Nature and Effect of the Alteration Layer During Nuclear Waste Glass Dissolution
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Nature and Effect of the Alteration Layer During Nuclear Waste Glass Dissolution
A. Gauthier,1,3 P. Le Coustumer, 2 and J-H. Thomassin3 1 UMR CNRS PBDS, USTL, UFR Sciences de la Terre, 59655 Villeneuve d'Ascq Cedex France 2 CDGA, Université Bordeaux1, Av. des facultés, 33405 Talence cedex, France 3 UMR CNRS 6532, ESIP, LMGE, 40, av. du Recteur Pineau 86022 Poitiers Cedex, France
ABSTRACT The goal of this study is to understand the role of the interface developed during R7T7 glass alteration. This glass has been leached in two different aqueous media (pure water, silica rich water and phosphorous rich water). The lixiviation tests have been optimized to assess the role of the alteration layer developed on the surface of the glass. The solution and the solid have been characterized by ICP-MS and TEM/X-EDS respectively. The results put in evidence that a complex alteration layer is formed. Its texture, structure and chemistry are discussed with respect to the evolution of the solution during the tests. The alteration layer is always present on the surface of the glass and is considered to control (at short time) diffusion of the different species through the layer. Further study must be undertaken to assess the evolution and the stability of the interface for longer time periods. INTRODUCTION High level radioactive waste produced by reprocessing irradiated nuclear fuel is isolated from the human environment by vitrification [1, 2]. Management and stabilization of nuclear waste is a big issue for the community since concentrated radionuclides must be trapped for long term storage. The French national radioactive waste management agency (ANDRA) is currently leading research on geological sites for their ability to store vitrified waste. For a better understanding of the long term behavior of these materials and the evaluation of the potential release of hazardous species into the environment, risk assessment studies require evaluation methodologies based on experimental predictive models [3, 4]. The objective is to specify the source term of the French R7T7 light water reference glass; i.e. to determi ne the release kinetics of the elements incorporated into the matrix according to the physical and chemical parameters of the site (pH, temperature, solution chemistry, environmental materials). In order to understand the mechanism responsible for the diffusion-limiting properties of a potential protective layer, some experiments were conducted. Thus, the validity of some experimental predictive models may be put in balance. This study tries to overcome those problems. The data are also discussed with TEM results of altered solid material which demonstrate the formation of an altered layer on the surface of the glassy matrix and its role in the trapping mechanisms of the heavy elements such as the lanthanides.
JJ13.4.1
MATERIAL AND METHODS Alteration tests were conducted on R7T7 reference material. This glass is an inactive analog of the radioactive waste storage glass, and was obtained by fusion at 1400°C of various o
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