We present here the global results of an eight-year project, where we attempted to complete the ThermoChimie database for cement minerals, zeolites and clay minerals. This work reports the methodology adopted to ensure the consistency between the three groups of minerals. Our first step concerns the relations between the three groups of minerals from field observations and experimental results gathered from the literature. A summary of the selection process is then given for clay and cement minerals and a specific focus is proposed for zeolites, with examples of analcime and mordenite. The global consistency of the selection is investigated with respect to the main chemical tendencies found for cement/ clay interactions, especially considering the "alkalinity" of the minerals. Consistency is checked by establishing predominance diagrams in the chemical sub-systems of interest for the three groups of minerals, then comparing the phase relations with respect to experimental results or field observations. The methodology is illustrated using the case of gismondine and zeolite P(Ca). (C) 2014 Elsevier Ltd. All rights reserved.

Thermodynamic data are an essential input for relevance of geochemical modeling and more particularly to assess the behavior of radionuclides and other pollutants in the performance assessment of a radioactive waste repository. ThermoChimie (http://www.thermochimie-tdb.com/), the thermodynamic database developed by Andra, meets the requirements of completeness, accuracy and consistency for numerous radionuclides and chemotoxic elements and various major components of a geological repository: solid phases constitutive of the host-rock, bentonites, concretes, and corresponding secondary minerals with respect to their long term evolution. ThermoChimie developments are also dedicated to evaluating specific conditions of the near field of radioactive waste, in particular regarding temperature increase and release of organic ligands or soluble salts. ThermoChimie database is extracted into compatible formats with different geochemical codes, allowing an overall consistency between different models using it in support. (c) 2014 Elsevier Ltd. All rights reserved.

This study aims at elucidating the mechanisms regulating the interaction of Eu and Ni with calcite (CaCO3). Calcite powders or single crystals (some mm sized) were put into contact with Eu or Ni solutions at concentrations ranging from 10−3 to 10−5molL−1 for Eu and 10−3molL−1 for Ni. The sorption durations ranged from 1week to 1month. Rutherford Backscattering Spectrometry (RBS) well adapted to discriminate incorporation processes such as: (i) adsorption or co precipitation at the mineral surfaces or, (ii) incorporation into the mineral structure (through diffusion for instance), has been carried out. Moreover, using the fluorescence properties of europium, the results have been compared to those obtained by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) on calcite powders. For the single crystals, complementary SEM observations of the mineral surfaces at low voltage were also performed. Results showed that Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation and (ii) incorporation at depth greater than 160nm after 1month of sorption. Ni was found to accumulate at the surface of calcite without incorporation.

The Callovo-Oxfordian (COx) clayed formation is chosen in France as the possible site for an underground nuclear waste disposal. The question raised in this paper concerns the ability of the COx to sorb iodine. Experimental set-ups working in both batch and dynamic systems have been designed for the accurate determination of weak retention factors (i.e. <0.1L/kg) under conditions relevant to the geological formation. Adsorption data measurements were combined with speciation studies performed by anion exchange chromatography. Iodide was shown to be the only form of iodine present in the system regarding both the natural pristine iodine content of the samples and iodine added to the samples. A weak but significant adsorption was observed at 20°C (Kd<0.31L/kg). The adsorption process is reversible when working under fixed PCO2 (1% CO2) with the necessity to consider a kinetic-controlled process under dynamic conditions. When the partial CO2 pressure was not controlled, a part of iodine was shown to be irreversibly bound, probably in a newly precipitated carbonate phase. A Kd value in the range of 0.01–0.14L/kg can be given under controlled PCO2 to describe the adsorption of trace concentrations of iodine by the COx formation.

Organic complexing species are known to affect radionuclide mobility in the environment. The migration behaviour of several organic ligands was evaluated in the context of a proposed French radioactive waste repository in the Callovo-Oxfordian clayrock formation (COx). This study focuses on four anthropogenic acids (ethylenediaminetetraacetate, isosaccharinate, phthalate, oxalate) that are used in the nuclear fuel cycle or that occur as hydrosoluble degradation products of waste materials. Batch sorption and diffusion experiments were performed with COx clayrock samples using C-14-labelled radiotracers. The observed effective diffusion coefficients were low (D-e similar to 1-6 x 10(-12) m(2) s(-1)), an order of magnitude lower than that of tritiated water in the same material, and roughly the same as values for inorganic anions such as I-, Cl- and SO42-. The observed correlation of D-e with molecular mass, M-1/3, differs significantly from that observed for cations. The organic ligands displayed significant affinity for the COx clayrock, with distribution ratios measured in batch experiments, R-d = 1-30 L kg(-1), which are much higher than usually observed for anionic species. While this result was confirmed by through-diffusion experiments, the K-d values obtained by fitting diffusion modelling were significantly lower than those measured in the batch experiments. (c) 2014 Elsevier B.V. All rights reserved.

