12 Matching Results

Search Results

Advanced search parameters have been applied.

Development of a ceramic form for immobilization of excess plutonium

Description: Between 8 and 50 metric tonnes of excess plutonium are currently planned to be immobilized in a glass or ceramic waste form in the US. The immobilized Pu would then be encased in HLW glass (the can-in-canister alternative), which would provide a radiation barrier to enhance the proliferation resistance of the material. Associated with the plutonium are about 15 metric tonnes of uranium primarily {sup 238}U and a variety of other impurities (primarily Ga, Mo, Al, Mg, Si, and Cl) totaling about 1 metric tonne or less. Immobilization of this material is complicated by the fact that the uranium content in the various feed streams varies widely, from 0 to about 95%. The proposed ceramic form is composed of about 90% zirconolite (CaZrTi{sub 2}O{sub 7}) and/or pyrochlore (CaPuTi{sub 2}O{sub 7}) with about 10% other phases, typically hollandite (BaAl{sub 2}Ti{sub 6}O{sub 16}) and rutile (TiO{sub 2}). The form is a variation of Synroc-C, which contains nominally 30% zirconolite, 30% perovskite, 30% hollandite, and 10% rutile and noble metal alloys. Zirconolite and perovskite are the actinide host phases in Synroc-C with zirconolite being the more durable phase. The pyrochlore structure is closely related to zirconolite and forms at higher actinide loadings. Thus, this mineral is of interest for plutonium deposition in ceramic. Pyrochlore has the advantage that it is cubic rather the monoclinic like zirconolite. Cubic mineral swell isotropically when radiation damaged. As a result, differential strain in the microstructure will be minimal, leading to significantly less microcracking of the form after thousands of years in a repository. Zirconolites and pyrochlores containing uranium and.or thorium exist in nature and have demonstrated actinide immobilizations for periods exceeding 100 million years.
Date: April 22, 1997
Creator: Van Konynenburg, R.; Ebbinghaus, B.; Ryerson, F.; Shaw, H. & Curtis, P.
Partner: UNT Libraries Government Documents Department

Minerals in fractures of the saturated zone from drill core USW G-4, Yucca Mountain, Nye County, Nevada

Description: The minerals in fractures in drill core USW G-4, from the static water level (SWL) at 1770 ft to the base of the hole at 3000 ft, were studied to determine their identity and depositional sequence and to compare them with those found above the SWL in the same drill hole. There is no change in mineralogy or mineral morphology across the SWL. The significant change in mineralogy and relationship to the host rock occurs at 1381 ft, well above the present water table. Below 1381 ft clinoptilolite appears in the fractures and rock matrix instead of heulandite, and the fracture mineralogy correlates with the host rock mineralogy. Throughout most of the saturated zone (below the SWL) in USW G-4, zeolites occur in fractures only in zeolitic tuff; however, zeolites persist in fracture below the base of the deepest zeolitic tuff interval. Nonzeolitic intervals of tuff have fewer fractures, and many of these have no coatings; a few have quartz and feldspar coatings. One interval in zeolitic tuff (2125-2140 ft) contains abundant crisobalite coatings in the fractures. Calcite occurs in fractures from 2575 to 2660 ft, usually with the manganese mineral hollandite, and from 2750 to 2765 ft, usually alone. Manganese minerals occur in several intervals. The spatial correlation of zeolites in fractures with zeolitic host rock suggests that both may have been zeolitized at the same time, possibly by water moving laterally through more permeable zones in the tuff. The continuation of zeolites in fractures below the lowest zeolitic interval in this hole suggests that vertical fracture flow may have been important in the deposition of these coatings. Core from deeper intervals in another hole will be examined to determine if that relationship continues. 17 refs., 19 figs.
Date: April 1, 1987
Creator: Carlos, B.A.
Partner: UNT Libraries Government Documents Department

