Second Hanford tunnel at risk of collapse; DOE has a plan to prevent it

The Department of Energy plans to stabilize a second radioactive-waste storage tunnel at the Hanford nuclear reservation by filling it with concrete-like grout.

The decision was announced Tuesday after an independent panel of experts considered several options for stabilizing the Hanford PUREX plant’s second and larger storage tunnel. It recommended grouting.

On May 9, the older and smaller of the two PUREX plant tunnels storing contaminated equipment was discovered partially collapsed.

No radioactive material is believed to have escaped. But DOE moved quickly to prevent further collapse.

Grouting the second tunnel would reduce risk to workers and the environment, and allow the future disposal of the equipment and the materials in the tunnel, DOE said.

The 1,700-foot-long tunnel holds 28 rail cars loaded with junked equipment. It is highly contaminated with radioactive waste from the chemical processing of irradiated uranium fuel to remove plutonium for the nation’s nuclear weapons program.

DOE had a deadline under an order by the Washington State Department of Ecology, a Hanford regulator, to propose a plan by the end of this work week to stabilize the tunnel.

Grouting was part of the solution for stabilizing the first tunnel. Contractor CH2M Hill Plateau Remediation Co. filled the caved-in hole at the top of the 360-foot-long tunnel with sand and soil within a day. Then it draped thick plastic over the length of the tunnel and had it filled it with grout to further stabilize it.

The second tunnel, which is 1,700 feet long, was built eight years later in 1964 and was better constructed. While the older tunnel was built of timbers and had a flat roof, the longer tunnel was built of steel and concrete with a curved top.

However, a structural analysis triggered by the partial cave in of the first tunnel showed that the second tunnel also was at serious risk of collapse.

The Department of Ecology had initially required a proposal for stabilizing the second tunnel by Oct. 2, but agreed to extend the deadline after DOE said it was convening an expert panel to look at options.

DOE drew up a list of possible options, including covering the tunnel with a layer of heavy plastic, a tent or a pre-engineered building. DOE also listed filling the tunnel with expanding foam or with sand or clay as options.

Other ideas included a controlled collapse of the tunnel, although DOE officials said it could be difficult to keep contamination from spreading and to protect workers.

It also considered retrieving the waste immediately. Although that would be a permanent solution, it would require funding immediately and take longer, leaving the tunnel at risk of collapse in the meantime.

The expert panel recommended grouting after assessing options based on safety, ease, cost of implementation and whether the alternative would allow for future disposal of the waste in the tunnels.

“In the panel’s opinion, the grout stabilization provide maximum protection to workers, the public and the environment,” said the panel’s report to DOE.

Grouting also would leave DOE’s options open for permanent cleanup of the tunnel, the panel said.

DOE heard some push back at the public meetings from people who were concerned that grouting might make it more difficult to eventually remove and dispose of the waste stored in the tunnel.

But the panel pointed to DOE’s experience in grouting waste at its nuclear cleanup sites across the nation.

The grout could be cut into blocks, some of the blocks possibly encasing an entire rail car, and lifted out of the tunnel for disposal in a lined landfill at Hanford.

DOE sent a letter with its plans and met with the Department of Ecology on Tuesday.

“We’re just getting a chance to take a look at it,” said Alex Smith, manager of Ecology’s Nuclear Waste Program.

Although DOE plans to proceed with grouting as a contingency plan, Department of Ecology officials believe the plan requires state approval through an amended Ecology permit.

Smith anticipates a DOE public comment period, followed by a state public comment period on a possibly amended draft of the DOE plan. At least one and possibly two public meetings will be held, she said.

This story was originally published December 5, 2017 at 4:13 PM with the headline "Second Hanford tunnel at risk of collapse; DOE has a plan to prevent it."