REMEDIATION OF FIVE UNDERGROUND STORAGE TANKS AT THE OAK RIDGE NATIONAL LABORATORY. James R. LaForest, CDM Federal Programs Corporation

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1 REMEDIATION OF FIVE UNDERGROUND STORAGE TANKS AT THE OAK RIDGE NATIONAL LABORATORY James R. LaForest, CDM Federal Programs Corporation Christopher A. Provost, Camp Dresser & McKee, Inc. Kelly L. Barger, CDM Federal Programs Corporation ABSTRACT This paper presents a case study in the removal of partially solidified mixed waste from underground storage tanks. CDM Federal transferred low-level radioactive waste from five aging, at-risk, underground storage tanks to an active waste management system at Department of Energy facilities on the Oak Ridge Reservation in Tennessee. Technology originally designed for use in the mining industry and operated by specifically designed computer-controlled operating systems, was used to flush the sludge and liquid from the tanks, allowing the waste to be transferred to safe storage. There were two primary challenges to completing this project. First, the high level of radioactivity (approximately 30,000 curies) necessitated the use of remotely operated equipment, which required extensive "cold" testing as well as operator training. Second, the nature of the waste occurring in both liquid and solid phases necessitated a sluicing system capable of reaching all areas of the tank with enough water pressure to dislodge and resuspend the sludge. These challenges were primarily met by modifying a sluicing arm and nozzle known as a Borehole Miner. The Borehole Miner, originally developed and used by the mining industry, delivered a high-pressure jet spray capable of dislodging the sludge using an extendable and remotely controlled nozzle capable of being directed to reach any portion of the tank. A system of remotely operated submersible, centrifugal, and positive displacement pumps recycled the tanks contents through the nozzle until an appropriate slurry was obtained. These systems were operated remotely by linking key components of the system through a programmable logic controller into a human/machine interface software system. Sensors and video cameras allowed constant monitoring of system functions as well providing real-time data. Through the use of the modified Borehole Miner and other system components, the radiological waste was successfully suspended and transferred to safe storage facilities. The work was performed in a safe manner and all project milestones and objectives were met. INTRODUCTION Organization This paper is organized into seven main sections, which include an abstract; introduction; remediation system design; system operations; challenges and solutions; conclusions; and references. Summary This paper summarizes the remediation of five horizontal underground storage tanks containing radioactive sludge and supernatant at the Department of Energy s (DOE) Oak Ridge National Laboratory (ORNL) Old Hydrofracture Facility (OHF) site in Tennessee. The OHF tanks, varying in size and submerged depth below grade, had accumulated approximately 199,000 liters of low-level (radioactive) waste. The remediation activities involved the transfer of the waste through sluicing and pumping operations, which were designed to pump the slurry in a closed circuit system using a sluicing nozzle to

2 resuspend the sludge. A remotely operated sluicing and pumping system was specifically designed with a sluicing nozzle and arm (Borehole Miner) originally used in the mining industry. The Borehole Miner is an in-tank device designed to deliver a high-pressure jet spray via an extendable nozzle. Additional components of the complete sluicing and pumping system consisted of a high pressure pumping system for transferring material to the storage area, a low pressure pumping system for transferring material to the recycle tank, a ventilation system for providing negative pressure on tanks, and instrumentation and control systems for remote operation and monitoring. Within a 3-week period, approximately 98 percent of the waste from the OHF tanks was successfully retrieved and transferred to the Melton Valley Storage Tanks (MVST) for secure storage. Project Objective The primary objective of the OHF tanks contents removal project was to safely transfer sludge and supernatant from five liquid low-level (radioactive) waste (LLLW) storage tanks associated with OHF to the MVST for final disposition. A sluicing and pumping system had been specifically designed for meeting this objective. A secondary objective of this project was to demonstrate the Borehole Miner s applicability to underground storage tank cleaning for future applications and benefit at other DOE sites. Site Location/History The OHF site is located in Melton Valley, approximately 1.8 km south of the ORNL main plant and within the secured area of Waste Area Grouping 5. The OHF was built in 1963 to dispose of liquid waste by mixing it with grout and injecting the waste into a deep shale formation approximately 305 m below ground surface. The facility began operation in 1964 and shut down in A total of about 8.7x10 6 L of the waste grout mixture containing approximately 650,000 curies of radionuclides was disposed of during 18 injections. Table I lists the sludge and supernatant contents remaining in each tank after facility shutdown. Table I. OHF Tank Waste Volumes Tank Tank Nominal Supernatant Total Sludge Tank Length Diameter Capacity Volume Waste Volume (L) (m) (m) (L) (L) (L) T ,780 40,810 5,340 46,140 T ,780 40,240 5,910 46,140 T ,640 7,420 11,810 19,230 T ,640 55,990 8,740 64,730 T ,210 18,660 4,320 22,980 Total , ,120 36, ,220 During the original 1963 construction, three carbon steel storage tanks (T-1, T-2, and T-9) were installed at the OHF to store LLLW for injection. In 1966, two carbon steel, rubber-lined storage tanks (T-3 and T-4) were installed at the OHF. Several modifications to the OHF tanks were made to allow installation of sluicing and pumping equipment. REMEDIATION SYSTEM DESIGN The sluicing and pumping system was designed to transfer contaminated slurry (supernatant and sludge) from the OHF underground storage tanks to the MVST using a batch process. The batch process began by

