Fracture properties characterization of nuclear fuel using micro-cantilever bending

International audienc

A complementary approach to estimate the internal pressure of fission gas bubbles by SEM-SIMS-EPMA in irradiated nuclear fuels

International audienceThe behaviour of gases produced by fission is of great importance for nuclear fuel in operation. Within this context, a decade ago, a general method for the characterisation of the fission gas including gas bubbles in an irradiated UO$_2$ nuclear fuel was developed and applied to determine the bubbles internal pressure. The method consists in the determination of the pressure, over a large population of bubbles, using three techniques: SEM, EPMA and SIMS. In this paper, a complementary approach using the information given by the same techniques is performed on an isolated bubble under the surface and is aiming for a better accuracy compared to the more general measurement of gas content. SEM and EPMA enable the detection of a bubble filled with xenon under the surface. SIMS enables the detection of the gas filling the bubble. The quantification is achieved using the EPMA data as reference at positions where no or nearly no bubbles are detected

Micro-mécanique sur combustible irradié 2 méthodes complémentaires nano-indentation et micro-essais

National audienc

fib/sem examination of a high burn-up uo2 in the center of the pellet

International audienceFIB/SEM examinations were conducted in the central part of a 73 GWd/tU UO2 fuel. They showed the formation of sub-domains within the initial grains. Most of the fission gas bubbles were found to be situated on the boundaries. Their shapes were far from spherical and far from lenticular. No interlinked bubble lattice was found. These observations enlighten previous unexplained observations. They plead for a revision of the classical description of the fission gas release mechanisms for the central part of the high burn-up UO2. Yet, complementary detailed observations are needed to better understand the mechanisms involved

Focused ion beam–scanning electron microscope examination of high burn-up UO2 in the center of a pellet

Focused ion beam–scanning electron microscope and electron backscattered diffraction examinations were conducted in the center of a 73 GWd/tU UO2 fuel. They showed the formation of subdomains within the initial grains. The local crystal orientations in these domains were close to that of the original grain. Most of the fission gas bubbles were located on the boundaries. Their shapes were far from spherical and far from lenticular. No interlinked bubble network was found. These observations shed light on previous unexplained observations. They plead for a revision of the classical description of fission gas release mechanisms for the center of high burn-up UO2. Yet, complementary detailed observations are needed to better understand the mechanisms involved. Keywords: Electron BackScattered Diffraction, Fission Gas Bubbles, Fission Gas Release, Focused Ion Beam–Scanning Electron Microscope, Grain, High Burn-Up, UO

Analyse 3D par MEB-FIB de la porosite d'un combustible irradie

International audienceC'est un poste

analyse 3D par MEB-FIB de la porosite d'un combustible irradie

International audienceC'est un poste

Caractérisation a l’échelle locale des propriétés mécaniques en rupture du matériau modèle du combustible irradié

International audienc

A new look on irradiated fuels at the CEA Cadarache

International audienc

New methods to estimate the internal pressure of xenon in fission bubbles using SEM-EPMA-SIMS and EBSD in irradiated fuels

International audienceDuring irradiation, in Pressurized Water Reactors, gaseous fission products are created (xenon and krypton) in the fuel pellets and form bubbles distributed heterogeneously. During fast heating in an accident situation, the internal pressure of nanoscale bubbles increases, producing stresses at grain boundaries. As part of a thesis in collaboration between the CEA Cadarache and MSMP Laboratory (Arts et Metiers ParisTech, Aix-en-Provence), a research program has been undertaken to develop new methods to evaluate the internal pressure of fission gas bubbles in irradiated fuels. The first experimental method was developed for the characterization of a large number of pressurized bubbles in an irradiated UO$_2$ nuclear fuel using SIMS, EPMA and SEM. The method is now performed by selecting with EPMA an area where few pressurized bubbles are present under the sample surface. The SIMS, Secondary Ion Mass Spectrometry, is carried out to open these bubbles and collect the amount of xenon in both the matrix and the bubbles. The EPMA, enables the calibration of the SIMS in order to provide quantitative results. SEM, provides information on the number and shape of the bubbles. The quantification of xenon in the bubbles by SIMS coupled to their size measured by SEM make it possible to obtain the atomic volume. Through adapted equations of state, the pressure of xenon in these bubbles is then estimated.The second method consists in the measurement of the local deformation around a bubble by Electron Back Scatter Diffraction (EBSD). The diffraction patterns are analyzed by cross-correlation to obtain the elastic deformation and rotation tensors. In parallel, a mechanical model by finite elements is developed to determine the bubble's internal pressure. At this point, the method is calibrated with a mechanical test by four points bending of a monocrystal silicon beam. The test results are compared to a relevant mechanical model.These experimental data will provide new points of validation for the models to predict the behavior of the fuel during nominal irradiation and accidental situations