Stabilization of Underground Solvent Storage Tanks

Abstract

The Old Solvent Tanks (OST), located at the Savannah River Site (SRS) Old Radioactive Waster Burial Ground (ORWBG), are comprised of 22 underground storage tanks that were used to store spent radioactive solvent and aqueous wastes generated from the plutonium-uranium extraction (PUREX) process. The OSTs were installed at various dates between 1955 and 1968 and used to store the spent solvents until 1974. The spent solvents stored in the OSTs were transferred out from 1976 through 1981 leaving only residual liquids and sludges that could not be pumped out. Final remediation goals for the ORWBG include an overlying infiltration control system. If the tanks were to structurally fail, they would collapse causing potential for onsite worker exposure and release of tank contents to the environment. Therefore, as an interim action, methods for stabilizing the tanks were evaluated. The preferred remedial action was “Grouting of the Tank Wastes In-situ.” The primary function of the grout is to provide structural stability of the tanks by filling void space with material that prevents tank collapse. Incidental to any mixing that may occur, residual material in the tanks will be incorporated into the grouting mixture. The incidental grouting will ultimately improve environmental protection by rendering the residual material immobile. To accomplish this task, the SRS Environmental Restoration Division (ERD) teamed with the Savannah River Technology Center (SRTC) to determine a remedial design strategy and to translate this strategy into a construction specification and drawings for implementation. The OST remedial design strategy contained the following key aspects for performance requirements and acceptance criteria: • Grout mix; • Tank atmosphere testing; • Grout delivery system and camera monitoring system; • Off-Gas HEPA filter system and environmental monitoring; • OST Sealing and labeling. From November 2001 through February 2003 all 22 Old Solvent Tanks were successfully stabilized. This paper will discuss the systems designed to perform and monitor the grouting operation, the grouting process, and the radiological controls and wastes associated with grouting the Old Solvent Tanks.