The Department of Energy is taking additional steps to stabilize two decades-old underground tunnels filled with radioactive waste at the Hanford Site in Washington state, after one of them partially collapsed earlier this year.
Hanford cleanup contractor CH2M Hill Plateau Remediation Co. announced Tuesday that it had selected a subcontractor to fill the damaged PUREX Plant Storage Tunnel 1 with grout by the end of 2017. Meanwhile, DOE has established a panel of experts to help set the strategy for stabilizing Tunnel 2, which remains intact but was determined to be at “high” risk of collapse.
The danger came to light on May 9, when Hanford workers discovered a roughly 20-foot by 20-foot breach in the top of the 61-year-old Tunnel 1. The tunnel, built primarily of creosoted timbers, holds eight railcars loaded with equipment from the Cold War-era facility once used to extract plutonium from irradiated fuel rods for use in nuclear weapons.
The finding led DOE to issue an emergency declaration and order thousands of Hanford workers to shelter in place, but there has been no sign of radiation release since the collapse was discovered. Soil and sand was poured into the hole to limit contamination or the release of radiation following the initial find, and a temporary cover was placed over the structure in mid-May.
The Energy Department and CH2M Hill in May selected grouting as a means for further stabilizing the tunnel. The contractor said this week it will pay Intermech Inc., a North Carolina industrial general specialist with an office near Hanford, $2.8 million to fill Tunnel 1 with the engineered concrete mix. The grouting is expected to start next month and to wrap up by Dec. 31, according to a CH2M press release.
“The placement of engineered grout in Tunnel 1 will improve tunnel stability, provide additional radiological protection, and increase durability while not precluding future remedial actions or final closure decisions,” CH2M spokesman Destry Henderson said by email Thursday.
The process will involve placing an elevated platform above the collapsed section, then driving pipes through the sand and soil into open space beyond, the contractor said. Hoses will be used to pour roughly 6,000 cubic yards of grout into the tunnel. The grouting is expected to cost $5 million to $8 million, Henderson said.
Dealing with Tunnel 2 is more complicated, according to the Washington state Department of Ecology, one of the regulators for the Hanford Site. The tunnel was built in 1964 of concrete and steel, but it holds far more waste (24 railcars of equipment) and is much longer than Tunnel 1 (1,686 feet vs. 358 feet).
The tunnel is well beyond its designed service life, and the Ecology Department ordered DOE by Aug. 1 to submit a plan for stabilization. CH2M on that date issued a report citing a number of alternatives, and said it would form a panel of “best and brightest” experts to help develop a detailed analysis that will be used to select a stabilization method.
The now-established eight-person group – consisting of DOE officials, representatives from Hanford cleanup contractor CH2M, U.S. academics, and a Canadian Nuclear Laboratories executive — will meet first today “to analyze options and identify needs for PUREX Storage Tunnel 2,” Doug Shoop, manager of DOE’s Richland Operations Office at Hanford, wrote in an Aug. 17 letter to Alexandra Smith, manager of the Ecology Department’s Nuclear Waste Program. Further meetings will be scheduled afterward.
Options being considered for Tunnel 2 include grouting, filling void spaces with sand or clay, installing some form of covering, and a controlled collapse.
The expert panel meets the first of three schedule requests laid out in an Aug. 4 notice to DOE from the Ecology Department. The state agency is still waiting on a complete initial analysis of options and identification of data needs, then the finished analysis of the alternatives for stabilizing Tunnel 2 and selection of the strategy to be used.
The state has directed the Energy Department to by Oct. 2 submit a modification to the Hanford site-wide permit that will lay out the detailed plan for Tunnel 2, Ecology spokesman Randy Bradbury said Wednesday.
