Study of Natural Minerals of U-Ryrochlore-Type Structure as Analogues of Plutonium Ceramic Waste-form

2002 ◽  
Vol 713 ◽  
Author(s):  
Roman V. Bogdanov ◽  
Yuri F. Batrakov ◽  
Elena V. Puchkova ◽  
Andrey S. Sergeev ◽  
Boris E. Burakov
Keyword(s):  
Chemical Shifts ◽  
Pyrochlore Structure ◽  
Type Structure ◽  
Waste Form ◽  
X Ray ◽  
Ceramic Waste ◽  
Natural Minerals ◽  
The Us ◽  
Pyrochlore Type

ABSTRACTAt present, crystalline ceramic based on titanate pyrochlore, (Ca,Gd,Hf,Pu,U)2Ti2O7, is considered as the US candidate waste form for the immobilization of weapons grade plutonium. Naturally occuring U-bearing minerals with pyrochlore-type structure: hatchettolite, betafite, and ellsworthite, were studied in orders to understand long-term radiation damage effects in Pu ceramic waste forms. Chemical shifts (δ) of U(Lδ1)– and U(Lβ1) – X-ray emission lines were measured by X-ray spectrometry. Calculations were performed on the basis of a two-dimensional δLá1- and δLδ1- correlation diagram. It was shown that 100% of uranium in hatchettolite and, probably, 95-100% of uranium in betafite are in the form of (UO2)2+. formal calculation shows that in ellsworthite only 20% of uranium is in the form of U4+ and 80% of the rest is in the forms of U5+ and U6+. The conversion of the initial U4+ ion originally occurring in the pyrochlore structure of natural minerals to (UO2)2+ due to metamict decay causes a significant increase in uranium mobility.

Aging Studies of Pu-238 and -239 Containing Calcium Phosphate Ceramic Waste-forms

2013 ◽  
Vol 1518 ◽  
pp. 73-78 ◽  
Author(s):  
Shirley K. Fong ◽  
Brian L. Metcalfe ◽  
Randall D. Scheele ◽  
Denis M. Strachan
Keyword(s):  
Calcium Phosphate ◽  
Accelerated Aging ◽  
Waste Form ◽  
Calcium Phosphate Ceramic ◽  
Ceramic Waste ◽  
Waste Forms ◽  
Aging Studies ◽  
Flow Through ◽  
Pyrochemical Reprocessing

ABSTRACTA calcium phosphate ceramic waste-form has been developed at AWE for the immobilisation of chloride containing wastes arising from the pyrochemical reprocessing of plutonium. In order to determine the long term durability of the waste-form, aging trials have been carried out at PNNL. Ceramics were prepared using Pu-239 and -238, these were characterised by PXRD at regular intervals and Single Pass Flow Through (SPFT) tests after approximately 5 yrs.While XRD indicated some loss of crystallinity in the Pu-238 samples after exposure to 2.8 x 1018 α decays, SPFT tests indicated that accelerated aging had not had a detrimental effect on the durability of Pu-238 samples compared to Pu-239 waste-forms.

Preliminary Studies of the Disposition of Cesium in a Glass-Bonded Sodalite Waste form

2002 ◽  
Vol 713 ◽  
Author(s):  
Marsha J. Lambregts ◽  
Steven M. Frank
Keyword(s):  
National Laboratory ◽  
Argonne National Laboratory ◽  
Fission Products ◽  
Waste Form ◽  
Resonance Spectroscopy ◽  
Ceramic Waste ◽  
Long Term Storage ◽  
Geological Repository ◽  
Term Storage

