Development of Nuclear Waste Tank Sludge Removal Using Scale Model

Hanford Site is in the process of removing radioactive waste from large storage tanks.  The tanks contain salty supernate, salt and sludge.  Nearly all of the actinides, such as uranium and plutonium, are in the sludge layer on the bottom of the tank.  Estimates of plutonium inventories indicate a potential criticality concern in some tanks.  Waste removal should not be performed in a way that significantly concentrates dense plutonium particles in the heel.  Savannah River National Laboratory (SRNL) developed a four component sludge simulant, including a surrogate for plutonium particles, which has rheology, density and settling properties typical of Hanford tank waste.  SRNL tested sludge removal in a 1:22 scale model waste tank using rotating submerged jets.  Photographic and laser techniques were used to measure the shape and volume of the residual tank heel.  Magnetic separation and a colorimetric technique were used to measure compositions of the heel and also of solids removed from the tank.  Sludge removal efficiency and tendency to concentrate the plutonium surrogate were measured.  The results will be used to guide larger scale tests.