CH2M HILL Technology for Waste Management
Hose-in-Hose Transfer Lines
Flexible, hose-in-hose transfer lines have helped CH2M HILL move waste out of aging single shell tanks and transfer it to safer double-shell tanks. The temporary hose-in-hose transfer lines were used in place of the existing underground transfer system, which was in poor condition and out of compliance with current environmental standards.
Much of the piping, valve systems, and other components of the existing underground infrastructure were installed in the 1940s and 1950s. Upgrading them to support waste retrieval would have involved costly excavation and installation. The hose-in-hose transfer lines provided a less expensive alternative and were part of the fieldwork completed to meet the TPA M-43 milestone.
Tank Management and Safety
Compatibility Assessment Automation Tool
Development of the Compatibility Assessment Automation Tool (CAAT) is providing CH2M HILL with faster, more reliable data for ensuring compatibility of waste transferred from single shell tanks to safer double-shell tanks. Indeed, with the CAAT software program, a job that once took weeks to perform is now accomplished in minutes. In the Hanford tank farms, where chemical and radioactive constituents differ from tank to tank, it is essential to confirm waste compatibility and manage the transfer process. Using CAAT, engineers have faster access to comprehensive data in advance of waste transfers, and they can analyze multiple transfers at the same time.
Knowledge about the chemical processes that generated the waste is incorporated into the CAAT program, and CAAT is connected to the long-established Tank Waste Information Network System (TWINS). TWINS is an electronic repository for data on tank waste inventories and includes information on waste volumes, data derived from waste sampling, and details on tank chemistry and levels of radioactivity.
Combining all this data, the CAAT program can automatically calculate the tank chemistry and alert engineers to potential problems, for example, with corrosion or the generation of flammable gas. Engineers then can respond with appropriate adjustments to minimize adverse chemical reactions.
Penetrometers
Cone penetrometer trucks (CPTs) have been used for years at Hanford to perform shallow soil investigations. The large trucks rely on their 30- to 45-ton weight to push rods into the ground. The rods measure resistance at the tip or along the shaft and collect soil samples at predetermined depths. They have instruments that detect subsurface radioactivity without bringing contaminants to the surface, as in drilling. However, in the tank farms, the CPTs cannot maneuver easily around the equipment, and weight limits restrict their use over the underground tanks.
Development of Advanced Field Penetrometers is solving these problems and providing enhanced subsurface-assessment capabilities. The new equipment uses a mast system and hydraulic hammer mounted on a backhoe-sized tractor that can maneuver readily around obstacles in the farms. With specially designed grooved rod tips and a rotating hammer, the system can penetrate compacted zones, gravel and other rugged subsurface features. At total depth, rod monitors can detect moisture and radioactive contamination and can differentiate soil layers.
To date, the new penetrometer system has reached depths as great as 113 feet below the surface. It has been used for 41 data-logging operations and 25 soil-sample collections in two tank farms. Additional demonstrations are planned in 2006 when the system will be used for ground penetrations at an angle to collect geophysical data and soil samples below surface obstructions.
Off-Riser Sampler System
A new off-riser sampler is making collection of waste samples from Hanford tanks easier and more productive. The sampling, which takes place following retrieval activities, provides essential data for regulatory decisions on tank closures and for site risk assessments. Historically, sample collection was restricted to waste materials that could be accessed directly beneath a tank riser. Material not near a riser was out of reach of the sampling system. With the new off-riser sampler, operators can reach in and around to collect residual waste material anywhere in the tank. The remotely controlled device is being further enhanced with an on-board camera so operators will not have to rely on separate in-tank cameras to locate the waste and control the device.
Remote Inspection of Double-Shell Tanks
A project that took nearly ten years to complete has given the Washington State Department of Ecology important assurances about the integrity of Hanford’s 28 double-shell radioactive waste storage tanks. The data, which were gathered using a remotely controlled, ultrasonic examination system, show the tanks are in good condition.
The remote inspection system uses electronic currents to examine the tank walls and look for corrosion, stress-corrosion cracking, pits, and defects from construction. Aided by a Synthetic Aperture Focusing Technique developed by DOE’s Pacific Northwest National Laboratory, examinations also can be made of the high-stress “knuckle region” of the tank, which is the curved area connecting the vertical walls with the bottom of the tank.