ABSTRACTArgonne National Laboratory has developed an electrometallurgical treatment for DOE spent metallic nuclear fuel. Fission products are immobilized in a durable glass bonded sodalite ceramic waste form (CWF) suitable for long term storage in a geological repository. Cesium is estimated to be in the waste form at approximately 0.1 wt.%. The exact disposition of cesium was uncertain and it was believed to be uniformly distributed throughout the waste form. A correlation of X-ray diffractometry (XRD), electron microscopy (EM), and nuclear magnetic resonance spectroscopy (NMR) performed on surrogate ceramic waste forms with high cesium loadings found a high cesium content in the glass phase and in several non-sodalite aluminosilicate phases. Cesium was not detected in the sodalite phase.

scholarly journals Ion-exchange properties of solid solutions based on hydrated forms of monovalent metals antimonate-tungstates

2020 ◽  
Vol 62 (6) ◽  
pp. 74-79
Author(s):  
Olga A. Firsova ◽  
◽  
Elena M. Filonenko ◽  
Yulia A. Lupitskaya ◽  
Hurshid N. Bozorov ◽  
...  
Keyword(s):  
Ir Spectroscopy ◽  
Ion Exchange ◽  
Solid Solutions ◽  
Rietveld Method ◽  
Type Structure ◽  
Water Molecules ◽  
X Ray Diffraction ◽  
X Ray ◽  
Pyrochlore Type ◽  
Exchange Properties

The research of tungsten-antimony crystalline acid (TACA) structural transformations in the condition of ion-exchange and thermolysis of its substituted M+, H+-forms (M+ – Li, Na, K, Ag) were conducted. The data of thermogravimetric and qualitative X-ray phase analyses made it possible to conclude that the thermolysis of TACA and its derivatives proceeds in a wide temperature range from 300 to 1150 K being accompanied by the removal of crystalline water molecules with the formation of phases mixture containing complex antimony oxides of the ( -,  - Sb2O4) modification and WO3. It was shown that compounds based on hydrated forms of monovalent metal antimonates-tungstates are stable up to 1023 K with a pyrochlore-type structure. For pyrochlore-like phases, a monotonic dependence of unit cell parameter a on ion-exchange degree α and the ionic radius of metals r was revealed indicating the formation of solid solutions Мх(Н3О)1–хWSbO6 nН2О (M+ – Li, Na, K, Ag; 0.0≤х<1.0; 0.0≤n<2.0) with a limited range of solubility from the crystal chemistry point of view. Within the framework of the Fd-3m space group, based on the data of X-ray diffraction analysis (Rietveld method), the structural characteristics of TACA and its substituted M+, H+-forms were refined, and a model for populating the corresponding metal ions by crystallographic positions of the pyrochlore-type structure was proposed. Using a complex of physicochemical methods (thermogravimetric, X-ray diffraction analyses and IR spectroscopy), a correlation between the composition of the obtained compounds, structural disorder, and ion-exchange properties were determined. According to the data of thermogravimetry and IR spectroscopy, it follows that the degree of compounds hydration analyzed depends on the nature of the alkaline ion. This allows to conclude that lithium and sodium ions are located in 16d– positions, dragging neutral water molecules into the structure occupying 8b-positions. In this case, potassium ions can partially occupy both 16d- and 8b-positions of the structure.

Transmission electron microscopy of alpha-decay damage and alteration of betafite

1987 ◽  
Vol 45 ◽  
pp. 376-377
Author(s):  
G. R. Lumpkin ◽  
R. C. Ewing
Keyword(s):  
Nuclear Waste ◽  
Pyrochlore Structure ◽  
Alpha Decay ◽  
Structure Type ◽  
Waste Form ◽  
Natural Analogue ◽  
The Core ◽  
Transmission Electron ◽  
Pyrochlore Group

The pyrochlore structure type occurs as a constituent of crystalline nuclear waste form assemblages proposed for the long term isolation of actinides. Betafite, the Ti-rich end-member of the pyrochlore group, is a natural analogue similar in composition to waste form pyrochlores. This study examines the effects of alpha-recoil damage and geochemical alteration on a specimen of betafite from Antanifotsy, Madagascar (Harvard no. 87876, UNM no. 205).Electron microprobe analyses were performed using a JEOL 733 Superprobe operated at 15 kV and 20 nA sample current crushed fragments of the sample were dispersed on holey-carbon grids and examined with a JEOL 2000 EX TEM operated at 200 kV. Phase compositions were checked using a Tracor TN5500 EDS.The 1.5 cm diameter betafite crystal displays an unusual zonal sequence of alteration. The core consists of relatively unaltered betafite containing ca. 27 wt.% U02 and 2.5 wt.% CaO (TABLE 1, analysis 1).

