The Department of Energy plans to step up monitoring of a Hanford tunnel storing highly radioactive waste while it studies ways to keep it from collapsing.
It proposes convening a “best and brightest” expert panel to analyze options for the intact tunnel at the nuclear reservation’s PUREX plant, it said in a report delivered Tuesday to the Washington State Department of Ecology.
More study is not what the state expected DOE to propose.
The state issued a legal order in May requiring DOE to submit a plan to stabilize the structure of both the plant’s intact tunnel and another waste-storage tunnel at PUREX that was discovered partially collapsed May 9.
No radioactive particles were detected in the air after the cave-in, but workers were ordered to take shelter for several hours in buildings with ventilation systems shut off as a precaution.
DOE had earlier proposed filling the breached tunnel with grout as a temporary stabilization method.
The plan that was due and delivered Tuesday does not identify a plan to also stabilize Tunnel 2, the state said.
“However, their proposal to convene a panel of experts to analyze options to stabilize Tunnel 2 and the waste in it has merit, especially if it results in a robust solution that all agree will be adequately protective,” the state said in a statement.
The state is concerned about whether DOE can meet its next deadline, submitting a proposal by Oct. 2 with a plan for ensuring the safe storage of the waste within both tunnels.
“It may be difficult for Energy to comply,” the state said.
“Our goal has been and remains to have a final plan . in hand by the Oct. 2 deadline, as set out in our enforcement order,” it said.
DOE and its contractor. CH2M Hill Plateau Remediation Co., took immediate steps to stabilize the first tunnel.
It filled the breach with sand and soil and covered its 360-foot length with a piece of heavy plastic to keep any rain from adding to the weight of eight feet of soil above its roof.
Plans are being made now to fill the tunnel with grout to help prevent further collapse and contain any radioactive particles that could become airborne in a collapse.
A structural review of the second tunnel, which was required by the state order, found that it also was at serious risk of a cave-in.
The enhanced surveillance proposed for the tunnel would include using video cameras that could be monitored off site to watch for any changes. Radiological surveys would be done near the tunnel. Laser and other technology would be used to check for changes in the ground level above the tunnel.
Geophysical surveys would provide information about the depth of soil over the tunnel and the location of the 28 rail cars holding radioactive waste within it. Geophysical surveys have been done before at Hanford with ground-penetrating radar.
In addition, robotic equipment would be inserted in the tunnel to look at the condition of its interior, check radiation levels and provide information about the location and condition of stored waste.
The surveillance would not provide any immediate help to stabilize the equipment or provide protection from radioactive particles becoming airborne in a collapse, the DOE report said.
But it could provide useful information about the tunnel and would not preclude additional protective options.
At a public meeting in July, DOE discussed multiple options it was considering to stabilize the tunnel until permanent cleanup of the waste is done.
Some options were similar to those used or planned for Tunnel 1 – covering it with heavy plastic and filling it with concrete-like grout that would flow around the waste within the tunnel.
Other proposals included covering it with a tent or a pre-engineered building.
DOE also is considering filling the tunnel with expanding foam or with sand or clay, an option it put on the list after it was suggested at the public meeting.
A controlled collapse of the tunnel is being evaluated, although it could be difficult to keep contamination from spreading and protect workers.
DOE also is considering whether to go ahead and retrieve the stored waste. It would be a permanent solution, but would take more time than other solutions to plan and carry out.
Options are being evaluated on factors including 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.
The expert review planned by DOE would consider the tunnel design, operating history and waste inventory. Information would be used for a detailed analysis for Tunnel 2 and then a decision on which option would be best for stabilization of the tunnel.
“We will continue to work closely with Ecology to review the options for ensuring safe storage of waste in the tunnels,” Doug Shoop, manager of the DOE Richland Operations Office, said on Tuesday.
The tunnel that partially collapsed was built of timbers in 1956 and had a flat roof. Eight rail cars loaded with highly radioactive waste from operations at the PUREX plant were pushed into the tunnel.
The second tunnel, built in 1964, was built in the shape of a Qunoset hut, with steel ribs supporting corrugated steel plate roof panels.
After two collapses during construction, it was re-engineered to add steel I-beams and reinforced, arched concrete girders over the top.
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