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 3.4: Air storage effect for Kr and Xe transport in UO2

Eric Gilabert1 , Gaëlle Carlot2, Amélie Michel2 .
  • 1: CENBG/Université de Bordeaux. Route du Solarium, 33175 Gradignan Cedex France,
  • 2: CEA, DEN, DEC/SFER, Centre de Cadarache, F–13108 Saint Paul Lez Durance Cedex, France

Abstract

Under separate effect study of UO2 fuel, the behavior of noble gases Kr and Xe were studied in collaboration with the LLCC / Cadarache and CENBG. The objective is to understand the transport of volatile elements depending on different manufacturing parameters (stoichiometry, sintering, polishing, irradiation).

For this, the samples are prepared at LLCC, and characterized by PAS, RBS and TEM. Then, they are irradiated by Kr or Xe ions at low fluences in order to limit radiation damage and the precipitation phenomena in the material. After that, these samples are analyzed by thermal desorption coupled with high-sensitivity mass spectrometry, which allows to trace back the different transport processes and to determine the diffusion coefficients. A first series of experiments (A. Michel, University of Caen, 2011) was to implant Kr and Xe ions at low fluence (~E 11 at/cm2) and at energies of 250 and 400keV. At these doses, the precipitation of the rare gas in the bubbles is low, and the release is dominated by vacancy diffusion. The measured isotherms clearly show a quick process (burst) superimposed on a slower process linked to the diffusion of noble gases in stoichiometric UO2. An interpretation of this burst is a surface oxidation layer which allows faster diffusion of atoms.

To demonstrate the influence of the air storage time and therefore oxidation, we will present the study of samples that were stored in contact with the air over periods ranging from seconds to year. It appears that the burst is visible when the sample is in contact with air for a minimum period. Diffusion coefficients and the thickness of the oxidized layer could be determined with a macroscopic model and Fick’s law.