Structural Analysis of a Complex Oxide Eu2Mn2/3Nb4/3O7 with a Pyrochlore-Related Structure

2004 ◽  
Vol 449-452 ◽  
pp. 969-972
Author(s):  
G. Chen ◽  
Hiromi Nakano ◽  
Hirohisa Sato ◽  
Naoki Kamegashira
Keyword(s):  
Structural Analysis ◽  
Pyrochlore Structure ◽  
Complex Oxide ◽  
Type Structure ◽  
Related Structure ◽  
X Ray Diffraction ◽  
Diffraction Profile ◽  
X Ray ◽  
Fundamental Reflection ◽  
Diffraction Patterns

The complex oxide Eu2Mn2/3Nb4/3O7 structurally characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results of XRD structure analysis shown that the X-ray diffraction profile calculated with monoclinic C2/c model is in a good agreement with the observed X-ray diffraction patterns. In addition to fundamental reflection peaks, super lattice lines could be also assigned with C2/c symmetry. Therefore, it is derived that Eu2Mn2/3Nb4/3O7 phase has not a pyrochlore structure but has a zirconolite-type structure (pyrochlore-related structure) with a C2/c space group. Eu2Mn2/3Nb4/3O7 has two kinds of distorted MO6 octahedra and HTB layers, which deviates from the regular forms. The microstructure of Eu2Mn2/3Nb4/3O7 investigated by TEM also proved the results of XRD structural analysis. It was viewed that HRTEM image of a characteristic twin structure in Eu2Mn2/3Nb4/3O7 which a zirconolite-type structure has.

Alpha-Decay Damage and Annealing Effects in Natural Pyrochlores: Analogues for Long-Term Radiation Damage Effects in Actinide, Pyrochlore, Structure Types

1988 ◽  
Vol 127 ◽  
Author(s):  
G. R. Lumpkin ◽  
R. C. Ewing
Keyword(s):  
Pyrochlore Structure ◽  
Alpha Decay ◽  
X Ray Diffraction ◽  
Final State ◽  
X Ray ◽  
Waste Forms ◽  
Annealing Effects ◽  
Long Term Performance ◽  
Term Performance

ABSTRACTCubic pyrochlore structure types, A2-mB2O6(O, OH, F) i-n*pH2O, and their derivatives (e.g., monoclinic zirconolite) are important actinide-bearing phases in polyphase, ceramic waste forms (e.g., SYNROC). These waste form phases may typically accumulate alpha-decay doses of 1025 alpha-events/m3 in 1, 000 years or 1026alpha-events/m3 in one million years (i.e., for SYNROC with 20 wt. % HLW). Natural pyrochlores have calculated doses ranging from 1024 to 1027 alpha-events/m3 (= 0.02 to 50 dpa) which have accumulated over ten to a thousand million years. Actinide doping experiments typically reach doses of 1025 alpha-events/m3over periods of several years. Detailed x-ray diffraction analysis of natural samples reveals that the alpha-decay dose at which there is an initial loss of crystallinity (i.e., transition from crystalline to the aperiodic, metamict state as a result of alpha-decay damage) increases as a function of the geologic age of the sample. The increase in the calculated alpha-decay dose which is associated with a specific degree of damage (e.g., loss of x-ray diffraction intensity) is attributed to annealing of isolated alpha-recoil tracks back to the original, crystalline structure. Based on a model of gradual track fading, the alpha-recoil tracks in natural pyrochlores have mean lives on the order of 108 years. In contrast, minerals which remain crystalline (e.g., uraninite, UO2) despite doses of over 1027 alpha-events/m3 have mean alpha-recoil track lives of approximately 104 years. This demonstrates that the microstructure of alpha-decay damaged materials depends not only on the total alpha-event dose, but also on the annealing kinetics of alpha-recoil track fading. Therefore, the prediction of the long-term performance and final state of crystalline phases in ceramic nuclear waste forms requires the determination of alpha-recoil damage annealing as a function of time and temperature.

