Hanford workers have begun emptying another underground tank of radioactive waste at Hanford, making this the first time in more than a decade that two tanks are being emptied simultaneously, according to Hanford officials.

Pumping on Tank C-112 began last week, helping end the year on a positive note, despite Hanford workers not completing waste retrieval for any tank in 2011. A tank has not been emptied to regulatory standards since spring 2007.

However, significant progress has been made to remove waste, said Chris Kemp, deputy project director for the Department of Energy. While getting the last of the waste out that is required to declare a tank empty to regulatory standards has been difficult, almost 2 million gallons of radioactive waste have been retrieved from single-shell tanks and transferred to newer, double-shell tanks to await treatment since 2002.

The waste is left from World War II and Cold War production of plutonium for the nation's nuclear weapons program.

"Ecology is encouraged that tank retrievals have resumed," said Dieter Bohrmann, spokesman for the Washington state Department of Ecology, the regulator on the project. "There is a lot of work still ahead, so we hope retrievals can stay on track and further delays are limited."

A court-enforced consent decree requires all 16 underground tanks in the grouping called C Tank Farm to be emptied by fall 2014. To date, six have been emptied.

Tank C-112 is being emptied with a technology called modified sluicing but with an improvement to the usual modified sluicing. Typically, two high pressure nozzles lowered into the top of the enclosed underground tanks spray liquid onto the waste and wash it to a central pump.

But Washington River Protection Solutions is using an enhanced-reach sluicing system for one of the two nozzles that will allow that nozzle to telescope down to get closer to the waste. The tool has been under development for a couple of years.

Tank C-112 is expected to be a tough tank because the sluicing system first must break through a hard layer of waste that's formed at the top of the 104,000 gallons of waste in the tank. Pumpable liquids earlier were removed from the tank.

At the same time, Washington River Protection Solutions is working to remove a hard layer that remained at the bottom of Tank C-108 after the rest of the solid waste in the tank was previously removed using modified sluicing.

Workers are soaking and then recirculating water in the tank to dissolve water-soluble salts. The process worked when tested at the laboratory scale, but it's taking significantly longer in the field, said Kent Smith, Washington River Protection Solutions project manager.

Then concentrated sodium hydroxide, a common industrial caustic already used in Hanford's newer tanks to preserve the correct pH level, will be added. The caustic is planned to convert the aluminum gibbsite salt, which is not water soluble, to sodium aluminate, which can be removed with a water wash.

Work also had started in October to remove waste from Tank C-107 with the largest and most robust waste retrieval system tried yet at the Hanford tank farms, the Mobile Arm Retrieval System, or MARS.

It retrieved 27 percent of the 253,000 gallons of waste in the tank during several weeks of operation. However, work has been temporarily halted because of an equipment failure not directly related to MARS.

MARS requires liquid to spray on waste to break it up and move it, but a pump that was providing liquid waste from a double-shell tank broke. Liquid waste rather than water is used when possible in emptying tanks to prevent the creation of more waste.

A new pump that can survive the harsh environment inside the double-shell tank should be installed this winter so work can resume at Tank C-107.

Washington River Protection Solutions is expecting to start up work on another C Farm tank every couple of months this year, Smith said.

The accelerated pace will be needed to meet the 2014 consent decree deadline, said Joanne Norton, DOE project director. Retrieval work on more than one tank at a time will become more the norm, she said.

-- Annette Cary: 582-1533; acary@tricityherald.com; more Hanford news at hanfordnews.com