[en] Full text of publication follows: The study of geological sites as analogues for high-level radioactive waste disposal sites may help to understand the behavior of radionuclides in geological formations. Within this framework we are investigating U-IV sorption and precipitation in clayey sediments sampled from the argillaceous Tertiary formation at the Ruprechtov site in the Czech Republic. This site represents typical geological and geochemical conditions often found in cap-rocks above potential disposal formations in Europe. Two boreholes (NA7 at 15 m and NA6 at 37 m, respectively) were drilled and cores (11- 15 m) for NA7 and 35-37 m for NA6 were stored in anoxic conditions. The geochemical conditions are supposed to be more oxidizing in NA7 compared to the deeper NA6. However, gamma-profiles showed U-enrichment in both sediments. For practical purposes a synthetic groundwater with composition similar to that found in the studied site was used. The Eh of the synthetic water was controlled by addition of sulfides. Humic substances were extracted from the sample with the highest amount of organic carbon (NA6-35 m) with 0.1 M NaOH and purified with DAX-8 and XAD-4 resins. Sorption experiments under nitrogen atmosphere use suspensions of sediments/groundwater and U-IV synthesized by electrochemical reduction of uranyl nitrate. Moreover, reduced ²³²U was used as a tracer to study the stability of U-IV in groundwater within the time selected for equilibrium to be reached between sediments and groundwater (48 h). The results showed that, for U-IV concentrations between 10^-6 and 10^-9 M, no significant precipitation of U-IV was observed unlike experiments with U-IV concentration of 10^-5 M. Sorption isotherms determinations of U-IV with/without humic substances are under way. Also, a mineralogical study of sediments is being conducted to determine the role of phases likely present in some sediments (pyrite, siderite, Fe-oxy-hydroxides) on uranium behavior. Chemical composition of synthetic groundwater (mg/L): Na = 27.1; K = 10.9; Mg = 19.2; Ca = 52.8; Cl^- = 141; SO₄^2- = 65; HCO₃^- = 190; NO₃^- = 16; pH = 8.6; Eh(mV) = -252. (authors)

[en] The uranium and thorium contents were evaluated in the 100-400 μm granulometric fraction of different sedimentary phosphate samples by using a method based on determining the mean critical angles of etching of the CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD) for detecting α-particles emitted by the nuclei of the uranium-238 and thorium-232 series. Data obtained were compared with the results of γ-ray spectrometry measurements performed on the same samples. The influence of the calcination and water washing treatments as well as the lithology and stratigraphy on the uranium concentration of the phosphate samples was investigated. (author)

[en] Full text of publication follows: This work aimed to study the contribution of organic matter on the retention of Eu(III) and Ni(II) on the Callovo-Oxfordian clay-stone from the underground laboratory site of Bure (France). The investigation was based on the study of the raw clay-stone as well as experimentally oxidized samples to test the effects of air alteration on the retention potential of Eu(III) and Ni(II). X-ray diffraction and XPS photoelectron spectroscopy reveal that the chemistry of the minerals is not significantly affected by oxidation, nor is the specific surface of the samples. On the contrary, the organic material shows clear alteration. The oxidation of the kerogen leads to an increase of the extractable hydrocarbons amounts from 6 to 15μg/g of rock after 1024 h of oxidation. The kerogen as well as the extractable polar compounds are enriched in oxygenated compounds (especially carboxylic acid functions as revealed by pyrolysis-gcms and FTIR). In the presence of clay water, the organic matter is not significantly mobilized, and this irrespective of its oxidation degree. Furthermore, the effect of the colloidal phase on the retention could be neglected. Oxidation increases significantly the retention capacity of the clay-stone. The removal of the dichloromethane soluble fraction did not lead to a significant decrease in Kd values for Eu(III) and Ni(II). A slight increase was rather observed for Ni(II), indicating that new adsorption sites may have been made accessible. The chloroform extractable fraction may therefore not be an important fraction for the adsorption process. It was shown that minerals, with the exception of pyrite, are not significantly affected by air oxidation, while kerogen is. The increase of adsorption after oxidation may be attributed to the formation of new oxygenated organic functions in the kerogen. Quantitative analysis of the data using a multi-site Langmuir model (one site is the clay+calcite while the second is the kerogen in 1.1 weight percent contribution) indicates that kerogen (containing a significant amount of pyrite) contributes for 35% for Ni(II) and 12% for Eu(III) in the total sorption on the raw rock. For the oxidized rock, the increase of retention is of a factor 2 for Eu(III) to 3 for Ni(II). (authors)

[en] This work aimed to study the retention potential and colloidal transport properties of Eu(III) and Ni(II) of the Callovo-Oxfordian clay-stone from the underground laboratory site of Bure (France). The investigation was based on the study of the raw clay-stone as well as experimentally oxidized samples to test the effects of air alteration on the generation properties of colloids and retention potential of Eu(III) and Ni(II). (authors)