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Comparison of ceramic waste forms produced by hot uniaxial pressing and by cold pressing and sintering

Description: Synroc C waste form specimens prepared using the Australian-developed technology are uniaxially pressed in stainless steel bellows at 1200{degrees}C and 20MPa. This produces a material with high chemical and physical durability and with the radioactivity enclosed inside both the waste form and the bellows. An alternative method of producing the ceramic product is to use cold pressing of pellets followed by reactive sintering to provide densification and mineralization. Depending on the scale of waste form preparation required and on the activity level and nature of the waste streams, the cold press and sinter method may have advantages. To evaluate the effects of production method on waste form characteristics, especially resistance to dissolution or leaching of waste elements, we have prepared two simulated waste samples for evaluation. Both samples were prepared from liquid precursor materials (alkoxides, nitrates, and colloidal silica) and then doped with waste elements. The precursor material in each case corresponded to a basic phase assemblage of 60% zirconolite, 15% nepheline, 10% spinel, 10% perovskite, and 5% rutile. One sample was doped with 25% by weight of U; the other with 10% by weight each of U and Gd. Each sample was calcined at 750{degrees}C for 1 hr. in a 3.5% H{sub 2} in N{sub 2} atmosphere. Then one portion of each sample was hot pressed at temperatures ranging from 1120 to 1250{degrees}C and 20MPa pressure in steel bellows. A separate portion of each sample was formed into pellets, cold pressed, and sintered in various atmospheres at 1200{degrees}C to produce final products about 2/3 cm in diameter. Samples were then examined to determine density of the product, grain sizes of the phases, phase assemblage, and the location of the U and Gd in the final phases. Density data indicate that sintering gives good results provided that the samples are ...
Date: September 1, 1994
Creator: Oversby, V.M. & Vance, E.R.
Partner: UNT Libraries Government Documents Department

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

Pu and Gd chemistry of zirconolite polytypes in a titanate ceramic

Description: Titanate-based ceramics are being developed as possible candidates for immobilizing excess plutonium from dismantled nuclear weapons. Evidence from testing of similar ceramics and natural analogues suggests that this material is very resistant to aqueous corrosion. The purpose of this work is to describe the phase(s) present in these ceramics. In particular the authors are interested in the disposition of important elements such as Pu and Gd (to be incorporated into the wasteform as a neutron absorber). In concert with data from corrosion tests, this characterization will allow one to describe the release behaviors of important elements from this type of ceramic. This is particularly difficult and important due to the heterogeneous nature of the material.
Date: October 1, 1997
Creator: Bakel, A.J.; Buck, E.C. & Ebbinghaus, B.
Partner: UNT Libraries Government Documents Department

EXAFS and XANES analysis of plutonium and cerium edges from titanate ceramics for fissile materials disposal.

Description: We report x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectra from the plutonium L{sub III} edge and XANES from the cerium L{sub II} edge in prototype titanate ceramic hosts. The titanate ceramics studied are based upon the hafnium-pyrochlore and zirconolite mineral structures and will serve as an immobilization host for surplus fissile materials, containing as much as 10 weight % fissile plutonium and 20 weight % (natural or depleted) uranium. Three ceramic formulations were studied: one employed cerium as a ''surrogate'' element, replacing both plutonium and uranium in the ceramic matrix, another formulation contained plutonium in a ''baseline'' ceramic formulation, and a third contained plutonium in a formulation representing a high-impurity plutonium stream. The cerium XANES from the surrogate ceramic clearly indicates a mixed III-IV oxidation state for the cerium. In contrast, XANES analysis of the two plutonium-bearing ceramics shows that the plutonium is present almost entirely as Pu(IV) and occupies the calcium site in the zirconolite and pyrochlore phases. The plutonium EXAFS real-space structure shows a strong second-shell peak, clearly distinct from that of PuO{sub 2}, with remarkably little difference in the plutonium crystal chemistry indicated between the baseline and high-impurity formulations.
Date: November 16, 1999
Creator: Fortner, J. A.; Kropf, A. J.; Bakel, A. J.; Hash, M. C.; Aase, S. B.; Buck, E. C. et al.
Partner: UNT Libraries Government Documents Department

Fundamental thermodynamics of actinide-bearing mineral waste forms.