3 pumping slurry from a tank containing wastes to the recycle tank (T-9). In the recycle tank, a mixer blended the slurry and maintained the solids in suspension. From the recycle tank, the slurry was pumped to the sluicer nozzle at high pressures. As the sluicer nozzle was aimed at sludge in the bottom of the tank being sluiced, more solids became suspended in the slurry, which was pumped back to the recycle tank completing the circuit. This closed loop system was continued until the sludge had been sufficiently resuspended, at which time the material was transferred to the MVST through the LLLW system. This transfer was accomplished independently and/or during sluicing. Figure 1 shows the process flow diagram for the OHF sluicing and pumping system. The sluicing and pumping system was designed to be operated remotely from a control trailer and to maintain the flows and pressures specified by the operators, while allowing an operating range providing the operator flexibility during sluicing and pumping operations. This flexibility allowed adjustment of sluicing nozzle pressures from nominal to N/m 2 and flows from 189 to 568 L/min; also, the system allowed bypassing of the recycle tank and/or the sluicer pump, if desired. The system was given a modular design to simplify construction and transport. Each module was designed to meet particular system requirements and to be integrated with other modules. The following sections describe the operational details of each module and their performance requirements. Figure 2 presents a plan view of the remediation system site layout at OHF. The following subsections describe the major components of the system. In Tank Equipment Several pieces of equipment were installed in each of the OHF tanks. Two submersible pumps were installed in each tank (except T-9) to transfer slurry and/or supernate from the tank being sluiced to the recycle tank. One submersible pump was installed in tank T-9 to feed slurry from the recycle tank to the high-pressure pump. An in-tank mixer was installed in tank T-9 to mix the slurry and maintain solids suspension in the recycle tank. In-tank video cameras were used to visually monitor sluicing and pumping operations Transfer Pump Skid The skid was fully enclosed and underlain by a drip pan for leak/spray containment. The sides of the skid were constructed of plate steel to provide radiation shielding and to provide a mounting surface for the electrical panel and valve panels. The top of the skid was constructed of plexiglass to allow remote observation of the skid with an on-site camera. Major equipment comprising the transfer pump skid and their primary purpose are: Two parallel progressive cavity pumps (high-pressure pumps) to directly feed the slurry to the sluicer nozzle, to feed slurry to the sluicer pump, and to transfer slurry from the OHF to the MVST Rupture disks to provide a final, mechanical safety measure against over pressurization across the discharge and intake of the high-pressure pumps Two parallel, in-line strainers downstream of the high-pressure pumps to protect the sluicer nozzle from particles larger than 0.32 cm Secondary containment in the form of containment piping, skid enclosures, and riser boxes to protect all pipes transferring waste

4 Sluicer Pump Skid The sluicer pump skid was part of the Borehole Miner extendable nozzle sluicing system provided by Pacific Northwest National Laboratory. The major equipment contained on this skid and their primary purposes are: Horizontal triplex piston sluicer pump used during sluicing operations Rupture disk on the sluicer pump discharge to act as a final, mechanical safety against over pressurization

5 Fig. 1. OHF sluicing and pumping system process flow diagram

6 Fig. 2. OHF remediation system site layout

7 Pulsation dampener, installed on the intake of the sluicer pump, to prevent operational problems from high-pressure spikes that occur because of flow pulsations during the normal operation of triplex pumps Sluicing System The Borehole Miner is a hydraulically actuated arm used to direct a high-pressure spray through a nozzle at the end of the arm. By aiming the spray at sludge in the bottom of the tanks, the sludge was physically dislodged and put into a suspended slurry. The sluicing system consisted of the Borehole Miner (sluicer), hydraulic power unit, and sluicer control panel. Figure 3 provides an illustration of the Borehole Miner. The components of the Borehole Miner extendable nozzle sluicing system are: (1) top mast assembly, (2) platform assembly, (3) bottom mast assembly, (4) arm assembly, (5) launch assembly, (6) control console, (7) bridge mount, and (8) containment hose assembly. Fig. 3. Borehole Miner Extendable-Nozzle Ventilation System A skid-mounted ventilation system was designed for the tanks contents removal project to maintain less than atmospheric tank pressure and to prevent the unfiltered release of vapors from the tanks. This system consisted of a ductwork manifold, intake assembly, demister, heater, high-efficiency particulate air filters, blower, and stack sampler Process Water System The process water system was designed to flush the OHF piping and the LLLW line and to provide other process water needs at the site. The system included a process water tank, a skid-mounted process water pump, and an electrical distribution panel.

