Visual evaluation of effective cleaning radius in model jet-agitated tank

Suspension of monosodium titanate (MST) and sludge in high level waste (HLW) tanks at Savannah River Site (SRS) is needed prior to processing of the salt solution (containing actinides, Sr-90, and Cs-137) from the supernate and the dissolved salt cake. One type III tank model, including cooling coils, was fabricated and used to carry out cost effective evaluation of jet mixing of MST and simulant sludge in surrogate salt solution. The model tank has a diameter of 0.3 m (1 ft). Experimental work was carried out utilizing five different sludge/MST mixtures in surrogate salt solution. The examined solutions included 5% wt sludge, 5% wt 4:1 sludge/MST, 5% wt 2:1 sludge/MST, 5% wt 1:1 sludge/MST, and 5% wt MST. The progress of the effective cleaning radius (ECR) formation was monitored during the mixing and suspension processes with and without the presence of cooling coils and at several pumping flow rates and nozzle orientations. Digital photographs of the bottom of the tank were analyzed and the ECR was measured at different pumping flow rate and nozzle orientation. It was found that it took 20 to 30 minutes in order to reach a fully developed ECR at the bottom of the tank. A qualitative analysis of the images taken for the fully developed ECR (at nozzle angles of 0 deg., 45 deg., and 90 deg. from the centerline of the tank) indicated that two counter-rotating eddies took place in the tank, resulting in full suspension of the sludge and MST except for two islands (spots) of settling sludge and MST particles. These islands of settling sludge and MST vary in size and location depending on the pump flow rate and the angle of the nozzle from the tank centerline. The presence of cooling coils in the tank hindered the suspension process and resulted in an undeveloped ECR even at high flow rates. (authors)