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Contenu archivé le 2024-04-15

MECHANISMS AND INTERACTION PHENOMENA INFLUENCING RELEASE IN LOW AND MEDIUM LEVEL WASTE DISPOSAL SYSTEMS (4.123)

Objectif

IMPROVED UNDERSTANDING OF INTERACTION PHENOMENA INFLUENCING THE NEARFIELD IN DISPOSAL SYSTEMS FOR CONDITIONED LOW-AND MEDIUM-LEVEL RADIOACTIVE WASTE IS NECESSARY FOR ADVANCED SAFETY ASSESSMENTS OF SUCH SYSTEMS.

ONE TOPIC IS THE DIFFUSIVE TRANSPORT FROM WASTE THROUGH BARRIERS OF CONCRETE OR CLAY AS INFLUENCED BY E.G. CORROSION PRODUCTS FROM STEEL. CONTAINERS. THE COMPOSITION OF WATER IN EQUILIBRIUM WITH VARIOUS TYPES POSSIBILITY OF CRACK-HEALING IN CONCRETE BARRIERS. THE INFLUENCE OF PORE TYPE DISTRIBUTION ON DIFFUSIVE TRANSPORT THROUGH CONCRETE WILL BE DEMONSTRATED. SANS-MEASUREMENTS ARE USED IN AN ATTEMPT TO FOLLOW THE STRUCTURE OF DEGRADING CONCRETE.

HYGROSCOPIC PROPERTIES OF CEMENTED OR BITUMINIZED WASTE CONTAINING SOLUBLE SALTS MAY LEAD TO RELEASES IF SUCH MATERIALS ARE DISPOSED OF IN THE UNSATURATED ZONE. RELATIONSHIPS BETWEEN RELATIVE HUMIDITY IN THE AIR AND WATER UPTAKE IN THE MATERIALS ARE INVESTIGATED.

SOME BITUMINIZED WASTE PRODUCTS TEND TO SWELL AND MAY THEREBY DAMAGE THE OUTER BARRIERS WHEN EXPOSED TO WATER. PRESSURE BUILD-UP DUE TO THIS MECHANISM WILL BE FOLLOWED. METABOLIC PRODUCTS FROM GROWTH OF MICRO-ORGANISMS ON BITUMEN MAY HAVE INDIRECT INFLUENCE ON SOLUBILITY-CONTROLLED LEACHING AND WILL BE INVESTIGATED. MEASUREMENTS OF FLOW PROPERTIES OF BITUMINIZED WASTE WILL BE INVESTIGATED. MEASUREMENTS OF FLOW PROPERTIES OF BITUMINIZED WASTE WILL BE USED TO DEMONSTRATE AGEING EFFECTS IN THE MATERIALS.
The following investigations were made and results obtained:

Waste product characterisation:
leaching and volume stability of cemented ion exchange resins (wet dry cycling was found to be an important degradation mechanism);
hydroscopic properties of cemented and bituminized radioactive waste (water uptake from the air can be an important release mechanism when waste containing soluble salts are disposed of by shallow land burial);
water uptake and swelling of bitumenised waste including studies on water migration in bitumen membranes and measurements of swelling pressure;
ageing of bitumenised products was demonstrated to result in increasing stiffness of the materials;
nickel ferrocyanide in precipitation sludge was found to be unstable in contact with concrete.

Barrier material properties:
the influence of the pore structure in concrete on the hydraulic or diffusive transport of water and ions through concrete barriers was investigated (the main parameter is the water cement ratio and a theoretical interpretation is given);
healing of cracks in concrete barriers by precipitation of calcium carbonate was demonstrated experimentally and described by a simplified model;
transport of components between 2 thin plates of cement paste with different compositions stored together in water was found to take place at a low rate;
the structure of degraded cement paste was studied using SANS (small angle neutron scattering).

Interaction phenomena:
integral experiments with migration of radioisotopes from cemented waste through barriers made from kaolin, chalk or concrete were made under different external conditions (the results can be used for model validation).
B1. DIFFUSIVE TRANSPORT IN POROUS BARRIERS.
B2. LEACHING COMPARED WITH DIFFUSION THROUGH SLABS.
B3. SELF-HEALING OF CRACKS OR MACRO-PORES IN CONCRETE.
B4. REACTIONS WITH THIN PLATES OF CEMENT PASTE.
B5. SANS-MEASUREMENTS.
B6. VOLUME STABILITY OF CEMENTED ION-EXCHANGE RESINS.
B7. HYGROSCOPIC OF BITUMINIZED OR CEMENTED WASTE.
B8. SWELLING FORCES DUE TO WATER UPTAKE IN BITUMINIZED WASTE.
B9. DIFFUSION THROUGH BITUMEN MEMBRANES.
B10. MICROBIAL DEGRADATION OF BITUMINIZED MATERIALS.
B11. FLOW PROPERTIES OF AGEING BITUMINIZED MATERIALS.

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RISOE NATIONAL LABORATORY
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Adresse
Frederiksborgvej 399
ROSKILDE
Danemark

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