The Department of Energy has come up with a range of options to protect the public and environment from the threat of collapse of another Hanford waste tunnel.
But none of them is perfect.
DOE discussed the options with about 50 people attending a public meeting and more listening on the internet Thursday night in Richland. It is required to tell the state Department of Ecology which it proposes to pursue by Aug. 1.
The concern was triggered by the partial collapse of a storage tunnel at the nuclear reservation’s PUREX processing plant discovered May 9. It holds eight rail cars with old equipment contaminated with highly radioactive material.
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The state ordered DOE to assess the structural integrity of a second, longer PUREX waste storage tunnel built a few years later in 1964. It holds 28 rail cars holding radioactive waste.
The results of the assessment were not good.
Tunnel No. 2 was built with materials that included corrugated sheets of steel, concrete girders and steel I-beams, rather than the timbers that were the primary building material of Tunnel No. 1.
But it still is at serious risk of collapse, the assessment found.
DOE now is considering options to either prevent a collapse of the second tunnel or protect people and the environment from a release of airborne radioactive particles in the event of a collapse.
Factors being weighed for different options include cost, the level of protection offered and whether the proposed fix would interfere with eventual permanent cleanup of the tunnel. DOE also is considering how long options would take to complete as the threat of a collapse looms.
No option has yet been picked, said Al Farabee, who spoke for DOE.
Least expensive would be to pull a heavy sheet of plastic over the length of the 1,700-foot tunnel, Farabee said.
That was done as an immediate measure at Tunnel No. 1, mostly to keep rain from seeping into the eight feet of soil piled on its roof and adding to the weight on its timbers.
But the plastic might only last for a matter of months, he said.
Criteria used for evaluation of options: protects people and the environment, allows future cleanup, ease of doing, ease of upkeep, speed of implementing and cost.
Different styles of tent covers are being considered, which also would be relatively low cost. While they might control the spread of contamination in a tunnel collapse, they would not contain it to the tunnel.
A pre-engineered steel building could be built over the tunnel, but it has the potential to trigger a collapse of the tunnel during construction, according to DOE.
Two options to fill the tunnel are being considered, with an additional new one proposed during the meeting.
Filling the tunnel with expanding foam would help stabilize the tunnel and provide contamination control. But the method has been considered at other projects, including for the glove boxes at the Plutonium Finishing Plant, but not used because the foam presents a potential fire hazard, Farabee said.
The tunnel also could be filled with a concrete-like grout, the stabilization method already planned as an emergency measure for the first tunnel. The state supports the plan at the tunnel that already has partially collapsed.
DOE said it could later saw the grout and the waste in the tunnel out in pieces for permanent disposal.
Options being evaluated: cover with plastic, cover with a tent, cover with a building, fill with expanding foam, fill with grout, cause a controlled collapse or retrieve the waste from the tunnel.
But the approach was met with skepticism by some at the Thursday meeting. Sawing through rail cars would be difficult and there could be a risk of contamination to workers cutting out heavily contaminated equipment, they said.
A better option might be to fill the tunnel with sand or bentonite clay that would not have to be sawed out, said Scot Adams, a Kennewick environmental scientist and geologist. He’s familiar with the second tunnel after inventorying its contents in the 1990s for a Hanford contractor.
DOE knows that flowing grout around the equipment in the tunnel to fill most of its space should be doable, based on experience with grout at other Hanford projects, Farabee said.
Adams said the 17 inspection holes along the tunnel should allow particles of bentonite to be blown into the tunnel.
DOE also is considering a controlled collapse of the tunnel, preempting any future collapse and filling any air space within the tunnel. But it could be difficult to to control contamination and protect workers during the collapse, according to DOE.
DOE also could move to a permanent solution, retrieving the waste from the tunnel. However, it would be a multi-year effort, requiring significant planning, Farabee said.
DOE has another deadline on Oct. 1, when it must propose a plan to the state for permanently cleaning up the waste in both tunnels.