Millions of gallons of radioactive waste are stored in underground tanks at the Hanford Site in Washington State. This waste will be vitrified at the Waste Treatment and Immobilization Plant that is under construction. Vessels in the pretreatment portion of the plant are being configured for processing waste slurries with challenging physical and rheological properties that range from Newtonian slurries to non-Newtonian sludge. Pulse jet mixing (PJM) technology has been selected for mobilizing and mixing this waste. In the pulse jet mixing process, slurry is expelled from pulse tube nozzles directed towards the vessel floor. The expelled fluid forms a radial jet that erodes the settled layer of solids. The pulse tubes are configured in a ring or multiple rings and operate concurrently. The expelled fluid and mobilized solids traverse toward the center of the tank. At the tank center, the jets from pulse tubes in the ring collide and lift solids upward in a central plume. At the end of the pulse, when the desired fluid volume has been expelled from the pulse tube, the applied pressure switches to suction and the pulse tubes are refilled. This cycle is used to mobilize and mix the tank contents.
An initial step of the process is the erosion of solids from the vessel floor by the radial jets that form on the vessel floor beneath each pulse tube. Experiments have been conducted using simulants to evaluate the ability of the pulse jet mixing system radial jets to combine to develop the central upwell and lift solids in the vessel. These experiments were conducted at three scales using a range of granular simulants over a range of concentrations in vessels with elliptical, spherical, or flanged and dished bottoms. Process parameters evaluated experimentally include the velocity of fluid expelled from the pulse tube, the duration of the pulse and the ratio of pulse duration to cycle time. Videos taken from beneath the vessel show the growth of the cleared area beneath each pulse tube as a function of time during the pulse. The focus of this paper is to describe measurement techniques and compare and contrast erosion patterns developed from different simulants and pulse tube configurations. The cases are evaluated to determine how changes in process parameters affect the PJM’s ability to mobilize solids from the vessel floor.