RICHLAND — Washington Closure Hanford has settled on a plan for one of its most hazardous environmental cleanup assignments -- retrieving radioactive waste dropped down long pipes buried vertically in the ground.
The Department of Energy contractor is proposing a keep-it-simple approach for the underground pipes at the 618-10 Burial Ground. It would use mostly commercially available equipment and technology to treat the waste underground -- breaking it up and in some cases grouting it -- before it's brought to the surface and packaged for disposal.
"It's doable, and it's safe," said Larry Gadbois, scientist with the Environmental Protection Agency, the regulator on the project.
Work already has begun to dig up waste at the 618-10 Burial Ground, which with the slightly newer 618-11 Burial Ground, has been expected to have some of the most hazardous materials in the burial grounds near the Columbia River.
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So far, workers have been digging up trenches, finding hundreds of bottles of laboratory waste and drums of radioactive waste, before tackling the nearby vertical pipe units in the burial ground.
From 1954 to 1963, some of the worst of the research waste generated at Hanford's 300 Area just north of Richland was trucked to the 618-10 Burial Ground about six miles north of Richland and a few hundred yards off Hanford's main highway.
That included highly radioactive waste left from the destructive testing of fuel irradiated for the weapons production of plutonium at Hanford's reactors, particularly the fuel that failed. Some waste from that research was collected in containers ranging from the size of juice cans to buckets and dropped into vertical pipe units that extended as far as 15 feet underground.
Soil, gravel or concrete was layered into the pipes at intervals to serve as shielding from radiation.
Most of the 94 vertical pipe units at 618-10 were made by welding five 50-gallon drums without tops and bottoms together to form a pipe. But the first 27 vertical pipe units, or VPUs, were made from corrugated pipes 12 to 14 inches in diameter buried in the ground.
"Some of the VPU's were fairly benign, but there are a couple with quite a bit of radiological material," said Cathy Louie, Department of Energy deputy project director.
In all cases, workers would use remotely operated equipment to handle and retrieve the waste. The process for all the vertical pipe units would start with driving a 30-foot-long, 48-inch-diameter steel pipe into the ground around each vertical pipe unit, which are up to 22 inches in diameter, to serve as an overcasing.
With the steel casing surrounding the pipes, the integrity of the walls of the vertical pipe units no longer would be an issue, Louie said.
Then an augur would be used to smash up the waste, including the walls of the vertical pipe units, breaking up and mixing up the waste and metal with soil.
"It size reduces everything. There won't be any intact containers," said Warren Bryant, Washington Closure manager of the 618-10 and 618-11 burial grounds.
The goal is to reduce the waste to small pieces and leave no voids or radiological hot spots.
By augering the waste and mixing it, the vertical pipe units are turned into waste sites similar to those Hanford workers are used to dealing with, Gadbois said.
Then a core sample would be pulled from the length of what remains of the vertical pipe unit to be analyzed for radioactive content. If the material in the vertical pipe units has enough transuranic waste -- such as plutonium or americium with radioactivity that decays over thousands of years -- the waste must be packaged for disposal at the nation's repository for transuranic waste, the Waste Isolation Pilot Plant in New Mexico.
For vertical pipe units with transuranic waste, Washington Closure would build an enclosure on the ground over the top of the pipe and then use a clamshell attached to heavy equipment operated outside the enclosure to scoop out the waste. It would be placed on a hopper that would drop it into a drum for packaging.
About 60 percent of the engineering for the equipment to deal with transuranic waste has been completed, Bryant said.
But if the vertical pipe unit waste can qualify as low level radioactive waste, the process would be simpler. Another augur would be inserted down the pipe, this one with a hollow stem to inject grout into the column, mixing it in from bottom to top.
An underground grout monolith would be created, which an excavator would then break into pieces as it is dug up. The pieces of grout then would be hauled to the Environmental Restoration Disposal Facility in central Hanford for disposal.
Except for the retrieval of the transuranic waste, "it's pretty much off the shelf with commercially available equipment and technology," Bryant said.
If the proposed cleanup method passes final reviews, Washington Closure could start driving the overcasings into the ground at 618-10 this fall. The same technology would be used for the 50 vertical pipe units at the 618-11 Burial Ground, which is near Energy Northwest's commercial nuclear power plant on leased land at Hanford.
As Washington Closure waits for approval of its plan, it also has had to come up with a new process to deal with the hundreds of bottles disposed on in the 12 trenches at the 618-10 burial ground.
With about half the trenches dug up, workers have found about 250 bottles ranging in size from about that of a pill bottle to a water bottle. But they have yet to start digging up the areas that ground penetrating radar has indicated contain heavier concentrations of bottles.
Most of those found so far are partially full of liquid, such as acids or bases, used for laboratory work.
Rather than determining the content of each bottle -- some don't have enough liquid to analyze -- Washington Closure plans to load bottles into a mixing box set inside a trench. They'll be crushed with the end of the excavator bucket and mixed with grout for disposal in 4-by-6-foot boxes at the Environmental Restoration Disposal Facility.
Sensors on the excavator will provide information, including on radiation and any temperature changes caused by chemical reactions.
Processing of the bottles could start in early March.
DOE has a 2018 legal deadline under the Tri-Party Agreement to finish cleanup of the 618-10 and 618-11 Burial Grounds, but it would like to have work finished in 2015 when most environmental cleanup along the Columbia River is planned to be completed.
* More Hanford news at hanfordnews.com.