Hanford workers gathered Thursday to watch the 394th, and final, special stainless-steel container being hauled away from the K Reactors area near the Columbia River.
The canister held the last of the "knockout pot sludge," one of two types of highly radioactive sludge stored underwater in the K Reactor basins.
The campaign to remove the sludge that began in mid-July was the first time highly radioactive sludge has been removed from underwater containers where it has been consolidated at the K West Reactor basin.
"This is a major step forward in protecting the river and a historic accomplishment in environmental cleanup," said Tom Teynor, DOE project director for sludge treatment.
The next step will be removing the second type of sludge, which is held underwater in the K West Basin in engineered containers. Technology is being developed to remove that sludge, which accounts for the majority of the waste.
After the Cold War, fuel irradiated to produce plutonium, but not yet processed to remove the plutonium, was stored in cooling basins attached to the K West and K East Basins.
The fuel deteriorated during the decades that passed, contributing to a radioactive sludge that built up in the basins.
Work to remove irradiated fuel, dry it at the nearby Cold Vacuum Drying Facility and then truck it in 13-foot-tall, multi-canister overpacks to the Canister Storage Building in central Hanford was completed eight years ago.
Since then, the same system has been used for fuel scraps and most recently the knockout pot sludge.
Knockout pots were used underwater at the K West Basin to filter out the heaviest particles removed when fuel in the basin was washed underwater before the fuel was removed for dry storage.
The material coming off the fuel that is smaller than a quarter inch is considered sludge.
"The more we looked into it, we saw it was more fuel-like than sludge-like," said Jim Mathews, manager of the sludge treatment project operations for CH2M Hill. "It was not fuel, but we handled it like it was."
The knockout pot sludge was hauled away from the K Reactors area in five loads between mid-July and Thursday.
But three years of work was required to prepare the sludge for removal and shipment.
"It's rather innocuous looking, but it's not chemically innocuous," said John Fulton, the incoming president for CH2M Hill at Hanford.
The knockout pot sludge totals less than half a cubic yard of the total 37 cubic yards of sludge that has been held in the K West Basin, including sludge consolidated from the now-demolished K East Basin.
But even though it's a small portion by volume, it is highly radioactive. It contains 15,000 curies of the total 51,000 curies of the K Basin sludge.
Workers wore respirators and stood on grates above the K West Basin pool, using long-handled tools to process the sludge beneath about 17 feet of water that shielded them from radiation. They transferred it into smaller containers and then loaded those into the stainless steel multi-canister overpacks.
But first the tools and processes for the work had to be developed. Engineers designed the tools with extensive input from the operators who would do the work, and then operators practiced and proved procedures would work at a mockup at the Maintenance and Storage Facility using no radioactive material.
"The work was done flawlessly," said Doug Shoop, deputy director of the DOE Hanford Richland Operations Office. "It just shows us that when we plan it right, it will be done safely and effectively."
Engineers fine-tuned the loading projections for the sludge to reduce the number of shipments from the K Reactor Area from the six shipments planned to five, which also reduced the need for worker handling, said Mike Johnson, CH2M Hill project director for sludge treatment.
Mathews, a 30-year veteran of Hanford work, watched the first multi-canister overpack filled with fuel leave the K Reactor area in 2000 and he watched the last multi-canister overpack filled with sludge leave for the Canister Storage Building on Thursday.
"I looked forward to this day," he said. "This has been one of the most successful projects I have been involved in."