Long-Term Behavior of Bituminized Waste: Modelling of Auto-Irradiation and Leaching
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Long-Term Behavior of Bituminized Waste: Modelling of Auto-Irradiation and Leaching P. Chaix1, S. Camaro2, B. Simondi2, P.P. Vistoli2 and V. Blanc3 1 CEA Centre d’Etudes de Saclay, BP11, 91191 Gif sur Yvette cedex, France 2 CEA Centre d’Etudes de Cadarache, 13108 St Paul les Durance, France 3 Cogema, 1 rue des hérons, 78182 St Quentin en Yvelines cedex, France ABSTRACT During interim storage, the main evolution factor of the bituminized wastes is radiolysis under auto-irradiation, while in deep disposal conditions, after radioactive decrease, site resaturation with water, and container corrosion, the main factor of evolution is leaching by water. This paper presents two models, designed to describe respectively radiolytic gas evacuation, and bituminized waste alteration under leaching. The first model is based on the integration of simple descriptions of gas production by radiolysis, gas diffusive transport, bubble nucleation and ripening, and bubble transport under buoyancy and viscosity. The second model is based on simple descriptions of water adsorption and solubilization at the surface, water diffusion into the matrix, water uptake by the most soluble salts, salt grain swelling and alteration of matrix waterproofing, diffusive transport of salts out of the waste. 1.
INTRODUCTION
The chemical compatibility of bitumen with most of reagents used to decontaminate radioactive liquid effluents, its binding capacity, its waterproofing and its easy implementation at low temperatures, have led to the choice of this material for the conditioning of low and medium activity waste in several countries (France, Japan, Belgium, Sweden, Russia…). About 70,000 drums of bituminized waste have been produced in France since 1966, and bituminization is also considered for the future conditioning of low and medium activity waste resulting from effluent processing. The French Atomic Energy Commission and COGEMA conduct research programs on the long term behavior of bituminized waste, both under long term interim storage conditions and under deep geological disposal conditions. Under deep geological disposal conditions, the main point is alteration of the bituminisate by water. Numerous studies have already been devoted to this subject (see e.g. [1,2,3,4]), mainly via extrapolations from experimental tests. Models have also been developed in order to support these extrapolations [5,6]. Section 3 of this paper describes our model, some related experimental results, and an estimation of bituminized waste durability. Under interim storage conditions, an important point is evacuation of the radiolytic gases produced within the waste. In the case of hard bitumen, the gases seem to be released through fractures within the matrix. COGEMA uses soft bitumen that can be processed at lower temperature, so that the gases can be released both through diffusion to the free surface, and through bubble
migration [7]. We propose in Section 4 a model for gas evacuation in soft bitumen, and describe some first results. 2.
LONG TERM BEHAVIOR PHENOME
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