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

Poster 3.1: Incorporation and migration mechanisms of Molybdenum in the stoichiometric and hyper-stoichiometric UO2.

Lola Sarrasin1, N. Moncoffre1, Y. Pipon1,2, C. Gaillard1, N. BĂ©rerd1,2, R. Ducher3, R. Dubourg3, L. Raimbault4, P. Simon5,6, L. Vieille7
  • 1: Université de Lyon, CNRS/IN2P3, Université Lyon 1, Institut de Physique Nucléaire de Lyon, 4 rue Enrico Fermi, F–69622 Villeurbanne Cedex, France
  • 2: Université de Lyon, Université Lyon 1, IUT Lyon 1, 43 bd du 11 novembre 1918, 69 622 Villeurbanne Cedex, France
  • 3: Institut de Radioprotection et de Sureté Nucléaire, BP3 13115 St. Paul Lez-Durance Cedex, France
  • 4: Ecole des Mines de Paris, Centre de Géosciences, 35 rue Saint Honoré, F–77305 Fontainebleau cedex, France
  • 5: CNRS UPR3079 CEMHTI, F–45071 Orléans 2, France
  • 6: Université d’Orléans, F–45067 Orléans 2, France
  • 7: LPMG, Ecole Nationale Supérieure des Mines de St-Etienne, Centre SPIN, Equipe PROCESS, 158, Cours Fauriel, 42023 St-Etienne Cedex 2, France

Abstract

Since the Fukushima accident, an increased attention has been paid to models used for evaluating the radiological impact of radionuclides (RN) potentially released to the environment. During an accident in a Pressurized Water Reactor (PWR), oxidation of the nuclear fuel likely occurs, causing an increase in the oxygen potential of UO2. It leads to the formation of UO2+x which impacts the local microstructure of the fuel and the RN transport properties [1]. A better understanding of the chemical and physical mechanisms responsible for the RN release in accidental conditions is then necessary.

Among fission products (FP), Molybdenum (Mo) is one of the most abundant with a fission yield equivalent to that of Xe. Moreover, it is poorly soluble into UO2 and can precipitate either as an oxide or as a metallic phase. Especially Mo is known to have an indirect impact on the radiotoxic species speciation as it can form complexes with other elements, like the CsMoO4 complex, thus changing the mechanisms and amounts of released FP [2,3]. In addition, Mo has a very important role in the fuel chemistry and is known to influence the oxygen potential of UO2 [4,5].

This work studies the incorporation mechanisms of Mo and its diffusion in a hyper-stoichiometric UO2 matrix, when subjected to high temperatures and/or irradiation. The aim is to determine the thermal (and athermal if possible) diffusion coefficient of Mo by coupling an experimental approach with DFT and molecular dynamics calculations. Depleted UO2 pellets are oxidized up to a O/U ratio equal to 2.1, using thermal annealing under a controlled oxidizing atmosphere. They are implanted with a stable isotope of Molybdenum (95Mo), and annealed and/or irradiated. The 95Mo migration in the UO2.1 matrix is followed by SIMS. Matrix microstructural modifications are characterized by XRD and Raman spectroscopy, and the superficial UO2 stoichiometry is determined by Nuclear Reaction Analysis. A comparison with first DFT results is proposed.

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