Description: This report summarizes work after completion of a three-year project and our current ongoing efforts. Research efforts at UC Davis have focused on establishing the thermodynamic properties of zirconolite and pyrochlore, and the synthesis of other minerals relevant to storage of nuclear material. Heat capacity, entropy, enthalpy of formation, and fkee energy of formation data were established for zirconolite, CaZrTi{sub 2}O{sub 7}, in the range from 0 to 1500 K. The heat capacity, entropy, enthalpy of formation, and free energy of formation at 298 K for zirconolite are 211.9 J/K mol, 193.3 J/K mol, -3713.8 kJ/mol, and -35 14.6 kJ/mol, respectively. Solution calorimetry experiments with cerium pyrochlore, Ca{sub 0.8}Ce{sub 1.2}Ti{sub 2}O{sub 7}, are complete. Heat capacity data and confirmation of the pyrochlore composition are required for final data analysis. Synthesis and characterization of CaHfTi{sub 2}O{sub 7}, CaZr{sub 0.5}Hf{sub 0.5}Ti{sub 2}O{sub 7}, Gd{sub 2}Ti{sub 2}O{sub 7}, and CeTi{sub 2}O{sub 6} is complete. Research efforts at Los Alamos have focused on establishing synthesis techniques for actinide-bearing minerals and preparation of the calorimetry laboratory. The preparation of Pu-pyrochlore, nominally CaPuTi{sub 2}O{sub 7} has been achieved by Ebbinghaus at Lawrence Livermore National Laboratory. A sample of this material has been sent to Putnam at Los Alamos National Laboratory.
Date: January 1, 2002
Creator: Gallegos, U. F. (Ubaldo F.) & Putnam, R. L. (Robert L.)
Partner: UNT Libraries Government Documents Department

Characterization of a Pu-bearing zirconolite-rich synroc

Description: A titanate-based ceramic waste form, rich in phases structurally related to zirconolite (CaZrTi{sub 2}O{sub 7}), is being developed as a possible method for immobilizing excess plutonium from dismantled nuclear weapons. As part of this program, Lawrence Livermore National Laboratory (LLNL) produced several ceramics that were then characterized at Argonne National Laboratory (ANL). The plutonium- loaded ceramic was found to contain a Pu-Gd zirconolite phase but also contained plutonium titanates, Gd-polymignyte, and a series of other phases. In addition, much of the Pu was remained as PuO{sub 2- x}. The Pu oxidation state in the zirconolite was determined to be mainly Pu{sup 4+}, although some Pu{sub 3+} was believed to be present.
Date: December 31, 1996
Creator: Buck, E.C.; Ebbinghaus, B.; Bakel, A.J. & Bates, J.K.
Partner: UNT Libraries Government Documents Department

Corrosion of a Pu-doped zirconolite-rich ceramic

Description: As part of a large Pu disposition program, a zirconolite-rich titanate ceramic is being developed at Lawrence Livermore National Laboratory (LLNL) as a possible immobilization material. This same material is being tested at Argonne National Laboratory (ANL). The goal of this study is to describe the corrosion behavior of this ceramic, particularly the release of Pu and Gd, using results from several static corrosion tests (MCC-1, PCT-A, and PCT-B). The release of relatively large amounts of Al, Ba, and Ca in short-term tests (3 day MCC-1 and 7 day PCT-A) indicates that these elements are released from grain boundaries or from highly soluble phases. Results from long-term (28, 98, and 182 day) PCT-B show that the releases of Al, Ba, and Ca decrease with time, the releases of U and Zr increase with time, and that the releases of Cs, Gd, Mo, and Pu remain fairly constant. Formation of alteration phases may lead to the decrease of Ba and Ca in leachate solutions. Due to the heterogeneous nature of the material, the formation of alteration phases, and the inherently low solubility of several elements, no element(s) could be recommended as good markers for the overall corrosion of this ceramic. Data show that, due to the complex nature of this material, the release of each element should be considered separately.
Date: June 1, 1997
Creator: Bakel, A.J.; Buck, E.C.; Wolf, S.F.; Chamberlain, D.B.; Bates, J.K. & Ebbinghaus, B.B.
Partner: UNT Libraries Government Documents Department

