Another pump problem has stopped work with the new Mobile Arm Retrieval System, or MARS, to empty an underground Hanford tank of radioactive waste.
Although that means Tank C-107 will not be emptied of waste this month as expected, Washington River Protection Solutions still believes it will be emptied by the end of the year.
"We won't miss any deadlines," said Kent Smith, Washington River Protection Solutions manager of single-shell tank retrieval and closure.
That would make it the fourth underground tank emptied this calendar year, if regulators sign off after studying the data. Before this, workers had made progress on emptying multiple tanks, but failed to finish waste retrieval of any tank for five years.
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Finishing work to empty Tank C-107 this year will keep the tank retrieval project on track under the latest plan to have four tanks completed this year, three in 2013 and three more in 2014.
The Department of Energy has a legal deadline to have all 16 underground tanks in the group called C Tank Farm emptied by fall 2014. Seven tanks remain, including the tank now using the MARS system.
Hanford has 56 million gallons of radioactive waste left from the past production of weapons plutonium. Waste is being emptied from 139 leak-prone single-shell tanks that still hold waste into 28 newer double-shell tanks.
This is the second time that work has stopped at Tank C-107 because of a pump problem.
MARS, the largest and most robust technology being used yet to empty a tank, has removed about 80 percent of the sludge and solid waste in Tank C-107. It's worked efficiently to remove all but an estimated 51,000 gallons of the estimated 253,000 gallons of waste held in the tank after all pumpable liquid was removed earlier.
Work stopped for months in the tank because a pump failed in double-shell Tank AN-106, which was being used to supply liquid waste to MARS. Its sluicing and high-pressure spray systems use liquid waste rather than water to prevent the creation of more radioactive waste.
The new pump that was installed has sprung a leak in its hydraulic system after pumping for several hundred hours, Smith said. The pump still is operable, but the mineral oil it uses for hydraulic fluid is leaking into the double-shell tank and could affect the pH balance, which is monitored to prevent corrosion of the tank.
Replacing the pump will stop work with MARS to empty Tank C-107 for an estimated four to six weeks.
"Encouraging progress has been made on single-shell tank retrievals this year, so the delay is unfortunate," said Dieter Bohrmann, spokesman for the Washington State Department of Ecology, the regulator on the project.
"The MARS unit is one of our key retrieval tools, and Ecology hopes the pump can be fixed quickly to allow retrieval in C-107 to resume," he said.
Smith estimates that about 150 hours of work remain in Tank C-107. MARS, a robotic arm, has removed the sludge in the tank and washed down a large quantity of waste clinging to the inside walls of the enclosed tank.
When work resumes, the system will be used to attack the hard layer of waste that was below the sludge at the bottom of the tank. The hope is that MARS will be able to remove that hard layer, without a second technology introduced into the tank as is typically required.
Work also will start next month to remove radioactive waste from Tank C-101 and Tank C-102, which will use liquid waste from a different double-shell tank than the one with the pump issue.
Tank C-101 and Tank C-102 are among the three remaining C Farm tanks that have had no solids or sludge yet removed. Other remaining tanks in C Farm have had waste removed down to the hard layer hidden beneath the sludge.
For Tank C-101 and Tank C-102 a sluicing system will be used to spray liquid waste on the sludge and help remove it with an pump. But the sluicing system traditionally used in Hanford tanks has been improved in two ways.
It's been enhanced to allow nozzles to telescope down lower into the tank to get closer to the waste, an improvement that aided retrieval in the one tank where it has been tested. In addition, the enhanced-reached sluicing system also will have a high-pressure system added when used in Tanks C-101 and Tanks C-102 to see if it can also break up and retrieve the hard layers expected to be found under the sludge.
Tank C-102 has a large volume of waste to be retrieved -- 316,000 gallons at least -- and Tank C-101 is expected to have at least 88,000 gallons of waste.
Washington River Protection Solutions is reducing the cost of emptying the two tanks, by doing design, purchasing of equipment components, construction of the retrieval systems and waste retrieval at the same time for both tanks.
-- Annette Cary: 582-1533; firstname.lastname@example.org