Progress is being made on the complex and difficult task of removing "pencil tanks" from Hanford's Plutonium Finishing Plant, despite problems with a crane that's more than 40 years old.
The project has taken skill and ingenuity on the part of the workers, who at one point brought in a remote-controlled hobby helicopter to practice with it to help repair the crane.
Work began in early 2011 to remove 196 pencil tanks and the racks that hold them inside an enclosed, six-story, canyon-like room in the plant's Plutonium Reclamation Facility. It is one of the most challenging projects attempted at the Plutonium Finishing Plant, which the Department of Energy has called Hanford's highest hazard facility.
The skinny tanks, which range from 3 feet to 22 feet long, were shaped to prevent an uncontrolled nuclear reaction of plutonium. They were used during the height of the Cold War to increase the production of plutonium for the nation's nuclear weapons program by recovering plutonium from scrap material that otherwise would have been waste.
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The tanks hang in about 41 steel racks, called strong backs, mostly in groups of four along the walls of the canyon.
CH2M Hill Plateau Remediation Co. considered different ways to remove the highly contaminated tanks for disposal, including performing the work robotically. But it settled on using the facility's crane to move the sets of tanks to the maintenance bay, where workers can process them by reaching through gloves attached to ports at different heights up and down the bay.
That appeared to be the safest and least expensive option, according to CH2M Hill.
Extensive work was done on the crane before removal of the tanks started last year. However, an electrical cable for the crane malfunctioned and stopped work on the pencil tanks for several months.
Workers practiced using a remote-controlled hobby helicopter to fly a rope to the crane, prepared to attach it as a tether so the crane could be pulled close to the maintenance bay, said Jerry Long, CH2M Hill vice president of Plutonium Finishing Plant closure. However, the work was accomplished without the helicopter.
But then repairs had to be made by workers entering the maintenance bay on the north end of the canyon. They used supplied air to enter the canyon for up to 45 minutes at a time and wore three layers of protective clothing. About 30 people were needed to support crews of three or four workers who entered the canyon.
Some delays also were caused by work to improve maintenance on the ventilation system at the plant.
"We're taking a fairly conservative posture on issues and events," Long said.
The pencil tanks were expected to be removed from the canyon this spring, but now work is expected to be completed in fall 2013.
However, since the crane has been fixed, workers have pushed ahead of the new schedule in the last three to four months, cutting up 45 pencil tanks or strong backs for a total of 70, Long said.
Workers cut off the bottoms of the tanks, assuring they are empty of processing liquid, as expected. Then they make more horizontal cuts to create shorter pieces. The tanks vary, with some including valves and piping.
Pieces that are 24 to 40 inches long are placed inside a steel container, which is lowered into a cardboard tube that will be wrapped in a sealed, clean plastic sleeve as it is removed from the maintenance bay. That goes into a PVC tube that will be shipped in a waste box to the Waste Isolation Pilot Plant in New Mexico for disposal.
While the crane is working again, CH2M Hill continues to evaluate other options. That includes taking a look at using a remote-controlled small track hoe with cutting devices on it that could require less work by the crane. It also could help with possible cleanup of the canyon walls, which may be done with a high-pressure liquid nitrogen spray.
-- Annette Cary: 582-1533; firstname.lastname@example.org
Video is courtesy of the Department of Energy