Hanford workers are practicing how they will lay a 400-foot-long piece of heavy plastic over a partially collapsed tunnel storing radioactively contaminated equipment.
“We need a very calm wind to work the cover,” said Ty Blackford, president of Department of Energy contractor CH2M Hill Plateau Remediation Co.
“It’s quite sizeable,” he said. “We don’t want it to sail and someone to get hurt with plastic tarp that is flying.”
The first calm day in central Hanford may be Friday, allowing work to start then. The project, using industrial plastic that is heavier than a conventional tarp, could be completed in eight to 10 hours.
The 100-foot-wide swath will be laid out along the nearly 360-foot-length of the tunnel. Ideally, it will be installed all in one piece, but if needed it will be installed in a couple of shorter, overlapping sections.
Then a manlift — a bucket that can be extended across the berm while holding a worker — will be used to help gently pull and drape it across the soil berm topping the tunnel. The plan would keep both equipment and people off the top of the tunnel.
The plastic will be held in place with close to 150 concrete ecology blocks lining each side of the berm. Each block is about 2-by-2 by 4 feet and weighs about 3,800 pounds.
The plastic will need to be fitted around several sampling ports, with sealed pipes sticking a few feet out of the ground.
100 by 400 feet size of plastic to be laid over tunnel
3,800 pounds weight of each concrete block that will hold the plastic in place
The dry run is allowing practice on moving the heavy plastic safely and determining what wind speeds can be tolerated, Blackford said.
On the morning of May 9, an area near one end of the older of two waste tunnels at the PUREX processing plant was discovered to have collapsed.
The breach, measuring about 20-by-20 feet, was filled with a mixture of sand and soil as an initial step to stabilize the collapse and prevent any radioactively contaminated particles from becoming airborne.
The plastic covering should help prevent airborne contamination in case more of the tunnel collapses and also will help keep rain from infiltrating the eight feet of soil covering the tunnel, putting more weight on the tunnel’s roof.
No evidence of any airborne contamination has been discovered, either from air monitoring or sampling the ground in the area of the tunnel, according to Hanford officials. It holds contaminated equipment from the defunct PUREX plant in central Hanford.
Data collected by both DOE and the Department of Health should be made public in the next several days.
The waste has not been characterized for disposal, but it likely contains enough plutonium or similar radioactive-emitting isotopes that much of it would be considered transuranic, said Doug Shoop, manager of the DOE Hanford Richland Operations Office. Hanford’s transuranic waste is shipped to the Waste Isolation Pilot Plant in in New Mexico for disposal.
Hanford officials have started to look at the possible cause of the collapse, but the reason for the failure may never be known for certain, Blackford said.
The tunnel, supported by creosoted timbers, has held waste since 1960 — more than 50 years. Past reports have speculated about how quickly gamma radiation from the waste might weaken the wood.
In all likelihood (the cause) was a combination of a lot of things. I’m more interested in correcting conditions such that it is not possible to have a failure like this in the future.
Doug Shoop, manager of the Richland Operations Office
The Northwest also had unusually harsh weather over the past winter, with nearly twice as much snow as usual at Hanford, and temperatures cold enough to make the winter the sixth coldest on record at Hanford.
“In all likelihood it was a combination of a lot of things,” Shoop said. “I’m more interested in correcting conditions such that it is not possible to have a failure like this in the future.”
DOE, CH2M and the state Department of Ecology plan to meet Monday to discuss next steps to stabilize the waste tunnel.
Talks are expected to include discussion of a schedule for work and a rough estimate of costs.
Although DOE has declined to discuss the next step until it has state agreement on a plan, the state Department of Ecology has said that filling the tunnel with grout is under consideration.
Hanford officials expect the cost of the work to be pulled from other work in its current appropriation from Congress for the fiscal year that ends in October.
As part of the bipartisan budget deal approved earlier this month, $114 million of $191 million proposed to be cut from the budget for the Richland Operations Office was restored.