Self-irradiation effects on the structural properties of the MIMAS type of nuclear fuels

Orhun Kahraman1,2,3

1CEA, DES, ISEC, DMRC, Univ. Montpellier, Marcoule, France; 2CNRS UPR 3079 CEMHTI, Université Orléans, 45071 Orléans, France; 3Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, 38000 Grenoble, France.


Mixed (U,Pu)O2 oxides (MOX) are widely used in the nuclear industry. One important aspect of these materials is the self-irradiation damage produced by the α-decay of plutonium isotopes and the subsequent lattice swelling. Although this swelling and its eventual saturation is described in the literature [1], the identification and description of the associated point defects, their stability and their consequences on the microstructure are yet to be revealed. The purpose of our work is thus to acquire information about the defect formation in the (U,Pu)O2 microstructure as a result of the self-irradiation damage cascades through continuous investigation of the sample microstructure.

The selected MOX fuel sample was fabricated using the MIMAS process and has an overall Pu/(U+Pu) content of about 10 wt.% while having an oxygen stoichiometry O/M (M=(U+Pu)) ratio equal to 2.00. The initial plutonium isotopy exhibits a relatively rich 238Pu fraction with 2.4 wt.% (238Pu /(Pu total). As a consequence of the synthesis process, 3 different phases are observed with different Pu contents using EPMA: UO2 agglomerates which contains almost no plutonium, the plutonium-rich agglomerates with a Pu/(U+Pu) content close to 30 wt%, and a third phase located between the two others’ agglomerates and having an intermediate Pu content. These phases are available in the microstructure in different sizes with an order of magnitude of 10-50 µm for the UO2 phase, 10-20 µm for the intermediate phase and 20-100 µm for the Pu-rich phase[2]. Thanks to the T2g line shift as a function of Pu content, these 3 phases are easily identified using µ-Raman imaging and their corresponding damage evolutions are individually studied in this work all within one sample. The sample was first thermally treated at 1200°C to start from a (virtually) defect-free microstructure without modifying the O/M ratio of 2.00. Within the scope of the study, the evolution of the lattice parameter is being recorded with continuous XRD experiments to acquire a spatially averaged information, while µ-Raman microscopy is employed to probe the sample at a local scale (µm).

The preliminary XRD results shows that there is not yet an observable increase in the lattice parameter of the UO2 agglomerates whereas the increase of lattice parameter is observable and rather faster in the phases of higher Pu contents. As of the second part of the study, the continuous Raman microscopy imaging measurements are being pursued upon the 3 phases on the sample to obtain further information on defect creation. The present finding shows that the T2g Raman band frequency is not influenced by the self-irradiation [3], whereas the width of the band exhibits a change due to the self-irradiation effect [4]. Finally, recent studies in the literature shows that the defect-related bands U1, T1u (LO), U3 as well as the second order Raman active band (2 T1u (LO)) give information related to the defects taking place in the microstructure upon self-irradiation.

Event Timeslots (1)

Tuesday – 14th September 2021
Orhun Kahraman