TEM Study of Short-Range-Order in Zirconolite Induced by High Temperature Ion Irradiation

1999 ◽  
Vol 5 (S2) ◽  
pp. 756-757
Author(s):  
S. X. Wang ◽  
L. M. Wang ◽  
R. C. Ewing
Keyword(s):  
Oxygen Vacancies ◽  
Ion Irradiation ◽  
Pyrochlore Structure ◽  
Fluorite Structure ◽  
Waste Immobilization ◽  
Temperature Irradiation ◽  
High Level Nuclear Waste ◽  
Nuclear Waste Immobilization ◽  
Shortrange Order ◽  
High Level

Zirconolite (CaZrTi207) is an important phase proposed for high level nuclear waste immobilization. Zirconolite was irradiated by 1 MeV Kr+ at various temperatures. At room temperature, zirconolite became amorphous after a dose of 7x1014 ions/cm2.1 Amorphization dose increased with temperature due to thermal annealing. The critical temperature, above which amorphization does not occur, was estimated to be 654 K. During the low temperature irradiation (<654 K), concurrent with amorphization, zirconolite transformed from a monoclinic structure to the cubic pyrochlore structure and then to the fluorite substructure. The structural change is due to the disordering between cations and between oxygen and oxygen vacancies.After an irradiation at 673 K to a dose of 3.6x1015 ions/cm, the zirconolite samples remained crystalline. The diffraction pattern consists of strong maxima from the fluorite structure and diffuse maxima surrounding the Bragg positions of the pyrochlore superlattice (FIG. 1). Diffuse scattering patterns have been reported in other phases, and were generally attributed to the shortrange- order (SRO) domains.

Product Models for the Vitrification of West Valley High-Level Wastes

1988 ◽  
Vol 127 ◽  
Author(s):  
I. L. Pegg ◽  
E. E. Saad ◽  
X. Feng ◽  
R. B. Adiga ◽  
W. P. Freeborn ◽  
...  
Keyword(s):  
Process Model ◽  
Process Variations ◽  
Product Performance ◽  
Borosilicate Glasses ◽  
The West ◽  
Product Models ◽  
Waste Immobilization ◽  
High Level Nuclear Waste ◽  
Nuclear Waste Immobilization ◽  
High Level

ABSTRACTProperty models have been developed for the major properties that need to be controlled in the production of borosilicate glasses for West Valley high-level nuclear waste immobilization. The chemical durability is the most important parameter for product performance, while melt viscosity is the most critical parameter in assuring the processability of the glass. Simple models for these properties are described that are based on data from numerous glasses which were prepared with compositions in the region around the West Valley reference glass. A scheme for optimization of the target glass and for predicting the acceptability of glasses resulting from natural process variations is illustrated. This involves integration of the product models with a process model that was described previously. This approach has guided the present placement of the West Valley reference glass.

scholarly journals Vitreous Materials for Nuclear Waste Immobilisation and IAEA Support Activities

MRS Advances ◽  
2016 ◽  
Vol 1 (63-64) ◽  
pp. 4201-4206 ◽  
Author(s):  
Rebecca A. Robbins ◽  
Michael I. Ojovan
Keyword(s):  
Radioactive Waste ◽  
Nuclear Waste ◽  
Chemical Elements ◽  
Phosphate Glasses ◽  
Waste Vitrification ◽  
Waste Immobilization ◽  
High Level Nuclear Waste ◽  
Nuclear Waste Immobilization ◽  
High Level ◽  
High Degree

ABSTRACTVitreous materials are the overwhelming world-wide choice for the immobilisation of HLW resulting from nuclear fuel reprocessing due to glass tolerance for the chemical elements found in the waste as well as its inherent stability and durability. Vitrification is a mature technology and has been used for high-level nuclear waste immobilization for more than 50 years. Borosilicate glass is the formulation of choice in most applications although other formulations are also used e.g. phosphate glasses are used to immobilize high level wastes in Russia. The excellent durability of vitrified radioactive waste ensures a high degree of environment protection. Waste vitrification gives high waste volume reduction along with simple and cheap disposal facilities. Although vitrification requires a high initial investment and then operational costs, the overall cost of vitrified radioactive waste is usually lower than alternative options when account is taken of transportation and disposal expenses. Glass has proven to be also a suitable matrix for intermediate and low-level radioactive wastes and is currently used to treat legacy waste in USA, and NPP operational waste in Russia and South Korea. This report is also outlining IAEA activities aiming to support utilisation of vitreous materials for nuclear waste immobilisation.

