W.T. Thompson

Low volatile fission-product release and fuel volatilization during severe reactor accident conditions

An analytical model has been developed to describe the release behavior of low-volatile fission products from uranium dioxide fuel under severe reactor accident conditions. The effect of the oxygen potential on the chemical form and volatility of fission products is determined by Gibbs-energy minimization. The release kinetics are calculated according to the rate-controlling step of diffusional transport in the fuel matrix or fission product vaporization from the fuel surface. The effect of fuel volatilization (i.e., matrix stripping) on the release behavior is also considered. The model has been validated against several out-of-pile annealing experiments performed at high temperature in various oxidizing and reducing conditions.

A procedure to estimate equilibrium concentrations in multicomponent systems amd related applications

Abstract A technique has been developed to provide a close estimate of the equilibrium composition in multiphase multicomponent systems. Both the standard Gibbs energies of species and mass constraints are considered in this computation. The estimates accelerate the rate of convergence of more general Gibbs energy minimization methods and are useful in predicting stoichiometric reactions. Special situations where the output may be taken as the final solution are discussed. These include the computation of multielement stability diagrams involving stoichiometric phases.

Thermodynamic treatment of uranium dioxide based nuclear fuel

Abstract Many projects involving nuclear fuel rest on a quantitative understanding of the co-existing phases at various stages of burnup. Since the fission products have considerably different abilities to chemically associate with oxygen, and the metal-to-oxygen molar ratio is necessarily increasing, the chemical potential of oxygen is a function of burnup. Concurrently, well-recognized small fractions of new phases such as inert gas, noble metals, zirconates, etc. also develop. To further complicate matters, the dominant UO2 fuel phase may be non-stoichiometric and most of the minor phases themselves have a variable composition dependent on temperature and possible contact with the coolant in the event of a sheathing breach. A thermodynamic database has been in development to predict the phases in partially burned CANDU (CANada Deuterium Uranium) nuclear fuel containing the major fission products. The building blocks are the standard Gibbs energies of formation of the many possible compounds expressed as a function of temperature. To these data are added mixing terms associated with the appearance of the component species in particular phases. In operational terms, the treatment rests on the ability to minimize the Gibbs energy in a multicomponent system using the algorithms developed by Eriksson. The treatment, considered applicable in the range 300 to 2000 °C, is capable of handling non-stoichiometry in the UO2 fluorite phase, dilute solution behaviour of significant solute oxides, noble metal inclusions, a second metal solid solution U(Pd – Rh – Ru)3, zirconate, molybdate, and uranate solutions as well as other minor solid phases, and volatile gaseous species. The paper highlights the current capability of an ongoing project.

Extension to solgasmix for interactive calculations with the F∗A∗C∗7T thermodynamic database

Abstract Professor Erikssons program SOLGASMIX has been combined with user-friendly interactive input and output and with an extensive thermodynamic database and has been made available on-line to North American subscribers to the F∗A∗C∗T (Facility for the Analysis of Chemical Thermodynamics) database. This permits the power of SOLGASMIX to be widely and easily applied to the practical calculation of chemical equilibria. In addition, a subroutine has been written to deal with those cases when SOLGASMIX cannot calculate the equilibrium composition.

Fission Product Chemistry in Oxide Fuels

This chapter provides an overview of the chemical state of the actinide/fission product system that arises in irradiated thermal and fast reactor oxide fuels. Experimental techniques for studying minor phase formation in irradiated fuels are reviewed. Thermodynamic computational methods are discussed in relation to the prediction of the chemical speciation of the fission products and their influence on the fuel oxygen potential with fuel burnup. For water-cooled reactors, the consequences of defective fuel operation on fuel oxidation kinetics, as it bears on the fission product release behavior, are discussed. In addition, release behavior during high-temperature reactor accidents is also reviewed taking into account that the fuel and fission products may further interact with the structural materials.

Assessing corrosion in oil refining and petrochemical processing

This paper summarizes the development of an information system used to manage corrosion of metals and alloys by high temperature gases found in many different oil refining, petrochemical, power generation, and chemical processes. The database currently represents about 7.9 million h of exposure time for about 5,500 tests with 89 commercial alloys for a temperature range of 200 - 1,200°C. The system manages corrosion data from well-defined exposures and determines corrosion product stabilities. New models used in the analysis of thermochemical data for the Fe-Ni-Cr-Co-C-O-S-N-H system are being compiled. All known phases based upon combinations of the elements have been analyzed to allow complete assessments of corrosion product stabilities. Use of these data allows prediction of stable corrosion products and hence identification of the possible dominant corrosion mechanisms. The system has the potential to be used in corrosion research, alloy development, failure analysis, lifetime prediction, and process operations evaluations. The corrosion mechanisms emphasized are oxidation, sulfidation, sulfidation/oxidation, and carburization.

