Microchim Acta 155, 183–187 (2006) DOI 10.1007/s00604-006-0540-y Original Paper Fission Gas Bubbles Characterisation in Irradiated UO 2 Fuel by SEM, EPMA and SIMS Je ´ro ˆme Lamontagne à , Lionel Desgranges, Christophe Valot, Jean Noirot, Thierry Blay, Ingrid Roure, and Bertrand Pasquet Commissariat  a l’Energie Atomique, Centre de Cadarache, DEN=DEC=SA3C=L2EC, B^ at 316, F-13108 St Paul Lez Durance, Cedex, France Received May 26, 2005; accepted October 31, 2005; published online April 18, 2006 # Springer-Verlag 2006 Abstract. The behaviour of gases produced by fission is of great importance for nuclear fuel operation. Within this context, an experimental method for the characterisation of the fission gas including gas bub- bles in an irradiated UO 2 nuclear fuel was developed in our laboratory using SIMS, EPMA and SEM results. SIMS and EPMA have been used to measure the radial distribution of xenon and SEM gives information on bubble formation across the fuel pellet radius. Using SIMS, xenon concentration can be determined in the matrix and in the bubbles. A quantification method, allowing the determination of the total inventory of xenon, is proposed and qualified with EPMA results. It is concluded that the complementary micro-analytical techniques SIMS, EPMA and SEM are very powerful tools for the characterisation of the fission gas bubbles in irradiated nuclear fuel. Key words: SEM; EPMA; SIMS; UO 2 ; xenon. In the strategy for extending the burn-up of Pressur- ized Water Reactor (PWR) fuels, a matter of concern remains the behaviour of fission gases. They are released in the free volume and they impact the inter- nal pressure of the fuel rod, the fuel swelling and the fuel behaviour during incidental or accidental events. For two decades, Electron Probe Micro Analysis (EPMA) and Scanning Electron Microscope (SEM) methods have been applied to study this fission gas behaviour on polished cross-sections of irradiated fuel pellets. SEM allows to study UO 2 microstructure changes across the fuel pellet radius and from EPMA measurement the radial distribution of the fission pro- ducts in the UO 2 fuel matrix is determined [1, 2]. This last method is limited by the fact that the EPMA analysis, only involves a layer at the sample surface thinner than 1 mm. The amount of fission gas in bub- bles opened by the sample preparation is not negligi- ble as soon as the bubbles are bigger than about 0.1 mm [3]. So there is a lack of detection of the gas from these bubbles [4, 5]. In order to improve the detection of xenon in irra- diated fuels some experiments have been conducted with the CEA newly installed shielded Secondary Ions Mass Spectroscopy (SIMS) [6–8]. In a previous paper, it was showed that xenon can be detected both in bubbles and in solid solution in the UO 2 matrix of an irradiated nuclear fuel [9]. In this paper, a meth- odology to characterize the total inventory of xenon along the radius of an irradiated nuclear fuel pellet is proposed using three complementary micro-analysis techniques. à Author for correspondence. E-mail: jerome.lamontagne@ cea.fr