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Wrangling hot waste.

The Department of Energy's Hanford Site, near the Columbia River in Washington, has close to 150 aging waste-storage tanks that are being cleared out so their radioactive contents can be transferred to more-secure double-wall containers. The contractor, CH2M Hill, hired to safely manage this waste, including the job of transferring it to safer tanks, has developed a lot of specialized machinery for the task.


One of the big challenges of the cleanup is that all the tools or machinery to do the work must fit down a 15-foot-deep pipe that may be only a foot wide. A scissor-like device called the Salt Mantis, which uses high-pressure water jets to break up salt deposits, was discussed in this department in April two years ago. The latest machine designed to fit into the storage tanks combines the high-pressure water with a plow to move the freed waste.

When it is ready for use, the new device, called Foldtrack, is essentially an 800-pound bulldozer 5.5 feet long and 30 inches wide. It is equipped with nozzles for high-pressure water jets that can scour the walls and floor of a tank. The vehicle has a plow blade that can move radioactive waste to make it accessible to a pump for removal. To fit through the access pipe, however, Foldtrack has to be able to change shape.

Its parts are hinged together so that they unfold to make a long, narrow chain. It can be lowered through the access pipe--first the tread assembly for one side, then the plow blade followed by the other tread. As it descends slowly into the tank, the entire assembly dangles from a thick umbilical that looks like a huge rat tail. The umbilical supplies power, control links, and water.

When the machine reaches the floor of the tank, it reconfigures itself into its working form. Each tread is powered by its own hydraulic motor. The folding and unfolding operations use a single hydraulic cylinder. The vehicle is controlled from a PC that can sit as far away as 800 feet.

Foldtrack carries two water jet systems to help remove waste and to clean tank walls. The front of the plow blade holds a four-nozzle manifold that can deliver water at 3,000 psi to loosen waste on the floor of the tank. A wall-cleaning jet articulates up to 40 degrees with the raising and lowering of the blade to spray water at pressures between 800 and 2,100 psi.

Cameras deployed inside the tank allow the operator to watch the unit as it is lowered to the tank floor and see whether it is in the right position or not. Foldtrack is geometrically designed to land in the right configuration to unfold, but should it land upside down, operators are trained to correct the situation and put it in the right orientation.


According to Rick Raymond, CH2M Hill's director of technology development, the device can reduce the amount of residual waste left in the tanks. "We expect Foldtrack to improve the quality of our waste retrieval program by speeding the process, reducing the cost, and improving protection of the environment," Raymond said.

The Foldtrack was designed by CH2M Hill's engineers working with Non Entry Systems Ltd., a company in Swansea, Wales, that develops remotely operated equipment for use in hazardous environments. The machine has been deployed in a demonstration tank at Hanford and is scheduled to enter service, in tank C-109, a 530,000-gallon tank, this month.

This section was edited by Executive Editor Harry Hutchinson.
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Title Annotation:technology focus: FLUID HANDLING AND FLUID POWER
Author:Hutchinson, Harry
Publication:Mechanical Engineering-CIME
Geographic Code:1USA
Date:Apr 1, 2008
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