With completion of the last four tank surveys (tanks AN-101, AN-103, AN-104 and AN-105), data have confirmed that all the double-shell tanks meet or exceed operating specifications. In some tanks, the steel used to construct the tanks was thicker than specifications required. Additionally, the conditions in many tanks that have stored waste for several decades were better than expected. The tank inspections are part of a major TPA milestone (M-48-14).
Double Salt Database
Over the years laboratory tests have provided a volume of data for use in understanding the underlying tank waste chemistry. The information has been studied and used extensively in preparation for retrieval and treatment of tank waste. Although the data have been useful, they have not supported accurate predictions of how double salts in the waste material would dissolve, which is important in managing and controlling the waste transfer process. Salts can form needle-like crystals that interlock in masses and clog transfer lines.
To expand prediction capabilities, CH2M HILL is conducting studies of the salt-based compounds and building a Double Salt Database. The work is comparing earlier predictions against available data and experimental results for salt matrix material, which include sodium-fluoride-phosphate, sodium-fluoride-sulfate and several others. The information will better explain dissolution and interactions of the double salt compounds and greatly increase our knowledge base on waste chemistry.
Residual Waste Measurement
CH2M HILL is exploring new technologies for improved measurement and documentation of waste remaining in Hanford’s single-shell tanks. Currently, project teams use in-tank video data to measure and document residual waste. The videos are recorded by cameras installed in the tanks to support waste retrieval activities. The videos provide topographical models of the waste surface and help determine waste volume.
An alternative is under development at Mississippi State University’s Diagnostic Instrumentation and Analytical Laboratory. The technology couples a Fourier Transform Profilometry system with an in-tank camera for more detailed imaging. This technology is a candidate for testing at the Cold Test Facility and for eventual fullscale installation.
Laser scanning is another alternative under review for residual waste measurement. A scan of the interior of the tank is used to compute the 3‑dimensional volume differential between the tank with residues and the original tank volume. The concept is in the early stages of evaluation.
High-Resolution Resistivity
A geophysical technology is being tested near two Hanford tanks to improve leak detection during waste removal operations. High-Resolution Resistivity is more sensitive to changes in moisture and contaminants in the ground. It is expected to provide faster, more reliable information for leak monitoring activities.
Constructed in the 1940s and 1950s, about 68 aging singleshell tanks are prone to leaking radioactive and chemical contaminants into the surrounding soil. Monitoring currently relies on periodic measurements in drywells around the tanks. Probes lowered into the drywells measure changes in moisture or radioactivity levels. Although this technique is effective, it does not provide real-time data and may not detect small tank leaks outside the immediate vicinity of the probe.
High-Resolution Resistivity records electronic measurements of soil resistivity for real-time detection of a tank leak. The data are used to construct tomographic images that show changes in moisture content in the sediments beneath the tank. Applied to the underground tanks at Hanford, the technology will detect leaks in locations where drywell measurements may not find them and will provide data on leak rates. CH2M HILL has successfully tested the technology in clean soil around a mock underground tank. Additional testing will continue at tanks S-102 and C-103 in 2006.
Subsurface Geophysical Exploration
CH2M HILL is exploring the use of a Subsurface Geophysical Exploration (SGE) system as an additional geophysical technology to aid in tracking and mitigating tank waste leaks into the surrounding soil. The SGE measures electrical resistivity of the soil beneath the tanks, taking measurements in a grid pattern throughout the tank farms. The data are then used to generate 3-dimensional maps of the area around the tanks. The maps indicate the location, size and configuration of any contaminant plumes in the vadose zone around the tanks. The ability to locate the contamination allows us to assess and respond with appropriate interim measures for restricting migration of contaminants. Interim measures may include installation of berms, curbs, culverts and gutters to divert surface water runoff from specified areas.
The SGE is being tested in conjunction with the High-Resolution Resistivity leak detection approach at tank S-102. The evaluations are part of the Tank Farm Vadose Zone Project, which is coordinated closely with other groundwater projects at the site.