When plutonium production ended at Hanford there were more than 100,000 uranium fuel rods and rod fragments that had been irradiated in Hanford's N reactor. These rods would not have their plutonium extracted from them and would need a place for temporary storage until a decision was made about where they would ultimately end up. The K-Basins were chosen as what was thought would be a temporary storage spot.

Each K-Basin is an open pool, approximately 67 feet wide, 125 feet long, and about 21 feet deep. They each have the capacity to hold around 1,300,000 gallons of water. The K-Basins were chosen because they had sufficient water depth for radiation shielding and enough water volume to adequately cool the spent fuel. They are located about 400 yards from the Columbia River.

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Each basin is comprised of five areas. The Discharge Chute will receive the spent fuel elements when they are discharged from the reactor. The North and South Loadout Pit areas were used to load the buckets, which contained irradiated elements, into railroad cars for shipment to the reprocessing facilities in the 200 Area. Loading and shipment of the irradiated fuel in the cask cars from the Loadout Pits was a routine operation which would happen while the reactors were operating. The Dummy Elevator Pit was used for lifting buckets of aluminum spacers which were used for positioning the fuel with the reactor process tubes so that they could be decontaminated and recycled. The Technical Viewing Pit contained an underwater scope for examination of fuel and other items without undue exposure to the viewer. This area also included some specialized handling equipment to manipulate and position fuel pieces for viewing. The Weasel Pit was used to check radiation levels in objects through the use of an underwater detector. The activity of an irradiated fuel piece would cause an alarm to go off. The squeal like alarm is the source of the name weasel.

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The K-Basins were used in the production of plutonium at the K-East and K-West Reactors. Each of the K-Reactors contained 3,220 horizontal process tubes loaded with 38 to 56 aluminum clad fuel elements and 18 to 25 aluminum spacers. Each month about 20% of the fuel in the K-Reactors was dropped into the K-Basin pool. From 1955, when the K-reactors went on line, until the early 1970s, over 10,000,000 spent fuel rods were discharged in the K-Basins.

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When the K-Basins were originally constructed, it was thought they would only be used for 20 years. The basins were past their anticipated service life when they were chosen as storage spots for the fuel rods. These basins had not been designed to hold spent nuclear fuel for decades of time.

The K-Basins did receive some modification before receiving and storing the fuel rods from the N-Reactor. The K-West Basin was completely drained of water and its floor and walls coated with an epoxy paint. However, the K-East Basin was neither drained nor epoxy coated before spent fuel rods were placed in it.

There were approximately 105,000 N-reactor spent fuel assemblies placed in the K-Basins. This irradiated fuel consisted mostly of metallic uranium, but also plutonium, and radioactive fission and activation products. Since the fuel rods were initially placed in the K-Basins for what was thought to be short term storage, there were no considerations, preparations, or analysis for long term storage. The storage of reactor fuel extended for almost 30 years. During this long period of time, there was an accumulation of non-radioactive materials, such as dirt, sand, silt, insects, and rodents from normal basin operations and monitoring, as well as from numerous dust storms that occurred in the lower Columbia Basin. The buildup of these materials was a result of the K-Basins having not been designed as environmentally controlled areas. Doors opened directly to the outside and there were no clothing restrictions on people who entered. The accumulation of non-radioactive material contributed to the buildup of sludge on the basins floors. The K-East basin accumulated more sludge than the K-West, since the K-East had not been cleaned prior to storing the spent fuel. If the water in the basins remained undisturbed the sludge could be seen sitting in a gray layer on top o the other wastes in the basins. If the water is disturbed the sludge would become mobile and make the water so cloudy that no one could see into it.

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The canisters, the storage racks, and the fuel cladding experienced a steady corrosion from being underwater. This introduced contaminants to the naturally occurring basin sludge. The underwater deposits of these corrosion products was visible from the viewing area.

By the 1990's it was discovered that the K-East Basin had started to leak contaminated water into the ground. Additionally, the fuel rods in both basins had started to deteriorate, resulting in the formation of a material called sludge. Since the fuel rods were deteriorating and with the threat of additional contaminated water leaking into the ground that was in close proximity to the Columbia River, removal of the water and materials in the K-Basins began in 1994. By 2004, over 2,100 metric tons of irradiated fuel rods had been moved from the basins and into Hanford's Canister Storage Building. The fuel rods will remain there until a permanent, national repository for spent fuel and vitrified nuclear waste is built.

Once the fuel rods were removed, workers could begin to vacuum out the sludge, sediment, and debris that had accumulated on the floors of both basins. It would then be containerized for safe storage. There was significantly more sludge than expected and workers dealt with many unexpected challenges with removing the sludge. Approximately 47 cubic yards of radioactive sludge was containerized for safe storage in the K-West Basin by the end of 2007. Once the sludge had been removed from the K-East Basin, workers at Hanford were able to drain its water and send it to a facility for treatment. After it had been treated, the water was disposed of into the ground.

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It took workers eight years to remove the fuel, vacuum up the underwater sludge and drain the one million gallons of water from it. They then tore out the structures covering the basins and filled them with a layer of grout and then a layer of sand like material to give heavy equipment a base to work on during demolition. Water was sprayed on the site while work was under way to control dust and soil cement. The DOE had known that radioactive cesium and strontium had leached into the walls of the basin, but encountered radiation levels that were lower than expected. The DOE does expect the final ten feet of the basin to be contaminated at higher levels. The bottom 14 inches of the basin is covered with grout that is used to secure any residual radioactive sludge in place. There is still equipment on the bottom of the basin that will be cut up with shears. The final stages of removal involve using diamond wire to cut out the sand filter and ion exchange column which are grouted in place at the end of the basin as part of the water filtration system. These structures, which each have a footprint of 75 square feet, must be removed so that workers can reach the soil beneath them.

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The license could not be verified: There is no license certificate installed for CustomWare Composition Plugin for Confluence.

The license could not be verified: There is no license certificate installed for CustomWare Composition Plugin for Confluence.

The license could not be verified: There is no license certificate installed for CustomWare Composition Plugin for Confluence.

The license could not be verified: There is no license certificate installed for CustomWare Composition Plugin for Confluence.

References

http://www.hanford.gov/page.cfm/K-Basins http://www.epa.gov/rpdweb00/docs/wipp/doeenclosure9_1.pdf http://www.tri-cityherald.com/2009/02/04/467712/k-east-basin-turns-into-hanford.html