Waste mixing and diluent selection for the planned retrieval of Hanford Tank 241-SY-102: A preliminary assessment

Abstract

Portions of this document rrmy be iIlegible in electronic image products. Images are produced from the best available original docmnent. SummaryThis preliminary assessment documents a set of analyses that were performed to determine the potential for Hanford waste Tank 241-SY-102 waste properties to be adversely affected by mixing the current tank contents or by injecting additional diluent into the tank during sludge mobilization. As a part of this effort, the effects of waste heating that will occur as a result of mixer pump operations are also examined. Finally, the predicted transport behavior of the resulting slurries is compared with the waste acceptance criteria for the Cross-Site Transfer System (CSTS). This work is being performed by Pacific Northwest National Laboratory in support of Westinghouse Hanford Company's W-211 Retrieval Project.We applied the equilibrium chemical code, GMIN, to predict potential chemical reactions. We examined the potential effects of mixing the current tank contents (sludge and supernatant liquid) at a range of temperatures and, separately, of adding pure water at a volume ratio of 1:2:2 (s1udge:supernatant 1iquid:water) as an example of further diluting the current tank contents. The main conclusion of the chemical modeling is that mixing the sludge and the supernate (with or without additional water) in Tank 241-SY-102 dissolves all sodium-containing solids (Le., NaN03(s), thenardite, NaF(s), and halite), but does not significantly affect the amorphous Cr(OH)3 and calcite phase distribution. A very small amount of gibbsite [AI(OH)3(s)] might precipitate at 25"C, but a somewhat larger amount of gibbsite is predicted to dissolve at the higher temperatures. Thus gibbsite precipitation might be avoided at moderate temperatures.within the sludge is saturated with respect to many of the solids species in the sludge, but that the supernatant liquid is not in saturation with many of major solids species in sludge. This indicates that a further evaluation of the sludge mixing could prove beneficial. This type of analysis could provide more detail about the potential chemical reactions and associated rheology changes by incorporating spatial distributions and temporal changes of reactions and kinetics using a model that couples the physical distributions and movements with equilibriumkinetic chemical reactions and associated rheology changes.The chemical constituents and phase distributions predicted by the chemical modeling work were also used to predict the transport behavior of the slurries that will result from sludge mobilization in Tank 241-SY-102. Several properties that impact the anticipated waste acceptance criteria for the CSTS were estimated for each of the cases considered. From these estimates it seems clear that the waste slurry that results from sludge mobilization in 241-SY-102 will have a specific gravity less than 1.2, a mixture viscosity less than 30 cP, and a solids volume fraction less than 0.06. Sedimentation data indicate that the"disp1aced solids volume frac...

Evaluation of scaling correlations for mobilization of double-shell tank waste

“…The typical values of the yield stress for the DSTs when a ball rheometer was used are in the -200 Pa range and consistent with the values based on the Poisson's ratio approximations (Stewart et al 1996). Onishi et al (1996) also report a value of 2.7 Pa for the yield stress of the waste. This measurement was performed in a hood with a rotational device using a cone-and-plate sensor.…”

“…They also measured the shear strength of the same material using a shear vane rheometer and found that in most cases the shear strength was lower than the tensile strength but closer to the tensile strength than to the yield stress. Extensive measurements of the compressive yield strength are not available other than what is presented by Onishi et al (1996). They found that the yield in the compressive mode for SY-102 sludge is approximately 8000 Pa.…”

“…will be the tendency for the material to fail or fracture like a solid. For all practical purposes, we can then treat the waste as a solid material prior to mobilization since in most cases the sludges have finite strengths that can be as high as -104 Pa, certainly in the compressive mode of failure (Onishi et al 1996).…”

“…Under conditions where the sludge to total waste volume in a tank is high, such as in the AN tanks, or if the supernatant liquid is near or at saturation point with respect to some of the solids in the sludge layer, then the eroded solids would potentially change the characteristics of the supernatant liquid during mobilization. Some of these issues have been addressed by Onishi and Hudson (1996) where they performed modeling of dilution during mobilization using the computational chemistry code, GMIN. The computational approach in conjunction with an empirical approach based on laboratory and hot-cell measurements where phase equilibria studies can be performed would provide information about what chemical and as a result rheological changes can be expected in the supernatant liquid (or mixture) during mobilization.…”

“…That is, during mixing, it is important to know which one of the species will go into solution (or precipitate) and the resulting influence on the solids content and size distribution as well as the rheological characteristics of the mixture (Onishi and Hudson 1996, Onishi et al 1996, Smith et al 1997). Once the properties are known or predicted then scaling can be approached from a purely mechanics point of view.…”