Leaching of Bituminized Waste Products (BWP) by Pure Water: The Contribution of NMR Techniques for the Investigation of
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Leaching of Bituminized Waste Products (BWP) by Pure Water: The Contribution of NMR Techniques for the Investigation of the Porous Layer S. Le Feunteun1, O. Diat1, A. Guillermo2, A. Ledieu 3 and A. Poulesquen3 1
ICSM – UMR 5257, 30207 Bagnols sur Ceze, France CEA Grenoble, INAC/SPrAM – UMR 5819, 38054 Grenoble Cedex 9, France 3 CEA Marcoule, Nuclear Energy Division, DEN/DTCD, 30207 Bagnols sur Ceze, France 2
ABSTRACT The aim of this study is to improve the understanding of the water infiltration within Bituminized Waste Products (BWP) and the associated phenomena such as the development of the porous layer, the matrix swelling or the water uptake kinetics. Two sets of leaching experiments have been performed on synthesized model samples that are constituted by inactive soluble and/or insoluble salts (40% wt) embedded in bitumen. Large samples were used to quantify the water uptake kinetics and to control the macroscopic swelling of the matrixes during experiments. Smaller samples were used to characterize the depth distribution of the infiltrated water and its motion properties by NMR techniques (1H-T1 relaxation times and 1D-NMR imaging). These techniques enabled us to study the influence of the matrix chemical composition on the water advance in depth as a function of the leaching time. Results show that insoluble salts have a significant influence on water transport while soluble salts entail the development of large porosities. Preliminary results obtained with an original method based on the measurement of NMR relaxation times along the water concentration in depth are presented. They illustrate the great potential of the approach to further improve our knowledge on the establishment of the aqueous network. INTRODUCTION In France, a great part of the long life radionuclides of low/intermediate activity that are extracted by insolubilisation treatments of the effluents have been managed by incorporation in bitumen, via an extrusion process. The inventory is consequential today and tends to be stabilized. The most active containers (tens of thousands) should be disposed in a geological storage site. After thousands of years, the interaction of the containers with water can entail some material modifications and hence impair the conditioning of the active elements. Indeed, the infiltration of water within the matrix (water uptake) can induce a swelling of BWP by osmotic pressures and can lead to a release of the embedded radionuclides. Previous studies [1, 2] on the behavior of BWP in contact with water have allowed their authors to propose a model aiming at predicting the water uptake and the salts release according to the proportion of soluble salts and the nature of the leachant. Recent studies [3] based on NMR techniques were launched to refine the phenomenological description of BWP leaching with special attention to the influence of insoluble salts. This paper proposes to extend NMRbased investigations to better characterize the effects of insoluble salts on the development of the aqueous network.
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