Abstract

The role of nuclear energy in the electricity production in Spain is critical. In 2016 it was the first energy source (21.4 % of the total electric energy generated) and amounts more than a third (35.2%) of the carbon-free energy. However, the spent nuclear fuel (SNF), even it is reprocessed, is a hazardous waste that remains active for tens to hundreds of thousand years. This makes it an important technical and social problem that will transcend for several generations. The construction of deep geological repositories (DGR) is the main option for the long-term disposal of this kind of waste. In this concept, bentonite barriers are expected to play a key role. Since different kinds of gaps are expected in the DGR (the “technological” ones due to the construction process and the “natural” ones, discontinuities in the host rock) and since these gaps are zones of potential weakness, one of the main functions of the bentonite is to seal the aforementioned gaps after its hydration and consequent swelling. Furthermore, the exerted swelling pressure must remain high enough to fulfil the safety requirements for the service life of the DGR.

Currently, there are several geomechanical models able to simulate the bentonite swelling behaviour at the repository scale. However, these models are implemented in codes that simulate only extremely simplified geochemical systems. This hampers, for example, the simulation of the effect of potential changes in the water salinity on the swelling pressure. Consequently, a tool able to simulate the coupled behaviour of the components of the DGR should be of interest, and its development is the main objective of this proposal.

In order to develop this computational tool, we will start from the base of the hydromechanical model with a simplified geochemical system that our Research Group has developed in the last years. Furthermore, we will use the geochemical modules implemented under different projects of the National Plan for the simulation electrokinetic soil remediation. We will carry out a review of the conceptual framework of the coupling between the hydromechanical and geochemical systems. We will put special effort into (i) analysing the effect that a “non-oversimplified” geochemical system can have on the modelization of the deformational behaviour of the bentonite microstructure; (ii) revising the coupling between the macro and microstructural strains; and (iii) studying the implications of considering a double porosity medium on the geochemical model. Nonisothermal conditions will be assumed.

In order to obtain data for the model verification and validation, a comprehensive bibliographic review is proposed with the purpose of producing a useful database for the research community.

Special attention will be paid to the communication of results and to the technology transfer. Easy-to-use applications based on the model with a geometrical parametrization of the DGR will be built so that interested organizations and companies use them. Moreover, technology transfer activities will be organised in order to make our work accessible to technology based companies interested in a commercial use of the model. In summary, a contribution to the long term management of the waste of one of the most important energy sources in the energy mix in Spain and the European Union is expected.