The potential effect of near-field alkaline perturbation in clayrocks on Cs retention was explored. Batch experiments were conducted to measure Cs sorption on Callovian-Oxfordian rock samples in alkaline perturbed conditions. Experimental results evidenced a marked effect of alkaline perturbation on the Cs retention properties of Callovian-Oxfordian rock samples. Using a modelling approach, this effect could be attributed to the competition of K+, originating from the alkaline solution, for Cs sorption sites on illite surfaces. Experimental results also showed that Cs sorption tends to increase with time. Additional experiments on a mineralogical assemblage representative of a Callovian-Oxfordian rock/concrete interface after long term alkaline perturbation showed that this mineralogical assemblage has a similar efficiency for Cs uptake as the intact clay rock, showing that long term alkaline perturbation of clayrocks and resulting mineralogical changes do not affect the barrier performance considerably with regard to Cs retention. (C) 2012 Elsevier Ltd. All rights reserved.

As Kd from radwaste elements in concrete systems show a wide range of values, a modelling of cesium and lead immobilization in Calcium Silicate Hydrate (CSH, xCaO.SiO 2 .H 2 O, with 0.7 (aged cements) SiOH) and precipitation equilibria. Values of Kd from cesium and lead in CSH matrix can thus be calculated with Ca/Si evolution and ionic strength effect. Predictive calculations have been carried out with success with different Ca/Si ratios, ionic strengths and liquid/solid ratios, and results are well superimposed with experimental isotherm data. If the CSH really allow accounting for the radwaste behavior in hydrated cement matrices, this model can be used in safety assessment calculations, with varying pH and [Ca 2+ ] as cement degradation state parameters.

B-Nb 2 O 5 was recrystallized from commercially available oxide, and XRD analyses indicated that it is stable in contact with solutions over the pH range 0 to 9, whereas solid polyniobates such as Na 8 Nb 6 O 19 ⋅13H 2 O(s) appear to predominate at pH>9. Solubilities of the crystalline B-Nb 2 O 5 were determined in five NaClO 4 solutions (0.1≤ I m /mol⋅kg −1 ≤1.0) over a wide pH range at (25.0±0.1) °C and at 0.1 MPa. A limited number of measurements were also made at I m =6.0 mol⋅kg −1 , whereas at I m =1.0 mol⋅kg −1 the full range of pH was also covered at (10, 50 and 70) °C. The pH of these solutions was fixed using either HClO 4 (pH≤4) or NaOH (pH≥10) and determined by mass balance, whereas the pH on the molality scale was measured in buffer mixtures of acetic acid + acetate (4≤pH≤6), Bis-Tris (pH≈7), Tris (pH≈8) and boric acid + borate (pH≈9). Treatment of the solubility results indicated the presence of four species, Nb(OH)_n^5-n (where n =4–7), so that the molal solubility quotients were determined according to: 0.5Nb_2O_5(cr)+0.5(2n-5)H_2O(l)_←^→Nb(OH)_n^5-n+(n-5)H^+ (n=47) and were fitted empirically as a function of ionic strength and temperature, including the appropriate Debye-Hückel term. A Specific Interaction Theory (SIT) approach was also attempted. The former approach yielded the following values of log 10 K sn (infinite dilution) at 25 °C: −(7.4±0.2) for n =4; −(9.1±0.1) for n =5; −(14.1±0.3) for n =6; and −(23.9±0.6) for n =7. Given the experimental uncertainties (2 σ ), it is interesting to note that the effect of ionic strength only exceeded the combined uncertainties significantly in the case of log 10 K s 6 to I m =1.0 mol⋅kg −1 , such that these values may be of use by defining their magnitudes in other media. Values of Δ f G o , Δ f H o , S o and C_p^o (298.15 K, 0.1 MPa) for each hydrolysis product were calculated and tabulated.

