Safety evaluation methodology of engineering barriers at repository for low and intermediate level radioactive waste

Analyses of the roles of cement-based barriers in radioactive waste isolation show that models used to estimate their characteristics during the lifetime of the repository must consider the alteration of material properties with time due to degradation processes. Reinforced concrete barriers at repositories shall be designed in such manner that they fulfil besides isolative capabilities also the required functions of mechanical resistance and stability. Key elements of safety evaluation are mainly the correct selection of materials for mineral composites with cement binder (cements, aggregates, mineral additives and chemical admixtures) and their design, execution of construction works and production of precast concrete containers (continuous casting of concrete - no cold joints, limited number of construction joints, proper placing and consolidation, finishing and curing), strict control of used materials and inspection of works, as well as investigation after the construction (visual inspection, non-destructive testing, monitoring, ageing assessment on test containers). According to the methodology presented in this paper the lifetime of the repository can be estimated and, if shorter than 300 years or shorter than the period resulting from safety analysis, appropriate corrective measures shall be taken. (author)