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Process for Making a Ceramic Composition for Immobilization of Actinides

Description: Disclosed is a process for making a ceramic composition for the immobilization of actinides, particularly uranium and plutonium. The ceramic is a titanate material comprising pyrochlore, brannerite and rutile. The process comprises oxidizing the actinides, milling the oxides to a powder, blending them with ceramic precursors, cold pressing the blend and sintering the pressed material.
Date: June 22, 1999
Creator: Ebbinghaus, Bartley B.; Van Konynenburg, Richard A.; Vance, Eric R.; Stewart, Martin W.; Walls, Philip A.; Brummond, William Allen et al.
Partner: UNT Libraries Government Documents Department

The impact of brannerite on the release of plutonium and gadolinium during the corrosion of zirconolite-rich titanate ceramics

Description: Titanate ceramics have been selected as the preferred waste form for the immobilization of excess plutonium. Corrosion tests are underway to try to understand the long-term behavior of this material. In this paper, results from PCT-B static dissolution tests are used to provide an explanation of the observed corrosion behavior of a zirconolite-based ceramic. Two important observations are made. First, Ca is released at a constant rate [7 x 10{sup {minus}5} g/(m{sup 2} day)] in PCT-B tests for up to two years. Second, the release rates for Pu and Gd increase with time (up to two years) in PCT-B tests. The first observation suggests that the ceramics continue to corrode at a low rate for at least two years in PCT-B tests. The second observation suggests that the release rates of Pu and Gd are controlled by some process or processes that do not affect the release rate of other elements. Evidence indicates that this is due to the preferential dissolution of brannerite from the ceramic.
Date: March 14, 2000
Creator: Chamberlain, D. B.; Hash, M. C.; Basco, J. K.; Bakel, A. J.; Metz, C. J.; Wolf, S. F. et al.
Partner: UNT Libraries Government Documents Department

Ceramic Composition for Immobilization of Actinides

Description: Disclosed is a ceramic composition for the immobilization of actinides, particularly uranium and plutonium. The ceramic is a titanate material comprising pyrochlore, brannerite and rutile.
Date: June 22, 1999
Creator: Ebbinghaus, Bartley B.; Van Konynenburg, Richard A.; Vance, Eric R.; Stewart, Martin W.; Jostsons, Adam; Allender, Jeffrey S. et al.
Partner: UNT Libraries Government Documents Department


Description: From ninety-five to ninety-nine per cent of the uranium was extracted from brannerite concentrates by digesting the sample with concentrated sulfuric acid and then leaching with water, using one ton of acid per ton of concentrate. Precipitates containing from sixteen to forty-eight per cent U{sub 3)O{sub 8} were obtained from pregnant solutions. Further research on the precipitation of uranium and the recovery of wolfram is needed to determine the proper treatment. (auth)
Date: March 1, 1950
Creator: George, D'A.R.
Partner: UNT Libraries Government Documents Department

Corrosion behavior of pyroclore-rich titanate ceramics for plutonium disposition ; impurity effects.

Description: The baseline ceramic contains Ti, U, Ca, Hf, Gd, and Ce, and is made up of only four phases, pyrochlore, zirconolite, rutile, and brannerite. The impurities present in the three other ceramics represent impurities expected in the feed, and result in different phase distributions. The results from 3 day, 90 C MCC-1 tests with impurity ceramics were significantly different than the results from tests with the baseline ceramic. Overall, the addition of impurities to these titanate ceramics alters the phase distributions, which in turn, affects the corrosion behavior.
Date: January 13, 1999
Creator: Bakel, A. J.
Partner: UNT Libraries Government Documents Department

Comparison of the layer structure of vapor phase and leached SRL glass by use of AEM [analytical electron microscopy]

Description: Test samples of 131 type glass that have been reacted for extended time periods in water vapor atmospheres of different relative humidities and in static leaching solution have been examined to characterize the reaction products. Analytical electron microscopy (AEM) was used to characterize the leached samples, and a complicated layer structure was revealed, consisting of phases that precipitate from solution and also form within the residual glass layer. The precipitated phases include birnes-site, saponite, and an iron species, while the intralayer phases include the U-Ti containing phase brannerite distributed within a matrix consisting of bands of an Fe rich montmorillonite clay. Comparison is made between samples leached at 40{degrees}C for 4 years with those leached at 90{degrees}C for 3-1/2 years. The samples reacted in water vapor were examined with scanning electron microscopy and show increasing reaction as both the relative humidity and time of reaction increases. These samples also contain a layered structure with reaction products on the glass surface. 15 refs., 5 figs.
Date: December 31, 1989
Creator: Biwer, B.M.; Bates, J.K.; Abrajano, T.A. Jr. & Bradley, J.P.
Partner: UNT Libraries Government Documents Department

Characterization of phase assemblage and distribution in titanate ceramics with SEM/EDS and x-ray mapping.

