Even though the tunnel is full of grout, this does not preclude future remedial actions or limit final closure decisions,” said Joe Franco, DOE Deputy Manager for the Richland Operations Office.
Approximately 4000 truckloads (40,000 cubic yards) of grout were placed in the Tunnel 2. 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.
Ty Blackford, CHPRC president and CEO said: “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 minimised.”
Continuous monitoring and detection systems were in place 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. Looking ahead, Hanford crews will continue to monitor the tunnel until the full mission is complete.