Erosion corrosion of tanks during solid waste retrieval

Several million gallons of radioactive liquid and solid wastes are being stored in doubleshell tanks (DSTs) at the Department of Energy's Hanford Site in southeastern Washington. These wastes will be retrieved and processed to create a waste form suitable for permanent disposal. Solids in some of these tanks have been settling for many years, creating sludge layers on the tank floors, and must be resuspended in the supernatant liquids before waste retrieval can begin. The waste will be retrieved from a tank using a submerged slurry pump in combination with one or more rotating slurry jet mixer pumps. The mixer pumps generate two opposing highvolume, high velocity jets of tank fluid and direct the jets at the settled solids. As the pump is slowly rotated, the jets sweep out arcs of fluid that suspend and mix the settled solids with the waste fluid. There is concern that the action of the jets will accelerate corrosion on the tank floor and wall. The Pacific Northwest Laboratory is performing tests to investigate this possibility. Two nonradioactive simulated wastes have been tested to date. The test results are reported here. Accelerated corrosion rates due to the action of the high-velocity slurry jets havemore » been measured on samples of the tank material during the tests, but they appear to be low enough to allow the planned retrieval operations to be conducted safely. 5 refs., 11 figs., 2 tabs.« less