A large, but little-used Hanford building has taken on a second life, smoothing the way for the challenging task of removing radioactive sludge from underwater containers near the Columbia River.
The K West Basin, where the sludge is stored, and the 28,000-square-foot Maintenance and Storage Facility, or MASF, are on opposite ends of Hanford.
But MASF, built to support the now deactivated Fast Flux Test Facility, has been reconfigured to duplicate key areas of the K West Basin and its newly built annex for safely removing sludge from the basin.
“We actually built a basin in this building,” said Neal Sullivan, director of the CH2M Hill Plateau Remediation Co. sludge treatment program, during a tour of MASF. “It was a concrete floor.”
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MASF is being used to develop equipment, test it, and allow workers to practice using it before they must use it for work in the radiological environment of the K West Basin.
The goal is to work out any issues before the equipment is used in a contaminated area.
“One of the keys is it is full-scale,” said Mark French, the Department of Energy project director.
DOE faces a Tri-Party Agreement deadline to start removing sludge from the K West Basin by September 2018. The sludge must be out of the basin a year later.
Radioactive sludge formed in the K Basins as irradiated fuel corroded and bits of fuel mixed with dirt and bits of concrete.
The sludge is planned to be stored in large containers at T Plant on the central Hanford plateau, likely for several years, until a process is approved and in place to treat the sludge.
The K West Basin now holds about 950 cubic feet of radioactive sludge in six large steel boxes in the water-filled basin. The water shields employees working on the grating above the basin from radiation.
Basins attached to Hanford’s K East and K West reactors were used to store irradiated fuel, stranded when processing to remove weapons-grade plutonium stopped near the end of the Cold War.
As the fuel corroded underwater, it combined with dirt and bits of concrete from the pools to form a highly radioactive sludge. The fuel has been gone for 12 years, but the sludge remains, now consolidated into the K West Basin.
The aging basin is just 400 yards from the Columbia River.
“It’s vitally important that we move that material onto the plateau so the Columbia River and all the people who live downstream are protected from that hazard,” Sullivan said.
The plan for removing the sludge calls for it to be pumped from the underwater containers out of the K West Basin and into the adjacent annex, where a container waits.
It will be held in a shielded cask on a transport trailer. Once the container is filled, the trailer can be pulled out of the annex and the storage container delivered to T Plant.
They were completely confident in the work, because they practiced it.
Neal Sullivan, sludge treatment program director
But it’s not as easy as it may sound.
One of the tasks that the mock-up basin at MASF was used to prepare for was placing new lids on the underwater sludge containers. The old lids had openings for sampling sludge, but they were insufficient for retrieving the sludge.
Workers practiced with long-handled tools reaching into the 17-feet-deep water to unbolt the tops of the boxes, using underwater video cameras to help guide their work. The low ceiling, replicated in the MASF mockup, adds to the skill required to maneuver the long-handled tools.
The new lids have openings with brush-like bristles that allow water to enter the containers, but keep the sludge largely contained.
Because of workers’ practice in MASF, the task of replacing lids in the K West Basin was done “in a fraction of the time anticipated. It just went so smoothly. They were completely confident in the work because they practiced it,” Sullivan said.
Engineers also have used the MASF basin to test specially designed equipment for removing the sludge. They’ve been able to test different components together to fine-tune operations and to get feedback from the operators who will use it in a radioactive environment.
A custom-made sludge retrieval tool stuck through the new lids of the boxes is planned to mobilize the sludge and suck it out to be pumped to the annex.
18 to 20 number of storage containers needed to transfer sludge to T Plant
At MASF, the equipment is tested with a mock, non-radioactive sludge designed to mimic the radioactive sludge’s mix of some particles that are heavier than lead and others that easily disperse in the water when disturbed.
Now, one of the sludge storage containers is at the annex to test the system. To pump the sludge from the basin to the annex, it will have to be in a mixture that is 95 percent water.
In the annex, the sludge will be allowed to settle to the bottom of the container. Then some of the water at the top of the container will be removed and more sludge added.
The containers, which are about 10 feet tall and 5 feet in diameter, still will be filled at least halfway with water to shield workers as they disconnect the sludge transfer hoses from the filled containers, which will be inside shielded transportation casks.
The containers can be filled using a control system outside the annex, so no worker needs to be in the annex during the transfer of the radioactive material.
About 18 to 20 containers are expected to be filled and stored at T Plant, with the same trailer and storage cask used for each trip.
Testing of the system with the nonradioactive equipment is about 85 percent complete. In August, cleaned equipment could be taken to the K West Basin and annex to prepare for use with K Basin sludge.
MASF will remain available as the equipment is tested with radioactive waste and then used to empty the sludge from K Basin containers to troubleshoot any issues that develop.