Pulse jet mixed (PJM) process vessels are being developed for storing, blending, and chemical processing of nuclear waste slurries at the Waste Treatment and Immobilization Plant (WTP) to be built at Hanford, Washington. These waste slurries exhibit variable process feed characteristics including Newtonian to non-Newtonian rheologies over a range of solids loadings. Waste feed to the WTP from the Hanford Tank Farms will be accomplished via the Waste Feed Delivery (WFD) system which includes million-gallon underground storage double-shell tanks (DSTs) with dual-opposed jet mixer pumps. Experience using WFD type jet mixer pumps to mobilize actual Hanford waste in DSTs may be used to establish design threshold criteria of interest to pulse jet mixed process vessel operation.
This paper describes a method to evaluate the pulse jet mixed vessel capability to process waste based on information obtained during mobilizing and suspending waste by the WFD system jet mixer pumps in a DST. Calculations of jet velocity and wall shear stress in a specific pulse jet mixed process vessel were performed using a commercial computational fluid dynamics (CFD) code. The CFD-modelled process vessel consists of a 4.9-m- (16-ft-) diameter tank with a 2:1 semi-elliptical head, a single, 10-cm (4-in.) downward facing 60-degree conical nozzle, and a 0.61-m (24-in.) inside diameter PJM. The PJM is located at 70% of the vessel radius with the nozzle stand-off-distance 14 cm (6 in.) above the vessel head. The CFD modeled fluid velocity and wall shear stress can be used to estimate vessel waste-processing performance by comparison to available actual WFD system process data.
Test data from the operation of jet mixer pumps in the 23-m (75-ft) diameter DSTs have demonstrated mobilization, solid particles in a sediment matrix were moved from their initial location, and suspension, mobilized solid particles were moved to a higher elevation in the vessel than their initial location, of waste solids. Jet mixer pumps were used in Hanford waste tank 241-AZ-101, and at least 95% of the 0.46-m (18-in.) deep sediment, with a shear strength of 1,500 to 4,200 Pa, was mobilized. Solids with a median particle size of 43 μm, 90th percentile of 94 μm, were suspended in tank 241-AZ-101 to at least 5.5 m (216 in.) above the vessel bottom. Analytical calculations for this jet mixer pump test were used to estimate the velocities and wall shear stress that mobilized and suspended the waste. These velocities and wall shear stresses provide design threshold criteria which are metrics for system performance that can be evaluated via testing. If the fluid motion in a specific pulse jet mixed process vessel meets or exceeds the fluid motion of the demonstrated performance in the WFD system, confidence is provided that that vessel will similarly mobilize and suspend those solids if they were within the WTP. The single PJM CFD-calculated jet velocity and wall shear stress compare favorably with the design threshold criterion estimated for the tank 241-AZ-101 process data. Therefore, for both mobilization and suspension, the performance data evaluated from the WFD system testing increases confidence that the performance of the pulse jet mixed process vessels will be sufficient to process that waste even if that waste is not fully characterized.