DIAL's Research Highlights

Characterization of Heavy Metals and Radionuclides

On-line isotopic monitoring and analytical protocol development for uranium and other actinides. For June, the CRDS group had originally planned to evaluate the isotopic resolution and detection sensitivity of the uranium 424-nm absorption line. However, the substrate of one of the cavity mirrors that had been purchased for this purpose was defective. Two replacement mirrors also suffered from this same defect, indicating that the mirror supplier had purchased a defective set of substrates prior to coating. It will likely take four to six weeks to receive a new set of mirrors for this wavelength. In the interim, a laser ablation sample introduction system on loan from CETAC has been under evaluation using emission measurements from the CRDS group's ICP. Uranium emission has been easily observed in the ICP using a 0.8-ppm NIST solid standard.

The LIF group has concentrated on developing bid specifications for a moderately high-resolution dye laser and also for a spectrograph/detector system. The dye laser bid will be sent out at the beginning of MSU's new fiscal year.

The Analytical Method Development (AMD) group has evaluated large volume injection methods for ion chromatography using UV/VIS detection of a post-column derivative. Detection limits of 10 ppb were obtained with transition metals with no pre-concentration. A 2-mL injection yielded good chromatographic peak shapes with concentrations of up to 100 ppb. A sample with 10-ppm concentration overloaded the separation column. Future work (AMD group) will focus on chelation chromatography that will allow larger injection volumes and the analysis of complex matrices.

Laser probe for technetium. LIBS spectra of various concentrations of iron in liquid solutions ranging from 10 ppb - 10 ppm were recorded using the liquid jet system. The magnetic field was used to decrease the background emission from the plasma. It was found that the signal-to-noise, as well as signal-to-background, ratio increases in the presence of a magnetic field. It was noted that in the optimum condition, the iron concentration of less than 10 ppb can be easily detected. The project is on schedule.

Two papers entitled "Dynamic, stability and emission of radiation from laser produced plasma expanding across an external magnetic field" and "Characterization of optical emission from laser produced plasma of metal seeded liquid target" were presented at the AIAA Plasmadynamics and Laser Conference held in Anaheim, CA.

Development of Tools for Long-term Monitoring

Monitoring plant physiological status in contaminated environments by high-resolution spectral imaging. During the month of May, a dedicated portable spectroradiometer system was ordered; during the month of June, this system was received and testing has begun to verify its operational performance. After consultation with plant scientists, we have selected two plants (Brassica juncea and barley) for our initial study to observe spectral signatures for metal uptake by plants. When construction of the mobile plant cart is completed next month, planting and, hence, monitoring will begin. Contact with SRS researchers interested in applying this technique to their site was made at a DOE Long-Term Monitoring Workshop in Orlando; this collaboration is being pursued. We are on schedule now.

Moisture fiber-optic diode laser sensor. The cladding was removed from the 200-m fibers. The exposed portion of the fiber was subsequently coated by an aqueous solution of 2% PVA and 1% CoCl₂. The fiber was then placed in a homemade environment chamber. The relative humidity (RH) in the chamber was varied rapidly by passing wet and dry gases through alternatively. The fiber probe responded quite well and rapidly during a RH change from 15% to 95%. Encouraged by this, we decided to make a slower change in RH and monitor the change in fiber output at various levels of humidity and calibrate it against a commercially available RH probe. It was then found that the fiber probe was actually responding to RH only above 78% and is quite fast in that range of RH. Fibers of different diameters were also tried then, but were found to give almost a similar result. This project is on schedule.

Application of Imaging Techniques: thermal imaging. The newly repaired NIR camera system has been received from the manufacturer. The complete integration test was successful. A dark current pixel intensity map for the InGaAs focal plane array has been acquired for future system calibration reference. The investigation of a new graphical file format-Portable Network Graphic (PNG)-has begun. The PNG format is used for DIAL's non-8bit monochrome cameras. Effort continued on establishing the InGaAs CCD bad pixels correction mask for the on-line imaging pixel correction and the computer controlled exposure time settings. We will continue thermal calibration and system software modification for the thermal imaging system utilizing a high-resolution visible digital camera. Manpower shortages may cause delays in progress on this project.

Application of imaging techniques: profilometry. Development of imaging acquisition software, with the new version of the driver system, for the FTP system has been completed. We will continue on the modification of current FTP system packages for the newly installed imaging acquisition and processing drivers. Efforts will also continue on the modification of FTP analysis software packages. Study on the phase unwrapping algorithms for target areas with large height discontinuities and/or surface isolations will also continue.

Application of imaging techniques: spectral imaging. During the month of June, we worked on integrating image collection and analysis into a single computer program. We modified our software to properly synchronize with our pulsed laser, so that we can now capture spectral images produced by every laser shot; previously the synchronization was not well done and spectral images of many laser shots were missed. We have utilized this system to record 307-nm spectral images of OH in an ICP plasma. The UV AOTF manufacturer is making progress toward completion of our system; delivery is currently expected in mid-summer. We are on schedule now, but further delay with delivery of the UV AOTF may cause us to fall behind schedule. Progress on the instrumentation development component of this project will be slow until the UV AOTF system is received.

