The Crystalline-Amorphous Transformation in Natural Zirconolite: Evidence for Long-Term Annealing

1997 ◽  
Vol 506 ◽  
Author(s):  
Gregory R. Lumpkin ◽  
Katherine L. Smith ◽  
Mark G. Blackford ◽  
Reto Gieré ◽  
C. Terry Williams
Keyword(s):  
Rate Constant ◽  
Preliminary Investigation ◽  
Deep Borehole ◽  
Waste Forms ◽  
Transmission Electron ◽  
Thermal Histories ◽  
Annealing Rate ◽  
Host Rocks ◽  
Saturation Dose

ABSTRACTDose-age relationships have been determined by analytical and transmission electron microscopy (AEM and TEM) for the onset dose and critical amorphization dose of a suite of natural zirconolites. Together with a preliminary investigation of the thermal histories of the zirconolite-bearing rocks, the results indicate that valid estimates of D0 (intercept dose at t = 0) and K (annealing rate constant) are obtained and that the host rocks experienced temperatures on the order of 100-200 °C averaged over time. The natural samples are therefore best suited as radiation damage analogues for waste forms stored under deep borehole conditions where temperatures of 100-450 °C are expected. Our results indicate that the critical amorphization (or saturation) dose of zirconolite will increase by a factor of approximately 2 or more as a result of storage at elevated temperature. The effect of long-term annealing on the critical amorphization dose is only important for times in excess of 107-108 years due to the low annealing rate constant of 10−9/yr.

An Overview of the Crystal Chemistry, Durability, and Radiation Damage Effects of Natural Pyrochlore

2000 ◽  
Vol 663 ◽  
Author(s):  
G.R. Lumpkin ◽  
R.C. Ewing ◽  
C.T. Williams ◽  
A.N. Mariano
Keyword(s):  
Radiation Damage ◽  
Large Body ◽  
Amorphous State ◽  
X Ray Diffraction ◽  
Natural Systems ◽  
Pyrochlore Group ◽  
Thermal Histories ◽  
Host Rocks ◽  
Long Term Behavior

ABSTRACTNumerous studies of pyrochlore group minerals have been completed over the previous 15 years, providing researchers in the field of nuclear waste disposal with a large body of data relevant to the behavior of these minerals in natural systems. The information obtained from studies of natural pyrochlore is applicable to the formulation of diverse waste form compositions and provides data for the assessment of the long-term behavior. Although resistant to dissolution, pyrochlore is subject to chemical alteration by ion exchange with hydrothermal fluids and low temperature ground water; however, Th and U are generally immobile and are retained in the structure. X-ray diffraction, TEM, EXAFS-XANES, and other techniques have been employed in studies of radiation damage. These studies reveal the classic sequence of damage microstructures with increasing dose and provide details about the structure of the amorphous state. Furthermore, the radiation damage studies are now complemented by data relating to the thermal histories of some of the host rocks.

Deep Borehole Disposal of Plutonium

2008 ◽  
Vol 1107 ◽  
Author(s):  
Fergus G.F. Gibb ◽  
Kathleen J. Taylor ◽  
Boris E. Burakov
Keyword(s):  
High Pressure ◽  
Waste Management ◽  
Management Problem ◽  
Deep Borehole ◽  
Security Threat ◽  
High Pressure And Temperature ◽  
Geological Disposal ◽  
Waste Forms ◽  
Deep Boreholes

AbstractExcess plutonium not destined for burning as MOX or in Generation IV reactors is both a long-term waste management problem and a security threat. Immobilisation in mineral and ceramic-based waste forms for interim safe storage and eventual disposal is a widely proposed first step. The safest and most secure form of geological disposal for Pu yet suggested is in very deep boreholes and we propose here that the key to successful combination of these immobilisation and disposal concepts is the encapsulation of the waste form in small cylinders of recrystallized granite. The underlying science is discussed and the results of high pressure and temperature experiments on zircon, depleted UO2 and Ce-doped cubic zirconia enclosed in granitic melts are presented. The outcomes of these experiments demonstrate the viability of the proposed solution and that Pu could be successfully isolated from its environment for many millions of years.

