EURAD Domain Insight (3.4.1) - EBS

The fundamental objective of disposing of radioactive waste is the protection of people and the environment from harmful effects of ionising radiation (IAEA 2006). Adequate safety standards for planning, development, operation and closure of a disposal facility have been defined by IAEA (2011). The disposal planning bases on the regulatory framework as well as on the definition of a safety approach and adequate design concepts for safety. A general requirement of the safety approach is that the safety of the closed disposal facility should rely on passive means that do not need any further actions. The safety strategy will be implemented by the Engineered Barrier System (EBS) consisting of diverse technical and geo¬technical barriers, which provide – in combination with the geological barrier – an acceptable level of safety. Understanding of the components of the repository system and their future evolution is fundamental for the development of a suitable safety concept and an adequate multi-barrier system. The multi-barrier system consists of a combination of the geological barrier and the EBS. The EBS is defined as a system of man-made components including the waste form, the waste canisters, the disposal containers, the buffer, the backfill, the repository seals and other engineered features, e.g. supercontainers (Belgium, Swedish/Finnish KBS-3H). Isolation and containment of radionuclides in the disposal system are principal safety functions that have to be met by the multi-barrier system for a safe geological disposal of long-lived radioactive waste (IAEA 2011). To comply with these safety objectives, the components of the multi-barrier system have to combine multiple safety functions and provide a high level of diversity and redundancy, so that the overall safety is not dependent upon any safety function, i.e. safety is maintained even if one or more safety functions underperform. The safety functions will be provided by physical and chemical properties of the barrier components, such as low water permeability to, limited corrosion, dissolution, leach rate and solubility, high retention of radionuclides and retardation of radionuclide migration. Due to comprehensive RD&D (research, development and demonstration) work especially in underground research laboratories (URL), maturity of knowledge and technology of EBS components is increased and their interaction with the geosphere have significantly advanced. But optimisation is a key issue in any deep geological repository (DGR) work and therefore corresponding future work may focus on increasing the functionality and efficiency of the barrier. Furthermore, outstanding uncertainties have to be analysed. These could include, for example the detailed characterisation and evolution of the geosphere, as well as climate evolution. Where uncertainties are addressed in models by simplifications and abstractions, these need to be evaluated and justified. With increasing progress of RD&D work on EBS, operational aspects and feasibility assessments and demonstrations will become more important as complements to performance and safety assessments as well as for associated RD&D work.