Objective
RADIOACTIVE WASTES DISPOSAL INTO DEEP CRISTALLINE ROCKS REQUIRES TO CARRY OUT IMPORTANT UNDERGROUND WORKS OR GEOLOGICAL INVESTIGATIONS BY THE MEANS OF BOREHOLES WHICH MIGHT INDUCE DIRECT PATHWAY OR SHORT CIRCUITS FOR WATER, BETWEEN REPOSITORY AND GROUND SURFACE. IT IS ESSENTIAL TO USE SPECIFIC TECHNICS AND METHODS ALLOWING THE SEALING OF THESE POTENTIAL PATHWAYS.
AMONG SEVERALL OTHER POSSIBILITIES, CLAY MATERIALS HAVE BEEN CONSIDERED TO FILL THE BOREHOLES AND SHAFTS. ONES OF THESE CLAYS, MONTMORILLONITE, IS WIDELY STUDIED BECAUSE OF ITS QUALITIES : GOOD ADSORBSION TOWARDS RADIONUCLIDES, SWELLING PROPERTIES IN CONTACT WITH WATER.
THE AIM OF THE STUDY, IS TO DETERMINE, IN LABORATORY AND IN SITU, THE BEHAVIOUR OF SUCH A CLAY, USED AS A PLUG IN A BOREHOLE IN CONTACT WITH AN HYDRAULIC FRACTURE, AND TO STUDY THE POSSIBLE EROSION OF SUCH A PLUG SO AS TO BE ABLE TO ESTIMATE THE LONGEVITY OF THE SEALING.
1.1. LABORATORY STUDIES :
1.1.1. AN EXPERIMENTAL EROSION APPARATUS WITH BENTONITE IS USED, THANKS TO A SCALE MODEL SIMULATING A FISSURE. APPROPRIATE TECHNICS ARE CARRIED OUT FOR THE DETERMINATION OF THE ERODED CLAY MASS BY A WATER FLOW INSIDE THE MODEL FISSURE.
TESTS WILL BE PERFORMED WITH TWO OR THREE TYPES OF REPRESENTATIVE CLAYS, I.E. THOSE ARE PRESENTELY INVESTIGATED AND COULD BE USED AS SEALING MATERIAL IN A REAL REPOSITORY :
- THE NA BENTONITE "GREEN BOND", FROM WYOMING (USA) (EQUIVALENT TO THE MX 80).
- ONE OR TWO BENTONITES EXTRACTED IN FRANCE.
THE WATERS WHICH WILL BE USED, WILL BE OF DIFFERENT TYPES, EITHER NATURAL (FROM CRISTALLINE FORMATIONS), OR RECONSTITUTED WITH DIFFERENT PERCENTAGES OF RELEVANT IONS.
1.1.2. THE BEHAVIOUR STUDY OF THIS SEALING MATERIAL IS COMPLETED WITH DIRECT OBSERVATIONS OF THE CLAY IN THE FISSURE, WITH GRANULOMETRIC ANALYSIS, AND MINERALOGIC X RAYS ANALYSIS, AND SCANING ELECTRON MICROSCOPE.
WE INTEND TO ASCERTAIN THE INFLUENCE OF THE NATURE AND VELOCITY OF THE WATER FLOW. THE EXPERIMENTAL PARAMETERS WILL BE THEN IONS CONCENTRATIONS CARACTERISTICS AND WATER FLOW RATES.
1.2. IN SITU STUDY :
A FRACTURE WITH A SIGNIFICATIVE WATER FLOW, IN A WELL KNOWN DIRECTION, WILL BE SELECTED, IN SITU, IN A MINE OR QUARRY. THE GEOMETRIC POSITION OF THIS FRACTURE WILL BE IDENTIFIED THANKS TO BOREHOLES, USED THEMSELVES FOR HYDRAULIC STUDIES AND SEALED WITH BENTONITE AT THE FRACTURE LEVEL.
THE RESULTING WATER FLOW WILL BE CHARACTERISED BY THE MEANS OF TRACERS, WATER FLOW RATES MEASUREMENTS AT THE FREE SURFACE OF THE DRIFT OR ON THE SURFACE OF THE QUARRY.
AFTER THE EXPERIMENTATION, FOR A TIME DEPENDING UPON THE AMOUNT OF THE RECOVERED CLAY MASS, AN OVER CORING OPERATION WILL BE DONE, PERPENDICULAR TO THE FRACTURE PLANE, BOTH AT THE PLUG LEVEL, AND AROUND.
MODIFICATIONS OF THE CLAY PLUG WILL BE ANALYSED IN THE LABORATORY, USING THE SAME TECHNICS AS THOSE FOR THE SCALE MODEL TESTS.
THE CLAY, USED FOR THIS TEST, WILL BE ONE OF THOSE USED IN THE LABORATORY.
1.3 NUMERICAL MODEL :
THE EVALUATION OF THE TRANSPORTED CLAY MASS WILL BE ANALYSED AND QUANTIFIED BOTH FOR THE LABORATORY AND IN SITU EXPERIMENTATIONS.
THE RESULTS WILL BE COMPARED, AND IT IS INTENTED TO ESTABLISH A CORRELATION BETWEEN THE TWO CONFIGURATION.
THIS MUST LEAD US TO PROVIDE A NUMERICAL MODEL CONCERNING THE EROSION BEHAVIOUR AND THE DURABILITY OF SUCH BENTONITE PLUGS IN BOREHOLES IN CONTACT WITH WATER.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- engineering and technology other engineering and technologies nuclear engineering nuclear waste management
- social sciences psychology behavioural psychology
- engineering and technology environmental engineering waste management
- natural sciences physical sciences optics microscopy
- natural sciences chemical sciences nuclear chemistry radiation chemistry
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Coordinator
92265 Fontenay-aux-Roses
France
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