ALTHOUGH THE EFFECTS OF PHYSICAL PARAMETERS (TEMPERATURE, PH, ETC.) ON THE ALTERATION OF NUCLEAR WASTE GLASSES IN PURE WATER HAVE BEEN WIDELY INVESTIGATED, INTERACTIONS BETWEEN THE GLASS AND VARIOUS MATERIALS LIABLE TO BE PRESENT IN A GEOLOGICAL REPOSITORY ARE RELATIVELY LITTLE KNOWN. THE ENVIRONMENTAL MATERIALS APPEAR TO AFFECT NOT ONLY THE BULK GLASS CORROSION RATE BUT ALSO THE ACTINIDE LEACHING BEHAVIOUR.
THE OBJECTIVE OF THIS PROGRAMME IS TO INVESTIGATE THE ALTERATION OF RADIOACTIVE SON 68 18 17 L1C2A2Z1 GLASS SPECIMENS AND THE CHARACTERISTICS OF RADIONUCLIDE RELEASE IN THE PRESENCE OF ENVIRONMENTAL MATERIALS FROM THE ENGINEERED BARRIER OR THE HOST ROCK. PARAMETER STUDIES WILL BE CONDUCTED TO DETERMINE WHETHER THE REPOSITORY ENVIRONMENTAL MATERIALS HAVE A SIGNIFICANT EFFECT ON ACTINIDE CONTAINMENT IN THE GLASS. INTEGRAL EXPERIMENTS WILL BE CONDUCTED TO COMPARE INTERACTIONS (GLASS CORROSION RATE, RADIONUCLIDE RELEASE RATE) INVOLVING BOTH RADIOACTIVE (ALPHA, BETA, GAMMA) AND INACTIVE GLASS WITH THREE TYPES OF HOST MATERIALS: GRANITE, SALT AND CLAY.
THE SECOND PART OF THIS PROGRAMME WILL BE CARRIED OUT JOINTLY WITH THE UNIVERSITY OF BORDEAUX, AND CONCERNS THE DETECTION OF IRRADIATION DAMAGE IN GLASS BY THERMOLUMINESCENCE (TL) WITH THE INTENTION OF REVEALING AN IRRADIATION DAMAGE SATURATION PHENOMENON AT A STRUCTURAL LEVEL.
R7T7 glass doped with neptunium-237 and plutonium-239 was leached in contact with 7 different environmental materials: smectite, illite, bentonite, sand, granite, Boom clay and French salt. Theinteraction test results confirm the significant role of these materials in glass alteration at 90 C as previously observed with nonradioactive glass.
An irradiation damage model was developed for silicate glass, and extended to nuclear glass formulations. A specific thermoluminescence device was implemented experimentally, and an actinide doped glass fabrication process was developed and qualified.
R7T7 glass doped with neptunium-237 and plutonium-239 was leached in contact with 7 different environmental materials: smectite, illite, bentonite, sand, granite, Boom clay and French salt. The corrosion test results confirmed the significant role of these materials in glass alteration. The best results were obtained with bentonite, which not only limited glass corrosion by supplying silicon to the solution, but also reduced the quantity of actinides in solution by fixing them on clay folia. Granite and sand did not result in increased corrosion compared with double distilled water: the actinide retention factor in the alteration film formed in contact with these materials was not lower than in double distilled water, and they appear better suited for fixing plutonium-239 and americium-241. The poorest results were obtained with Boom clay, not only because of increased glass corrosion (this clay consumes silicon, and thus delays the rise to saturation conditions) but also because of the presence of humic acids and organic compounds that lead to the formation of complexes maintaining a large fraction of the actinides in solution. Integral TAV tests showed that glass is only slightly altered in salt and granite media provided they are not implemented with a clay engineered barrier of the type used in these experiments (smectite in TAV 7 and 9). A very small amount of clay in the granite environment is sufficient to result in significantly higher corrosion. Major alteration was observed in the clay medium itself (TAV 16, 17 and 20) because of the high clay mass to glass surface area ratio in these tests. The effects of fracturation of the glass block on the degree of corrosion also depended on the environmental materials. Finally, the feasibility of integral tests was demonstrated in a shielded cell.
The creation of radiation damage in silicate glasses can be evidenced by studying their thermoluminescence (TL). Until now, damage resulting from irradiation has been described by physical or mechanical methods. TL can corroborate other methods to detect and describe alpha radiation damage.
TL was investigated in a pure silica glass, in which radiation damage can be described as the creation of 'oxygen vacancy and displaced oxygen atom' pairs induced by alpha particles. This model was extended to glass with a more complex composition: the basic frit used for radioactive waste containment glass. The results must still be extended to nuclear glasses such as the French R7T7 reference glass.
TL allows radiation damage to be monitored in this type of glass. For this purpose, a specific TL chamber was built, a general experimental method and a test procedure were defined.
The contract initially called for experimentation with alpha-doped radioactive glass specimens, but these experiments could not be carried out. However, R7T7 glass specimens doped with americium-241 and with plutonium-238 are now available, as well as first generation SON 58 30 24 light water reactor (LWR) glass samples. Experimental implementation of these glasses is underway.
It has been shown that the evolution of the crystallinity of silicate glasses can be determined by studying their TL behaviour. This type of analysis can be expected to aid in understanding the TL mechanism, and in measuring the degree of crystallization. This can be of considerable importance in assessing the crystallinity of glasses submitted to heating cycles, as TL appears to be more sensitive than X-ray diffractometry.
PART A - RADIOACTIVE GLASS INTERACTION WITH ENVIRONMENTAL MATERIALS
1.1. EFFECT OF ENVIRONMENTAL MATERIALS ON LEACHING OF TRANSURANIUM NUCLIDES: PARAMETER TESTS WITH 7 DIFFERENT ENVIRONMENTAL MATERIALS IN CONTACT WITH 2 RADIOACTIVE GLASSES (237NP AND 239PU) AFTER 4 DIFFERENT LEACHING DURATIONS.
1.2. INTEGRAL TESTS IN GRANITE, CLAY AND SALT:
1.2.1. INACTIVE TESTS.
1.2.2. ALPHA, BETA AND GAMMA RADIONUCLIDE RELEASE IN GRANITE, CLAY AND SALT.
PART B - THERMOLUMINESCENCE INVESTIGATION OF IRRADIATION DAMAGE IN GLASS
2.1. THEORETICAL INVESTIGATION OF TL MECHANISMS IN THE R7T7 GLASS MATRIX.
2.2. EXPERIMENTAL THERMOLUMINESCENCE EXAMINATION OF RADIOACTIVE R7T7 GLASS SPECIMENS.
Funding SchemeCSC - Cost-sharing contracts