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Book The corrosion of uranium dioxide an atomic scale investigation thesis

Download or read book The corrosion of uranium dioxide an atomic scale investigation thesis written by Frances Nakai Skomurski and published by . This book was released on 2008 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book The Corrosion of Uranium Dioxide

Download or read book The Corrosion of Uranium Dioxide written by Frances Nakai Skomurski and published by . This book was released on 2007 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Resume of Uranium Dioxide Oxide Data

Download or read book Resume of Uranium Dioxide Oxide Data written by J. Belle and published by . This book was released on 1957 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book The Corrosion of Uranium Dioxide Thin Films

Download or read book The Corrosion of Uranium Dioxide Thin Films written by and published by . This book was released on 2013 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Uranium Dioxide

Download or read book Uranium Dioxide written by J. Belle and published by . This book was released on 1961 with total page 762 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book A Review of the Corrosion Behavior of Uranium

Download or read book A Review of the Corrosion Behavior of Uranium written by James Thomas Waber and published by . This book was released on 1958 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book The Corrosion of UO2 Versus ThO2

Download or read book The Corrosion of UO2 Versus ThO2 written by and published by . This book was released on 2005 with total page 1 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum mechanical surface energy calculations have been performed on both uranium dioxide (UO2) and thorium dioxide (ThO2) (111), (110), and (100) surfaces to determine their relative reactivities. While UO2 and ThO2 both have the fluorite structure Fm3m, they differ in that uranium has two dominant oxidation states, U{sup 4+} and U{sup 6+}, while thorium only has one, Th{sup 4+}. Furthermore, UO2 is an intrinsically weak p-type semi-conductor with a band gap of 2.14 eV (Killeen, 1980), while ThO2 is an insulator. Dissolution and spectroscopic studies indicate that UO2 and ThO2 have different solubilities (Sunder and Miller, 2000). We use the quantum mechanical program, CASTEP (CAmbridge Scientific Total Energy Package) to perform surface and adsorption energy calculations on the (111) surface of both materials, with specific attention to O, H2O, and combined adsorption cases. UO2 and ThO2 bulk unit cells were optimized to find the most stable configuration of atoms. Surface slabs were ''cleaved'' from the relaxed bulk for each orientation, placed in a 10 Å vacuum gap in order to simulate a free surface and were optimized. Relative surface energy trends and atomic relaxation were compared between the surfaces of UO2 and ThO2. The (111) surface is found to have the most energetically stable configuration of atoms in both cases, although ThO2 has higher surface energy values than UO2 on all three surfaces. The (111) surface slab is doubled in width in order to increase the number of surface sites, and different starting positions for adsorbates are tested in order to calculate the most energetically favorable adsorption sites. Adsorption energy results indicate that adsorption is more favorable on the UO2 (111) surface than the ThO2 (111) surface. Adsorption calculations are accompanied by partial density of state (PDOS) and bandstructure analyses in order to understand the role of electrons during adsorption on semi-conducting versus insulating mineral surfaces.

Book Uranium Dioxide

Download or read book Uranium Dioxide written by J. Belle and published by . This book was released on 1961 with total page 744 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book A Review of the Oxidation of Uranium Dioxide at Temperatures Below 400 C electronic Resource

Download or read book A Review of the Oxidation of Uranium Dioxide at Temperatures Below 400 C electronic Resource written by Atomic Energy of Canada Limited and published by Pinawa, Man. : Whiteshell Laboratories. This book was released on 1997 with total page 74 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book The Electrochemistry of Hydrogen Peroxide on Uranium Dioxide and the Modelling of Used Nuclear Fuel Corrosion Under Permanent Disposal Conditions