Description: Titanate ceramics have been selected for the immobilization of excess plutonium. The baseline ceramic formulation leads to a multi-phase assemblage, which consists of a majority pyrochlore phase plus secondary phases. The phase distribution depends on processing conditions and impurity loading. In this paper, we report on the characterization of the phase assemblage and distribution in titanate ceramics using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and x-ray dot mapping. Two titanate ceramics were studied a baseline ceramic and a ceramic with impurities. In the baseline ceramic, the secondary phases that were observed include zirconolite, brannerite, and rutile. Additional phases, such as perovskite, an Al-Ti-Ca phase, and a silicate phase, formed in the impurity ceramic. The distribution of these phases was characterized with backscattered electron (BSE) imaging, except for zirconolite. While the zirconolite exhibited weak contrasts in BSE images and could not be easily distinguished from the pyrochlore matrix, its distribution was effectively characterized with x-ray mapping. Quantitative analyses of BSE images and x-ray maps reveal that the impurity ceramic contains less brannerite, rutile, and pores than the baseline ceramic.
Date: June 16, 1999
Creator: Luo, J. S.
Partner: UNT Libraries Government Documents Department

Technical Progress Report on Single Pass Flow Through Tests of Ceramic Waste Forms for Plutonium Immobilization

Description: This report updates work on measurements of the dissolution rates of single-phase and multi-phase ceramic waste forms in flow-through reactors at Lawrence Livermore National Laboratory. Previous results were reported in Bourcier (1999). Two types of tests are in progress: (1) tests of baseline pyrochlore-based multiphase ceramics; and (2) tests of single-phase pyrochlore, zirconolite, and brannerite (the three phases that will contain most of the actinides). Tests of the multi-phase material are all being run at 25 C. The single-phase tests are being run at 25, 50, and 75 C. All tests are being performed at ambient pressure. The as-made bulk compositions of the ceramics are given in Table 1. The single pass flow-through test procedure [Knauss, 1986 No.140] allows the powdered ceramic to react with pH buffer solutions traveling upward vertically through the powder. Gentle rocking during the course of the experiment keeps the powder suspended and avoids clumping, and allows the system to behave as a continuously stirred reactor. For each test, a cell is loaded with approximately one gram of the appropriate size fraction of powdered ceramic and reacted with a buffer solution of the desired pH. The buffer solution compositions are given in Table 2. All the ceramics tested were cold pressed and sintered at 1350 C in air, except brannerite, which was sintered at 1350 C in a CO/CO{sub 2} gas mixture. They were then crushed, sieved, rinsed repeatedly in alcohol and distilled water, and the desired particle size fraction collected for the single pass flow-through tests (SPFT). The surface area of the ceramics measured by BET ranged from 0.1-0.35 m{sup 2}/g. The measured surface area values, average particle size, and sample weights for each ceramic test are given in the Appendices.
Date: December 3, 2000
Creator: Zhao, P.; Roberts, S. & Bourcier, W.L.
Partner: UNT Libraries Government Documents Department

Fissile Materials Disposition Formulation Report

Description: The Department of Energy (DOE) has chosen a titanate-based ceramic as the preferred form for the immobilization of surplus plutonium [COCHRAN]. The baseline formulation being developed includes a pyrochlore matrix, (Ca,Gd,Pu,U,Hf){sub 2}Ti{sub 2}O{sub 7} the primary site for plutonium and uranium, and several minor phases such as brannerite, (Pu,U)Ti{sub 2}O{sub 6}, and rutile, (TiHf)O{sub 2}. This baseline and ten other formulations were prepared to provide test specimens for characterization and corrosion testing. The purpose of this report is to document the fabrication and characterization of these ceramics. The fabrication procedure initially employed to produce specimens was provided by Lawrence Livermore National Laboratory (LLNL). During the preparation of the baseline ceramic, several aspects related to LLNL's procedure were evaluated. This report will discuss how these techniques were refined to reproducibly provide ceramics appropriate for corrosion testing. The baseline formulation represents a titanate ceramic for which the plutonium feed stream would be free of any impurity elements. The other formulations were designed to provide information about potential phase formation due to variations in precursors, specifically the waste streams in which the surplus plutonium is contained. Nominal compositions representing the 11 formulations investigated are shown in Table I.
Date: June 1, 1999
Creator: Hash, M.C.; Zyryanov, V.N.; Basco, J.K. & Chamberlain, D.B.
Partner: UNT Libraries Government Documents Department

Solid Solubilities of Pu, U, Gd and Hf in Candidate Ceramic Nuclear Wasteforms

Description: This goal of this research project was to determine the solid solubility of Pu, U, Gd, and Hf in candidate ceramics for immobilization of high-level nuclear waste. The experimental approach was to saturate each phase by adding more than the solid solubility limit of the given cation, using a nominated substitution scheme, and then analyzing the candidate phase that formed to evaluate the solid solubility limit under firing conditions. Confirmation that the solid solution limit had been reached insofar as other phases rich in the cation of interest was also required. The candidate phases were monazite, titanite, zirconolite, perovskite, apatite, pyrochlore, and brannerite. The valences of Pu and U were typically deduced from the firing atmosphere, and charge balancing in the candidate phase composition as evaluated from electron microscopy, although in some cases it was measured directly by x-ray absorption and diffuse reflectance spectroscopies (for U). Tetravalent Pu and U have restricted (< 0.1 formula units) solid solubility in apatite, titanite, and perovskite. Trivalent Pu has a larger solubility in apatite and perovskite than Pu4+. U3+ appears to be a credible species in reduced perovskite with a solubility of {approximately} 0.25 f.u. as opposed to {approximately} 0.05 f.u. for U4+. Pu4+ is a viable species in monazite and is promoted at lower firing temperatures ({approximately} 800 C) in an air atmosphere. Hf solubility is restricted in apatite, monazite (< 0.1 f.u.), but is {approximately} 0.2 and 0.5 f.u. in brannerite and titanite, respectively. Gd solubility is extended in all phases except for titanite ({approximately} 0.3 f.u.). U5+ was identified by DRS observations of absorption bands in the visible/near infrared photon energy ranges in brannerite and zirconolite, and U4+ in zirconolite was similarly identified.
Date: April 2, 2001
Creator: Vance, Eric R.; Carter, M. L.; Lumpkin, G. R.; Day, R. A. & Begg, B. D.
Partner: UNT Libraries Government Documents Department