Emptying of Hanford's C Tank Farm tanks continues after delay

By Annette Cary, Tri-City HeraldDecember 12, 2012 

Pumping to empty radioactive waste from Hanford's aging underground tanks has resumed after about a three-month delay.

Department of Energy contractor Washington River Protection Solutions has had promising new technologies ready to go in single-shell tanks that are being emptied into double-shell tanks.

But there have been problems with pumps in the double-shell tanks, causing delays.

The Department of Energy has emptied waste to what it believes is the regulatory limit from three tanks this year but the delays mean it won't get a fourth tank emptied as planned.

However, it still will be a good year for tank-waste retrievals.

Washington River Protection Solutions broke a streak of five years without emptying any of Hanford's 149 single-shell tanks this year, although it made progress in multiple tanks.

DOE is required by the legally binding Tri-Party Agreement to have all 16 tanks in the group called C Tank Farm emptied by fall 2014. To meet that schedule its contractor had planned to have four tanks emptied this year, three in 2013 and three more in 2014.

Work to start emptying Tank C-101 had been delayed until a pump was replaced in double-shell Tank AN-101, which will receive the waste.

With that task done, work to empty Tank C-101 began Monday night using a souped-up version of the Enhanced Reach Sluicing System inside the enclosed tank.

The system, which telescopes to get sluicing nozzles closer to waste in the bottom of a tank, was first used this year on another tank.

At Tank C-101 its power has been more than doubled. Rather than a single system, a pair has been inserted down risers into the tank and both have been equipped with two additional higher pressure nozzles to help dissolve crystallized salt and sludge waste and to sweep it toward a pump in the tank for removal.

In the first hour of sluicing in Tank C-101, the system began breaking through the hard crust at the top of the waste, said Rob Roxburgh, Washington River Protection Solutions spokesman.

Although pumpable liquids were removed earlier from the tank to protect against possible leaks, no sludge or other solids had been removed from the tank until Monday. The tank holds about 88,000 gallons of waste, Roxburgh said.

For now Hanford workers will pump from Tank C-101 only until the sludge in the double-shell tank reaches 170 inches. Caution is being used until a safety analysis is completed to show the waste will be chemically compatible.

As organic chemicals in the tank waste are broken down by heat and radiation, hydrogen is created. Because it is flammable, the concentration of hydrogen in the head space of the tanks must be limited.

Washington River Protection Solutions also has been working to empty single-shell Tank C-107, but will not finish by the end of the year. Work is stopped now because a pump failed in double-shell Tank AN-106.

The halt to retrieval in Tank C-107 is being used to do maintenance for a plugged line on the Mobile Arm Retrieval System, or MARS, a robotic arm. It's the largest and most robust retrieval technology developed yet for the Hanford tank farms and required the underground tank to be uncovered and a larger riser installed to allow MARS to be inserted.

It has removed all but 51,000 gallons of the estimated 253,000 gallons of sludge and solids in Tank C-107.

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