A pluridisciplinary approach was used to define iodine immobilization mechanisms by biocarbonates in a natural marine carbonate-bearing clayey formation. For this purpose, different techniques of observation (optical microscope, scanning electron microscope (SEM), cathodoluminescence (CL)) and of analyses (infrared spectrometry (IR), electron microprobe (EPMA), spatially resolved synchrotron-based X-ray fluorescence (μ-XRF) and X-ray diffraction (μ-XRD)) were performed on two entire and centimeter-sized carbonate shells of the Callovian–Oxfordian (160Ma) clayey formation from the ANDRA (French Radioactive Waste Management Agency) Underground Research Laboratory (Meuse/Haute Marne, France), in the Eastern part of the Paris Basin. Combined (SEM, CL, IR and μ-XRD) data indicates that the biostructure of the Rhynchonella shell is relatively well-preserved but bio-aragonite slowly transforms into calcite, whereas the bivalve shell is entirely recrystallized into diagenetic calcite and celestite. EPMA and μ-XRF data show bioaccumulation of iodine in carbonate shells, confirming previous work on present-day mollusks. EPMA analyses give evidence of iodine content up to 1200ppm in the preserved Rhynchonella shell and up to 2000ppm in recrystallized bivalve shell. μ-XRF elemental mapping shows that iodine is more homogeneously distributed in bio-calcite of the Rhynchonella shell than in recrystallized calcite of the bivalve shell, suggesting a loss of iodine during re-crystallization processes, but not a total exclusion of iodine from the carbonate structure. Combined EPMA data and μ-XRF elemental maps do not give evidence of any correlation between the iodine location and the distribution of other elements.

Iodine is one of the most problematic radioisotopes in the context of nuclear waste geological disposal due to its high mobility. Considerable effort has been dedicated to the measurement of its potential retardation during diffusive transport leading to conflicting results, from no retardation to significant retardation, leading in turn to considerable debate. The present study aims at providing new insights into this aspect of the iodine problem by careful quantification of iodine reservoirs in the Callovian–Oxfordian (COx) clay rock taken here as model material for these studies. The present study confirmed the ubiquitous presence of iodine at 1–5mgkg−1 level in the COx clayey formation. The iodide concentration level in the porewater is also confirmed at a value in the range ∼20–40μmolL−1, i.e. higher than the expected range of radio-iodine concentration in the far-field of the storage. Surprisingly, most of the iodine was found not to be associated with organic matter but rather in an inorganic form associated with carbonate minerals. This result has potentially significant implications for the fate of radio-iodine. In undisturbed far-field conditions, most natural iodine would not be accessible for isotopic exchange with radioactive iodine, reducing the effective Kd to negligible values. During laboratory experiments, good monitoring of the geochemical parameters (at least the Eh, pH, PCO2, [Ca] and [Mg]) is mandatory to avoid iodine-bearing carbonate precipitation and to enable rigorous interpretation of the iodide diffusion/retention experiments.

