Characterization of DWPF Melter Off-Gas Quencher and Steam Atomized Scrubber Deposit Samples

摘要

This report summarizes the results from the characterization of deposits from the inlets of the primary off-gas Quencher and Steam Atomized Scrubber (SAS) in the Defense Waste Processing Facility (DWPF), as requested by a technical assistance request. DWPF requested elemental analysis and compound identification to help determine the potential causes for the substance formation. This information will be fed into Savannah River National Laboratory modeling programs to determine if there is a way to decrease the formation of the deposits. The general approach to the characterization of these samples included x-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis. The following conclusions are drawn from the analytical results found in this report: (1) The deposits are not high level waste glass from the DWPF melt pool based on comparison of the compositions of deposits to the composition of a sample of glass taken from the pour stream of the melter during processing of Sludge Batch 3. (2) Chemical composition results suggest that the deposits are probably a combination of sludge and frit particles entrained in the off-gas. (3) Gamma emitters, such as Co-60, Cs-137, Eu-154, Am-241, and Am-243 were detected in both the Quencher and SAS samples with Cs-137 having the highest concentration of the gamma emitters. (4) No evidence existed for accumulation of fissile material (U-233, U-235, and Pu-239) relative to Fe in either deposit. (5) XRD results indicated both samples were primarily amorphorous and contained some crystals of the iron oxides, hematite and magnetite (Fe(sub 2)O(sub 3) and Fe(Fe(sub 2)O(sub 4))), along with sodium nitrate (NaNO(sub 3)). The other main crystalline compound in the SAS deposit was mercurous chloride. The main crystalline compound in the Quencher deposit was a uranium oxide compound. These are all sludge components. (6) SEM analysis of the Quencher deposit revealed crystalline uranium compounds within the sample. SEM analysis of the SAS sample could not be performed due to the presence of a significant concentration of Hg in the sample. (7) Essentially all the Na and the S in the off-gas samples were soluble in water. (8) The main soluble anion was NO(sub 3)(sup -) with SO(sub 4)(sup 2-) being second. (9) In contrast to the results for the off-gas deposits analyzed in 2003, soluble compounds of fluoride and chloride were detected; however, their concentrations in the Quencher and SAS deposits were less than one weight percent. (10) The results suggest that the S is primarily in the deposits as the sulfate anion.