EELS characterization of “Smut” layer films on steel surface prepared for chrome plating by anodic etching

1995 ◽  
Vol 53 ◽  
pp. 538-539
Author(s):  
E Y. Wang ◽  
J. T. Cherian ◽  
A. Madsen ◽  
R. M. Fisher
Keyword(s):  
Steel Surface ◽  
Surface Preparation ◽  
Treatment Method ◽  
Chrome Plating ◽  
Transmission Electron ◽  
Alloy Steels ◽  
Pre Treatment ◽  
Hard Chrome ◽  
Electron Energy Loss

Many steel parts are electro-plated with chromium to protect them against corrosion and to improve their wear-resistance. Good adhesion of the chrome plate to the steel surface, which is essential for long term durability of the part, is extremely dependent on surface preparation prior to plating. Recently, McDonnell Douglas developed a new pre-treatment method for chrome plating in which the steel is anodically etched in a sulfuric acid and hydrofluoric acid solution. On carbon steel surfaces, this anodic pre-treatment produces a dark, loosely adhering material that is commonly called the “smut” layer. On stainless steels and nickel alloys, the surface is only darkened by the anodic pre-treatment and little residue is produced. Anodic pre-treatment prior to hard chrome plating results in much better adherence to both carbon and alloy steels.We have characterized the anodic pre-treated steel surface and the resulting “smut” layer using various techniques including electron spectroscopy for chemical analysis (ESCA) on bulk samples and transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) on stripped films.

Ultrastructural observations of the aorta of calves implanted with a mechanical left ventricular assist device

1990 ◽  
Vol 48 (3) ◽  
pp. 834-835
Author(s):  
J P Cassella ◽  
V Salih ◽  
T R Graham
Keyword(s):  
Left Ventricular Assist Device ◽  
Ventricular Assist Device ◽  
Left Ventricular ◽  
Aortic Tissue ◽  
Assist Device ◽  
Ventricular Assist ◽  
Transmission Electron ◽  
Left Ventricular Assist ◽  
Preliminary Study

Left ventricular assist systems are being developed for eventual long term or permanent implantation as an alternative to heart transplantation in patients unsuitable for or denied the transplant option. Evaluation of the effects of these devices upon normal physiology is required. A preliminary study was conducted to evaluate the morphology of aortic tissue from calves implanted with a pneumatic Left Ventricular Assist device-LVAD. Two 3 month old heifer calves (calf 1 and calf 2) were electively explanted after 128 days and 47 days respectively. Descending thoracic aortic tissue from both animals was removed immediately post mortem and placed into karnovsky’s fixative. The tissue was subsequently processed for transmission electron microscopy (TEM). Some aortic tissue was fixed in neutral buffered formalin and processed for routine light microscopy.

scholarly journals The Effect of Long-Term Impact of Elevated Temperature on Changes in Microstructure and Mechanical Properties of HR3C Steel

2016 ◽  
Vol 61 (2) ◽  
pp. 761-766 ◽  
Author(s):  
A. Zieliński ◽  
M. Sroka ◽  
A. Hernas ◽  
M. Kremzer
Keyword(s):  
Mechanical Properties ◽  
Elevated Temperature ◽  
X Ray ◽  
Qualitative And Quantitative ◽  
Microstructure And Mechanical Properties ◽  
Transmission Electron ◽  
Quantitative Identification ◽  
Working Parameters ◽  
Long Term Impact

Abstract The HR3C is a new steel for pressure components used in the construction of boilers with supercritical working parameters. In the HR3C steel, due to adding Nb and N, the compounds such as MX, CrNbN and M23C6 precipitate during service at elevated temperature, resulting in changes in mechanical properties. This paper presents the results of microstructure investigations after ageing at 650, 700 and 750 °C for 5,000 h. The microstructure investigations were carried out using scanning and transmission electron microscopy. The qualitative and quantitative identification of the existing precipitates was carried out using X-ray analysis of phase composition. The effect elevated temperature on microstructure and mechanical properties of the examined steel was described.