Np and Pu Sorption to Manganese Oxide Minerals

Description: Manganese oxide minerals are a significant component of the fracture lining mineralogy at Yucca Mountain (Carlos et al., 1993) and within the tuff-confining unit at Yucca Flat (Prothro, 1998), Pahute Mesa (Drellack et al., 1997), and other locations at the Nevada Test Site (NTS). Radionuclide sorption to manganese oxide minerals was not included in recent Lawrence Livermore National Laboratory (LLNL) hydrologic source term (HST) models which attempt to predict the migration behavior of radionuclides away from underground nuclear tests. However, experiments performed for the Yucca Mountain Program suggest that these minerals may control much of the retardation of certain radionuclides, particularly Np and Pu (Triay et al., 1991; Duff et al., 1999). As a result, recent HST model results may significantly overpredict radionuclide transport away from underground nuclear tests. The sorption model used in HST calculations performed at LLNL includes sorption to iron oxide, calcite, zeolite, smectite, and mica minerals (Zavarin and Bruton 2004a; 2004b). For the majority of radiologic source term (RST) radionuclides, we believe that this accounts for the dominant sorption processes controlling transport. However, for the case of Np, sorption is rather weak to all but the iron and manganese oxides (Figure 1). Thus, we can expect to significantly reduce predicted Np transport by accounting for Np sorption to manganese oxides. Similarly, Pu has been shown to be predominantly associated with manganese oxides in Yucca Mountain fractured tuffs (Duff et al., 1999). Recent results on colloid-facilitated Pu transport (Kersting and Reimus, 2003) also suggest that manganese oxide coatings on fracture surfaces may compete with colloids for Pu, thus reducing the effects of colloid-facilitated Pu transport (Figure 1b). The available data suggest that it is important to incorporate Np and Pu sorption to manganese oxides in reactive transport models. However, few data are available for inclusion in our ...
Date: August 30, 2005
Creator: Zhao, P; Johnson, M R; Roberts, S K & Zavarin, M
Partner: UNT Libraries Government Documents Department


Description: The Savannah River National Laboratory (SRNL) is developing crystalline ceramic waste forms to incorporate CS/LN/TM high Mo waste streams consisting of perovskite, hollandite, pyrochlore, zirconolite, and powellite phase assemblages. Simple raw materials, including Al{sub 2}O{sub 3}, CaO, and TiO{sub 2} were combined with simulated waste components to produce multiphase crystalline ceramics. Fiscal Year 2011 (FY11) activities included (i) expanding the compositional range by varying waste loading and fabrication of compositions rich in TiO{sub 2}, (ii) exploring the processing parameters of ceramics produced by the melt and crystallize process, (iii) synthesis and characterization of select individual phases of powellite and hollandite that are the target hosts for radionuclides of Mo, Cs, and Rb, and (iv) evaluating the durability and radiation stability of single and multi-phase ceramic waste forms. Two fabrication methods, including melting and crystallizing, and pressing and sintering, were used with the intent of studying phase evolution under various sintering conditions. An analysis of the XRD and SEM/EDS results indicates that the targeted crystalline phases of the FY11 compositions consisting of pyrochlore, perovskite, hollandite, zirconolite, and powellite were formed by both press and sinter and melt and crystallize processing methods. An evaluation of crystalline phase formation versus melt processing conditions revealed that hollandite, perovskite, zirconolite, and residual TiO{sub 2} phases formed regardless of cooling rate, demonstrating the robust nature of this process for crystalline phase development. The multiphase ceramic composition CSLNTM-06 demonstrated good resistance to proton beam irradiation. Electron irradiation studies on the single phase CaMoO{sub 4} (a component of the multiphase waste form) suggested that this material exhibits stability to 1000 years at anticipated self-irradiation doses (2 x 10{sup 10}-2 x 10{sup 11} Gy), but that its stability may be rate dependent, therefore limiting the activity of the waste for which it can be employed. Overall, these preliminary results ...
Date: September 22, 2011
Creator: Fox, K. & Brinkman, K.
Partner: UNT Libraries Government Documents Department

Manganese-oxide minerals in fractures of the Crater Flat Tuff in drill core USW G-4, Yucca Mountain, Nevada

Description: The Crater Flat Tuff is almost entirely below the water table in drill hole USW G-4 at Yucca Mountain, Nevada. Manganese-oxide minerals from the Crater Flat Tuff in USW G-4 were studied using optical, scanning electron microscopic, electron microprobe, and x-ray powder diffraction methods to determine their distribution, mineralogy, and chemistry. Manganese-oxide minerals coat fractures in all three members of the Crater Flat Tuff (Prow Pass, Bullfrog, and Tram), but they are most abundant in fractures in the densely welded devitrified intervals of these members. The coatings are mostly of the cryptomelane/hollandite mineral group, but the chemistry of these coatings varies considerably. Some of the chemical variations, particularly the presence of calcium, sodium, and strontium, can be explained by admixture with todorokite, seen in some x-ray powder diffraction patterns. Other chemical variations, particularly between Ba and Pb, demonstrate that considerable substitution of Pb for Ba occurs in hollandite. Manganese-oxide coatings are common in the 10-m interval that produced 75% of the water pumped from USW G-4 in a flow survey in 1983. Their presence in water-producing zones suggests that manganese oxides may exert a significant chemical effect on groundwater beneath Yucca Mountain. In particular, the ability of the manganese oxides found at Yucca Mountain to be easily reduced suggests that they may affect the redox conditions of the groundwater and may oxidize dissolved or suspended species. Although the Mn oxides at Yucca Mountain have low exchange capacities, these minerals may retard the migration of some radionuclides, particularly the actinides, through scavenging and coprecipitation. 23 refs., 21 figs., 2 tabs.
Date: July 1, 1990
Creator: Carlos, B.A.; Bish, D.L. & Chipera, S.J.
Partner: UNT Libraries Government Documents Department

