IN ORDER TO GUARANTEE THE SAFETY OF UNDERGROUND DISPOSAL, COMING FROM SPENT FUEL REPROCESSING, ENGINEERED BARRIERS WILL BE IMPLEMENTED AS BACKFILL MATERIALS IN GALERIES AND ACCESS SHAFTS AND AS BUFFER MATERIALS BETWEEN THE HOST MEDIUM AND THE WASTE PACKAGES. ONE OF THE FIRST REQUIREMENTS FOR ENGINEERED BARRIERS IS TO MINIMIZE WATER AND CHEMICAL SPECIES TRANSFER.
THE MATERIALS BEING CONSIDERED ARE ESSENTIALLY SWELLING CLAYS, IN PARTICULAR CALCIUM SMECTITE CLAYS COMING FROM FRENCH DEPOSITS.
THE LONG TERM STABILITY OF CLAY MATERIALS, AS A FUNCTION OF TEMPERATURE, WATER SALINITY AND IONIC SPECIES IN SOLUTION, HAS TO BE EVALUATED FOR THE DIFFERENT TYPES OF HOST ROCK (GRANITE, CLAY AND SALT).
THE FINAL OBJECTIVE OF THE PROGRAMME IS TO TAKE INTO ACCOUNT MATERIAL PROPERTY MODIFICATION WITH TIME IN THE CHOICE AND DESIGN OF THE ENGINEERED BARRIERS USED FOR BOTH VITRIFIED AND T.R.U. WASTE DISPOSAL.
The materials being considered are essentially swelling clays, in particular calcium smectite clays coming from French deposits, and hydraulic binders, more particularly a ternary cement. Vitrified waste disposal in granite is taken as the most constraining scenario as far as an engineered barrier is concerned. The clay buffer material is placed between the packages and the host rock. The main properties which are determined are directly related to the engineered barrier requirements: thermal conductivity, hydraulic conductivity, swelling pressure and swelling capacity. Moreover results are obtained on temperature effects on clay microstructure and properties, in both cases with and without water intake.
The concrete durability with regard to clay pore water attack is evaluated taking into account previous results.
B1. MATERIAL CHOICE AND EXPERIMENTAL CONDITION DEFINITION.
B2. VITRIFIED WASTE DISPOSAL : DEFINITION AND CHARACTERIZATION OF CLAY BARRIERS.
B3. VITRIFIED WASTE DISPOSAL : TEMPERATURE EFFECT ON CLAY MATERIAL PROPERTIES.
B4. VITRIFIED WASTE DISPOSAL : HYDROTHERMAL DEGRADATION OF CLAY MATERIALS.
B5. T.R.U. WASTE DISPOSAL : STUDY OF CONCRETE DURABILITY.