SST Sample Characterization Analysis of Archive Samples 102-C, 105-C, and 106-C

Abstract

A major effort at Hanford over the next few years will be to sample and analyze wastes contained in 149 single-shell tanks (SSTs). In preparation for this effort, selected analyses were performed on four archived samples to compare analytical methods and to determine applicability of these methods to the waste samples. The analyses, performed by the Pacific Northwest Laboratory (PNL), used a variety of analytical methods including both PNL technical procedures and adaptations of U.S. Environmental Protection Agency (EPA) technical procedures. Although data are reported for analyses of actual waste tank samples, the data do not serve to characterize any waste in Hanford tanks. Since this investigation was intended only as a comparison of analytical methods, and the samples are from an archive repository, the results are preliminary in nature. The numerical values are to be evaluated with appropriate respect for the limited usefulness of small amounts of data generated through an analytical development process using only four samples. The analysis of the archived SST waste material provides three important types of data for use in planning later phases of sample analysis. The data serve as input for 1) establishing analysis procedures and methods for waste samples, 2) evaluating the impact that using a silicon-based lubricant and normal paraffin hydrocarbon (NPH) in field sampling has on extracting inorganics or radionuclides from the SST sample, and 3) identifying trends in amounts of occupational radiation exposure expected from performing the various analysis procedures. Inorganic analysis work was undertaken to determine 1) the applicability of various analytical methods to the test samples, 2) if mercury can be determined by cold vapor atomic absorption (CVAA), 3) if the inductively-coupled plasma (ICP) spectrometer has sufficient sensitivity for the analysis of EP Toxicity metal ions (excluding mercury), and 4) which of the 22 EPA pollutant metal ions can be determined by ICP analysis. Poor reproducibility was obtained with water leach and EP Toxicity methods, but acid digestion gave good reproducibility. Some of the procedures were changed if, due to interference by other elements, the methods did not provide the levels of sensitivity, accuracy, or precision usually required for EPA work. When appropriate, other methods are suggested for trial as alternatives. Some procedural adjustments were required for mercury analysis by CVAA. Problems areas identified are ICP sensitivities and ICP spectral corrections when analyzing for minor constituents (e.g., Ag, As, Pb, Se, Tl, and V); if elements of this class are critically important, they should be determined by alternative methods. Organics analysis investigations were conducted to determine if the EPA semivolatile organic method can be employed on SST samples. Silicone·based lubricants and NPH from the sampling process impact the semivolatile analysis; however, with slight modification the procedure of EPA SOW 288 can be used. The results show that the gas chromatograph/mass spectrometer (GC/MS) is vulnerable to fouling and overload and that a combination of dilution and acidification is required to provide acceptable results. Work also included evaluation of 1) screening procedures for gas chromatography (GC) and total organic carbon (TOC), 2) extraction procedures and related problems, and 3) surrogate spiking to test extraction efficiencies and matrix effects. Development work was performed to gather information relevant to the potential use of radionuclide ratioing and parent-daughter relationships for the estimation of radionuclides within samples. The radionuclides expected in the SST tank waste samples were measured to determine the level of accuracy and precision that can be expected. These data reveal that some level of procedure development is needed for a large number of the radionuclides analyses. Tests were conducted to determine whether the NPH from the field sampling process extracted significant quantities of the inorganics or radionuclides from the SST samples. No such extraction was observed; however, the NPH does have a significant adverse effect on organic analysis, and alternatives to NPH should be investigated. Effects of silicon-based lubricant were not experimentally evaluated apart from sample analysis. Trends in expected occupational exposure were obtained by measuring the radiation level of samples and having the analysts record estimates of the contact time with the samples. Data revealed that the analysts received no significant exposure and that, as expected, the potential dose is directly proportional to the sample size and handling times.