The relative radiation resistance of zirconolite, pyrochlore and perovskite to 1.5 MeV Kr{sup +} ions

Description: Zirconolite (CaZrTi2O7), pyrochlore (VIIIA2 VIB2 IV X6Y) and perovskite (CaTiO3) are candidate phases for the immobilisation of rare earth elements (REEs) and actinides (ACTs) in various high level radioactive waste (HLW) forms 1. The effect of radiation damage on the structure and consequently on the durability of these phases is important to predictive modelling of their behaviour in the repository environment and risk assessment.
Date: March 1, 1997
Creator: Smith, K.L.; Zaluzec, N.J. & Lumpkin, G.R.
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

HVEM-Tandem and EELS study of radiation damage in zirconolite

Description: Zirconolite (CaZrTi{sub 2}O{sub 7}) is the major host phase for actinides in Synroc, a promising waste form for the immobilization of high-level radioactive waste. The effect of radiation damage on the structure and durability of zirconolite are important to predictive modeling of zirconolite`s behavior in the repository environment and risk assessment. In this study, radiation damage effects in zirconolite were investigated by irradiating samples with 1.5 MeV Kr{sup +} ions using the HVEM-Tandem at Argonne National Laboratory (ANL) and energy loss electron spectroscopy (EELS). The HVEM-Tandem consists of a modified AEI high voltage transmission electron microscope interfaced to a 2 MV tandem ion accelerator. EELS spectra were collected using a Philips 420 TEM, operated at 120 kV, fitted with a Gatan Model 607 Serial EELS. EELS data were recorded at resolutions of {approximately} 1.0 eV and at a dispersion of about {approximately} 0.25 eV. Selected area diffraction patterns (SADs) of individual grains of various zirconolites were monitored as a function of dose to establish the critical dose for amorphization (D{sub c}). The authors found that (1) D{sub c}(zirconolite) is independent of the atomic weight of dopants in zirconolite and the mean atomic weight of the sample and that (2) the Bragg reflections in SAD patterns which persist to the highest doses are firstly those resulting from the fluorite sublattice and secondly the four (110)-type reflections which lie on the innermost of the two diffuse rings representative of amorphous zirconolite.
Date: March 1, 1997
Creator: Smith, K.L.; Lumpkin, G.R. & Zaluzec, N.J.
Partner: UNT Libraries Government Documents Department

The CaO-TiO{sub 2}-ZrO{sub 2} system at 1,200{degree}C and the solubilities of Hf and Gd in zirconolite

Description: In recent years, significant technological advancements have been made in the Synroc scheme for the immobilization high-level nuclear waste. However, many basic scientific issues related to Synroc fabrication have yet to be addressed. The CaO-TiO{sub 2}-ZrO{sub 2} system is an integral part of the Synroc formulation. Phase equilibria are established in the CaO-TiO{sub 2}-ZrO{sub 2} system at 1,200 C, using X-ray diffraction and electron probe microanalysis. The existence of two previously reported ternary phases, zirconolite (CaZrTi{sub 2}O{sub 7}) and calzirtite (Ca{sub 2}Zr{sub 5}Ti{sub 2}O{sub 16}), is confirmed. Each of these phases exhibits a significant range of homogeneity between TiO{sub 2} and ZrO{sub 2} while maintaining a nearly constant concentration of CaO. The ternary solubilities of the constituent binary phases are found to be negligible, with the exceptions of the perovskites, which display mutual solubility of at least 22 mol.% and may in fact form a series of continuous solid solutions. The solubilities of Hf and Gd in zirconolite are also investigated. While Hf-bearing samples did not reach thermodynamic equilibrium under the experimental conditions employed, the existence of a Hf analog to zirconolite, CaHfTi{sub 2}O{sub 7}, is conclusively demonstrated. The phase is stable at the stoichiometric composition, and its lattice parameters are very close to those reported in the literature for stoichiometric zirconolite. A Gd-bearing sample of the composition Ca{sub 0.88}Zr{sub 0.88}Gd{sub 9.24}Ti{sub 2}O{sub 7} is found to be essentially single phase zirconolite, in agreement with previous investigations at higher temperatures.
Date: December 1, 1995
Creator: Swenson, D.; Nieh, T.G. & Fournelle, J.H.
Partner: UNT Libraries Government Documents Department