Phase Equilibrium Calculations in Multicomponent Systems

ABSTRACT Extensive computer databases are being prepared for the thermodynamic properties of a large variety of multicomponent solutions. Evaluated data for binary and ternary phases are stored in the form of parameters of model equations. The same models are then used to calculate properties of multicomponent phases. The modified interaction parameter formalism, which we have developed to be thermodynamically correct beyond infinite dilution, is used to model dilute solutions such as steel. We have developed an extended quasichemical model which provides very good representations of properties of multicomponent silicate melts and other ordered solutions. We have extended the sublattice model for use in multicomponent salt solutions. The Pitzer equations are used for concentrated aqueous solutions. Other models are employed where appropriate. The solution databases, along with a large database for the properties of pure compounds, are accessible by general interactive on-line programs which calculate multicomponent phase equilibria. The equilibria can be calculated under a variety of constraints such as mass constraints, chemical potential constraints, total enthalpy constraints, etc. Users of the program can also employ their own private data in conjunction with data from the public databases.

PHASE EQUILIBRIA, THERMODYNAMIC MODELLING AND NEUTRON DIFFRACTION OF THE AlN-Al2O3-Y2O3 SYSTEM

Abstract Aluminum nitride (AlN) is usually sintered using yttria (Y2O3) as an additive where it reacts with the surface species to form a Y-Al-O-N liquid that promotes particle rearrangement and densification. Construction of the phase relations in this multicomponent system is important for the development of this ceramic. The ternary phase diagram of the AlN-Al2O3-Y2O3 was developed by Gibbs energy minimization using interpolation procedures based on the modelling of the binary subsystems. Binary diagrams of Al2O3-Y2O3, AlN-Al2O3, and AlN-Y2O3 were thermodynamically modelled. The calculated Gibbs energies of components, stoichiometric phases and solution parameters were used for the calculation of isothermal sections of the AlN-Al2O3-Y2O3 ternary system. Five ternary eutectic points occur in this system in the temperature range of 1776 to 1861 °C. The ternary phase diagram was thermodynamically modelled and experimentally verified for the first time in this work. Le nitrure d’aluminium (AlN) est habituellement fritté en utilisant de l’oxyde d’yttrium (Y2O3) comme additif où il réagit avec les espèces de la surface pour former un liquide de Y-Al-O-N qui stimule la réorganisation de particule et la densification. La construction des relations de phase de ce système à plusieurs constituants est importante pour le développement de cette céramique. Le diagramme de phase ternaire de l’AlN-Al2O3-Y2O3 a été développé par minimisation de l’énergie de Gibbs en utilisant des procédures d’interpolation basées sur la modélisation de sous-systèmes binaires. On a modélisé au moyen de la thermodynamique les diagrammes binaires Al2O3-Y2O3, AlN-Al2O3 et AlNY2O3. On a utilisé les énergies de Gibbs calculées pour les constituants, les phases stoechiométriques et les paramètres de solution pour le calcul de sections isothermes du système ternaire AlN-Al2O3-Y2O3. Il y a cinq points eutectiques ternaires dans ce système dans la gamme de température de 1776 °C à 1861 °C. On a modélisé le diagramme de phase ternaire au moyen de la thermodynamique et on l’a vérifié expérimentalement pour la première fois au cours de ce travail.

F*A*C*T Thermochemical Database for Calculations in Materials Chemistry at High Temperatures

This paper summarizes the software and thermodynamic data that are offered through the online F*A*C*T thermochemical database system. Particular emphasis is placed on the treatment of materials at high temperatures. In the F*A*C*T system, extensive databases are being prepared for the thermodynamic properties of a large variety of multicomponent solutions. Models are used to calculate the thermodynamic properties of multicomponent phases from evaluated data of the binary and ternary subsystems. A Unified Interaction Parameter Formalism has been developed to treat dilute solutions, such as steels. A modification to the Quasichemical Model is employed to represent structured liquids such as silicates. Ionic systems such as molten salts are treated by the Sublattice Model.

ZINC SOLUBILITY MEASUREMENTS AND THERMODYNAMIC EVALUATION OF Zn-Pb-Bi TERNARY SYSTEM

Abstract Bismuth may be used in place of lead to confer spangle on hot dipped galvanized components and to decrease the melt viscosity to facilitate drainage of the liquid alloy. A thermodynamic model of the Zn-Pb-Bi ternary alloy system has therefore been developed based on the computed phase diagrams for Bi-Pb, Pb-Zn and Bi-Zn. The observed diagrams are well reproduced with self-consistent sets of compatible thermodynamic data. Experimental work in the form of zinc solubility measurements in the molten Bi-Pb rich alloy was performed to refine the treatment of the ternary molten phase. Computations of phase equilibrium can now be made in the Zn-Pb-Bi system for all compositions and temperatures of interest in hot dip galvanizing from entirely liquid to entirely solid. On peut remplacer le plomb par le bismuth pour donner de la brillance aux éléments galvanisés par immersion à chaud ainsi que pour diminuer la viscosité du bain afin de faciliter le drainage de l’alliage liquide. On a donc développé un modèle thermodynamique du système d’alliage ternaire Zn- Pb-Bi basé sur le calcul des diagrammes de phase de Bi-Pb, Pb-Zn et Bi-Zn. Les diagrammes observés sont bien reproduits avec des ensembles auto-cohérents de données thermodynamiques compatibles. On a effectué le travail expérimental sous forme de mesures de solubilité du zinc dans l’alliage fondu riche en Bi-Pb afin de raffiner le traitement de la phase ternaire fondue. On peut maintenant effectuer des calculs d’équilibre de phase dans le système Zn-Pb-Bi pour toutes les compositions et toutes les températures d’intérêt de la galvanisation depuis l’état entièrement liquide à l’état entièrement solide.