 on the tanks focus area About the focus areas The U.S. Department of Energy's Office of Environmental Management has established an integrated approach for addressing waste issues based on problem, or focus areas. The focus areas are subsurface contaminants; mixed waste characterization, treatment, and disposal; radioactive tank waste remediation; decontamination and decommissioning; and plutonium stabilization. Three crosscutting technology areas support the focus areas: characterization, monitoring, and sensor technology; efficient separations and processing; and robotics. The tanks focus area provides the leadership and organization for users at four U.S. Department of Energy tank sites to work together to safely and efficiently remediate tank waste. The 273 large, underground storage tanks and seven calcine vaults under TFA are located at the Hanford Site near Richland, Washington; the Idaho National Engineering and Environmental Laboratory near Idaho Falls, Idaho; the Oak Ridge Reservation in Oak Ridge, Tennessee; and the Savannah River Site near Aiken, South Carolina. These tanks, containing approximately 1 million gallons of high- and low-level radioactive and mixed waste, are approaching the end of their design life. More than 70 tanks are known or suspected to have leaked. Because of the cumulative risk to the environment and humans, the waste in these tanks must be characterized, retrieved, treated, and immobilized. The tanks must then be closed. In this article, the first of two on the tanks focus area, Initiatives will highlight recent characterization and retrieval activities undertaken by TFA. In the next issue, Initiatives will feature TFA activities in the areas of tank waste treatment and immobilization, and tank closure. Characterization TFA is developing and deploying tools to discover the types, concentrations, and forms of chemicals that compose tank waste. TFA is also acquiring data on the physical properties of the waste, such as temperature, moisture content, solid particle density, and fluid dynamics. By characterizing the waste, TFA will ensure that the waste is safely stored and can be safely retrieved and transferred for treatment. More effective separation and treatment technologies can also be developed by using characterization data. Accurate, rapid, and cost-effective characterization techniques are also being used to detect types and extent of contaminants leaking from tanks. See TFA's Web site at http://www.pnl.gov/tfa for information on tank characterization technologies: laser ablation/mass spectrometry, near infrared spectroscopy, and the Raman probe system. TFA involvement with the Hanford Tanks Initiative. TFA is pursuing several characterization activities in cooperation with the Hanford Tanks Initiative, a joint venture between DOE's offices of Waste Management (EM-30) and Science and Technology (EM-50) to demonstrate technologies applicable to closing Hanford's single-shell tanks. One TFA/Hanford Tanks Initiative characterization project is using cone penetrometer techniques to map the location, extent of migration, and concentration of radionuclides and hazardous chemicals in the backfill and vadose zone around the Hanford Site's single-shell tanks. The U.S. Army Corps of Engineers' Waterways Experiment Station was awarded the contract to design, fabricate, and test multisensor and soil-sampling probes using existing cone penetrometer techniques and equipment. WES will develop a single miniaturized multisensor probe with a metal tip sensor to avoid hitting pipes and other metal objects; a gamma spectrometer probe for conventional gamma logging; an X-ray fluorescence sensor for detecting RCRA metals, uranium, plutonium, and zirconium; sleeve and tip rheology sensors to classify soils; and a grout tube to close void spaces when the sensor assembly is retracted. Applied Research Associates will partner with the Hanford Tanks Initiative and WES to provide development, system integration, and deployment support. One of the major challenges facing tank sites is determining how much residual waste is left on the bottom of the tanks. The depth of waste can be quite small in some tanks-less than an inch to several inches-but even this depth of waste presents a serious problem when it is spread across the diameter of a tank. In-tank equipment that was built with the tanks was not designed to provide this information, and standard measuring techniques are difficult. Probes deployed with the Light-Duty Utility Arm will be able to measure the depth of waste on tank floors. During an in-tank measurement of Tank 241-AX-104 that was completed in August, the Hanford Tanks Initiative characterization project measured the waste depth, gained a better understanding of the radiation levels inside the tank, and captured new video image data. A combined magnetrometer/gamma/temperature/video probe was used to obtain this data, which updates the database being kept on Tank 241-AX-104. Another activity inside Tank 241-AX-104 is the deployment of an extended-reach end-effector. Deployed from the Light-Duty Utility Arm, the extended arm will lengthen the LDUA from 13.5 feet to 20.25 feet. This extra length will allow end-effectors on the arm to access, examine, and sample waste from hard-to-reach places inside tanks and to sample a larger area on the tank floor. A final design review was completed in early July, assembly of the unit has been completed, and testing was completed in early October.
