[en] Environmental management decisions require the use of models with varying degree of sohpistication to represent the evolution of natural and engineering systems. These models are of a predictive kind and they are based on our interpretative knowledge of of time between 1.000 to 10.000 years. In order to build up our confidence in the possibilities of using the models to predict the geochemical behaviour of the future repository systems, we study natural systems than reflect processes and/or materials used in the repositories. These studies are known as Natural Analogues. We have undertaken, within these investigations the checking of geochemical models to describe the aqueous speciation and the solubility of trace elemento, i.e. U, Th, Sr... The mobility of these elements is critical to assess the behaviour of nuclear waste repositories. These tests are known as Blind Predictive Modelling exercises and attempt to simulate the modelling of radionuclide solubilities and speciation in a repository environment. It can be seen in the paper that the concentrations of uranium in solution are more accurately predicted when using the formation of a mixed solid phase of U(VI) and Fe(III) than assuming a pure U(VI) solid phase. On the other hand, the concentrations of Ba predicted are slightly higher than the actual ones if assuming a congruent codissolution of a mixed solid phase of Ba with calcite. This is very useful result when trying to asses the environmental risk. The same results are obtained when predicting the concentration of other trace metals, such as Mn and Sr

[en] Solubility and aqueous speciation calculations constitute the backbone of the assessment of radionuclide mobility under repository conditions. To this respect, geochemical codes and their associated databases have to be verified and quality assured prior to their use in Performance Assessment exercises. The main objective of this Blind Prediction Modelling (BPM) Exercise was to test the ability of the different geochemical tools (codes and databases) to predict the concentrations of trace metals in a well characterised natural system. In this respect, widely used geochemical codes and databases have been tested. Eight water samples, representative of the different boreholes studied during the El Berrocal Project were selected for this purpose. The four participating groups were provided with the information needed to perform the predictions. The type of information released was separated into two main groups: - Concentration of major ions in the selected groundwaters - Mineralogical analyses of the site. (Author)

[en] The Swiss Federal Nuclear Safety Inspectorate (ENSI) is in charge of reviewing the work developed by the National Cooperative for the Disposal of Radioactive Waste (NAGRA) in Switzerland. Within the context of the Opalinus Clay project, the performance and safety assessment exercise developed by NAGRA involved the derivation of Biosphere Dose Conversion Factors (BDCF). The objective is the derivation of BDCF by using an alternative modelling tool and the study of how several simplifications incorporated to the model can affect the results. It constitutes the basis of an expanded study aiming at developing ENSI's biosphere modelling capabilities, including the selection of a suitable computer program for biosphere transport and dose calculations alternative to the one used by NAGRA. The compartmental code AMBER has been used to obtain the values of the BDCF, in contrast to the code Tame used in the assessment of NAGRA. The results obtained agree with the ones reported by NAGRA. The project has been divided into four sections dealing with (1) the description of the conceptual model and its implementation in AMBER, (2) the comparison between BDCF results obtained by NAGRA and the ones derived in this study, (3) sensitivity analyses of the results versus different exposure pathways and contamination paths and (4) the comparison of the BDCF resulting from the reference model with the ones obtained by other biosphere approaches carried out by different national radioactive waste management agencies. Twelve radionuclides have been included in the analyses: four non-metallic elements (¹⁴C, ³⁶Cl, ⁷⁹Se, ¹²⁹I) and 8 metallic elements that are part of the decay chain of ²⁴⁶Cm (²⁴²Pu, ²³⁸U, ²³⁴U, ²³⁰Th, ²²⁶Ra, ²¹⁰Pb, ²¹⁰Po). Ingestion is the pathway contributing most to the total received dose for an individual. Two general trends can be distinguished between metallic and non-metallic elements: metallic elements present high sorption coefficients, resulting in higher concentration in the top-soil and bed sediments, while non-metallic elements are more concentrated in the local aquifer and surface water. Ingestion of milk provides a good example to study this distinctive behaviour. Soil consumption and pasture consumption contaminated by root uptake are the main mechanisms of milk contamination in the case of metallic elements, while drinking water and consumption of pasture contaminated by irrigation are the ones dominating for non-metallic elements. The elimination of the solid material fluxes in the model results in calculated BDCF higher than the ones of the reference case. A comparison has been done between the model implemented and the approaches followed by different radioactive waste management agencies. The following three aspects of the comparison and sensitivity analyses exercise can be highlighted: 1) The model implemented in TAME by NAGRA is transportable to the AMBER code, the results do not depend on the numerical code used; 2) The sensitivity analyses have shown that ingestion is the main contributor to the dose, and that the exposure pathways through fish and eggs can be neglected; 3) For most of the metallic radionuclides, BDCF up to 3 times larger are obtained if solid material fluxes are neglected. This highlights the relevance of accurately describing the association of radionuclides with solid material as well as the adequacy of selecting an appropriate set of data to describe solid/radionuclide interactions.

