Deformation stresses and mechanical behaviour of engineered barriers in the repository environment

The report surveys functioning of the engineered barriers in the Loviisa repository under deformation stresses of the solidification product and the concrete filling material. The survey is based on the latest estimates of the waste amounts and the corresponding repository plans, and on solidification product compositions and properties. The IVOFEM and NASTRAN software was used in the structural analyses. The materials were supposed to be homogeneous and linearly elastic and dislocations small. Accordingly, the design loads were chosen conservatively so that the impacts of deformation stresses are sufficiently overestimated. A reinforced concrete container lined with cellular plastic remains a watertight structure, meeting the requirements set in view of expansion of a solidification product. In view of the stresses, the decisive time is the intermediate storage stage. The greatest stresses are found in junctions between the container wall and the bottom and cover. The concrete filling between the waste packages cannot resist the drying shrinkage and wetting expansion stresses without cracking. Concrete walls of the repository can withstand the stress caused by wetting expansion of the waste packages only when strongly reinforced. However, the forces against the walls are so big that if cracks in the concrete walls are desired to be restricted, due to reinforcement steel corrosion or wall tightness, the present type of filling material between the waste packages is not necessarily technically the best alternative