Work resumed despite recent frigid temperatures to empty an underground tank at Hanford with radioactive waste leaking between its double shells.
The Department of Energy faces a Washington state deadline of March 4 to have enough waste removed from Tank AY-102 to determine the source of the leak. Then a decision will be made on whether the tank can be repaired or must be closed.
A federal judge ordered work stopped that disturbed waste until he ruled on a request from the state of Washington and other plaintiffs to immediately increase worker protections.
As the lawsuit advances toward an October 2017 trial, U.S. Judge Thomas Rice ruled last month that supplied air respirators adequately protected workers in the interim from chemical vapors associated with waste in underground tanks.
Work to empty tanks disturbs the waste they hold, which can increase the chances of chemical vapors being released.
Work had been halted to empty waste from Hanford’s oldest double-shell tank first because new retrieval equipment needed to be installed but had been expected to resume in September before the judge’s initial order. No waste is known to have escaped from the outer shell into the ground.
“Our team has spent months preparing for this final phase of AY-102 retrieval,” said Mark Lindholm, president of DOE contractor Washington River Protection Solutions, in a message to employees Monday.
Hanford workers emptied most of about 800,000 gallons of waste from the tank in March and April of this year, but then needed to switch to more nimble waste retrieval equipment to get to the remaining 40,000 gallons of radioactive sludge at its bottom.
Because disturbing the waste increases the risk of chemical vapor releases, Hanford officials have planned all work for nights and weekends when no other workers should be in the area of the AY Tank Farm.
Work started the second weekend of this month, but stopped after 20 minutes because of equipment issues. The night of Dec. 13 workers tried again and began to spray liquid waste on the sludge in the tank to move it toward a central pump for retrieval.
But then bad weather disrupted work, with snow and temperatures dipping to minus 4, delaying more work.
Hanford officials were considering restarting Monday night, but work was uncertain because of a forecast of a possible mix of snow, sleet and freezing rain.
In the spring multiple reports were made of possible odors or symptoms related to chemical vapors as waste retrieval began on Tank AY-102.
Before work restarted to empty the tank this month, almost all Hanford workers were offered briefings on plans to resume work, said Doug Greenwell, manager of tank waste retrieval for Washington River Protection Solutions.
During night and evening shifts when work on the tank is scheduled, barricades are set up to prevent any worker from accidentally driving into the area and reader boards announce that only authorized workers are allowed in much of the 200 East Area. More than half of the nuclear reservation’s tank farms are in the 200 East Area.
Workers are required to wear supplied air respirators as protection from vapors both in the AY-102 Tank Farm and near the stacks for Tank AY-102 and the sturdier double-shell tank receiving the waste. The waste is being stored until it can be treated for disposal at the Hanford vitrification plant.
Greenwell calls the precautions “defense in depth.”
Tank AY-102 has had a slow leak into the space between its shells for several years before the state and DOE reached a settlement agreement requiring it to be emptied by March 4.
As work started to retrieve waste in the spring, more waste began leaking into the space between the shells. Washington River Protection Solutions had anticipated it and had installed a pump between the shells that was used periodically to pump waste back into the main tank this spring.
Hanford officials fully expect the same issue as more waste is retrieved this winter and are prepared to again address it, Greenwell said. Workers now know what section of the interior leak may have the leak and can be more careful there.
Work started in the spring with two sluicers, which spray liquid waste to break up sludge and move it toward a central pump in the enclosed tank. Hanford officials knew they likely would not be capable of finishing the job.
Since spring workers have been replaced them with four extended-reach sluicers that are more robust, have a longer reach and can be maneuvered into more areas of the tank. The new sluicers also have a high-pressure water spray feature that can be used, if needed, to break up waste. Some tanks have a layer of waste the consistency of asphalt beneath liquid sludge and waste.
This summer workers practiced using the equipment and maneuvering it around many pipes installed in the tank at a full-scale mockup of a Hanford tank at the Cold Test Facility.
Now workers are looking forward to getting on with waste retrieval, Greenwell said.
“We want to inspect the tanks and learn from them how to manage the (other double-shell) tanks going forward,” he said.
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