Workers should begin emptying waste from the Hanford double-shell tank with a leak from its inner shell in fewer than three months, according to the Department of Energy and the state of Washington.
The leak within the oldest of Hanford’s double-shell waste storage tanks, Tank AY-102, was discovered in 2012. But the state agreed to allow DOE until March 4 of next year to start emptying the tank after concerns were raised about keeping its radioactive sludge from overheating.
DOE said last year that the spring 2016 deadline would provide enough time to have equipment in place to retrieve not only the liquid portion of the waste in the tank but also the radioactive sludge that sits beneath it. The liquid helps cool the sludge, which generates heat.
The engineering work for the project has been completed and construction and installation of equipment is 85 percent complete for the waste retrieval work, said Reggie Eakins, the technical program manager of the project for DOE, at a recent committee meeting of the Hanford Advisory Board.
DOE has spent about $58 million on the project and expects to spend $25 million more to complete waste retrieval.
Plans call for starting retrieval with a set of sluicing systems inserted into the top of the enclosed tank. The systems, which have been used for more than a decade at Hanford to empty single-shell waste tanks, use a jet of recycled liquid to dissolve and move waste toward a pump for removal.
As work goes deeper into the tank, which holds about 750,000 gallons of waste, more recently developed enhanced reach sluicing systems will be used. They can reach deeper into the tank and fold out to reach more areas. The sluicers also include a high pressure water system that may be needed to break up hardened waste at the bottom of the tank.
The newer equipment also has been used successfully in other Hanford tanks.
“We are not going to reinvent the wheel with this retrieval,” said Joni Grindstaff, the deputy designated federal officer to the advisory board.
DOE is required by the state, the regulator on the project, to have the waste retrieved by March 4, 2017.
Sixty gallons of waste is believed to have leaked at three sites into the 2.5 feet wide space between the tank’s shells, Eakins said. Monitoring of those sites is done biweekly by dropping cameras down risers that extend into the space between the underground tank’s shells.
Eakins estimated that about five gallons had leaked over the last year. A pump was installed this fall in the space between the shells in case the leak rate increases and waste needs to be removed.
The tank loses about 20,000 gallons of volume a year to evaporation because of the heat generated by the radioactive waste.
As long as DOE starts removing the solid waste in the tank as soon as the liquid waste above it is removed, the temperature rise should be manageable, said Jeremy Johnson a DOE deputy project director in the tank farms.
If a problem occurs that requires a shutdown to retrieval operations for a long period, liquid waste could be added back into the tank for cooling, he said.
The state is pleased with the efforts of DOE and its tank farm contractor, Washington River Protection Solutions, said state officials.
“It’s a hard job and lots of people are doing a good job,” said Jim Alzheimer, a tank engineer with the state Department of Ecology.
The waste will be transferred into one of Hanford’s 27 usable double-shell tanks, just as waste from Hanford’s 149 leak-prone single-shell tanks is being transferred into the double-shell tanks. The waste will be stored there until it can be treated for disposal at the vitrification plant under construction.
Hanford has 56 million gallons of radioactive waste left from the past production of plutonium at Hanford for the nation’s nuclear weapons program.
Preparations also are being made at the double-shell tank that will receive the waste from Tank AY-102. Waste will be moved through 1,500 feet of transfer line.
Because the receipt tank is nearly full, its waste must be emptied into other double-shell tanks that have space available and compatible waste. Double-shell tank space is nearing capacity with no waste expected to be sent to the vitrification plant to free up more tank space until at least 2022.
Experts continue to disagree about whether emptying Tank AY-102 is the best use of Hanford’s budget. DOE has maintained that the leak is confined within the shells of the tank, unlike one single-shell tank that is leaking radioactive waste into the ground of central Hanford now and dozens of others where waste has leaked or spilled in the past.
Because tank farm workers are preparing Tank AY-102 for waste retrieval, just one shift of workers rather than two are available to empty single-shell tanks, according to DOE.
Higher risk projects are being deferred because of work to empty Tank AY-102, said Dick Smith, who represents the city of Kennewick on the advisory board. Higher risks include the 1,936 radioactive cesium and strontium capsules stored underwater in the Hanford Waste Encapsulation and Storage Facility, he said.
The DOE Office of Inspector General said last year that the storage facility is at the highest risk of any DOE plant across the nation in the event of a natural disaster, such as an earthquake, beyond what it was designed to sustain.
But Johnson said emptying Tank AY-102 will allow it to be inspected to learn what caused the leak, which could provide helpful information regarding Hanford’s other double-shell tanks.
The outer shell of Tank AY-102 is an eighth inch thick and has been rusting for 40 years, said Dirk Dunning, who represents the state of Oregon on the board. Its construction is poor compared to the inner shell, he said.
It’s unknown what could happen if the tank overheats, he said. The Defense Nuclear Facilities Safety Board has raised concerns about the ability to keep the waste cool because leaking waste likely is running through channels at the bottom of the tank intended to help with cooling.
“The problems are severe and this tank needs to be emptied soon,” he said.