Host Phases for Actinide Elements in the Metallic Waste Form

2002 ◽  
Vol 757 ◽  
Author(s):  
D. E. Janney
Keyword(s):  
Stainless Steel ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Transmission Electron Microscope ◽  
Waste Form ◽  
Dissolution Behavior ◽  
Release Rates ◽  
Waste Forms ◽  
Transmission Electron ◽  
Simulated Waste

ABSTRACTArgonne National Laboratory has developed an electrometallurgical process for conditioning spent sodium-bonded metallic reactor fuel prior to disposal. A waste stream from this process consists of stainless steel cladding hulls that contain undissolved metal fission products such as Tc, Ru, Rh, Pd, and Ag; a small amount of undissolved actinides (U, Np, Pu) also remains with the hulls. These wastes will be immobilized in a waste form whose baseline composition is stainless steel alloyed with 15 wt% Zr (SS-15Zr). Scanning electron microscope (SEM) observations of simulated metal waste forms (SS-15Zr with up to 11 wt% actinides) show eutectic intergrowths of Fe-Zr-Cr-Ni intermetallic phases with steels. The actinide elements are almost entirely in the intermetallics, where they occur in concentrations ranging from 1–20 at%. Neutron- and electron-diffraction studies of the simulated waste forms show materials with structures similar to those of Fe2Zr and Fe23Zr6.Dissolution experiments on simulated waste forms show that normalized release rates of U, Np, and Pu differ from each other and from release rates of other elements in the sample, and that release rates for U exceed those for any other element (including Fe). This paper uses transmission electron microscope (TEM) observations and results from energy-dispersive X-ray spectroscopy (EDX) and selected-area electron-diffraction (SAED) to characterize relationships between structural and chemical data and understand possible reasons for the observed dissolution behavior.Transmission electron microscope observations of simulated waste form samples with compositions SS-15Zr-2Np, SS-15Zr-5U, SS-15Zr-11U-0.6Rh-0.3Tc-0.2Pd, and SS-15Zr-10Pu suggest that the major actinide-bearing phase in all of the samples has a structure similar to that of the C15 (cubic, MgCu2-type) polymorph of Fe2Zr, and that materials with this structure exhibit significant variability in chemical compositions. Material whose structure is similar to that of the C36 (dihexagonal, MgNi2-type) polymorph of Fe2Zr was also observed, and it exhibits less chemical variability than that displayed by material with the C15 structure. The TEM data also demonstrate a range of actinide concentrations in materials with the Fe23Zr6 (cubic, Mn23Th6-type) structure.Microstructures similar to those produced during experimental deformation of Fe-10 at% Zr alloys were observed in intermetallic materials in all of the simulated waste form samples. Stacking faults and associated dislocations are common in samples with U, but rarely observed in those with Np and Pu, while twins occurred in all samples. The observed differences in dissolution behavior between samples with different actinides may be related to increased defect-assisted dissolution in samples with U.

Dissolution Characteristics and Morphology of Large-sized Scorodite Particles Synthesized from Fe(II) and As(V) in Aqueous Solution

2012 ◽  
Vol 31 (4-5) ◽  
pp. 451-458 ◽  
Author(s):  
S. Fujieda ◽  
K. Shinoda ◽  
T. Inanaga ◽  
M. Abumiya ◽  
S. Suzuki
Keyword(s):  
Electron Microscopy ◽  
Aqueous Solution ◽  
Surface Defects ◽  
Atmospheric Temperature ◽  
Orthorhombic Structure ◽  
X Ray ◽  
Long Term Storage ◽  
Transmission Electron ◽  
Term Storage

AbstractA novel process for preparing scorodite particles with a diameter of approximately 20 µm from Fe(II) and As(V) in aqueous solution has been developed by DOWA Metals and Mining. In the present study, the dissolution characteristics of iron and arsenic from the scorodite particles synthesized by this process have been investigated under different conditions. The results show that the concentration of arsenic dissolved from the particles in aqueous solution is very low, but it has a complicated dependence on the temperature and pH of the solution. Transmission electron microscopy (TEM) with an energy dispersive X-ray spectrometer (EDS) was used to analyze the morphology, structure, and composition of the scorodite particles. The results indicate that the scorodite particles exhibit a nearly octahedral shape with planes composed of almost (111) planes in the orthorhombic structure. The concentration of iron at the surface of the particles is higher than that of iron inside of the particles. This characteristic morphology, along with the minimal surface defects of the scorodite particles, is considered to be responsible for the low dissolution of arsenic from the particles in aqueous solution. Atmospheric temperature and solution conditions were also found to be important for the safe, long-term storage of arsenic using scorodite particles.

Long-term leaching scenarios for cement-based waste forms

1987 ◽  
Vol 5 (1) ◽  
pp. 55-66 ◽  
Author(s):  
P COTE ◽  
T BRIDLE
Keyword(s):  
Waste Forms
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