Effets d'irradiation dans les argiles. Applications environnementale et géologique.

Irradiation defects in minerals present at the earth surface gave rise to an important number of studies. Among these minerals, clays possessed properties (cationic exchange capacity, swelling properties) which make them suitable candidate for the retention of actinides in the context of high level radioactive waste storage. In order to insure the stability of the clay located around the waste, it is necessary to study their physico-chemical properties after irradiation. This thesis is divided in three parts that are related to this thematic. In the first part, we will discuss the effect of ionizing irradiation of alpha particles on the specific surface area of kaolinite and the consequences of such an irradiation on the observed spectra by IRTF. The second part is dealing with the solubility of amrophized smectite in alkaline conditions and more especially with the dissolution kinetics. We will present new results on this process. Finally, in the third part, we studied a natural analogue geosysteme Nopal which is located in Chihuahua (Mexico). We will discuss how the kaolinite dosimeter can be a powerfool tool to asses' ancient uranium migration in the U-deposit.Les défauts d'irradiations dans les minéraux présents à la surface de la terre ont donné lieu à de nombreuses études. Parmi ces minéraux, les argiles ont des propriétés (capacité de rétention des radioéléments, gonflement...) qui les rendent utiles dans le cadre du stockage des déchets radioactifs. Afin de s'assurer de la stabilité des argiles se trouvant autour du colis de déchets, il est nécessaire d'étudier leurs propriétés physico-chimiques après irradiation. Cette thèse est séparée en trois parties qui sont axées autour de cette thématique. Dans une première partie, nous verrons quels sont les effets des rayons alpha sur la surface spécifique de la kaolinite et nous exposerons les phénomènes physique induits par ces rayonnements ionisants. La seconde partie traitera de la solubilité des smectites amorphisées dans un milieu basique et plus particulièrement de la cinétique de dissolution. Nous verrons que cette dissolution est favorisée par l'amorphisation. Enfin dans une troisième partie, nous nous sommes intéressés au géosystème analogue naturel de Nopal (Chihuahua, Mexique), où le dosimètre kaolinite peut permettre d'étudier les migrations anciennes de l'uranium au sein de la roche

Effets d'irradiation dans les argiles (applications environnementale et géologique)

PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Theoretical OH stretching vibrations in dravite

International audienceDensity functional theory is used to investigate the vibrational stretching properties of OH groups in ideal and chemically disordered dravite models. Different schemes of cationic occupancy are considered, including the occurrence of vacancies at the X site and Mg–Al inversion between the Y and Z sites. The harmonic coupling between different OH groups is found to be smaller than 1 cm−1, indicating that the OH stretching dynamic in dravite can be described by considering a collection of nearly independent single OH oscillators. Their harmonic stretching frequency is linearly correlated with the corresponding OH bond length and most of the bands observed in the experimental vibrational spectra can be interpreted as consequences of the cationic occupancy of the sites coordinated to the OH group. The V(OH) and W(OH) stretching frequencies are affected by the Mg–Al inversion and by the presence of vacancies at the X site. In this last case, the frequencies depend on the isolated or more concentrated character of the X vacancy distribution along the c axis. Based on theoretical stretching frequencies, new interpretations are proposed for some of the bands experimentally observed in synthetic samples of dravite and magnesio-foitite

Impact of biogenic exudates on the dissolution and browning of stained glass windows

International audienc

Impact of biogenic exudates on the dissolution and browning of stained glass windows

International audienc

Impact of biogenic exudates on the dissolution and browning of stained glass windows

International audienc

Effect of radiation-induced amorphization on smectite dissolution kinetics

International audienceIn the high level nuclear radioactive waste repositories (HLNWR) management, smectite (a major constituent of bentonite) is considered to limit the dissemination of radionuclide in the environment 1. Indeed, smectite exhibits interesting properties such as a high cation exchange capacity and swelling capacity that are expected to enhance the retention of radionuclides in a case of a leakage of the waste. For this reason, in France, smectite will be found in the near and far field of the waste. In the near field of the waste, bentonite will be a major constituent of the engineering barriers used mainly for backfilling and in the far field, deep argillaceous formations are the expected host rock. However, it was recently reported that the conditions for induced amorphization of smectite by heavy ions were consistent with a leakage scenario in a HLNWR 2. Such amorphization is expected to induce strong modifications of the mineral properties such as sorption capacity, swelling and dissolution kinetics. In this study, we used a purified smectite issued from the MX80 bentonite in order to evaluate the influence of amorphization on the dissolution kinetics. The sample was irradiated with 925 MeV xenon ions at the GANIL facility (Caen, France). Amorphization was controlled by X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy. Besides, an important coalescence of the smectite sheets was observed by scanning electron microscopy, which lead to a loss of interparticle porosity. Furthermore, it was observed that the dissolution rate far-from-equilibrium is two times larger in the amorphous sample than in the reference clay. We will discuss the result with previous observations on other minerals and the potential implications for the dissemination of radionuclides in the environment

Effect of Cu, Ni and Zn on Fe(II)-driven autotrophic denitrification

International audienc

Structural investigations of neodymium incorporation in calcium stannate perovskite CaSnO3

International audienc

Experimental study of trivalent rare-earth element incorporation in CaTiO3 perovskite: evidence for a new substitution mechanism

International audienc