8 Backup Generator A 100-kilowatt generator was included to allow operation of the ventilation skid and the process water skid if a power outage occurred at the OHF. The continued operation of these skids could maintain a negative pressure on the tanks, allow flushing of waste lines, and allow flushing of the LLLW line. Electrical service to these skids could be switched to the backup generator by manually changing electrical receptacles at the local skid panels. Instrumentation and Controls An extensive system of monitoring, instrumentation, and controls was included in the design because (1) the radioactive nature of the materials at the OHF required extreme caution to prevent or minimize any leaks or line clogging and (2) the system was operated remotely to minimize radiation exposure. The system consisted of pressure indicators and switches, flowmeters, tank liquid level indicators, video systems, and liquid sensors in skid drip pans. Information from each of the monitoring devices was connected to the control system for operational monitoring. In addition to the automatic mode (running from set points), the operator had the option of running part or all of the system in a manual mode where system variables could be specified. SYSTEM OPERATIONS Cold Test A cold test of the operations was performed to evaluate the operational status of the full sluicing and pumping systems as well as individual components of the system. This was also done to train the field operators and to demonstrate readiness of both the system and the crew to proceed to the OHF site to conduct the tanks contents removal action. The cold test system included two ~29,900 L tanks (2.4-m diameter and 6.4-m long). One was used as the sluice tank; the other was used as the recycle tank. A series of tests were conducted with a waste simulant, pulverized kaolin, to evaluate the operational status of the full sluicing and pumping systems as well as individual components of the system. The initial sluicing operation was performed over 6 hours, but upon mixing the simulant, subsequent tests required 1 to 2 hours of sluicer and pump operations. In all tests, the amount of sludge remaining in the tank was based on the suction limit of the submersible retrieval pumps. These pumps were capable of retrieving wastes to within 7- to 10-cm from the bottom of the tank. The remaining slurry was diluted to ensure that little sludge remained in the tank after pumping operations. In summary, the system components performed as designed. The tests demonstrated that the Borehole Miner was an effective tool in dislodging dense materials even at relatively low pressures. During the cold test, operating methods were developed, practiced, and perfected for several critical operational activities. These included methods for 1) moving cameras from tank to tank 2) moving the Borehole Miner from tank to tank 3) rupture disk change out 4) basket strainer change out, 5) sluicer pump operations 6) balanced operations for three pumps in series, and 7) overall system operations and control. These methods were formalized and detailed work procedures were developed. Site Operations On April 8, 1998, equipment was moved from the cold test facility to the Old Hydrofracture Facility site. From April 8 through June 28, 1998, equipment was installed at OHF and its operation verified.

9 Based on lessons learned during the cold tests, operations were conducted with four operators: one instrumentation and controls engineer, two operations technicians, and one operating engineer to oversee and direct the operation, but not actively operate the equipment. All sluicing was conducted using the following approach. The process was started at low pressure (around 3.4 x 10 5 N/m 2 ) and when systems were confirmed operational, the 1.4 x 10 6 N/m 2 high pressure pump speed was increased to achieve 1.2 x 10 6 to 1.3 x 10 6 N/m 2. When the high-pressure sluicer pump was used, the pressure was raised to approximately 2.8 x 10 6 N/m 2. During retrieval operations, two approaches for nozzle movements were used: Fixed arm angle and extension: establish a fixed target using the in-tank camera; map the target via arm angle, extension, and mast rotation; execute sluicing with a fixed arm angle and extension. Reinspect the target area, repeat as necessary or assign a new target. Fixed arm extension and mast rotation: vary the arm angle to push a sludge mass toward a retrieval pump. The retrieval operations were initiated in the evening to take advantage of cooler ambient temperatures at night since the heat of the day caused the retrieval pumps to overheat and trip. Based on this scenario, the retrieval pumps were alternately operated in one end of the tank and then the other. The extendable nozzle was oriented to point toward the retrieval pump in operation. Waste retrieval operations were conducted from June 26, 1998 to July 19, The total volume of material transferred to MVST from OHF summarized in Table II. Approximately 98 percent (this is the maximum extent practicable using pumping technology) of the waste was transferred to the MVST. The remaining 2 percent of the waste will be grouted in place. The waste stored at the MVST is awaiting final disposal at a permanent disposal facility to be determined at a later date. Table II. Total volumes sent to the MVST Tank Sent to MVST Total, L T-3 T-9 87,117 T-4 50,418 T-2 40,288 T-1 49,778 Totals 228,506 CHALLENGES AND SOLUTIONS The project s primary challenge was the high level of radioactivity at the site. This restricted accessibility to the tank interiors, limited the ability to visualize the work, and required remote, hands-off methods of sludge removal. Extra health and safety measures for project personnel were also required. The system had to be designed to allow remote operations of the extendable nozzle and other system components. The operators did not have a direct line of vision to perform the work and, therefore, they had to rely on television monitors, video feeds visualization system, and computer readouts of instrumentation readings. Key components of the system were linked electronically through a programmable logic control and a computer-generated schematic of the entire system. Operations continuously monitored system function and integrity, relying on in-tank cameras, electronic sensors, and