Application of imaging techniques: data mining. During the month of June, we located spectral and imaging libraries that can be utilized for analysis of spectral images and of diffuse reflectance spectra. They will be generated as part of the off-line melter inspection effort and the plant monitoring effort. Development of a search engine to utilize these libraries to extract information from spectra and images has begun. We are on schedule now; however, progress may be slowed if a graduate student is not found soon to work on this project.

Hanford Tank Waste Chemistry

Saltcake Dissolution. Additional time dependent studies on the Na₃FSO₄ double salt system have been completed. In all cases solid-liquid equilibration was achieved in a period of between one and two weeks. All of the experimentally determined solubilities were subjected (along with the very limited literature data) to regression analysis. Data at 25 and 50°C in water, 1 m and 3 m OH were reduced to a three-parameter KFIT expression. The expression is being used to recalculate the solubility envelope for the system. If necessary, the like anion binary interactions (F-OH, F-SO₄, and SO₄-OH) will be incorporated in the fit.

A titration method for carbonate was adapted for use in the presence of sulfate. Carbonate ion concentrations were determined to within 5% with varying levels of added sulfate indicating that the method is suitable for use in the analysis of the equilibrium data for the Na-SO₄-CO₃-OH system. All of the samples for the later system have achieved equilibrium and are awaiting analysis for CO₃. Carbonate loadings will also be determined using a TIC instrument available on campus.

Prevention of solids formation. Analysis of images obtained during salt well pumping flow loop experiments at a Reynolds number of 450 were completed. Particle growth was found to be the same as in the lower velocity experiments. Critical velocities were, as expected, higher than those found during the earlier experiments. Various analyses of the data are in progress. Specifically a correlation of the increase in pressure with growth of the particle bed appears promising.

Companion ESP calculations using the recently released version (6.5) predicted considerably larger NaNO_3(s) loadings for the salt well surrogate than earlier versions of ESP (6.2 and 6.3). Reasons for this discrepancy are being investigated. Additional comparisons for other simulations are in progress.

Additional literature searches were performed with regard to the replacement cross-site transfer line at Hanford. This work has provided some estimated limits for the characteristics of the waste that will be transferred prior to vitrification. These limits will, in turn, be used to develop a 3-D surface plot that is expected to be of use to site operators. A comparison with the existing Wasp model will be performed. Simulations will commence following the receipt of the latest version of the transport model code.

Environmental Control Device Testing

HEPA filter testing. After the meeting with members of the HEPA NTW at the Incineration Conference in Philadelphia last month, enough progress was made for us to begin work on a test plan for the HEPA project. Work toward that goal has begun. A first draft of some sections of the test plan is scheduled to be sent to members of the NTW for review and comments in July. Once all sections are completed it will be subjected to peer review by the ASME in October.

Process Monitoring and Control of Toxic Organics

Sampling system for dioxins, furans and other semi-volatile products of incomplete combustion and characterization. A search continues to locate valves that have a minimal void volume, are fabricated from a material that can be coated with an inerting material, have a straight flight path to avoid deposition of PM, do not use a lubricant on the valve assembly, and will withstand a temperature of greater than 350°C. A heated transfer line to connect the heated filter assembly to the trap of the system has been designed and fabricated. The 150-watt Peltier coolers have been received, water cooled heat sinks have been designed and fabricated for these units, and their cooling capabilities are being evaluated.

The low mass particle feeder that has been developed for use on this project has been modified to make its feed rate more consistent and the unit more portable. An updated control system is also being developed to make the feed rate more variable and to allow interfacing with a computer. Delivery of ash from the feeder to the test stand is accomplished using a stream of compressed air/nitrogen. The flow rate of this carrier gas is currently too large and in the delivery system is being resized to minimize the volumetric flow rate of the carrier gas while maintaining a transport velocity of the particulate material.

A series of prototypes for the adsorption trap have been evaluated in terms of pressure drop across the unit as a function of volumetric flow rates. The inlet and outlet tubing diameter must be shortened significantly or increased from 1/8-inch i.d. in order to achieve an acceptable flow rate. The transition from valve assemblies to trap body is being redesigned to reduce pressure drop and increase volumetric flow rate.

During the coming month the filter holder for separating particulates from the gas stream will be fabricated. Heating mantles for the transfer lines will be secured from Apex and the necessary valves will be obtained from a variety of vendors. These entities complete the items needed to assemble a prototype of the sampling system that can be evaluated for thermal and operational performance.

Toxic organic compound monitoring using cavity ringdown spectroscopy. The system design and purchase of primary components for the supersonic-jet dioxin CRDS system has been completed. Work has been initiated toward construction of a frame for mounting the vacuum system that will house the slit-jet valve. Assembly of the system will begin upon the arrival of the major components.

Work on the diode laser cavity ringdown system has focused on improving the reproducibility of VOC measurements. A new absolute pressure gauge operating at a lower pressure was installed to compare with previous measurements made using a higher pressure gauge combined with the volume ratio method. The results from both methods thus far are in good agreement for chlorobenzene. We are now using the DFB diode laser rather than the more broadly tunable external cavity diode laser (ECDL). Repair of the ECDL was necessary due to excessive mode-hops (discontinuous frequency shifts). This has not significantly hindered our ability to evaluate reproducibility, although it does delay our final evaluation of detection limits.