The Department of Energy is asking the state of Washington to consider whether an underground waste tank that must be emptied by fall to meet a court-enforced deadline is empty enough.
It also has stopped work to empty a second tank while it considers if more waste can or must be removed from it.
Two technologies have been used to retrieve radioactive and hazardous chemical waste in each of the two tanks, but together they failed to empty the tanks to the allowed equivalent of about an inch of waste spread across their bottoms.
However, the state appears inclined to say that at least one tank has enough waste removed for waste retrieval to be considered complete under the consent decree. More waste could be required to be removed eventually to meet the Tri-Party Agreement requirements for closing tanks.
The court-enforced consent decree requires that the last of 16 tanks in the group called the C-Tank Farm be emptied by the end of September. But DOE still has six tanks there with waste, including the two on which two waste retrieval technologies have been tried without finishing the work.
The consent decree requires that DOE try three technologies to remove waste if needed, but it can forgo the third technology if it would not substantially reduce the risk. In that case DOE must sample the waste and work with the Washington State Department of Ecology to do a performance assessment to show the risk of leaving the remaining waste in the tank.
DOE has sent the state a letter asking to skip the third technology on Tank C-101, which has an estimated 5,000 gallons left in it. Regulatory requirements allow a maximum of about 2,700 gallons of waste to remain, which would be about an inch spread across its bottom, for eventual closure of the tank.
"DOE decided there was not a technology it could use that would substantially reduce the risk from the waste in the tank," said Jeff Lyon, the state's tank waste storage project manager.
The state is waiting for DOE to complete sampling of the tank, but it does not appear that a high level of risk remains in the tank, Lyon said. However, the sampling must verify that before the state makes a determination.
The tank had 77,500 gallons of solid waste when work to retrieve the waste started in December 2012.
Hanford workers used a telescoping sluicing system to move nozzles close to waste and then spray liquid to dissolve waste and move it toward a central pump for removal. They also used a high pressure spray added to the sluicing system as the second technology, said Rob Roxburgh, spokesman for DOE contractor Washington River Protection Solutions.
Retrieval also has stopped on Tank C-112, in which roughly 13,000 gallons of waste remain after removing about 91,000 gallons, Roxburgh said. It is in a hard layer on the bottom of the tank, with some chunks broken out that are too large to pump out. It's not quite as hard as concrete, but comes close, Lyon said.
DOE says it has nothing left in its toolbox of technologies that could break it up and allow it to be pumped out of the tank, said Nancy Uziemblo, a state specialist on retrieving waste from single-shell tanks.
Waste was retrieved from the tank using the same telescoping sluicing system used on Tank C-101. Then Washington River Protection Solutions tried soaking the waste with water and a caustic solution to remove the hard layer of waste at its bottom.
DOE and Ecology agree that the next step should be sampling the tank to determine the chemical makeup of the tank and are in talks about how that should be done, Uziemblo said. Collecting a sample will not be easy, she said.
Work continues with the Mobile Arm Retrieval System, or MARS, to remove waste from Tank C-107. Retrieval work restarted in February after a pump that failed in July was replaced.
It is DOE's most robust waste retrieval system and it's retrieved about 198,000 gallons of waste. Work is being done now to get waste clinging to the sides of the tank down and a thick pad of waste remains at the bottom of the tank that needs to be broken up, said J.D. Dowell, deputy manager of the DOE Hanford Office of River Protection..
Preparations are being made to use the MARS system, but with a vacuum rather than sluicing attachment, in Tank C-105 when that tank is empty. They will be emptied into the same double-shell tank and some of the same infrastructure will be used on both tanks.
Work is expected to begin this spring to empty another tank, Tank C-111, of about 35,000 gallons of waste using a sluicing system. That work is on track to be completed in September, Dowell said. The remaining C Farm tank, Tank C-102, is being prepared for retrieval.
-- Annette Cary: 582-1533; email@example.com; Twitter: @HanfordNews