[en] In this paper we evaluate the state of the fuel discharged from the reactor and later incorporate the results in the study of behavior of the stage during storage.

[en] This report discusses in a quantitative manner the evolution of the near field aqueous chemistry as a result of the interactions between three different intruding groundwaters (Aespoe, Gideaa and Finnsjoen) with the MX-80 bentonite buffer material. The main emphasis has been placed on studying the evolution of the main chemical buffers of the system (alkalinity and redox capacities) and the resulting master variables (pH and pe). The calculations have been done by using a set of thermodynamic and kinetic parameters previously calibrated against experimental data on bentonite/granitic groundwater interactions, in combination with the PHREEQC geochemical code. The results of the calculations indicate that the alkalinity buffer capacity is mainly exerted by the accessory content of carbonate minerals (calcite) in the bentonite system, while the ion exchange process plays a secondary (but not negligible) role. The Ca(II) content of the intruding groundwater has an impact on the resulting pH. For Ca(II) rich waters, like Aespoe, the resulting pH remains in the range of granitic groundwaters (7.5-9.5) during the overall repository lifetime (1 million years). For Ca(II) poor groundwaters, the systems evolves to high alkalinity (pH : 10.5 - 10.8) due to the depletion of calcite and the release of carbonate in to the near field aqueous chemistry. Concerning the reducing capacity of the system, this is mainly controlled by the accessory pyrite content, although the Fe(II) content in montmorillonite and in the carbonates cannot be disregarded. Reducing conditions in the bentonite/groundwater system are ensured throughout the lifetime of the repository system unless this is placed in direct and lifetime contact with the atmosphere (surface storage)

[en] The Proceedings of the Second Annual Workshop of the Collaborative Project CEBAMA addresses key scientific questions related to the use of cement-based materials in nuclear waste disposal applications. Progress beyond the state-of-the-art is achieved by providing basic knowledge, new experimental data, improved modeling and arguments for the Nuclear Waste Disposal Safety Case. CEBAMA is funded by the European Commission under the Horizon 2020 frame of EURATOM.

[en] The objective of this paper is a critical discussion of the main processes that determine the structure and radiological inventory CG UOX type and the very conditions of temporary storage. This study has allowed the configuration of state CG in potential function of oxygen affects the physico-chemical characteristics of irradiated fuel.

[en] This report discusses in a quantitative manner the evolution of the near field geochemistry as a result of the interactions between two different introducing granitic groundwaters and the FEBEX bentonite as a buffer material. The two granitic groundwaters considered are: SR-5 water, sampled in a borehole at 500 m depth in Mina Ratones, and a mean composition of different granitic groundwaters from the iberian Massif. The steel canister has also been introduced by considering the iron corrosion in anoxic conditions. (Author)

[en] The aim of the work is the presentation MAJVI model and its validation against experimental data obtained in different experimental conditions, including alteration of U0₂ results in the presence of alpha, beta and gamma, and carbonates and chlorides, as well as behavioral data irradiated fuel under reducing and oxidizing conditions.

[en] Solubility limits constitute a critical parameter for the determination of the mobility of radionuclides in the near field and the geosphere, and consequently for the performance assessment of nuclear waste repositories. Mounting evidence from natural system studies indicate that trace elements, and consequently radionuclides, are associated to the dynamic cycling of major geochemical components. We have recently developed a thermodynamic approach to take into consideration the co-precipitation and co-dissolution processes that mainly control this linkage. The approach has been tested in various natural system studies with encouraging results. The Pocos de Caldas natural analogue was one of the sites where a full testing of our predictive geochemical modelling capabilities were done during the analogue project. We have revisited the Pocos de Caldas data and expanded the trace element solubility calculations by considering the documented trace metal/major ion interactions. This has been done by using the co-precipitation/co-dissolution approach. The outcome is as follows: A satisfactory modelling of the behaviour of U, Zn and REEs is achieved by assuming co-precipitation with ferrihydrite. Strontium concentrations are apparently controlled by its co-dissolution from Sr-rich fluorites. From the performance assessment point of view, the present work indicates that calculated solubility limits using the co-precipitation approach are in close agreement with the actual trace element concentrations. Furthermore, the calculated radionuclide concentrations are 2-4 orders of magnitude lower than conservative solubility limits calculated by assuming equilibrium with individual trace element phases. 34 refs, 18 figs, 13 tabs