Temperature dependence of ion irradiation induced amorphization of zirconolite

Description: Zirconolite is one of the major host phases for actinides in various wasteforms for immobilizing high level radioactive waste (HLW). Over time, zirconolite's crystalline matrix is damaged by {alpha}-particles and energetic recoil nuclei recoil resulting from {alpha}-decay events. The cumulative damage caused by these particles results in amorphization. Data from natural zirconolites suggest that radiation damage anneals over geologic time and is dependant on the thermal history of the material. Proposed HLW containment strategies rely on both a suitable wasteform and geologic isolation. Depending on the waste loading, depth of burial, and the repository-specific geothermal gradient, burial could result in a wasteform being exposed to temperatures of between 100--450 C. Consequently, it is important to assess the effect of temperature on radiation damage in synthetic zirconolite. Zirconolite containing wasteforms are likely to be hot pressed at or below 1,473 K (1,200 C) and/or sintered at or below 1,623 K (1,350 C). Zirconolite fabricated at temperatures below 1,523 K (1,250 C) contains many stacking faults. As there have been various attempts to link radiation resistance to structure, the authors decided it was also pertinent to assess the role of stacking faults in radiation resistance. In this study, they simulate {alpha}-decay damage in two zirconolite samples by irradiating them with 1.5 MeV Kr{sup +} ions using the High Voltage Electron Microscope-Tandem User Facility (HTUF) at Argonne National Laboratory (ANL) and measure the critical dose for amorphization (D{sub c}) at several temperatures between 20 and 773 K. One of the samples has a high degree of crystallographic perfection, the other contains many stacking faults on the unit cell scale. Previous authors proposed a model for estimating the activation energy of self annealing in zirconolite and for predicting the critical dose for amorphization at any temperature. The authors discuss their results and earlier published ...
Date: December 22, 1999
Creator: Smith, K. L.; Blackford, M. G.; Lumpkin, G. R. & Zaluzec, N. J.
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

Intergrowth structures in synthetic pyrochlores : implications for radiation damage effects and waste form formulation.

Description: Titanate-based ceramic waste forms are currently under development for the immobilization of excess weapons plutonium. Both Hf and Gd are added to the ceramic formulation as neutron absorbers in order to satisfy a defense-in-depth concept for the waste form. The introduction of significant amounts of hafnium may be responsible for the presence of zirconolite-2M crystals in pyrochlore-based ceramics and the formation of zirconolite lamellae within pyrochlore. The zirconolite grows epitaxially on {l_brace}111{r_brace}planes of pyrochlore. Although the zirconolite lamellae within pyrochlore are non-cubic, any volume expansion due to radiation damage in the pyrochlore should still be isotropic; in addition, the presence of these intergrowths may allow some stress relief in the ceramic.
Date: March 30, 1999
Creator: Buck, E.
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

Fundamental Thermodynamics of Actinide-Bearing Mineral Waste Forms

Description: The recent arms reduction treaties between the U.S. and Russia have resulted in inventories of plutonium in excess of current defense needs. Storage of this material poses significant, and unnecessary, risks of diversion, especially for Russia whose infrastructure for protecting these materials has been weakened since the collapse of the Soviet Union. Moreover, maintaining and protecting these materials in their current form is costly. The United States has about sixty metric tons of excess plutonium, half of which is high-purity weapon material. This high purity material will be converted into mixed oxide (MOX) fuel for use in nuclear reactors. The less pure excess plutonium does not meet the specifications for MOX fuel and will not be purified to meet the fuel specifications. Instead, it will be immobilized directly in a ceramic. The ceramic will be encased in a high level waste (HLW) glass monolith (i.e., the can-in-canister option) thus making a form that simulates the intrinsic security of spent nuclear fuel. The immobilized product will be placed in a HLW repository. To meet the repository requirements, the product must be shown to be durable for the intended storage time, the host matrix must be stable in the radiation environment, the solubility and leaching characteristics of the plutonium in the host material must be established, and optimum processing parameters must be determined for the entire compositional envelope of feed materials. In order to provide technically sound solutions to these issues, thermodynamic data are essential in developing an understanding of the chemistry and phase equilibria of the actinide-bearing mineral waste forms proposed as immobilization matrices. However, the relevant thermodynamic data (e.g., enthalpy, entropy, and heat capacity) for the ceramic forms are severely lacking and this information gap directly affects the Energy Department's ability to license the disposal matrices and methods. High-temperature solution ...
Date: June 1, 1999
Creator: Williamson, Mark A.; Ebbinghaus, Bartley B. & Navrotsky, Alexandria
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