Download or read book The Electrochemistry of Hydrogen Peroxide on Uranium Dioxide and the Modelling of Used Nuclear Fuel Corrosion Under Permanent Disposal Conditions written by Linda (Michael Wu and published by . This book was released on 2014 with total page 472 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis reports a series of investigations examining the corrosion process of used nuclear fuel under permanent disposal conditions. The motivation of the project is that the safety assessment of deep geological disposal of spent nuclear fuel requires a fundamental understanding of the processes controlling fuel corrosion which could lead to the release of radionuclides to the geosphere from a failed container. One primary objective of this project was to develop a computational model in order to simulate fuel corrosion under the disposal conditions. The mathematical model was developed using COMSOL Multiphysics based on the finite element method. The chemical engineering module and the diluted species transportation module of the software are suitable for the simulations required. Literature research of the model development on the radiation-induced spent fuel corrosion revealed many key features required in modelling radiolytic corrosion (in particular for -radiation). These features were incorporated into the model presented in the thesis along with the recently available kinetics data and mechanisms. Evaluation of different model setups and sensitivity tests of different parameters were performed. A series of simulations were designed and developed to determine the influence of redox conditions, with the emphasis on -radiolysis and steel vessel corrosion products, on the corrosion rate of spent fuel. The model presented in the thesis takes into account the -radiolysis of water, the reaction of radiolytic H2O2 with UO2 both directly and via galvanic coupling with noble metal particles, the reaction with H2 via galvanic coupling, the Fenton reaction and other redox reactions involving H2O2 and H2. The calculated fuel corrosion rate is very sensitive to [Fe2]bulk produced by corrosion of the steel vessel. When the [Fe2+]bulk is greater than 4.2 mol L−1 even the radiolytically produced H2 alone can suppress fuel corrosion without assistance from external H2 for CANDU fuel with an age of 1000 years or larger. The ability of H2 to suppress fuel corrosion is shown to be sensitive to fuel burnup (density of noble metal fission products) and a complete suppression of corrosion can be achieved at bulk H2 concentrations in the order of 0.1 mol L−1. This approach is 1-dimensional and considers only the corrosion of a planar fuel surface. It will act as a preliminary step in the eventual development of 2-D and 3-D models involving the customized geometries necessary to account for the fractured nature of the spent fuel and the complex fuel bundle geometry. A second objective of this project was to develop a more detailed understanding of the H2O2 decomposition process and its influence on UO2 corrosion. Several variables (potential, pH, carbonate/bicarbonate, and fission products) can influence the reactivity of H2O2. Their influence on the surface composition and electrical conductivity of UO2 will affect surface redox reaction rates and significantly alter the overall fuel corrosion rate. Electrochemical methods were used to separate a corrosion reaction into its two constituent half reactions allowing the determination of the rate dependence on potential for each half reaction. The primary electrochemical techniques used were cyclic voltammetry (CV) to examine a system in general, cathodic stripping voltammetry (CSV) to determine the consequences of a period of oxidation, corrosion potential (E CORR) measurements to monitor redox conditions, linear polarization resistance (LPR) measurements to calculate corrosion rates, and electrochemical impedance spectroscopy (EIS) measurements to monitor changes in uranium oxide film properties. Since the changes in surface condition also have a significant impact on the H2O2 reactivity, the surface/solution analytical techniques were used to link the electrochemical/chemical processes to the compositional and structural changes observed on a UO2 surface. These techniques included scanning electron microscopy (SEM) to analyze surface morphologies, X-ray photoelectron spectroscopy (XPS) to etermine the oxidation states of UO2 surface, and inductively coupled plasma atomic emission spectroscopy (ICP-AES) to measure the dissolved U in solutions. In this thesis, the mechanisms of H2O2 decomposition on fuel surface and the consequent effect on UO2 dissolution have been investigated under various conditions (pH, carbonate/bicarbonate). At the lower pH values both the anodic oxidation and decomposition reactions are almost completely blocked by a thin surface layer of U VI oxide. At higher pH this layer becomes more soluble and anodic oxidation occurs on the sublayer of U IV 1-2xUV2xO2+x, but is partially controlled by transport through a permeable, chemically dissolving UVI oxide/hydroxide layer. At positive electrode potent ial, approximately 70% of the anodic current is consumed by H2O2 oxidation the remaining 30% going to produce soluble UO22+. At higher pH values peroxide decomposition occurs on an unblocked U IV1-2xUV2xO2+x surface and the pH dependence of the reaction suggests HO2− is the electroactive form of peroxide. The anodic behaviour of simulated nuclear fuel (SIMFUEL) in solutions containing H2O2 and HCO3−/CO32− has been studied electrochemically and using surface analytical techniques, in particular XPS. Two anodic reactions are possible, the oxidative dissolution of UO2 and H2O2 oxidation. The rate of both reactions is controlled by the chemical release of U VI surface species, and the rates can both be increased by the addition of HCO3−/CO32−. Under anodic conditions the dominant reaction is H2O2 oxidation, although UO2 dissolution may also be accelerated by the formation of a uranylperoxycarbonate complex. Similarly, under open circuit (corrosion) conditions both UO2 corrosion and H2O2 decomposition are also controlled by the rate of release of U VI surface species which blocks access of H2O2 to the underlying conductive U IV1-2xUV2xO2+x surface. A series of electrochemical experiments has been conducted on SIMFUEL electrodes containing different dopants with the primary purpose of determining the relative importance of the UO2 and ɛ-particle surfaces in the balance between UO2 oxidation/dissolution and H2O2 decomposition. On the electrode containing both rare earth elements and noble metal particles, the anodic current is increased at high potentials, which is absence on the electrode containing only rare earth elements. The direct anodic oxidation of H2O2 occurs on -particles is interpreted at high potentials, making H2O2 oxidation the dominant reaction, the UO2 surface being partially blocked by the presence of U VI surface species.

