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Cebama Report Summary

Project ID: 662147

Periodic Reporting for period 1 - Cebama (Cement-based materials, properties, evolution, barrier functions)

Reporting period: 2015-06-01 to 2016-11-30

Summary of the context and overall objectives of the project

The HORIZON 2020 EURATOM Collaborative Project “Cement-based materials, properties, evolution, barrier functions (CEBAMA)” is developed with the overall objective to support the implementation of nuclear waste disposal in deep underground facilities. Radioactive waste poses potential health hazards and risk to the biosphere including humans. The best way to handle and dispose this material is a topic of broad public debate and concern. Supporting safe options for the long-term disposal of nuclear waste is therefore a key component in developing sustainable strategies to implement nuclear energy as part of the energy mix in Europe but also within decisions to finally phase out the use of nuclear energy.

Cement-based materials are highly relevant for the nuclear waste disposal Safety Case, because they are widely used in a repository, e.g. as waste matrix, liners and structural components or sealing materials. In order to make reliable assessments of the potential evolution and performance of a repository with time, it is important to understand the specific chemical and physical processes affecting cement materials and their effect on radionuclide behavior and migration. Specific technical objectives tackled within CEBAMA are therefore chosen in order to give answers to key questions:

- How do cement-based materials affect the isolation properties of other barriers, like the host rock and the clay backfill material? Experimental studies are performed in CEBAMA to understand the interface processes between cement-based materials and the host rocks (crystalline rock, Boom Clay, Opalinus Clay, Callovo-Oxfordian) or bentonite backfill and assess the impact on physical and geochemical properties.

- How do specific radionuclides or toxic elements of interest behave in the presence of cement-based materials, or in media altered by the presence of these materials? Experimental investigations study the behaviour of elements which have high priority from the scientific and applied perspective in cement-driven environments (Be, C, Cl, Ca, Se, Mo, I, Ra).

- How well are we able to predict changes in transport properties coupled with chemical and physical processes on the cementitious matrix or in the cement host rock interface? Modeling work performed in CEBAMA is supporting advanced data interpretation and process modelling, covering mainly physical and chemical processes responsible for the changes in transport properties and extrapolate the models to different scales for application to Safety/Performance assessment.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Within the first 18 months of CEBAMA project, the main effort was focused on establishing the experimental programme and setting up modeling studies. A comprehensive summary of the work performed by the research groups involved in CEBAMA was presented at the First Annual CEBAMA Workshop in Barcelona (May 2016) and later summarized in the workshop proceedings which are made available at the CEBAMA website and as a KIT Scientific Report.

New experimental studies on interface processes and the impact on physical properties constitute the main working effort in CEBAMA. The multifold studies are considering several different interfaces and investigate a large variety of specific cement based materials. The work performed so far in CEBAMA includes for example the preparation of concrete samples casted for verification studies, determining the pH of various low-pH mix designs or studying the effect of the leaching of cementitious materials on clay materials of engineered barrier systems.

The chemical behaviour of selected radionuclides and toxic elements (Be, C, Cl, Ca, Se, Mo, I, Ra) in aquatic systems characteristic for cementitious environments are investigated in CEBAMA. The studies performed on these elements generate new basic data in relatively simplified systems and address sorption, diffusion and solubility. The information derived is incorporated in more complex models in order to predict radionuclide retention or mobilization processes in a repository.

Modeling approaches and modelling tools are developed in CEBAMA in order to analyze and predict processes that can impact the physical and chemical properties of cementitious materials and the interface between cement and host rocks or bentonite. Work is performed in close connection with the experimental studies conducted in CEBAMA. Modeling also establishes a close link with the Safety Case and Performance Assessment requirements. Activities so far, include the modelling of the coupling between cement paste microstructure changes and its physicochemical properties, upscaling the microstructural features of cement and concrete changes for incorporating them in macro scale reactive transport models, or extrapolating numerical models for long-term conditions.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The studies performed in CEBAMA offer various perspectives to progress beyond the current state of the art in this field including new methodologies to study the changes in microstructure and impact on transport properties. At this early stage the projected impact defined in the description of the CEBAMA action is still valid.

As main outcome and key impact of the CEBAMA project, comprehensive advanced modelling approaches are developed which will allow predicting the transport characteristics such as porosity, permeability and diffusion parameters of cement-based materials in contact with the engineered and natural barriers of repositories in crystalline and argillaceous host rocks and the retention of radionuclides by cement-based materials. These improved models may be applied for high level waste disposal but also for scenarios in low and intermediate level waste disposal, currently implemented in several countries. CEBAMA will enhance the publically available knowledge on the performance and reliability of the barrier systems for nuclear waste repositories. This has impact on the public debate on nuclear waste disposal, also by keeping non-scientific stakeholders informed.

Besides pure scientific and technical based impacts in terms of generating specific knowledge and decreasing uncertainties, the enhanced cooperation/exchange and knowledge transfer between different institutions on an international level is highly valuable. CEBAMA partners from countries with less advanced programs can perform research in close cooperation with leading European research institutions with access to advanced state-of-art analytical equipment. In general, an important impact from implementing the work program is that CEBAMA Consortium members will become aware of the respective complementary competencies and thus can jointly tackle follow-up problems in the future. The experimental and modelling work in CEBAMA is to a significant extend performed within PhD theses. This contributes to the continuing availability of highly trained specialists for implementers and regulators.

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