Cement bentonite interactions need to be studied since they will occur in deep geological repositories. They are specifically relevant in the clay host rock reference concept. The reactivity of a Mg-homoionic FEBEX bentonite was studied at 60 oC in contact with a young cement water characterized by the leaching of alkaline hydroxides (K/Na 4/1 –OH, pH = 13.5 at 25 oC) and with an evolved cement water controlled by the portlandite dissolution (Ca(OH)2, pH = 12.5 at 25 oC). The experimental approach was to run diffusion experiments carried out in a cylindrical compacted bentonite sample, 2.1 cm long with a diameter of 7.0 cm, which is exposed on one circular face to a solution of cementitious water. A second reservoir of fluid is located at the opposite face of the bentonite sample; this contained MgCl2 solution which was used during the homoionization process. The bentonite sample is maintained at a constant temperature of 60 oC throughout the experiments run for 6 and 12 months. The key processes investigated were to identify and confirm, considering previous studies (Sánchez et al., 200; Savage et al., 2007), the nature of the newformed mineral phases (i.e., zeolites, CASH andMg-silicate phases) as a result high pH reactivity of bentonite. This was complemented by addressing the spatial extension affected by mineralogical and geochemical modifications in compacted bentonite, including the extension of cationic exchange. The diffusion of the hyperalkaline plume (OPC K/NaOH solution) through compacted bentonite (1.6 g/cm3 dry density) produces a mineralogical alteration front characterized by a critically cemented rim of approximately 2-3 mm (Figure 1). The cemented material is characterized by a drastic reduction on its external specific surface (from 80 to 20 m2/g) as well as the CEC (100 to 50 m2/g). The thickness of the rim did not evolve with time, then, diffusion becomes very slow due to the reduction of porosity. The self sealing of the high pH concrete-bentonite interface has been predicted in some models and this process should be taken into account as a potential self-stopped reactivity scenario. The mineralogical composition of the rim is a mixture of poorly ordered, Mg-rich, clay materials, mainly brucite, hydrotalcite and tri-octahedral Mg-smectite. Montmorillonite is partially dissolved and a part of it remained trapped within the newformed cements. The alteration rim has been accurately measured by means of EDX-chemical profiles in flat polished sections examined under SEM microscopy (Figure 2) Alkali-zeolites have not formed at all as far as no pore-space is available for these lower density silicates. Then, alkaline cations (mainly K+) have diffused beyond the altered rim, affecting the whole 2.1 cm length of the compacted bentonite disc. The K+ exchange in the montmorillonite is homogeneous in the bentonite probe but it did not saturate completely the exchangeable positions. This can be another indication of the stopped reactivity process. The same studies are being performed at 90 oC in order to compare the extent of the diffusion and reaction processes. At pH 12.5 and 60 oC there was not detected any significant mineralogical alteration. The main outcome of these experiments evidence the very limited thickness of mineralogical alteration affecting a highly compacted bentonite exposed to the effect of hyperalkaline solutions.

Cementitious materials are an integral part of the engineered barrier system in the French design of a deep geological radioactive waste repository. A maximum increase in temperature to 70°C resulting from exothermic hydration reactions and heat generation by the radioactive waste could lead to significant changes in hydrated cement paste mineralogy, which in turn will affect the sorption of radionuclides. Cementitious materials were prepared with ordinary Portland Cement at 20 and 70°C using different temperature conditions of hardening, cure and alteration. Selenite uptake was measured in each system. The sorption of selenite was studied in a pH and Eh range where Se(IV) is stable. Sorption kinetics and sorption isotherms of selenite were determined at 20 and 70°C for up to 140 days in the concentration range of 2 × 10−11 to 8 × 10−4 mol/l for initial selenite. With increasing temperature, the hydrogarnet phase appeared and the crystallinity of C–S–H phases increased (formation of afwillite). Ettringite could no longer be detected. With the temperature increase, the specific surface area was about four times lower than the specific surface area of the sample aged at 20°C. The distribution ratios (Rd) decreased with temperature as a result. At 20°C, there was an initial fast sorption process (surface process) followed by a slower process such as a diffusion process into the solid phases. Rd values of 3600 ± 400 l/kg were obtained for 20°C altered cement suspensions at 30 days and for selenite concentration ranging from 8 × 10−12 to 6 × 10−7 mol/l. At 70°C, the sorption kinetics were similar and Rd values were found to be 1290 ± 80 l/kg. Saturation of the sorption site(s) was observed for selenite concentrations greater than approximately 2 × 10−7 mol/l.

The sorption of Eu(III) onto kaolinite and montmorillonite was investigated up to 150°C. The clays were purified samples, saturated with Na in the case of montmorillonite. Batch experiments were conducted at 25, 40, 80 and 150°C in 0.5M NaClO4 solutions to measure the distribution coefficients (Kd) of Eu as a trace element (<10−6mol/L) between the solution and kaolinite. For the Na-montmorillonite, we used Kd results from a previous study [Tertre, E., Berger, G., Castet, S., Loubet, M., Giffaut, E., 2005. Experimental study of adsorption of Ni2+, Cs+ and Ln3+ onto Na-montmorillonite up to 150°C. Geochim. Cosmochim. Acta 69, 4937–4948] obtained under exactly the same conditions. The number and nature of the Eu species sorbed onto both clay minerals were investigated by time resolved laser fluorescence spectroscopy (TRLFS) in specific experiments in the same temperature range. We identified a unique inner-sphere complex linked to the aluminol sites in both clays, assumed to be AlOEu2+ at the edge of the particles, and a second exchangeable outer-sphere complex for montmorillonite, probably in an interlayer position. The Kd values were used to adjust the parameters of a surface complexation model (DLM: diffuse layer model) from 25 to 150°C. The number of Eu complexes and the stoichiometry of reactions were constrained by TRLFS. The acidity constants of the amphoteric aluminol sites were taken from another study [Tertre, E., Castet, S., Berger, G., Loubet, M., Giffaut, E. Acid/base surface chemistry of kaolinite and Na-montmorillonite at 25 and 60°C: experimental study and modelling. Geochim. Cosmochim. Acta, in press], which integrates the influence of the negative structural charge of clays on the acid/base properties of edge sites as a function of temperature and ionic strength. The results of the modelling show that the observed shift of the sorption edge towards low pH with increasing temperature results solely from the contribution of the AlOEu2+ edge complexes. Finally, we successfully tested the performance of our model by confronting the predictions with experimental Kd data. We used our own data obtained at lower ionic strength (previous study) or higher suspension density and higher starting concentration (TRLFS runs, this study), as well as published data from other experimental studies [Bradbury, M.H., Baeyens, B., 2002. Sorption of Eu on Na and Ca-montmorillonite: experimental investigations and modeling with cation exchange and surface complexation. Geochim. Cosmochim. Acta 66, 2325–2334; Kowal-Fouchard, A., 2002. Etude des mécanismes de rétention des ions U(IV) et Eu(III) sur les argiles: influence des silicates. Ph.D. Thesis, Université Paris Sud, France, 330p].

