[en] The complexation behaviour of organic extracts obtained after acid alteration of Callovo-Oxfordian argillites toward europium (III) is studied in time resolved laser induced spectrofluorimetry. The presence of fluoride ions in one extract, originated from the dissolution of remaining silicates in HCl/HF, precludes the correct study. Nevertheless, the dialysis of the extract at 500 Da permits to obtain a clearer evolution of the complexation pattern. The fluorescence spectrum and decay are strikingly different the ones obtained on alkaline degradation products of the Callovo-Oxfordian argillite, and resemble more to a small organic molecule pattern

[en] The coherence of tetravalent actinide complexation by humic substances is reviewed. In a first attempt, the values of independent data from literature on Th, U, and Pu are collected, selected, and compiled. The data obtained follow the 'classical' trend of increasing conditional formation 'constant' with pH, led by the increase in the extensive hydrolysis of the tetravalent actinides. Even though a fair agreement is evident, the experimental uncertainties do not permit a full analogy between the tetravalent actinides to be ascertained. In a second attempt, the experiments from which the original data are available were reinterpreted using only one hydrolysis constant set for U(IV), considering that all actinides have analogous behaviour. Hence, the obtained evolution of conditional formation 'constants' is fully coherent. This exercise demonstrates the treatment of data through analogy in the case of tetravalent actinides, and would permit to limit the number of necessary, but difficult, experiment with redox sensitive elements like U, Np, or Pu

[en] This work forms part of the FUNMIG project which aims to: (i) generate data and process understanding for phenomena that cannot be obtained from laboratory studies, and (ii) to verify process up-scaling with respect to time, spatial scale and heterogeneity. It is based on the Swedish site investigation programmes for a nuclear waste repository in fractured crystalline rock. A database with background information has been established for the Forsmark site and a detailed analysis has identified plausible endmembers as primary mixing components to explain the present groundwater chemistry. The portions of different groundwater contributors together with knowledge of the evolution history provide a good picture of the present hydrological situation. A large number of geochemical processes have been identified, including a detailed analysis of the origin of excessive U concentrations in some deep groundwater samples from Forsmark. Investigations of the palaeo aspects by using natural environmental isotopes are under development. The results contribute to the safety assessment of nuclear waste disposal in the granitic rock investigated by considering the hydrological situation and relevant geochemical processes, both at the present day and also to predict future site evolution with the onset of climatic changes

[en] Sequential extraction (SE) is used for determination of U and other elements in a U-rich sediment from the Natural Analogue Site Ruprechtov. In Tertiary clayey samples U is found to be bound onto organic matter and/or be present in reduced form. In granitic samples carbonates/alumosilicates play a more important role in the U distribution. Extended element analyses (Na, K, S, Fe, As, P) of SE leachates were completed. Cluster analyses of these results are used for identifying possible correlations between elements and for comparing these to previous correlations derived from μ-XRF and μ-XAFS investigations. According to the SE cluster analysis P, As and P can be assigned into one group. Fe and S are separated from U, i.e. we find no direct dependence of U on Fe and S. K and Na are mainly associated with residual minerals. Agreement with micro-scale measurements is observed: U in the sediment is associated with As and is present as phosphate in reduced U(IV) form

[en] Limitations on aqueous solution chemistries of humic acid, and also hydrolysis of some cationic species, restrict measurement of conditional stability constants of 4f- and 5f-series elements as humate complexes. Reported log β values are determined by using non-linear regression binding isotherms, of Am(III) and Th(IV), and also Ag(I) and Sr(II), bound by a humic acid composite

[en] This Workshop combined various types of activities and meetings with the following objectives: Inform about the scientific progress; Inform about the administrative status; Inform/agree upon forthcoming reporting; Discuss various topics of interest (for example, various aspects of Integration ); Inform about and discuss training; Agree upon the forthcoming work program. Emphasis was on scientific-technical topics with administrative issues kept to the minimum necessary. The proceedings are divided into the following sections: Research, Technology and Development Components activity overviews, with summaries where scientific highlights were presented. These were: RTDC1: Influence of inorganic carbon of Ni(II) and Co(II) sorption on Na-illite and Opalinus clay; Adsorption of humics to iron oxides and its effects on ion adsorption. RTDC2: Sorption of Uranium onto granite and altered material from Aespoe HRL; Sorption and reduction of uranyl by Fe(II) minerals; Mobility of uranium during the reductive dissolution of iron oxides by sulfide; U(VI/IV) adsorption mechanism on biotite surfaces and clarification of the influence of redox reactions on the U(VI) adsorption. RTDC3: Interlayer hydration H₂O 'paradigm' (mono-porosity model); Porosity/mineral distribution characterisation (mm-cm scale), GIS system for CO_x 'transport pertinent' data sets. A topical session was held around subjects associated with performance assessment/the Safety Case, especially relevant for geologic disposal in crystalline rock. The topics were: Role of biogeochemical processes on radionuclide migration; Characterization of geochemical conditions in crystalline rock/ Process identification and verification by real system analysis; Fluid flow system characterization in crystalline rock (Effects of the heterogeneity and up-scaling). Individual Scientific and Technical Contributions, containing reviewed scientific and technical manuscripts: European OBservatory for Long-term Governance on RAdioactive Waste Management, OBRA Co-ordination Action running from October 2006; Integrated Project PAMINA, running from October 2006; Integrated Project NF-PRO, running from 2004, will finish end of 2007; Treatment of influences of the near field on the geosphere in the Safety Case; Recent developments of the Euratom (Fission) Programme - Priority research area 'Management of Radioactive waste - Disposal of HLW and LLW Towards FP7