Radionuclide migration as a function of mineralogy

Description: The migration of radionuclides is studied as a function of mineralogy utilizing batch sorption and column experiments. The transport behavior of alkaline, alkaline-earth, and transition metals, and actinide species is studied in pure mineral separates. The solid phases utilized for these investigations are silicates, alumino-silicates, carbonates, and metal oxides and oxyhydroxides. The results of this effort are utilized to aid in the elucidation of the dominant chemical mechanisms of radionuclide migration, the prediction of radionuclide transport in conditions similar to those expected at the proposed high-level nuclear waste repository at Yucca Mountain, Nevada, and the identification of materials that act as natural geological barriers or that can be utilized as strong sorbers in engineered barriers. 9 refs., 2 figs., 2 tabs.
Date: February 1, 1991
Creator: Triay, I.R.; Mitchell, A.J. & Ott, M.A.
Partner: UNT Libraries Government Documents Department

Study of selected off-gases produced during the immobilization of nuclear wastes in the SYNROC process. Final report for the year ended December 31, 1982

Description: The vaporization of cesium from the SYNROC mineral barium-cesium hollandite was studied over the temperature range 900/sup 0/C to 1150/sup 0/C using the transpiration method. With a dry argon-5% hydrogen carrier gas, the pressure of cesium over barium-cesium hollandite solid solution follows the relationship, log P/sub Cs/(atm) = 2.743 - 1.135 X 10/sup 4//T(K). The heat of vaporization is 217 +- 15 kJ/mole. The presence of water vapor increased the volatility of cesium.
Date: December 31, 1982
Creator: Carpenter, J.H.; McMullen, J.C.; Olmscheid, B.A. & Chezick, P.
Partner: UNT Libraries Government Documents Department

Investigations on SYNROC mineralogy. Progress report

Description: Progress reports are presented for the following projects: (1) factors influencing the leaching performance of hollandiate; (2) incorporation of uranium and rare earths into zirconolite; (3) reconnaissance studies of the stability relations of Ca-Ti-Al phases in SYNROC C formulations; (4) immobilization of highly aluminous sludges; (5) SYNROC D formulations produced by sintering in air; (6) crystallization behavior of interstitial glass in SYNROC D formulations. Some of the highlights are: (1) leaching performance of all hollandites irrespective of preparation technique, can be improved by hot-pressing under specific controlled redox conditions, below Ni-NiO; (2) there is no satisfactory crystal-chemical reason why the leaching performance of Ti/sup 3 +/-bearing hollandite should be superior to that of Al/sup 3 +/ hollandite; (3) experiments have shown that the zirconolite lattice can accept up to 30% rare earths (Sm/sub 2/O/sub 3/) before becoming destabilized in favor of pyrochlore or a related f.c.c. structure; (4) SYNROC zirconolites will therefore be well below their saturation limits in rare earths and trivalent actinides; (5) experiments have established that the Ca-Ti-Al phase (CTA) is compatible with perovskite, hollandite and zirconolite; (6) magnetoplumbite-type phases coexists with hollandite, perovskite, zirconolite and Fe-bearing pseudobrookite, but do not coexist with the CTA phase CaTi/sub 3/Al/sub 8/O/sub 19/; (7) experiments demonstrated that it is not possible to convert highly aluminous sludges to a waste form comprising zirconolite, perovskite, spinel and nepheline plus corundum, by adding appropriate minimum amounts of the inert SYNROC additives (CaO, TiO/sub 2/, ZrO/sub 2/, SiO/sub 2/); (8) sintering of SYNROC D in air at temperatures just above the solidus (1200 to 1250/sup 0/C) produced a dense compact ceramic, but the optimum SYNROC-D mineralogy was not produced. (ATT)
Date: January 21, 1982
Creator: Ringwood, A.E.
Partner: UNT Libraries Government Documents Department

