Contribution of the results of the CEBAMA project to decrease uncertainties in the Safety Case and Performance Assessment of radioactive waste repositories

Cement-based materials are key materials used in repositories of low, intermediate and high-level radioactive waste in any host-rock concept. These materials are used for waste conditioning, liners, seals as well as structural components. The CEBAMA (CEment-BAsed MAterials, properties, evolution, barrier functions) project (2015–2019) has been an initiative granted by the European Commission under the Horizon 2020 Research and Training Programme of the European Atomic Energy Community (EURATOM), focused on the study of cementitious materials. The project has addressed key issues of relevance for long-term safety and key scientific questions related to the use of cement-based materials in nuclear waste disposal applications. This publication presents the advances resulting from the research undertaken in the CEBAMA project, with special emphasis on their contribution to decrease uncertainties in the Safety Case and the Performance Assessment of radioactive waste repositories. The analysis is presented in three different axes, in coincidence with the lines of research of the project: degradation of cement-based materials and its impact on cement/clay interfaces; retention of safety relevant radionuclides and toxicants on cement-based materials and modelling advances in cementitious related systems. The research investigations have provided important new insights on process understanding and model developments which have significantly decreased the level of uncertainty. •Concrete and clay can co-exist safely in radioactive waste repositories.•Low-pH cement contributes to preserving the properties of the clay barrier.•Sorption analogies considered in Safety Cases for anionic radionuclides should be revised.•First time modelling on impact of hydration of low-pH cement on final mineralogical composition.•Good level of agreement in a long-term reactive transport modelling benchmark has provided confidence on the Safety Case.