To provide reliable K-d data for Cs required for the performance assessment of cement-based radioactive waste repositories, two complementary approaches were followed. First, Cs sorption was determined on a range of hydrated cement paste (HCP) and mortar samples of CEM I and CEM V for different degradation states and solution compositions, as well as on some single mineral phases. Second, a surface complexation-diffuse layer model previously developed by Pointeau et al. [Pointeau, L, Marmier, N., Fromage, F., Fedoroff, M., Giffaut, E.. 2001. Cs and Pb uptake by CSH phases of hydrated cement. Material Research Society Symposium Proceedings, 663, 105-113] for Cs sorption on synthetic CSH phases was simplified to facilitate its application to whole HCP and mortars or concrete, following re-assessment of the model parameters. All measurements were compared with model predictions.The sorption data obtained on the different solid phases as a function of conditions corroborate that CSH minerals are the main sorbing phase for Cs in HCP. The data also clearly show the important influence of pH and the dissolved concentration of Na, K and Ca on K-d. It is further suggested that a decrease of pH is concomitant with a decrease of the Ca/Si ratio and a corresponding increase in surface sites with high affinity for Cs and, thus, K-d. Elevated concentrations of cations able to compete with Cs for these sites lead to a decrease of K-d, on the other hand.The simplified model was applied to the sorption measurements performed within this study as well as to a variety of literature data, mainly K-d values for a variety of fresh HCP and mortar or concrete samples based on different samples of Ordinary Portland Cement as well as blended cements. The results show that the model can be applied reasonably well to a very large variety of conditions in terms of solid and solution compositions that cover a range of K-d values from 10(-4) to ca. 3.2 m(3)/kg. The large scatter typically observed for Cs sorption, especially on fresh HCP samples prepared from different formulations, can be explained quantitatively by the variable concentrations of Na and K in the respective solutions, which compete with Cs for fixation sites. On the other hand, the comparatively uniform conditions in degraded HCP typically render the prediction of K-d values less uncertain than in case of fresh HCP. (c) 2006 Published by Elsevier Ltd.

Coupled modelling has been performed using geochemical/transport codes and radiolysis models to describe the chemical evolution of the waste forms "high-level waste glass" and "spent nuclear fuel" together with its waste package and engineered barrier surroundings. Near field processes considered include container corrosion, hydrogen generation, mass transfer for radionuclides and other waste matrix components in corrosion products and buffer materials, geochemistry of near field solution chemistry, sorption of radionuclides on surface sites in the nano-sized pore space of near field materials and the radiolytic decomposition of pore water. The rate limiting steps in waste form dissolution and secondary phase formation mechanism and the associated radionuclide mobilisation chemistry (solubility, solid solution formation, speciation, redox stability) are strongly influenced by the near field constraints.

A multi-site surface complexation/ion exchange model for dispersed MX 80 bentonite has been calibrated, considering the dissolution properties of the constituting mineral assemblage, for sorption of a large number of radionuclides, using experimental data from the present study together with well constrained literature data. Emphasis was on tri- and tetravalents actinides and fission products and reducing groundwater compositions.