Radioactive waste resulting from production of weapons is stored at five U.S. Department of Energy (DOE) locations. The waste characteristics range from fluid to sludge to granular salts with radiation levels exceeding 10,000 rad/h.
Innovative tools are used to remotely remove the solidified radioactive waste from underground storage tanks. When available, commercial systems are evaluated for waste dislodging and retrieval applications. A waste dislodging and sluicing system developed to dislodge and fracture deposits of ore in underground mining, called a borehole miner, was evaluated by Pacific Northwest National Laboratory (PNNL) and Waterjet Technology, Inc., for removing solidified nuclear waste stored in underground tanks. This compact system may be installed in tanks via small diameter risers and has the capability to both dislodge and retrieve in a single unit. The borehole miner arm includes an extendible nozzle that operates at high pressure using either water or slurry as the dislodging fluid, while providing a focused high-pressure jet to dislodge solidified material. The sluicer nozzle is attached to a retractable arm that can extend and angle to enhance dislodging in specific areas of the tank by changing the standoff distance.
This paper describes the borehole miner system and presents results of experiments to evaluate its ability to dislodge solidified saltcake and sludge materials. Tests were conducted with a stationary jet to evaluate the potential to develop an extendible-nozzle borehole miner system for deployment to dislodge radioactive saltcake and sludge wastes stored in underground storage tanks. The tests were successful and identified ranges of parameters for jet diameter and standoff distance applicable for waste remediation. For saltcake simulants, erosion models were developed that represent the data.