SYNROC C: preparation and radwaste distribution

Description: Results of the synthesis of SYNROC C from both high surface area (16m/sup 2//g) and low surface area (4m/sup 2//g) powders at low and high oxygen fugacities indicate variations in radionuclide distribution. These results are most striking for the partitioning of uranium between perovskite and zirconolite. In highly active powders, the formation of a pyrochlore precursor ensures that equilibrium partitioning is approached. In less active powders, no low temperature pyrochlore is formed. As a result, the uranium partitioning is a function of nucleation processes. At high oxygen fugacities, uranium is rejected from perovskite and an additional uranium rich phase is formed precluding the synthesis of SYNROC C in air.
Date: October 16, 1981
Creator: Ryerson, F.J.; Hoenig, C.L. & Smith, G.S.
Partner: UNT Libraries Government Documents Department

Study of selected off-gases produced during the immobilization of nuclear wastes in the SYNROC process. Final report for year ended December 31, 1981. [Pollucite, CsAlSi/sub 2/O/sub 6/, and barium-cesium hollandite, (Ba,Cs)Al/sub 2/Ti/sub 6/O/sub 16/]

Description: Calculation of possible off-gases expected during the fabrication of SYNROC showed that volatilization of cesium would be a significant problem. Samples of the cesium containing minerals pollucite, CsAlSi/sub 2/O/sub 6/, and barium-cesium hollandite, (Ba,Cs)Al/sub 2/Ti/sub 6/O/sub 16/, were prepared for vaporization studies. Fifteen vaporization runs were made with the hollandite samples. With dry air as the carrier gas, the vapor pressure of cesium over Ba/sub 0/ /sub 8/Cs/sub 0/ /sub 4/Al/sub 2/Ti/sub 6/O/sub 16/ was found to be about 1 x 10/sup -7/ atm at 1050/sup 0/C.
Date: December 31, 1981
Creator: Carpenter, J.H.
Partner: UNT Libraries Government Documents Department

Hydrothermal investigation of SYNROC formulations from 150/sup 0/ to 610/sup 0/ at 100-MPa water pressure

Description: The static leaching behavior of seven formulations of SYNROC and two preparations of hollandite have been investigated under hydrothermal conditions. Each formulation was tested at several times (1 to 60 days) and temperatures (150 to 610/sup 0/C) at 100-MPa water pressure, using distilled water as the fluid. Both cored and powdered samples were employed in the hydrothermal experiments. Leach rates (g SYNROC/m/sup 2/ day) were calculated on the basis of element concentrations observed in the leachate. Postrun SEM and XRD observations of some core specimens revealed crystalline precipitates occurring on core surfaces, which are interpreted to be metastable phases and/or precipitates that were formed during quenching. As a result, calculated leach rates based on some elements in the fluid phase are not true leach rates. The temperature dependence of apparent leach rate was erratic. The time dependence of apparent leach rate was consistent and well defined for all SYNROC formulations; it decreased as a function of time. Analysis of hydrothermal results suggests that runs of 30 to 60 days are required to approach, or to attain, steady-state apparent leach rates. Sample form appears to have a demonstrable effect on leaching behavior. For comparable run conditions, powders generally have lower apparent leach rates but have a higher percentage of material leached than cores. The mineral hollandite appears to be very resistant to hydrothermal leaching, with only titanium found in the leachate.
Date: December 1, 1980
Creator: Page, L.E.; Bazan, C.; Piwinskii, A.J.; Smith, G.S. & Wootton, S.
Partner: UNT Libraries Government Documents Department

Immobilization of high level nuclear reactor wastes in SYNROC: a current appraisal. [Synthetic perovskite and hollandite; natural zirconolite and perovskite]

Description: Results are presented for leach testing at 95/sup 0/C and 200/sup 0/C of SYNROC containing 9% and 20% simulated high level radioactive waste, synthetic hollandite and pervoskite samples, and natural zirconolite and pervoskite samples. Single phase synthetic minerals show much higher leach rates than natural mineral samples and polyphase SYNROC samples. Natural zirconolite samples with low radiation damage have leach rates at 200/sup 0/C based on U which are identical to those measured on SYNROC samples. Natural zirconolites with very large accumulated ..cap alpha.. dose and radiation damage have leach rates at 200/sup 0/C which are only 5 times higher than those of low dose samples.
Date: October 13, 1981
Creator: Oversby, V.M. & Ringwood, A.E.
Partner: UNT Libraries Government Documents Department