The Department of Energy is making plans to fill the partially collapsed waste tunnel at the Hanford PUREX plant with grout, the agency said in a Wednesday meeting with state regulators and site contractor CH2M Plateau Remediation Company.
Personnel at the Hanford Site near Richland, Wash., discovered a 20-foot-long breach in the Purex tunnel May 9.
“Of all the options evaluated and laid out it seems to do the best job of stabilizing the tunnel as well as stabilizing and encasing the waste in the tunnel,” said Alex Smith, director of the Washington State Department of Ecology’s Nuclear Waste Program. Grouting also would provide radiation shielding, she said. Ecology is a Hanford regulator, along with the U.S. Environmental Protection Agency.
The decision to grout the tunnel partially meets an Aug. 1 deadline set in a legal order by the Department of Ecology.
The deadline, one of three in the order issued in response to the tunnel breach, requires DOE to submit a plan to the state on how it plans to ensure the safe storage of waste in the breached PUREX tunnel and a longer waste tunnel built nearby in 1964. Hanford officials do not believe there is an immediate risk that the longer tunnel will collapse. While the first tunnel was built mostly of creosoted timbers, the second tunnel was built of steel and concrete. Other deadlines in the state’s order include preparing structural integrity evaluations for both tunnels by July 1 and proposing a plan for final cleanup of the tunnels by Oct. 1.
Other tunnel-sealing options considered during discussions in Washington included near-term removal of the eight rail cars and the radioactively contaminated equipment stored in the tunnel. DOE and CH2M also considered placing a tent or a building over the tunnel. The grouting plan allows more immediate protection, is realistic given limited funds and would be more durable than some of the options considered, Smith said.
Two measures already have been used to temporarily stabilize the tunnel. The breach has been filled with 53 truckloads of sand and soil and a 400-foot-long piece of plastic has been pulled over the length of the tunnel and held in place with concrete blocks.
DOE and the state agreed that more needs to be done.
“As we cannot quickly determine the exact cause of the partial collapse of the tunnel, the rest of the tunnel is still subject to collapse,” said Doug Shoop, manager of the DOE Richland Operations Office.
Grouting already is commonly used at Hanford to stabilize radioactive waste. It has been used in the K Reactor East Basin, the hot cells of the Waste Encapsulation and Storage Facility and below deck at the U Plant canyon, Shoop said. It also is planned to be used for the highly radioactive spill beneath the 324 Building after the soil is dug up and placed in one of the building’s hot cells. If grouting is done in large areas, it can later be cut out in blocks for disposal.
Grouting the waste in place within the tunnel could make it easier to remove eventually, Smith said, although no plan has been considered and approved yet for permanent disposal of the waste. Filling the tunnel with grout could be done quickly without hindering the eventual permanent cleanup of the tunnel and its contents, Shoop said.
“All options are still in play by using this methodology,” said Shoop.
DOE and CH2M did not say how much the grouting would cost.
CH2M will hire a subcontractor to grout the 360-foot length of the PUREX tunnel, said Ty Blackford, CH2M president at Hanford. His goal is to have the job completed by November, and DOE has told the state the work will be done by the end of the year.
Smith said ideally, the state would like to have the tunnel grouted well before winter starts.
“We want to make sure they take the time to engineer the project safely and still do it as fast as they can get it done,” Smith said.
Although the exact cause of the tunnel collapse is not known, the unusually cold and wet winter may have contributed.
“We’re trying to not subject the tunnel to another hard winter or any further stress,” Blackford said.
The tunnel already has sampling ports that may be used to inject grout. Whether additional entry ports need to be added for the grouting is under consideration. A ventilation system will be needed to control heat and humidity while the grout cures. The tunnel’s ventilation system likely dates to the tunnel’s construction in 1956. Blackford said CH2M is more likely to add a simple, temporary ventilation system for the project.
