Retrieval of Hanford’s tank waste is one of the most challenging environmental cleanup projects in the DOE complex. There are numerous physical restrictions that must be dealt with in order to successfully retrieve the waste.
The Tanks:
- 177 tanks: 149 SST and 28 DST
- Capacity ranges from 55,000 to 1-million gallons
- Are buried underground beneath 7 to 10 feet of soil
- Have limited access via small-diameter pipes that extend from the top of the tank to above the ground surface
- Contain high-level radioactive and hazardous chemical waste, requiring all work to be performed remotely
- Contain a variety of waste requiring multiple retrieval technologies
WRPS is developing and testing new techniques and technologies that aim to speed waste retrieval and reduce cost.
The most current methods include:
Modified Sluicing
Modified sluicing uses high-pressure water jets to dissolve the waste and move it to the pump. The pump sends the waste through specialized pipes to an approved receipt tank. WRPS has a closed-loop system, using recycled liquid waste in place of water, when possible, to reduce the amount of water added to the tanks.
View Modified Sluicing Video
Enhanced Reach Sluicing System
The Enhanced Reach Sluicing System (ERSS) consists of a sluicer on the end of a hydraulically driven, retractable boom that extends into the tank. The sluicer dissolves crystalized salt and sludge waste using high-pressure water or recycled liquid waste and directs the waste to a pump for transfer into a double-shell receiving tank.
View ERSS VideoMobile Arm Retrieval System
The Mobile Arm Retrieval System (MARS) is a unique robotic arm that rotates 360 degrees, extends to the tank wall and uses powerful sluicing tools to drive waste toward a centralized pump for removal.
View MARS Video
Chemical Dissolution
For tanks containing difficult-to-remove concrete-like waste solids, chemical dissolution dissolves and dislodges much of the hardened material so it can be pumped out. Sodium hydroxide is added to the tank and the waste is allowed to soak in a highly caustic solution. This softens the stuck-on material and prepares the tank for a final water rinse before the waste is pumped out.
Foldtrack
Resembling a small bulldozer, the Foldtrack is a remotely operated, track-mounted tool that uses a plow blade to move waste from the floor of a tank to an awaiting pump. A very nimble device, the Foldtrack unfolds to fit down a 12-inch-diameter pipe to enter the tank. The unit also has two onboard waterjet systems, three high-pressure turbo nozzles, and a sluicing cannon for sweeping the tank floor.
View Foldtrack Video
Cold Test Facility
Many of these technologies are tested at Hanford’s Cold Test Facility (CTF), a mockup of a waste tank where new waste retrieval and other technologies can be evaluated in a safe, non-radioactive environment. CTF is also used to train operation teams and work through various options to refine operating methods, streamline transfer processes and identify ways to enhance productivity which can be applied to actual retrieval operations. The testing and training improves safety, helps alleviate potential problems, and increases the quality of cleanup upon deployment of new systems in the tanks.
In addition to the technologies used for tank retrieval and those proposed for supplemental treatment and disposal, WRPS is exploring ways to gain operational efficiencies while safely and effectively completing the tank operations mission. The technical advances are important to a strategy for making swift and steady progress in our work.