Developing tools and processes for the safe and efficient removal of tank waste from aging tanks is a daunting challenge. Because of the waste's high radioactivity, access to the tanks is limited and a remote-controlled retrieval method must be used. Standard practice for removing saltcake, sludge, and hardpan is sluicing, which applies a high-pressure water stream into the tanks to dislodge and flush waste. Sluicing is slow, adds a high volume of water to tanks (increasing the waste disposal problem), and generates a mist that makes directing the nozzle difficult. Further, sluicing compounds the problem of leaking tanks, and it is ineffective in moving some rock-hard wastes. Another retrieval problem is that tanks are buried under several feet of soil, and entry to tanks is restricted through small openings called risers in the top of the tanks. Borehole mining, which was developed for the oil and gas industry as an enhancement to sluicing, is being investigated by TFA. The borehole miner uses an extendible nozzle to remove tank waste and a jet pump to convey the waste and water to the surface of the tank. During July and August, the miner underwent acceptance testing at the Hanford Site's Tank Technology Development Test Facility. The miner was delivered to Oak Ridge National Laboratory in August. The Light-Duty Utility Arm is a remotely operated, robotic system for deploying tools and sensors to collect data on tank and waste conditions and deploying retrieval tools. The tools attached to the LDUA are called end-effectors and will be used for retrieval, surveillance, confined sluicing, inspection, and waste analysis. The components of the LDUA system include a flexible and adaptive robotic arm that can be positioned in tanks through risers, a telescoping deployment housing, a deployment vehicle, an operations trailer, and end-effectors. TFA managed the development of the LDUA by working with site users and Spar Aerospace, a private-sector manufacturer of robotic equipment. In September 1996, the LDUA system was officially transferred from the developers to the first set of users, the Tank Waste Remediation System characterization program at the Hanford Site. During the first deployment of the LDUA into Tank 241-T-106 at the Hanford Site, the arm carried a high-resolution stereo video system to inspect the tank dome, risers, and walls. A modified LDUA, adapted to the Oak Ridge Reservation's 16 gunite and associated tanks, began waste retrieval during late July at Tank W-3. The waste was removed using the Confined Sluicing End-Effector deployed on the modified LDUA and on the remotely operated Houdini vehicle. The sludge depth (up to 23 inches) in Tank W-3 was much deeper than expected. The CSEE was deployed on the arm to pump off the supernate and excavate a landing spot into which Houdini could be lowered without burying its umbilical connection. Most of the sludge retrieval thereafter was performed using the CSEE manipulated with the Schilling arm on the Houdini vehicle. Gamma/beta detectors on the Characterization End-Effector performed a tank inspection after retrieval was completed in the fall of 1997. Following the completion of waste retrieval from Tank W-3 at the Oak Ridge Reservation, preparations began for retrieval from Tank W-4 on November 18. Tank W-4 contains a supernatant, a soft sludge layer of 2 to 4 feet, and a hard sludge layer up to 16 inches deep. Approximately 22,000 gallons of water has been used to remove approximately 4,000 gallons of supernatant and 15,000 gallons of sludge.
CSEE was developed as another alternative to sluicing. Because CSEE is one-fourth the mass of conventional sluicing technologies, it's less of a strain on deployment systems. CSEE can be deployed on a Schilling Titan II arm mounted on a remote vehicle, such as RedZone's Houdini, or on a robotic arm system like the modified LDUA. In addition to waste removal, CSEE can be set with higher-pressure jets to shave the concrete layers inside a gunite tank. The end-effector can also clean and decontaminate tank walls and residual hardware inside the tank. Cooling-coil cleaning and retrieval end-effector was demonstrated in May at the Hydraulic Test Bed at the Hanford Site. This end-effector was developed specifically for cleaning around cooling coils on the floors and walls at the Idaho National Engineering and Environmental Laboratory and the Savannah River Site. The cooling-coil cleaning and retrieval end-effector employs a two-step strategy. First, the end-effector is positioned just above the cooling coils; then high-pressure water jets scour the coils. The end-effector stirs up particulate on the bottom of the tank to assist in the scouring action for floor-mounted coils. Then, the end-effector is positioned near the floor to remove the remaining debris underneath the coils. Data analyses of testing results began during the summer; a final recommendation report will be completed; and the technical details will be incorporated into the Retrieval Analysis Tool. Retrieval Analysis Tool is an online compendium of tank and technology data on radioactive waste retrieval from DOE tanks. The first version of RAT is now available at http://www.tanks.org. It also can be accessed directly at http://www2.hanford.gov /ratlib/index.asp. RAT can help users match candidate retrieval systems to specific types of tank wastes. As RAT continues to evolve, it will contain data on DOE retrieval testing to date, ongoing retrieval projects, and decision methodology. For more information on TFA's
characterization activities, contact: For more information on TFA's retrieval
activities, contact: Technical highlights from the tanks focus area are updated on a monthly to biweekly basis and published on the Internet at http://www.pnl.gov/tfa/hilight. If you would like to receive an e-mail version of the highlights, follow the instructions given at the bottom of the above-referenced Web page. |
    |
Retrieval
The
Confined Sluicing End-Effector is
another tool developed under the auspices of TFA to
retrieve tank waste. This tool uses three rotating water
jets to cut up and slurry sludge and saltcake, so they
can be pumped from the tank. This waste can be
simultaneously removed using a close-coupled water-jet
pump, which was provided to the Oak Ridge National
Laboratory for use in its gunite and associated tanks.