[en] In first experiments the reduction sequence of Pu starting with Pu(VI) was studied in presence of hydroquinone (HQ) and fulvic acid (FA) as reducing compounds at various pH values between pH 1 and 7. The Pu species were monitored by UV-Vis spectroscopy and liquid-liquid extraction. Pu(V) and (VI) are not stable in aqueous solutions containing hydroquinone and fulvic acid (FA) at pH 1 to 7. With 200 mg/L FA the reduction of Pu(VI) to Pu(V) is fast and complete after 30 minutes at pH 3. Compared to the reduction reaction at similar concentration of HQ, the FA reduction is slower. We also observed that Pu(VI) is unstable in solutions devoid of FA at pH values > 3, but that the rate is much slower than in presence of FA and HQ. Pu(V) in same solutions is converted to Pu(IV), the most stable oxidation state in aqueous solutions containing FA at pH 3 - 7 (relevant for natural aquifers). Reduction of Pu(IV) to Pu(III) was found only at pH values < 5 for HQ and < 3 for FA. The reactions were also monitored by Eh measurements. The present studies showed that a correlation between Eh values and thermodynamic calculations might be a capable tool for modelling redox reactions between Pu ions and hydroquinone or hydroquinone-like compounds like FA. It cannot be excluded that Pu(III) is more stable in solutions containing organic compounds with lower redox potential than the GoHy-573-FA batch used in the present studies

[en] To guarantee the long-term safety of a high-level waste repository, all mechanisms that could affect the radionuclide (RN) migration rate must be well defined and quantified. The particular interest of this work lies on the possible contribution of bentonite colloids, generated at the compacted bentonite barrier, to RN transport. The main parameters necessary to assess the colloid-mediated RN transport are the source term and the stability behavior in the medium geochemical conditions. In the present work, two experimental set-ups were designed, with the aim of quantifying the bentonite colloid generation rates, at laboratory scale and under 'realistic' conditions, by static hydration (no flow) of the compacted bentonite, in a confined system. Preliminary results showed that bentonite particles were generated with an average size in the colloid range, equivalent to that of bentonite colloids prepared in the laboratory. At the same time, the experimental set-up allowed performing stability studies which indicated that the colloids generated in the lower strength waters remained stable over months. The possible mechanisms responsible of colloid generation are discussed according to the obtained preliminary results in different experimental conditions

[en] A method for separation of uranium (IV) and uranium (VI) has been further developed for application to natural samples from uranium-rich tertiary clay horizon at Ruprechtov site, Czech Republic. It has been applied to four samples with different uranium content from different boreholes. The ²³⁴U/²³⁸U activity ratio in each phase was determined. The results show, that both forms U(IV) and U(VI) exist in the tertiary clay horizon. The ²³⁴U/²³⁸U ratio significantly differs between the forms with values below unity between 0.45 and 0.91 in the U(IV) phase and values above unity between 1.26 and 3.37 in the U(VI) phase. On one hand it clearly shows the impact of a-recoil process on the U(IV) phase, indicating its low mobility in this horizon. On the other hand the finding of clear U(VI) phases and their high ²³⁴U/²³⁸U ratio indicate that at least part of the U(VI) phase was recently formed. Results are discussed with regard to uranium enrichment scenarios at the site

[en] Previous work has shown that humic substances can bind metal ions in two modes: the exchangeable, where it is available instantaneously for reaction with other sinks (such as mineral surfaces); and the non-exchangeable, from which it may only dissociate slowly. In the absence of metal ion/humic/mineral surface ternary complexes, if the dissociation rate is slow compared to the residence time of the humic in the groundwater column, then metal in the non-exchangeable will have a significantly higher mobility than that in the exchangeable. The critical factor is the ratio of the non-exchangeable first order dissociation rate constant and the residence time in the groundwater column, metal ion mobility increasing with decreasing rate constant. Sorption of humic/metal complexes at mineral surfaces may reduce mobility. In addition to direct retardation, sorption also increases the residence time of the non-exchangeable fraction, giving more time for dissociation and immobilisation. The magnitude of the effect depends upon the concentrations of the mineral surface humic binding sites and the humic in solution, along with the magnitudes of the equilibrium constant and the forward and backward rate constants. The non-exchangeable dissociation reaction and the sorption reaction may be classified in terms of two Damkohler numbers, which can be used to determine the importance of chemical kinetics during transport calculations. These numbers could be used to determine when full chemical kinetic calculations are required for a reliable prediction, and when equilibrium may be assumed, or when the reactions are sufficiently slow that they may be ignored completely