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STUDY OF THE MIGRATION OF U, TH AND REE IN A INTRAGRANITIC URANIUM DEPOSIT

Objective

THE INTRAGRANITIC URANIUM DEPOSIT OF THE JALERYS (GRANITE DE GRURY-MORVAN-FRANCE) IS CONSIDERED IN THIS STUDY AS A NATURAL ANALOGUE OF A HIGH LEVEL RADIOACTIVE WASTE REPOSITORY REALIZED IN A SIMILAR GEOLOGICAL FORMATION. THE PHYSICO-CHEMICAL PROCESSES OF TRANSPORT FOR SOME TRACE ELEMENTS OF INTEREST ARE BEING INVESTIGATED MAINLY IN THE NEAR FIELD.

MORE SPECIFICALLY, THE AIMS OF THIS INVESTIGATION ARE :

- TO OBTAIN INFORMATION ON THE ELEMENTAL MOBILISATIONS OF U, TH, AND REE THROUGH SURROUNDING ARGILLACEOUS AND GRANITIC BARRIERS FROM A PARTICULARLY HIGHLY CONCENTRATED SOURCE TERM,

- TO DETERMINE THE GEOCHEMICAL MECHANISMS INVOLVED DURING THE TRANSPORT OF RADIONUCLIDES AND TO EVALUATE, AS FAR AS POSSIBLE, THEIR MIGRATION RATES,

- TO ESTABLISH THE RELATIONSHIP BETWEEN EXPERIMENTAL DATA ON THE GEOCHEMICAL BEHAVIOUR OF TRANSURANIC ELEMENTS AND THOSE OF THEIR "NATURAL ANALOGUES"

- TO CHARACTERIZE, ON THE BASIS OF ALL THE AVAILABLE DATA, THE RETENTION CAPACITY OF A REPOSITORY, WHICH RELIES EITHER ON THE PROPERTIES OF THE NEAR FIELD ONLY OR ON THOSE OF THE OVERALL GEOLOGICAL FORMATION,

- FINALLY, TO MODEL THE INTERACTION BETWEEN THE GRANITE, THE FLUID AND THE ORE BODY BY MEANS OF A GEOCHEMICAL CODE (EQ3/6)

A COLLABORATION WITH COGEMA AND CREGU IS PLANNED ON THIS SUBJECT.

1. SAMPLING OF THE GRURY GRANITE INTRUDED BY URANIFEROUS MINERALIZATIONS (THE JALERYS MINE AND THE JACQUOT OPEN QUARRY)
1.1 SAMPLES ARE TAKEN AT REGULAR INTERVALS ALONG A DIRECTION ROUGHLY PERPENDICULAR TO THE VEIN, FROM THE MINERALIZED BODY TO THE FRESH GRANITE.

2. MINERALOGICAL STUDIES AT THE LABORATORY
2.1 PETROGRAPHICAL AND MINERALOGICAL WORKS ON PRIMARY AND SECONDARY PARAGENESES, SPECIALLY ON U-TH-REE-RICH ONES, WITH OPTICAL AND ELECTRON MICROSCOPY (SCANNING AND TRANSMISSION COUPLED WITH X-RAY ANALYSIS) AS WELL AS FISSION TRACK MICROMAPPING.
2.2 STUDY OF THE GEOCHEMICAL PROPERTIES OF THE GRANITE AND OF THEIR EVOLUTION DURING ALTERATION (MAJOR AND TRACE ELEMENTS ANALYSIS BY ICP AND NEUTRON ACTIVATION ANALYSIS)
2.3 DETERMINATION OF THE PHYSICO-CHEMICAL PROPERTIES OF FLUIDS RESPONSIBLE FOR THE ALTERATION BY THE STUDY OF FLUID INCLUSIONS (MICROTHERMOMETRY, RAMAN MICROPROBE).
2.4 EVALUATION OF TEMPERATURES ACTIVE DURING THE FUNCTIONING OF THE SYSTEM BY THE STUDY OF THE THERMAL ANNEALING OF FISSION TRACKS REGISTERED IN APPROPRIATE MINERALS.

3. ISOTOPIC STUDIES AT THE LABORATORY
3.1 STUDY OF RADIONUCLIDE MOBILIZATIONS USING URANIUM AND THORIUM-SERIES DISEQUILIBRIA FOR DATING THE LAST OPENING OF THE SYSTEM (ALPHA AND GAMMA SPECTROMETRIES, ION MICROPRODE).
3.2 DATING OF THE ALTERATION MINERALS, WHENEVER FEASIBLE
3.3 EVALUATION OF THE SORPTION EFFICIENCIES FOR U, TH AND REE OF GRANITE-FORMING MINERALS FOR VARIOUS DEGREES OF ALTERATION CORRESPONDING TO DIFFERENT SURFACE STATES (RUTHERFORD BACKSCATTERING, SPECIFIC NUCLEAR REACTION ANALYSIS)

4. MODELLING
4.1 MODELLING OF INTERACTION BETWEEN SOLID/SOLUTION BY MEANS OF THE EQ3/6 GEOCHEMICAL CODE AND COMPARISON WITH DATA OF THE NATURAL SYSTEM.
4.2 SIMULATION WITH THIS CODE OF THE EVOLUTION WITH TIME OF HIGH LEVEL RADIOACTIVE WASTE INTRAGRANITIC REPOSITORY.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Commissariat à l'Energie Atomique (CEA)
Address
Centre D'études De Fontenay-aux-roses
92265 Fontenay-aux-roses
France