NuFuel & MMSNF 2015

First Workshop on Research into Nuclear Fuel in Europe
and Materials Modeling and Simulation for Nuclear Fuels Workshop
Karlsruhe, Germany, November 16th to 18th, 2015

Updated: Tue 08 Dec 2015, 14:27

Talk 4.5: Thermodynamic Investigations of the Uranium-Molybdenum-Oxygen System by a Coupling of Density Functional Theory and Calphad Methodologies

Emily Corcoran1, R.A. Barry1, J.-L. Flèche2, C. Guéneau2 and J. Scott1
  • 1: Department of Chemistry and Chemical Engineering, Royal Military College of Canada, Kingston, Ontario, Canada
  • 2: CEA, DEN, DPC, SCCME, Centre de Saclay, F–91191 Gif-sur-Yvette, France

Abstract

The process of fissioning uranium oxide or mixed oxides of uranium plutonium nuclear fuels results in the production of a large number of fission and activation products (e.g., Mo, Ce, Ru, Sr, Ba, La, Nd, Pd, Rh, Cs, Pu, Xe, Np, Y, Tc, Pr, Rb, Te, I, etc.). These elements distribute themselves into phases (e.g., gas, liquid, or solid) depending on burnup (composition), temperature, and pressure. The chemical state of the fuel has a direct influence on the physical properties and consequently on fuel behaviour (e.g., melting point, swelling, fission gas release, thermal conductivity, etc.). Thermodynamic modelling to predict the chemical state can be beneficial for safety analysis, understanding fuel oxidation, ascertaining potential interaction with other reactor materials, interpretation of experimental data of discharged fuel, corrosion, waste disposal, and waste reprocessing. As Molybdenum (Mo) is one of the more abundant fission products in nuclear fuel and has a large influence on the fuel oxidation; a thermodynamic model for high burnup oxide fuels must include a careful assessment of the uranium (U) – molybdenum (Mo) –oxygen (O) system.

The U-Mo-O system has been reviewed extensively. Numerous ternary oxides have been identified by crystallographic means, however only a few compounds have been thermodynamically studied. Therefore, when no thermodynamic data was available in the literature, further experiments were completed or (where possible) an ab-initio paired quasi-harmonic model was used to generate these data.

This presentation reviews:

  1. the available thermodynamic data in the literature for the U-Mo-O system,
  2. experiments completed to gather missing data,
  3. a review of the ab-initio paired quasi-harmonic model,
  4. the thermodynamic equations used to assess these data, and
  5. the thermochemical model developed for the U-Mo-O system.