The Use of Cerium Valence State for Evaluation of Accessory Minerals Durability to Radiation Damage

2002 ◽  
Vol 713 ◽  
Author(s):  
Roman V. Bogdanov ◽  
Yuri M. Zaytsev ◽  
andrey S. Sergeev
Keyword(s):  
Radiation Damage ◽  
Valence State ◽  
Chemical Shifts ◽  
Environment Effect ◽  
Crystalline Materials ◽  
X Ray ◽  
Natural Minerals ◽  
Waste Forms ◽  
Two Samples ◽  
Long Time

ABSTRACTCerium-actinide bearing natural minerals which demonstrate their long-time physicochemical durability under the environment effect would be considered as analogues of actinide ceramic waste forms. Radiation damage of crystalline materials causes oxidation of cerium from initial Ce(III) to Ce(IV). Therefore, cerium valence state in actinide-cerium bearing natural minerals in some cases reflects the resistance of such minerals to radiation damage. Cerium valence state was determined in the following natural minerals of similar age and similar U-Th-contents: monazite (four samples), britholite (two samples), and aeschynite (one sample). The method of chemical shifts of X-ray emission (CeKá1 line) was used. The following contents of Ce(IV) were observed: more then 30 % in britholite, 11 % in aeschynite, 0 % in monazite. The results obtained suggest that durability of these actinide host phases with respect to radiation damage decreases in the monazite-aeschynite-britholite series.

Pyrochlores. III. X-Ray, neutron, infrared, and dielectric studies of A2Sn2O7 stannates

1968 ◽  
Vol 46 (6) ◽  
pp. 859-873 ◽  
Author(s):  
François Brisse ◽  
Osvald Knop
Keyword(s):  
Oxygen Atom ◽  
Lower Limit ◽  
Systematic Study ◽  
Room Temperature ◽  
Pyrochlore Structure ◽  
Dielectric Studies ◽  
Ionic Radii ◽  
X Ray ◽  
Upper Limit ◽  
Pyrochlore Type

A number of compositions [Formula: see text] and of related mixed phases were prepared and investigated. For the trivalent lanthanons from La to Lu, and for Y, the homogeneous A2Sn2O7 phases were of the cubic pyrochlore type (space group Fd3m, No. 227). Their lattice parameters gave a very good linear relationship when plotted against the Templeton–Dauben radii of A3+. The applicability of other sets of ionic radii was also tested. The lower limit of the r(A3+):r(Sn4+) ratio for cubic pyrochlore stannates is about 1.19 (Ahrens radii), while the upper limit is at least 1.60. Attempts to extend the lower limit by preparing mixed Yb + Sc stannates were only partially successful. Bi2Sn2O7 is not a cubic pyrochlore.The structures of Y2Sn2O7 and Sm2Sn2O7 were refined from X-ray powder data, and that of La2Sn2O7, from neutron powder data. The positional parameter of the majority oxygen atom, x(O2), has been found to increase with the size of A3+. The distortion of the SnO6 octahedra in the pyrochlore structure thus decreases with increasing r(A3+).From a systematic study of the infrared spectra of the stannates it appears that it is the size of the Y3+ ion rather than its chemistry (as distinct from the Ln3+ ions) that determines its place among the 3–4 pyrochlores. No evidence of ferroelectricity was found in Pr, Er, and Lu stannates between room temperature and 4.2 °K.

