Low-pressure, single-point grout injection for tank heel sludge mixing and in-situ immobilization

This report describes tests conducted in an approximately 9-ft diameter test tank situated outside the 336 building in Hanford`s 300 area. The tests were performed to measure the ability of jets of grout slurry to mobilize and mix simulated tank sludge. The technique is intended for in situ immobilization of tank waste heels. The current approach uses a single, rotated, larger-diameter nozzle driven at lower pressure. Due to the larger diameter, the potential for plugging is reduced and the effective radius around an injection point over which the jet is effective in mobilizing sludge from the tank bottom can be made larger. A total of three grout injection tests were conducted in a 9-ft diameter tank. In each case, a 2-in. layer of kaolin clay paste was placed on a dry tank floor to simulate a sludge heel. The clay was covered with 4 inches of water. The grout slurry, consisting of Portland cement, class F fly ash, and eater, was prepared and delivered by an offsite vendor. In the third test, the sludge in half of the tank was replaced by a layer of 20x50 mesh zeolite, and bentonite clay was added to the grout formulation. After injection, the grout was allowed to set and then the entire grout monolith was manually broken up and excavated using a jack hammer. Intact pieces of clay were visually apparent due to a sharp color contrast between the grout and clay. Remaining clay deposits were collected and weighed and suspended clay pieces within the monolith were photographed. The mobilization performance of the grout jets exceeded expectations