What We Are Doing
Emptying Old Tanks
Since the beginning of waste removal from Hanford’s single-shell tanks a total of seven tanks have been emptied. Six meet the criteria of the Tri-Party Agreement that governs cleanup and the seventh is under review. In addition, waste has been removed to the limits of technology in six additional tanks and reviews are under way now to determine the best course of action to remove the remaining waste.
Modified sluicing technology is most often used to remove waste from tanks. It uses high pressure water or liquid waste to mobilize the sludge and other solid material so it can be pumped to safer double-shell tank storage.
When cleanup of the Hanford Site began in 1989 the technology to remove waste from underground storage tanks did not exist. Hanford has been pioneering new technologies to safely and efficiently move waste out of the aging single-shell tanks and store it in newer double-shell tanks until it can be prepared for disposal.
Through innovation and hard work WRPS developed a new approach that allowed retrieval to resume ahead of schedule and at less cost than anticipated.
When the limits of modified sluicing technology had been reached, more than 90 per cent of the waste had been removed from C-110. Additional technologies are now being considered to remove the remainder of the waste to meet the terms of the Tri-Party Agreement.
New Generation of Robotic Arm in Tank Cleanout Future
In one of the most complex projects ever undertaken at Hanford tank farms a 55-inch diameter hole was cut into the top of single-shell thank C-107 to improve access for a new robotic arm that will speed waste retrieval. The tank holds 267,000 gallons of radioactive and chemical waste. The arm, known as the Mobile Arm Retrieval System, or MARS, used high pressure liquids to “rake” waste to a central pump so it can be removed. The successful cut culminated more than a year of planning and was completed safely with near flawless precision.
Testing of the MARS arm has been completed and the arm will be installed following operator training which is now under way. MARS offers the potential for increased efficiency of waste removal from Hanford’s single-shell tanks because it can replace a variety of technologies and will eliminate the need for repeated entries into a tank with multiple retrieval technologies.
Robotic arms for tank waste retrieval have been studied since the beginning of the Hanford cleanup, but arms that would fit through existing access risers were too light to do the job and arms that were strong enough to do the job were too big to fit into the tanks. Cutting the hole in tank C-107, combined with advanced technology development has solved that problem.
Part of the design challenge has been to make a large portion of the system transportable so it can be moved from one tank to another and make use of existing tank farm utilities such as electrical and water systems, saving both time and money. The arm is expected to be operational in the summer of 2011.
Development of new and innovative technologies to speed the retrieval of tank waste and make retrieval operations more efficient and cost-effective are goals of Washington River Protection Solutions.