scholarly journals Preparation and characterization of multiphase ceramic designer waste forms

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Braeden M. Clark ◽  
Priyatham Tumurugoti ◽  
Shanmugavelayutham K. Sundaram ◽  
Jake W. Amoroso ◽  
James C. Marra
Keyword(s):  
Fixed Ratio ◽  
Chemical Durability ◽  
Waste Form ◽  
Ceramic Waste ◽  
Waste Forms ◽  
Plasma Sintering ◽  
Long Term Performance ◽  
Term Performance ◽  
Elemental Release

AbstractThe long-term performance, or resistance to elemental release, is the defining characteristic of a nuclear waste form. In the case of multiphase ceramic waste forms, correlating the long-term performance of multiphase ceramic waste forms in the environment to accelerated chemical durability testing in the laboratory is non-trivial owing to their complex microstructures. The fabrication method, which in turn affects the microstructure, is further compounding when comparing multiphase ceramic waste forms. In this work, we propose a “designer waste form” prepared via spark plasma sintering to limit interaction between phases and grain growth during consolidation, leading to monolithic high-density waste forms, which can be used as reference materials for comparing the chemical durability of multiphase waste forms. Designer waste forms containing varying amounts of hollandite in the presence of zirconolite and pyrochlore in a fixed ratio were synthesized. The product consistency test (PCT) and vapor hydration test (VHT) were used to assess the leaching behavior. Samples were unaffected by the VHT after 1500 h. As measured by the PCT, the fractional Cs release decreased as the amount of hollandite increased. Elemental release from the zirconolite and pyrochlore phases did not appear to significantly contribute to the elemental release from the hollandite phase in the designer waste forms.

scholarly journals Ion transport in hydrated compounds based on crystalline polyantimonic acid

2020 ◽  
Vol 62 (6) ◽  
pp. 80-84
Author(s):  
Vladimir A. Burmistrov ◽  
◽  
Lilia Yu. Kovalenko ◽  
Olga A. Firsova ◽  
Elena M. Filonenko ◽  
...  
Keyword(s):  
Rietveld Method ◽  
Structural Characteristics ◽  
Specific Conductivity ◽  
Silver Ions ◽  
Type Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Polyantimonic Acid ◽  
Substitution Degree ◽  
Pyrochlore Type

The present work is devoted to the study of crystalline polyantimonic acid (CPA) structural properties in conditions of ion exchange and heat treatment of its substituted Ag+, H+-forms. According to the obtained data of X-ray diffraction qualitative phase analysis, the compounds analyzed crystallize within the framework of the pyrochlore type structure (space group Fd-3m). For phases being isomorphic to this structural type, it was shown that with an increase in the degree of substitution α, a relative intensity redistribution of the group of reflections with even and odd indices and decrease of unit cell parameter a were observed.. The data of thermogravimetric analysis allows to conclude that the thermolysis of CPA’s ion-substituted forms proceeds in a wide temperature range from 297 to 973 K being accompanied by a decrease of samples weight. Applying the Rietveld method, the structural characteristics of CPA and its derivatives were refined, and a model of populating the corresponding metal ions by crystallographic positions within a pyrochlore-type structure was proposed. Using a complex of physicochemical methods (thermogravimetric and X-ray diffraction analyses), the effect of hydration of CPA compounds with a pyrochlore type structure on transport properties was determined. It is shown that with an increase of substitution degree α in samples of CPA’s Ag+, H+-forms in conditions of alternating current the value of the specific conductivity decreases monotonically. An increase of silver ions content in the phases of Ag+, H+-forms leads to the change of proton-binding energy with the crystal lattice. In the condition of elevated temperature in hydrated CPA compounds, charge transfer is performed by silver ions. It was found that the electrical conductivity in the samples analyzed can also rise with a silver ions amount decrease (16d-positions are partially filled with Sb3+).

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