Book Microscopic Examination of a Corrosion Front in Spent Nuclear Fuel

Download or read book Microscopic Examination of a Corrosion Front in Spent Nuclear Fuel written by R. J. Finch and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Spent uranium oxide nuclear fuel hosts a variety of trace chemical constituents, many of which must be sequestered from the biosphere during fuel storage and disposal. In this paper we present synchrotron x-ray absorption spectroscopy and microscopy findings that illuminate the resultant local chemistry of neptunium and plutonium within spent uranium oxide nuclear fuel before and after corrosive alteration in an air-saturated aqueous environment. We find the plutonium and neptunium in unaltered spent fuel to have a +4 oxidation state and an environment consistent with solid-solution in the UO{sub 2} matrix. During corrosion in an air-saturated aqueous environment, the uranium matrix is converted to uranyl U(VI)O{sub 2}{sup 2+} mineral assemblage that is depleted in plutonium and neptunium relative to the parent fuel. At the corrosion front interface between intact fuel and the uranyl-mineral corrosion layer, we find evidence of a thin ({approx}20 micrometer) layer that is enriched in plutonium and neptunium within a predominantly U{sup 4+} environment. Available data for the standard reduction potentials for NpO{sup 2+}/Np{sup 4+} and UO{sub 2}{sup 2+}/U{sup 4+} couples indicate that Np(IV) may not be effectively oxidized to Np(V) at the corrosion potentials of uranium dioxide spent nuclear fuel in air-saturated aqueous solutions. Neptunium is an important radionuclide in dose contribution according to performance assessment models of the proposed U.S. repository at Yucca Mountain, Nevada. A scientific understanding of how the UO{sub 2} matrix of spent nuclear fuel impacts the oxidative dissolution and reductive precipitation of neptunium is needed to predict its behavior at the fuel surface during aqueous corrosion. Neptunium would most likely be transported as aqueous Np(V) species, but for this to occur it must first be oxidized from the Np(IV) state found within the parent spent nuclear fuel [1]. In the immediate vicinity of the spent fuel's surface the redox and nucleation behavior is likely to promote/enhance nucleation of NpO{sub 2} and Np{sub 2}O{sub 5}. Alternatively, Np may be incorporated into uranyl (UO{sub 2}{sup 2+}) alteration phases [2]. In some cases, less-soluble elements such as plutonium will be enriched near the surface of the corroding fuel [3]. We have used focused synchrotron x-rays from the MRCAT beam line at the Advanced Photon Source (APS) at Argonne National Lab to examine a specimen of spent nuclear fuel that had been subject to 10 years of corrosion testing in an environment of humid air and dripping groundwater at 90 C [4]. We find evidence of a region, approximately 20 microns in thickness, enriched in plutonium and neptunium at the corrosion front that exists between the uranyl silicate alteration mineral rind and the unaltered uranium oxide fuel (Figures 1 and 2). The uranyl silicate is itself found to be depleted in these transuranic elements relative to their abundance relative to uranium in the parent fuel. This suggests a low mobility of these components owing to a resistance to oxidize further in the presence of a UO{sub 2}{sup 2+}/U{sup 4+} couple [5].

Book The Oxidation of Uranium Dioxide with Formation of Intermediate Phases

Download or read book The Oxidation of Uranium Dioxide with Formation of Intermediate Phases written by H. Scheibe and published by . This book was released on 1964 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Uranium Metallurgy Uranium corrosion and alloys

Download or read book Uranium Metallurgy Uranium corrosion and alloys written by Walter D. Wilkinson and published by . This book was released on 1962 with total page 756 pages. Available in PDF, EPUB and Kindle. Book excerpt: