26 research outputs found
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Evaluation of high-level waste pretreatment processes with an approximate reasoning model
The development of an approximate-reasoning (AR)-based model to analyze pretreatment options for high-level waste is presented. AR methods are used to emulate the processes used by experts in arriving at a judgment. In this paper, the authors first consider two specific issues in applying AR to the analysis of pretreatment options. They examine how to combine quantitative and qualitative evidence to infer the acceptability of a process result using the example of cesium content in low-level waste. They then demonstrate the use of simple physical models to structure expert elicitation and to produce inferences consistent with a problem involving waste particle size effects
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Uncertainty and approximate reasoning in waste pretreatment planning
Waste pretreatment process planning within the DOE complex must consider many different outcomes in order to perform the tradeoffs necessary to accomplish this important national mission. One of the difficulties encountered by many who assess these tradeoffs is that the complexity of this problem taxes the abilities of any single person or small group of individuals. For example, uncertainties in waste composition as well as process efficiency are well known yet incompletely considered in the search for optimum solutions. This paper describes a tool, the pre-treatment Process Analysis Tool (PAT), for evaluating tank waste pretreatment options at Hanford, Oak Ridge, Idaho National Environmental and Engineering Laboratory, and Savannah River Sites. The PAT propagates uncertainty in both tank waste composition and process partitioning into a set of ten outcomes. These outcomes are, for example, total cost, Cs-137 in iLAW, iHLW MT, and so on. Tradeoffs among outcomes are evaluated or scored by means of an approximate reasoning module that uses linguistic bases to evaluate tradeoffs for each process based on user valuations of outcomes
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Microstructural properties of high level waste concentrates and gels with raman And infrared spectroscopies. 1998 annual progress report
'The concentrated caustic waste slurries stored in waste tanks at Hanford and Savannah River have large amounts of aluminate along with nitrate, nitrite, hydroxide, carbonate, and phosphate-all species are present both in solution and as solids. The dominant cation is sodium with few percent potassium and other species. These slurries have sodium concentrations on the order of 10--15 mol/L and therefore very high ionic strengths and low water activities. These slurries have been the source of many safety problems at Hanford and Savannah River Sites and the slurry rheologies, gelling points, and gas retention properties are largely responsible for those safety issues. Even though both Hanford and Savannah River have produced large volumes of these slurry concentrates, the microstructural properties that are important for understanding slurry behavior are not well understood. For example, aluminate solid formation has been associated with Hanford concentrates, but is not observed at Savannah River. Another example is that although hydrogen gas retention in slurries is a prevailing safety issue at Hanford, it is only a relatively minor issue in SRS tanks.
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Resonance Raman excitation profiles of polyacetylene/polyisoprene block co-polymers in toluene
We have measured the resonance Raman spectra and excitation profiles of a soluble polyacetylene/polyisoprene block-copolymer in toluene solution. These are the first reported excitation profiles that have been referenced to an internal solvent standard, the toluene Raman bands. We find that this copolymer exhibits the same two bands in the C=C stretch region, i.e., 1463 and 1519 cm/sup /minus/1/, that have been attributed to a bimodal distribution in conjugation length for polyacetylene thin films. The 1519 cm/sup /minus/1/ peak has been associated with short chain segments of polyacetylene and we assign it to an average chain length of N=11 C=C's based on the frequency of the peak of its excitation profile. The excitation profile of the 1463 cm/sup /minus/1/ mode peaks at 2.15 eV corresponding to a chain length of 31 C=C's. Based on the relative integrated intensities of these two excitation profiles, our block copolymer contains a 35% mole fraction of long chain segments to short chain segments. In contrast to previous results, we find that the 1294 cm/sup /minus/1/ band, which is a mode with a mixture of C-C stretch and C-H deformation, is resonance enhanced, with an excitation profile that peaks at 2.6 eV, the same energy as the 1519 cm/sup /minus/1/ mode's profile. 2 figs
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Poly(vinyl pyridine)-based stabilizers for aqueous polypyrrole latices
The preparation and characterization of sub-micronic polypyrrole latex particles using polymeric stabilizers based on poly(vinyl pyridine) is described. These novel colloidal dispersions enhance the usually limited processability of the electroactive component, and in addition exhibit usefully high solid-state conductivity, despite the presence of the insulating stabilizer component. Furthermore, these latices exhibit reversible base/acid induced flocculation-stabilization behavior. The latter phenomenon is of fundamental interest and is expected to have commercial applications. The latices were characterized by transmission electron microscopy, visible absorption spectroscopy, FTIR and Raman spectroscopy, microanalysis, and compressed pellet dc conductivity. Base-induced particle flocculation was studied as a function of latex particle concentration. 24 refs., 4 figs., 2 tabs
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Fiscal Year 1997
'Monosodium aluminate, the phase of aluminate found in waste tanks, is only stable over a fairly narrow range of water vapor pressure (22% relative humidity at 22 C). As a result, aluminate solids are stable at Hanford (seasonal average RH {approximately}20%) but are not be stable at Savannah River (seasonal average RH {approximately}40%). Monosodium aluminate (MSA) releases water upon precipitation from solution. In contrast, trisodium aluminate (TSA) consumes water upon precipitation. As a result, MSA precipitates gradually over time while TSA undergoes rapid accelerated precipitation, often gelling its solution. Raman spectra reported for first time for monosodium and trisodium aluminate solids. Ternary phase diagrams can be useful for showing effects of water removal, even with concentrated waste. Kinetics of monosodium aluminate precipitation are extremely slow (several months) at room temperature but quite fast (several hours) at 60 C. As a result, all waste simulants that contain aluminate need several days of cooking at 60 C in order to truly represent the equilibrium state of aluminate. The high level waste (HLW) slurries that have been created at the Hanford and Savannah River Sites over that last fifty years constitute a large fraction of the remaining HLW volumes at both sites. In spite of the preponderance of these wastes, very little quantitative information is available about their physical and chemical properties other than elemental analyses.
