Less than two weeks before the Department of Energy is required to have waste emptied from a double-shell tank with an interior leak, work to empty the tank appears to have stopped.
Hanford officials declined to discuss the status of Tank AY-102 last week.
But comments made about the tank on Feb. 1 at the Tri-Cities Regional Economic Outlook forum in Kennewick were promising.
“It is now going through the final steps of retrieval,” said Tom Fletcher of the DOE during an update on Hanford nuclear reservation projects. “It looks like we will be done with that in the very near future — down to what we can get to.”
A Hanford Advisory Board committee also was told by Hanford officials on Jan. 18 that work was on track to meet the deadline for waste removal from the tank.
DOE is required by a settlement agreement with the state of Washington, a regulator of Hanford waste tanks, to have enough waste removed from the tank by March 4 to determine the cause of the leak.
26,000 gallons estimated waste left in Tank AY-102 Jan. 10
20,400 gallons estimated waste left in Tank AY-102 Jan. 30
Tank AY-102 has had a slow leak of radioactive waste from its inner shell into the space between its inner and outer shell for several years. None of the waste is believed to have breached the outer shell to contaminate the environment.
When work began to empty the tank almost a year ago, it had 593,000 gallons of liquid waste that was quickly removed and 151,000 gallons of waste in the form of sludge that is more difficult to remove.
On Jan. 30, Hanford tank farm workers were told that the total volume of waste remaining in the tank was estimated to be 20,400 gallons, down from 26,000 gallons as of Jan. 10. The tank has a capacity of about 1 million gallons.
DOE is expected to notify the state when it believes as much waste as possible has been removed from the tank.
Tank AY-102 was the first of 28 double-shell tanks built, and they have been used to hold waste transferred from older, leak-prone single-shell tanks at Hanford. Hanford has 56 million gallons of radioactive waste left from the past production of plutonium for the nation’s nuclear weapons program and stored in underground tanks until it can be treated for disposal.
Tank AY-102, which had documented construction problems, has held waste since about 1970.
Information learned from inspecting the tank after removing waste may be helpful in assessing the condition of other double-shell tanks. DOE also has not ruled out the possibility of determining if Tank AY-102 could be repaired and put back into service, although officials have said a return to service seems unlikely.
Four extended-reach sluicers with an additional high-pressure water spray have been used most recently to remove waste from Tank AY-102.
As waste in tank AY-102 has been disturbed by retrieval, significantly more waste has flowed into the space between the shells. The issue was anticipated, and a pump was installed between the pump’s shells before work to empty the tank began. The pump has been used periodically to remove as much waste as possible when levels rose to several inches deep between the shells.
Workers have already observed that when waste retrieval is done in one part of the tank, the rate of leakage into the space between the shells increases, indicating the likely area of the leak.
Work to retrieve sludge from the tank began with two sluicers inserted into the tank to spray liquid waste to break up the sludge and move it toward a central pump in the enclosed tank.
Hanford officials knew when retrieval began that those sluicers likely would not be capable of finishing the job.
As they became less effective, work halted and they were replaced 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 are equipped with a high-pressure water spray that can be used to break up waste.