Fundamental Thermodynamics of Actinide-Bearing Mineral Waste Forms - Final Report

Description: The end of the Cold War raised the need for the technical community to be concerned with the disposition of excess nuclear weapon material. The plutonium will either be converted into mixed-oxide fuel for use in nuclear reactors or immobilized in glass or ceramic waste forms and placed in a repository. The stability and behavior of plutonium in the ceramic materials as well as the phase behavior and stability of the ceramic material in the environment is not well established. In order to provide technically sound solutions to these issues, thermodynamic data are essential in developing an understanding of the chemistry and phase equilibria of the actinide-bearing mineral waste form materials proposed as immobilization matrices. Mineral materials of interest include zircon, zirconolite, and pyrochlore. High temperature solution calorimetry is one of the most powerful techniques, sometimes the only technique, for providing the fundamental thermodynamic data needed to establish optimum material fabrication parameters, and more importantly understand and predict the behavior of the mineral materials in the environment. The purpose of this project is to experimentally determine the enthalpy of formation of actinide orthosilicates, the enthalpies of formation of actinide substituted zirconolite and pyrochlore, and develop an understanding of the bonding characteristics and stabilities of these materials.
Date: March 1, 2001
Creator: Williamson, Mark A.; Ebbinghaus, Bartley B. & Navrotsky, Alexandra
Partner: UNT Libraries Government Documents Department

DEVELOPMENT OF CRYSTALLINE CERAMICS FOR IMMOBILIZATION OF ADVANCED FUEL CYCLE REPROCESSING WASTES

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

PRELIMINARY STUDY OF CERAMICS FOR IMMOBILIZATION OF ADVANCED FUEL CYCLE REPROCESSING WASTES

Description: The Savannah River National Laboratory (SRNL) developed a series of ceramic waste forms for the immobilization of Cesium/Lanthanide (CS/LN) and Cesium/Lanthanide/Transition Metal (CS/LN/TM) waste streams anticipated to result from nuclear fuel reprocessing. Simple raw materials, including Al{sub 2}O{sub 3}, CaO, and TiO{sub 2} were combined with simulated waste components to produce multiphase ceramics containing hollandite-type phases, perovskites (particularly BaTiO{sub 3}), pyrochlores, zirconolite, and other minor metal titanate phases. Identification of excess Al{sub 2}O{sub 3} via X-ray Diffraction (XRD) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) in the first series of compositions led to a Phase II study, with significantly reduced Al{sub 2}O{sub 3} concentrations and increased waste loadings. Three fabrication methodologies were used, including melting and crystallizing, pressing and sintering, and Spark Plasma Sintering (SPS), with the intent of studying phase evolution under various sintering conditions. XRD and SEM/EDS results showed that the partitioning of the waste elements in the sintered materials was very similar, despite varying stoichiometry of the phases formed. The Phase II compositions generally contained a reduced amount of unreacted Al{sub 2}O{sub 3} as identified by XRD, and had phase assemblages that were closer to the initial targets. Chemical composition measurements showed no significant issues with meeting the target compositions. However, volatilization of Cs and Mo was identified, particularly during melting, since sintering of the pressed pellets and SPS were performed at lower temperatures. Partitioning of some of the waste components was difficult to determine via XRD. SEM/EDS mapping showed that those elements, which were generally present in small concentrations, were well distributed throughout the waste forms. Initial studies of radiation damage tolerance using ion beam irradiation at Los Alamos National Laboratory (LANL) showed little if any modification of the material after irradiation. Additional study in this area is needed. Chemical durability was briefly studied ...
Date: September 22, 2010
Creator: Fox, K.; Billings, A.; Brinkman, K. & Marra, J.
Partner: UNT Libraries Government Documents Department