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Spectroscopic studies of carbon disulfide at high pressure
The authors have identified the pressure for the onset of CS/sub 2/ chemistry at ambient temperature and have correlated it with the several other indicators of increasing electronic interaction. They further explained the rather small shift of v/sub 1/ and v/sub 3/ with pressure as due to compensating effects of intermolecular repulsion and electronic ground-state mixing. Their measurement of the uv absorption edge with pressure matches that measured in an isothermal ramp shock and they have been able to estimate the temperature of a step shock at 2.4 GPa as well. There are further indications of various molecular and polymer species present as a result of their infrared work and the relative amounts of these species are affected by the temperature, pressure, and physical state of the CS/sub 2/. 14 refs., 6 figs
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Chemistry of nitromethane at very high pressure
Decomposition of nitromethane is reported over the range of 115- 180/degree/C and 0.6-8.5 GPa. About 5 /mu/g of nitromethane is compressed with a diamond-anvil cell, heated to the point that reaction occurs, and held typically 10-20 minutes at the reaction temperature. The cell is cooled and the volatile contents of the cell are frozen as a thin layer in vacuo and an infrared absorption spectrum is recorded. The three volatile products observed are N/sub 2/O, CO/sub 2/, and water, with N/sub 2/O production peaking at 1.5 GPa, 135/degree/C, and 35% of NME; CO/sub 2/ production peaking at 3.5 GPa, 135/degree/C, and 65% of NME, and water yields at 20-50% of NME at the highest pressure measured, 8.5 GPa and 175/degree/C. Water yields were difficult to quantify due to background contamination. Results indicate three different reactions for solid NME dependent primarily on the pressure of the reaction, and that fluid NME does not decompose at 0.6 GPa and 175/degree/C, although the solid decomposes readily at 1.1 GPa and 120/degree/C. The authors conclude that, while various decomposition mechanisms are possible, the initial step CH/sub 3/NO/sub 2/ /yields/ /center dot/CH/sub 3/ + /center dot/NO/sub 2/ is very unlikely. 14 refs., 5 figs
Quantifying the Effects of Small-Scale Heterogeneities on Flow and Transport in Undisturbed Cores from the Hanford Formation
Accelerated migration of contaminants in the vadose zone has been observed beneath tank farms at the U.S. Department of Energy’s Hanford Reservation, Richland, WA. This paper focuses on quantifying hydrologic processes that control the fate and transport of contaminants in the unsaturated sediments beneath the Hanford tank farms. The experimental approach involved the use of field relevant, long-term unsaturated nonreactive transport experiments in undisturbed sediments from the Hanford Formation. Undisturbed sediment cores were collected from a laminated fine-grained sand unit within the Hanford Formation in both the vertical direction (flow cross bedding) and the horizontal direction (flow bedding parallel). Laboratory-scale saturated and unsaturated flow experiments were conducted using multiple nonreactive tracers to investigate hydrologic processes controlling the vertical and lateral spread of contaminants. The nonreactive tracers differ in their free-water molecular diffusion coefficients, thus providing a quantitative measure of diffusional processes and the presence of immobile water. Asymmetric breakthrough curves (BTCs) and coelution of tracers were observed during saturated flow in both horizontal and vertical cores, indicating advection enhanced solute dispersion with no accompanying immobile water. Unsaturated tracer transport in the vertical and horizontal cores resulted in earlier breakthrough, asymmetric BTCs, and differential breakthrough of tracers where the elution of piperazine-1-4-bis(2-ethanesulfonic acid) (PIPES) preceded that of pentafluorobenzoic acid (PFBA), which preceded that of Br−. These results suggest that physical nonequilibrium processes (PNE) such as preferential finger flow coupled with immobile water may control the unsaturated movement of contaminants in the Hanford Formation