In Situ Radiation Damage Studies of Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12

2008 ◽  
Vol 1124 ◽  
Author(s):  
Karl R Whittle ◽  
Mark Blackford ◽  
Gregory R Lumpkin ◽  
Katherine L Smith ◽  
Nestor J Zaluzec
Keyword(s):  
Nuclear Waste ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Voltage Electron ◽  
Significant Difference ◽  
User Facility ◽  
High Level Nuclear Waste ◽  
Nuclear Waste Immobilization ◽  
High Level

AbstractGarnets, A3B2C3O12, are considered to be potential host phases for the immobilization of high-level nuclear waste as they can accommodate a number of elements of interest, including Zr, Ti and Fe. The naturally occurring garnet, kimzeyite, Ca3(Zr,Ti)2(Si,Al,Fe)3O12, can contain ˜30wt% Zr. An understanding of the radiation tolerance of these materials is crucial to their potential use in nuclear waste immobilization. In this study two synthetic analogues of kimzeyite of composition Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12 were monitored in situ during irradiation with 1.0 MeV Kr ions using the intermediate voltage electron microscope-Tandem User Facility (IVEM) at Argonne National Laboratory. The structure of these materials was previously determined by neutron diffraction and 57Fe Mössbauer spectroscopy. Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12 have very similar structural properties with cubic Ia3d symmetry, the only significant difference being the presence of Zr and Hf, respectively, on the 6 coordinated B sites.

Formulation and Processing of Polyphase Ceramics for High Level Nuclear Waste

1981 ◽  
Vol 6 ◽  
Author(s):  
Alan B. Harker ◽  
Peter E. D. Morgan ◽  
David R. Clarke ◽  
John F. Flintoff
Keyword(s):  
Full Range ◽  
Hot Isostatic Pressing ◽  
Fluorite Structure ◽  
Savannah River ◽  
Radioactive Elements ◽  
Fine Grain ◽  
Savannah River Plant ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Tetravalent State

ABSTRACTTwo basic crystalline phase assemblages have been developed for incorporating the full range of Savannah River Plant waste compositions into polyphase ceramic forms. Both phase assemblages provide crystalline host phases, with stable mineral analogues, for all radionuclides in the waste. The first, an alumina based assemblage, immobilizes the radioactive elements in solid solutions of magnetoplumbite and uraninite with the bulk non-radioactive waste elements being present in spinel and nepheline. The second assemblage uses the titanate based “zirconolite” type fluorite structure and the alumina/iron based magnetoplumbite phases to host the radioactive nuclei with spinel and nepheline, again providing crystalline hosts for the non-radioactive elements. Both phase assemblages can be consolidated to a fine grain ceramic by hot isostatic pressing at 1040°C pressures from 20,000 to 30,000 psi. Redox control during processing, just sufficient to reduce uranium to the tetravalent state, is used.

Radiation Effects in Silicate Glasses - A Review

1988 ◽  
Vol 125 ◽  
Author(s):  
Ned E. Bibler ◽  
David G. Howitt
Keyword(s):  
Fiber Optics ◽  
Nuclear Waste ◽  
Radiation Effects ◽  
Alpha Particles ◽  
Phase Changes ◽  
Silicate Glasses ◽  
Atomic Displacements ◽  
High Level Nuclear Waste ◽  
Nuclear Waste Immobilization ◽  
High Level

ABSTRACTThe study of radiation effects in complex silicate glasses has received renewed attention because of their use in special applications such as high level nuclear waste immobilization and fiber optics. Radiation changes the properties of these glasses by altering their electronic and atomic configurations. These alterations or defects may cause dilatations or microscopic phase changes along with absorption centers that limit the optical application of the glasses. Atomic displacements induced in the already disordered structure of the glasses may affect their use where heavy irradiating particles such as alpha particles, alpha recoils, fission fragments, or accelerated ions are present. Large changes (up to 1%) in density may result. In some cases the radiation damage may be severe enough to affect the durability of the glass in aqueous solutions.In this paper, we review the literature concerning radiation effects on density, durability, stored energy, microstructure and optical properties of silicate glasses. Both simple glasses and complex glasses used for immobilization of nuclear waste are considered.

