The thesis investigates pipeline plugging mechanisms that have occurred during interim stabilization transfers at Hanford. A laboratory-scale saltwell pumping test loop was designed to evaluate a surrogate of Hanford Tank 241-SX-104 supernate. The effect of surrogate flow rate, cooling water flow rate and phosphate concentrations on plugging mechanisms was investigated. Critical parameters like particle and agglomerate size, velocity and bed growth rate were determined. Theoretical models were used to compare the experimental pressure rise and temperature drop of the surrogate in the channel. An operating region in which a plug would not form was developed, based on the experimental results. Experiments are also reported on plug remediation. Unplugging experiments at varying pump pressure heads and residence time of plug in the line were performed.

This thesis is divided into two projects. The first project investigates the dissolution of the Hanford salt cakes, the chemical properties of the effluent and the physical properties such as viscosity of the effluent, the porosity and the permeability of the salt cake bed as the dissolution proceeds. The chemical results are compared to predictions using a thermodynamic model. Physical properties are important because they govern the rate at which the Hanford tanks can be emptied thus facilitating the remediation process. Two simulants were investigated for the dissolution process. The chemical analysis matched with the model predictions for both the simulants. A typical gibbsite layer formation was observed in the chemically complex simulant and experiments were performed to remediate the layer. The second project of this thesis studied the remediation of sodium phosphate dodecahydrate plug using water and sodium carbonate solutions at varying concentrations. A flow loop previously used to study the sodium phosphate dodecahydrate plugging mechanisms, was used to form a plug followed by the addition of water and sodium carbonate solutions. Results indicate that there was a drastic decrease in time to remediate the plug when sodium carbonate solutions were used.