Ceramic Hosts for Fission Products Immobilization

Description: Natural spinel, perovskite and zirconolite rank among the most leach resistant of mineral forms. They also have a strong affinity for a large number of other elements and including actinides. Specimens of natural perovskite and zirconolite were radioisotope dated and found to have survived at least 2 billion years of natural process while still remain their loading of uranium and thorium . Developers of the Synroc waste form recognized and exploited the capability of these minerals to securely immobilize TRU elements in high-level waste . However, the Synroc process requires a relatively uniform input and hot pressing equipment to produce the waste form. It is desirable to develop alternative approaches to fabricate these durable waste forms to immobilize the radioactive elements. One approach is using a high temperature process to synthesize these mineral host phases to incorporate the fission products in their crystalline structures. These mineral assemblages with immobilized fission products are then isolated in a durable high temperature glass for periods measured on a geologic time scale. This is a long term research concept and will begin with the laboratory synthesis of the pure spinel (MgAl2O4), perovskite (CaTiO3) and zirconolite (CaZrTi2O7) from their constituent oxides. High temperature furnace and/or thermal plasma will be used for the synthesis of these ceramic host phases. Nonradioactive strontium oxide will be doped into these ceramic phases to investigate the development of substitutional phases such as Mg1-xSrxAl2O4, Ca1-xSrxTiO3 and Ca1-xSrxZrTi2O7. X-ray diffraction will be used to establish the crystalline structures of the pure ceramic hosts and the substitution phases. Scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX) will be performed for product morphology and fission product surrogates distribution in the crystalline hosts. The range of strontium doping is planned to reach the full substitution of the divalent metal ions, Mg and Ca, in ...
Date: July 1, 2010
Creator: Kong, Peter C
Partner: UNT Libraries Government Documents Department

Preparation and Characterization of {sup 238}Pu-Ceramics for Radiation Damage Experiments

Description: The results from this initial characterization of the {sup 238}Pu- and {sup 239}Pu-bearing ceramics showed that the target phase assemblage was achieved in all but one material, {sup 238}Pu-zirconolite baseline. This {sup 238}Pu-zirconolite baseline material appears to have been prepared incorrectly with a 14 mass% excess of Pu (9.6 mass% actual vs. 8.4 mass% target; 4.8 mole% actual vs. 4.1 mole% target). It is not surprising that PuO{sub 2} was found to be one of the dominant phases. The densities of these materials compared well with the theoretical densities given by Stewart, Vance, and Ball [14]. For all but three of the materials, the average density was >94% of theoretical. Of the three, one was {sup 238}Pu-zirconolite baseline (108%) that contained unreacted PuO{sub 2}. In our MCC leach testing, the normalized elemental mass losses from the various ceramic specimens depended on the elemental ceramic constituent, the Pu isotope, and the ceramic. Of the primary constituents, Al and Ca were the most easily released. Plutonium and U were the next most susceptible to release. In general, the Hf had the lowest releases during the tests. The Gd and Ti releases varied, depending on the ceramic and the Pu isotope in the ceramic. The Mo, which was added as a trace constituent to monitor the stability of the crystalline structure, exhibited consistently high-normalized elemental releases. The amount of Pu leached depended the most on the Pu isotope in the ceramic with more Pu released from the {sup 238}Pu specimens than from the {sup 239}Pu specimens, independent of ceramic type. Interestingly, the Mo releases were typically higher for the {sup 239}Pu specimens than for the {sup 238}Pu specimens. The higher Pu release from the {sup 238}Pu specimens is not yet understood; the consistency between the ICP/MS- and GEA-measured Pu releases from the {sup ...
Date: June 15, 2000
Creator: Strachan, Denis M; Scheele, Randall D; Buchmiller, William C; Vienna, John D; Sell, Richard L & Elovich, Robert J
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