This study aims at better understanding the chemical and physico-chemical phenomena of uranium dioxide dissolution reactions in nitric acid media in the Purex process, which separates the reusable materials and the final wastes of the spent nuclear fuels. | A method for phenomenological and chemical kinetics study of autocatalytic reactive dissolution by optical microscopy. The case of uranium dioxide dissolution in nitric acid media EPJ Nuclear Sci. Technol. 4 2 2018 Nuclear Sciences P. Marc et al. published by EDP Sciences 2018 amp Technologies https epjn 2017026 olm Available online at https REGULAR ARTICLE A method for phenomenological and chemical kinetics study of autocatalytic reactive dissolution by optical microscopy. The case of uranium dioxide dissolution in nitric acid media Philippe Marc1 Alastair Magnaldo1 Jérémy Godard1 and Éric Schaer2 1 CEA Nuclear Energy Division Research Department on Mining and Fuel Recycling Processes Research Service for Dissolution and Separation Processes Laboratory of Dissolution Studies 30207 Bagnols-sur-Cèze France 2 Laboratoire Réactions et Génie des Procédés UMR CNRS 7274 University of Lorraine 54001 Nancy France Received 14 December 2016 Received in final form 4 October 2017 Accepted 10 October 2017 Abstract. Dissolution is a milestone of the head-end of hydrometallurgical processes as the stabilization rates of the chemical elements determine the process performance and hold-up. This study aims at better understanding the chemical and physico-chemical phenomena of uranium dioxide dissolution reactions in nitric acid media in the Purex process which separates the reusable materials and the final wastes of the spent nuclear fuels. It has been documented that the attack of sintering-manufactured uranium dioxide solids occurs through preferential attack sites which leads to the development of cracks in the solids. Optical microscopy observations show that in some cases the development of these cracks leads to the solid cleavage. It is shown here that the dissolution of the detached fragments is much slower than the process of the complete cleavage of the solid and occurs with no disturbing phenomena like gas bubbling. This fact has motivated the