Ion Irradiation Effects for Two Pyrochlore Compositions: Gd2Ti2O7 and Gd2Zr207

1998 ◽  
Vol 540 ◽  
Author(s):  
S. X. Wang ◽  
L. M. Wang ◽  
R. C. Ewing ◽  
K. V. Govindan Kutty
Keyword(s):  
Nuclear Waste ◽  
Ion Irradiation ◽  
Pyrochlore Structure ◽  
Fluorite Structure ◽  
Irradiation Effects ◽  
Critical Temperatures ◽  
Short Range Ordering ◽  
Radiation Induced ◽  
Diffraction Patterns ◽  
Ion Species

AbstractPyrochlore is an important nuclear waste form phase for actinide immobilization. Two synthetic pyrochlores, Gd2Ti2O7 and Gd2Zr2O7 were irradiated at various temperatures (25 K to 1073 K) by different ion species (1.5 MeV Xe+, 1.0 MeV Kr+, and 0.6 MeV Ar+). The titanate pyrochlore amorphized at relatively low doses (0.5 ∼ 0.6 dpa). Temperature dependence of the amorphization dose for titanate pyrochlore was measured, and the critical temperatures for amorphization were 1300 K, 1100 K and 950 K by 1.5 MeV Xe+, 1.0 MeV Kr+ and 0.6 MeV Ar+, respectively. The higher critical temperature for the heavier ion irradiation is consistent with an amorphization mechanism by which the heavier ion produces a larger cascade. The zirconate pyrochlore, Gd2Zr2O7, showed a strong amorphization “resistance”. Gd2Zr2O7did not become amorphous under 1.0 MeV Kr+ and 1.5 MeV Xe+ irradiation. After prolonged irradiation (up to 7 dpa) even at a temperature of 25 K, no amorphization was observed. The irradiated zirconate pyrochlore showed abundant dislocations as observed by TEM. The pyrochlore structure of Gd2Zr2O7 transformed to the fluorite structure after irradiation. The diffraction patterns of irradiated Gd2Zr2O7 showed the existence of short-range ordering of cations. The large difference between these two pyrochlores emphasizes the strong effect of chemical composition on radiation-induced amorphization.

Ion-Induced Amorphization of Murataite

2002 ◽  
Vol 713 ◽  
Author(s):  
Jie Lian ◽  
Sergey V. Yudintsev ◽  
Sergey V. Stefanovsky ◽  
Olga I. Kirjanova ◽  
Rodney C. Ewing
Keyword(s):  
Ion Irradiation ◽  
Ion Beam ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Pyrochlore Structure ◽  
Fluorite Structure ◽  
In Situ Tem ◽  
Cell Parameters ◽  
Unit Cells ◽  
Radiation Resistant

ABSTRACTMurataite A4B2C7O22-x, where A = Na+, Ca2+, REE3+, An3+/4+; B = Mn2+/3+, Zn2+; C = Ti4+, Fe3+, Al3+; 0≤x≤1, is an isometric, derivative of the fluorite-structure. Murataite is potentially suitable as a phase for the immobilization of rare earth (REE) and actinide elements (An). Murataite structures with three-(3C), five-(5C), and eight-fold (8C) multiples of the fluorite unit cell parameters have been identified. Radiation-induced amorphization of murataite has been investigated by 1 MeV Kr+ ion irradiation of three ceramic samples produced by melting in a resistive furnace and a cold crucible at 1400-1600 °C. The 1 MeV Kr+ ion irradiations were performed at room temperature using IVEM-Tandem Facility at Argonne National Laboratory. Radiation damage was observed by in-situ TEM. Initially, the irradiation caused disordering of the murataite structure. Murataite was rendered fully amorphous at a dose of (1.7∼1.9)Á1018 ion/m2. The pyrochlore structure phase (2C) is more radiation resistant to ion irradiation-induced amorphization than the murataite structure. Combining results on murataite with those pyrochlore and fluorite, a generally increasing trend in the susceptibility to ion beam damage is found in the fluorite-related structures as a function of the increasing multiples of the fluorite unit cells.

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