The second Hanford PUREX plant tunnel storing highly radioactive waste has been stabilized to prevent a collapse.
Work to fill the tunnel with concrete-like grout began in early October and was completed at the end of last week.
Local government officials are relieved.
“We experienced a horrible winter with a massive amount of snow,” said Pam Larsen, executive director of Hanford Communities, a coalition of local governments, at a recent meeting of the Hanford Advisory Board.
“The tunnel could have collapsed,” she said. “It would have been catastrophic for our regional economy.”
Concerns about the second PUREX tunnel were raised after the first tunnel partially collapsed in spring 2017. An unusually wet winter may have contributed to the collapse.
Filling the second tunnel with grout is a temporary measure to prevent a possible collapse and release of radioactive particles into the air, with plans to clean up the waste in the tunnel to be made in the future.
“We’ve significantly reduced the risk of contaminating Hanford workers, the public or the environment,” said Brian Vance, Department of Energy manager for the Hanford nuclear reservation.
Recent weeks have been spent topping off the grout and filling any voids, after 90 percent of the work had been completed at the start of the month.
About 40,000 cubic yards of grout, or 4,000 truckloads, were needed to fill the tunnel, which is 1,700 feet long.
It holds 28 rail cars loaded with obsolete and failed equipment that is contaminated with highly radioactive waste from the past production of plutonium at Hanford for the nation’s nuclear weapons program.
When the first tunnel partially collapsed, thousands of Hanford workers were ordered to take cover and the Tri-Cities-area anxiously waited for information until it was determined that there had been no release of radioactive particles.
The soil topping the tunnel fell into the breach, covering the waste.
DOE, under orders from the Washington state Department of Ecology, quickly began a structural evaluation of the second tunnel.
The tunnel that partially collapsed was built in 1956 of Douglas fir timbers and had a flat roof. The second tunnel was built in 1964 with concrete and steel with a rounded roof.
Concerns of collapse increased
Despite the second tunnel’s more modern materials and design, it was also at risk of collapse, according to an assessment completed by DOE in June 2017.
Concerns increased in 2018 as a spring video inspection of the highly radioactive interior of the tunnel showed corrosion of bolts and weld plates.
The risk of failure was raised to “anticipated” based on DOE nuclear safety standards.
DOE asked that it be allowed to start grouting the tunnel in August, which would have meant not completing a public comment and hearing process underway by the state.
Mayors of the three Tri-Cities and West Richland urged the Washington state Department of Ecology to skip additional public meetings, saying any delay could put adjoining communities at risk.
Ecology refused, saying communities in Washington state have a right to review and weigh in on important Hanford decisions.
Hanford watchdogs were concerned that grouting might become a permanent solution, with the radioactive waste left in the ground permanently.
“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,” Ecology officials said in a statement Monday.
It congratulated DOE for completing the project.
Ecology officials moved quickly through its public process, reviewing comments as they came in, and gave DOE approval to begin grouting the tunnel immediately after the public comment period ended.
Contractor CH2M Hill Plateau Remediation Co. was prepared. It already had ports installed to pump the grout into the tunnel, a grout batch plant standing by and trucks ready to roll.
CH2M had begun preparations as soon as grouting was identified by an independent expert panel in late 2017 as the best way to stabilize the tunnel.
“We spent an awful lot of time doing upfront planning,” said Mark Wright, vice president of project technical services for CH2M at Hanford.
Filling the tunnels
The first tunnel had been stabilized with grout by fall 2017 under emergency conditions. CH2M subcontracted grouting work to Intermech Inc. of Richland, and Intermech was also picked as a subcontractor for the second tunnel.
In both tunnels, grout was added in layers, with each layer allowed to set before the next layer was added.
But the second tunnel was five times longer, requiring changes to procedures and equipment as grout was added every 100 feet along the tunnel.
Workers practiced and tested equipment for grouting the the tunnel at mock up sites off Hanford, which was key to the success of the project, said Al Farabee, DOE project director.
Hanford staff were able to determine the best mixture for grout and how to pour the grout safely with the piping systems designed for the project, he 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 minimized,” said Ty Blackford, president of CH2M at Hanford.