The Hanford tank farm contractor is having success on a difficult waste retrieval project with its newest tool.
More than 53,000 gallons of the solid radioactive waste stored in underground Tank C-112 has been removed with Washington River Protection Solutions' new enhanced-reach sluicer.
"We are making historic progress in our tank waste retrievals right now," said Tom Fletcher, assistant manager for tank farms. "We've retrieved more than half the hard-to-pump waste out of C-112, and are in various stages of retrieval or retrieval preparation in nine other tanks."
WRPS is working to empty radioactive waste from 142 old single-shell tanks, some of which have leaked in the past, to store the waste in sturdier double shell tanks until it can be treated for disposal. The waste is left from the past production of weapons plutonium.
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 WRPS is using an enhanced-reach sluicing system for one of the two nozzles that will allow it to telescope down to get closer to the waste. The tool has been under development for a couple of years.
Tank C-112 was expected to be a tough tank because the sluicing system first needed to break through a hardpan crust of waste several inches thick that formed at the top of the 104,000 gallons of waste in the tank. Pumpable liquids earlier were removed from the tank.
Work started Dec. 28 with the telescoping nozzle, and a video shot inside the enclosed tank in February showed the crust starting to soften and shift, said WRPS spokesman Rob Roxburgh.
Then the traditional nozzle was used to attack the weak spot, allowing the crust and the waste beneath it, which has a consistency of peanut butter, to begin to be removed.
"All retrievals get us closer to our goal of having all C Farm tanks retrieved by 2014," said Dieter Bohrmann, spokesman for the Washington State Department of Ecology, the regulator on the project. C Farm has 16 tanks with 10 not emptied yet to regulatory requirements.
The enhanced sluicer is one tool to help meet the 2014 goal, he said.
But "what is needed now, and over the next few years, is consistent and sustained momentum in these retrieval efforts," he said.
Work also is in progress at Tank C-108, where a combination of water soaks and chemical additions is being used to remove waste. Just 6,800 gallons of waste remained in a hard layer at the bottom of the tank after earlier work to remove waste with modified sluicing could get no more waste out of the tank.
Work continues to be temporarily halted at Tank C-107, where work started in October to remove waste 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 during several weeks of operation starting in October. Then an equipment failure not directly related to MARS halted work.
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.
Work continues to replace the broken pump with one that can survive the harsh environment inside the double-shell tank.
* More Hanford news at hanfordnews.com.