10 programmed set points (for problem identification and prevention) to provide them with real-time data to minimize worker exposure and maximize reaction time in the event of an emergency. Because of high background radiation levels made it impossible to get accurate reading from the personnel monitors used to detect contamination on workers, a lead-shielded "frisking facility was designed and used the site. Another challenge was that removal of the sludge from the tanks using conventional sluicing technologies was not feasible because of hardened sludge deposits on the bottom of the tanks. In addition, each tank varied slightly from the others in configuration (in terms of size and internal structures). In response, an extendable nozzle originally used in industrial mining was adapted to circumvent this problem. The mast of the Borehole Miner was shortened and modifications were made which would allow the nozzle to be extended downward and rotate 360-degrees. These modifications made it possible to spray all the bottom portions of the tanks. Instrumentation, controls, cameras, visualization systems, and operating procedures were used to overcome the variations in tank configuration. A further challenge came in the form of limited room for this waste once it was removed. Because of a shortage of available storage for the waste once it was transferred, the addition of water used to aid in the sluicing operations was restricted. Therefore, the system was designed to mix the sludge and supernate in each tank into a slurry to use as feed for the Borehole Miner during sluicing operations. This was done by recycling slurry into Tank T-9. The Borehole Miner created the slurry in the target tank. The slurry was then transferred into the recycle tank where an in-tank mixer was installed to keep all of the solids suspended into solution. From the recycle tank the slurry was used to feed the Borehole Miner for sluicing operations. This process was performed until all solids were suspended into the slurry and at this point the waste was transferred to safe storage off-site. Screens were placed on each of the submersible pumps and basket strainers were used in the recycle system to prevent clogging in the transfer system. A fourth challenge encountered was that no single pump could be found that could provide the sufficient range of lift, flow, and discharge pressure needed to recycle, remove, provide flow to the Borehole Miner (for sluicing), and transfer of waste. To address this problem, one submersible and two positive displacement pumps were designed, installed, and operated in series to get the range of required lift, flow, and discharge pressure to conduct recycle, removal, sluicing, and waste transfer operations. Pressure relief valves, recycle lines, pulsation dampeners, instrumentation and control, and operating procedures were used to ensure smooth and efficient operations of this pump configuration. CONCLUSIONS Although some equipment, site, and operational problems were encountered, the design, fabrication, installation, cold testing, and deployment of the extendable -nozzle Borehole Miner system at ORNL were successfully completed. The system was used to dislodge, mix, and suspend radioactive sludge waste from the OHF tanks. Approximately 228,500 liters of the waste were transferred from the tanks to a safe storage area. Retrieval of 98 percent of the waste was completed in approximately 3 weeks. At the end of the remedial action, the State of Tennessee Department of Environment and Conservation agreed that the tanks were cleaned to the maximum extent practicable using pumping technology. The project was completed with no reportable health and safety incidents or releases of radioactive materials. Additionally, actual worker radiation exposure was approximately one-third of original estimates. No leaks or spills were experienced. The project provided valuable data showing the effectiveness of the Borehole Miner for other similar projects. REFERENCES 1. Bamberger, JA and BF Boris Oak Ridge National Laboratory Old Hydrofracture Facility Waste Remediation Using the Borehole -Miner Extendable Nozzle Sluicer. PNNL-12225, Pacific Northwest National Laboratory, Richland, Washington.

11 2. CDM Federal Programs Corporation Old Hydrofracture Facility Tanks Contents Removal Action Operations Plan at the Oak Ridge National Laboratory, Oak Ridge, Tennessee Volume 1 Text. ORNL/ER-433/V1, Oak Ridge National Laboratory, Oak Ridge, Tennessee. 3. Department of Energy Borehole Miner - Innovative Technology Summary Report, OST/TMS ID 1499 (DOE/EM-0492), Oak Ridge National Laboratory, Oak Ridge, Tennessee.