Hanford crews have begun work to remove radioactive waste from the bottom of another of Hanford's underground tanks, with a goal of having it emptied by the end of the calendar year.
Workers have not finished emptying one of Hanford's 149 leak-prone, single-shell tanks since spring 2007, but the Department of Energy faces a consent decree requirement to have 10 more emptied by fall 2014.
"It appears there is a lot of work ahead of us, but we've always planned to ramp up retrieval with the technology that we're implementing," said Joanne Norton, DOE project director for tank waste retrieval.
DOE and its contractor, Washington River Protection Solutions, are on pace to meet the 2014 deadline, she said.
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Washington River Protection Solutions expects to be retrieving waste from three tanks this calendar year.
Earlier this month, it began retrieving radioactive waste from Tank C-107 with new technology, the MobileArm Retrieval System, or MARS, the largest and most robust system tried yet to get highly radioactive solids out of enclosed underground tanks.
It removed 20 percent of the 253,000 gallons of waste in Tank C-107 before work was moved to the latest tackled tank, C-108, said Kent Smith, tank retrieval manager for Washington River Protection Solutions.
"I think MARS is working fabulously," said Nancy Uziemblo, of the Washington State Department of Ecology, a Hanford regulator. "It is doing what it is designed to do."
However, work likely will slow as retrieval continues on the tank and the waste becomes more difficult to retrieve, based on experience with other retrieval technologies.
Work has shifted recently from Tank C-107 to TankC-108. The method being used to empty the latest tank requires intermittent work and work can only be done on one at a time. The two tanks share a common pipe and valve system and their waste is pumped to the same newer, double-shell tank to await treatment for disposal.
Tank C-108 has just 6,800 gallons of waste in a hard layer at its bottom that tank farm workers were not able to dissolve and pump out when the rest of its solid waste was removed using a modified sluicing system four years ago.
"Removing the hard layer of waste from our tanks is normally the most difficult part of the retrieval process, and we needed time to find a way to do it that would be fast and economical," said Dave Saueressig, C-Farm retrieval manager, in a statement.
The contractor is trying a system of water soaks with the addition of 9,000 gallons of concentrated sodium hydroxide, a common industrial caustic already used in Hanford's newer tanks to preserve the correct pH level.
The water is planned to remove water soluble salts and the caustic is planned to then convert the aluminum gibbsite salts to sodium aluminate, which can be removed with water.
As soaking is being done, work will alternate between Tanks C-108 and C-107. But Washington River Protection Solutions expects to have Tank C-108 emptied in December, making it the eighth tank to be emptied.
Washington River Protection Solutions also plans to start waste retrieval soon on a third tank, Tank C-112, which has 104,000 gallons of waste.
"Our expectation is that sometime this fall we will be operating two retrieval systems in C Farm at the same time," Smith said. "That's exciting."
Tank C-112 will be emptied using modified sluicing, the typical retrieval method at Hanford, but with the addition of a new system that telescopes to give greater reach within the enclosed tank. It allows the end of the nozzle to get much closer to the waste at the bottom of the tanks.
There is no reason that work on Tank C-112 also could not be finished by the end of December, Uziemblo said.
The new MARS system requires too much of a lead time to be practical for use in all C Farm tanks, which include the 10 tanks that must be emptied by 2014. MARS is planned now for use in two tanks.
Although a tank hasn't been emptied since 2007, partial removal of waste in multiple tanks has been done since then.
In fiscal 2012, which started this month, Washington River Protection Solutions, plans to remove waste from six of the 10 tanks required to be emptied by the 2014 deadline and will do construction work on three more to prepare them for retrieval.