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THE PURPOSE IS TO VALIDATE BY MEANS OF FIELD STUDIES THE PREVIOUSLY DEVELOPED MODEL OF RADON-222 TRANSFER IN A FRACTURED MEDIUM.
THE EXPERIMENTAL VALIDATION WOULD BE CARRIED OUT IN TWO FRACTURED MEDIA, ONE EXTREMELY PERMEABLE, WHICH WOULD MAKE IT POSSIBLE TO DEMONSTRATE THE FEASIBILITY OF CONTROLLING RADON SOURCES, AND THE OTHER OF LOW PERMEABILITY.
THE FIRST MEDIUM IS COMPRISED OF EXTENSIVELY WEATHERED SCHIST OF HIGH PERMEABILITY, DESATURATED BY WORK AT LOWER LEVELS. THE LAYERS OF RADON-LADEN AIR ARE DRAINED BY MEANS OF A PUMP WITH A DELIVERY RATE OF 2M.3 PER S WHICH PLACES THE ENTIRE ROCK MASS UNDER DEPRESSION. IT WAS OBSERVED THAT THE PRIMARY AIR OF THE GALLERIES WAS SUCKED IN BY THE WALLS.
THE PURPOSE OF THE EXPERIMENT IS TO DETERMINE THE TRANSIT TIME OF THE AIR BETWEEN THE DIFFERENT SECTIONS OF THE GALLERIES AND THE PUMP. THE TECHNIQUE TO BE USED WILL BE HELIUM TRACING, MEASURED BY MEANS OF A FIELD MASS SPECTROMETER. THE PATHWAYS FOLLOWED BY THE AIR WILL BE ASCERTAINED IN THIS WAY. FROM THE KNOWN URANIUM-238 CONTENT OF THE ENVELOPING ROCKS AND THE DATA ON RADON-222 EMISSION RATES, THE VARIATION IN THE RADON CONTENT OF THE AIR WILL BE CALCULATED. CHECKS WILL BE CARRIED OUT TO DETERMINE WHETHER THE FLOW RATE OF THE RADON COLLECTED BY THE PUMP CORRESPONDS TO THE CALCULATED EMISSION.
THE SECOND MEDIUM COMPRISES NON-URANIUM-BEARING SATURATED HEALTHY GRANITES OF LOW POROSITY AND PERMEABILITY. THE WORK IS TO BE CARRIED OUT IN A SECTION OF HORIZONTAL GALLERY WHICH HAS BEEN SPECIALLY EQUIPPED, SINCE IT FORMS THE LABORATOIRE D'ETUDE METHODOLOGIQUES ET INSTRUMENTALES WHICH OUR DEPARTMENT OPERATES UNDER ITS STUDY PROGRAMME ON THE STORAGE OF HIGH ACTIVITY WASTE IN GEOLOGICAL FORMATIONS. A CONSIDERABLE AMOUNT OF INFORMATION CAN THUS BE OBTAINED, IN PARTICULAR ON THE WATER (BRGM). SIMULTANEOUSLY, THE WATER CIRCULATION IN THIS FRACTURED MEDIUM IS MODELLED ON THE BASIS OF THE EXPERIMENTAL STUDY OF THE FRACTURE PATTERNS.
BY USING THE DATA ON THE FLOW RATE OF THE WATER INFLOWS AND MEASUREMENTS OF RADON-222 CONCENTRATION IN THIS WATER, IT WILL BE POSSIBLE TO PREDICT WHAT THE RADON-222 INFLOWS WILL BE. WITH INSTRUMENTS FOR THE CONTINUOUS MEASUREMENTS OF RADON CONCENTRATION (LARGE VOLUME DIFFERENTIAL IONIZATION CHAMBERS) WE WILL BE ABLE TO MEASURE WITH REQUISITE PRECISION THE LOW PARIETAL FLOW RATES IN THIS GALLERY AND THUS TO VALIDATE THE HYPOTHESIS ACCORDING TO WHICH CIRCULATION OF WATER IN SUCH EXPERIMENTAL CONDITIONS BRINGS THE ALL RADON-222 WHICH COMES IN THE ATMOSPHERE OF THE GALLERY.
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