Concrete containments in Swedish nuclear power plants. A review of construction and material

The purpose of project is the long-term accumulation of knowledge related to the status of existing structures in order to facilitate answers to questions that may arise in the future. We have visited all the power stations in Sweden and in conjunction with these visits we have gone through all the relevant documents relating to the constructional concrete. An assessment of the structural integrity, related to the question of cracking and hence seepage, has been conducted. Currently, the work has only been done on a random sampling basis as in many cases important information is still missing. Generally, it can be said that the relevant constructions are, from a structural integrity point-of-view, correctly designed and detailed and have very high safety margins for the load cases which constitute the functional demands placed upon the installation. Each containment structure (vessel) appears to have been designed and built using the best available knowledge at the time of construction. It may be of interest to note that when these structures were built there was a very high level of competence and experience of how to design, detail, and construct large concrete structures. The cement used for the majority of these large concrete structures forming nuclear power stations, namely a slowly hardening cement (LH cement), had very good properties, perhaps even better than those available today. Later structures were built with other cements and concrete mixes, although this has been partly compensated for by a choice of a higher nominal quality. The environment is favourable regarding potential degradation of the concrete, the reinforcement steel and the steel liner. Questions remain regarding the uncertainties of the methods used for continuous inspection of the cement injected prestressing steel. This is even the case for possibly insufficient injection around grouting mounting parts for manholes and other openings. Assessment of prestressing losses may also require attention. Current investigation shows that the documentation on the concrete containment structures of the Swedish nuclear power stations is fairly complete after the authors have obtained new information through a survey during 2001 and included these data in the report. The target group of this report are structural engineers and other people interested in knowing how the prestressed concrete containments in the Swedish nuclear power stations are designed, detailed and constructed. Uprising questions regarding the structural behaviour of the containment structures ought to be evaluated by using present material properties and not the data describing the used building materials at the design stage. The aim of this research project is to gain new knowledge on life span questions regarding prestressing steel in concrete structures, partly generally and partly with focus on Swedish nuclear power stations and Swedish bridges. The project covers both bonded and un bonded prestressing steel. This report describes the containment structures for all Swedish nuclear power stations. The information is both given in Chapters 5 through 16 and assembled in tables in Appendix A. The intention is that the documentation shall grow and be supplemented as soon as new information, either new data describing the containment structures or new measuring results, will be obtained or produced within current research project. Design and detailing of prestressed concrete structures are among others based on the knowledge of time-dependent material changes regarding concrete (creep and shrinkage) and prestressing steel (relaxation). The intention is that the following items will treated: general evaluation; testing of prestressing steel and concrete properties; assessment of the risk of a time-dependent increase of brittleness of the prestressing steel; comparisons with codes; modelling of steel relaxation; unidimensional modelling of prestressing losses; regard to elevated temperatures, temperature changes, simultaneous corrosion and mechanical stress, friction between steel and concrete, concrete elasticity, concrete creep and concrete shrinkage. Computing the structural capacity of concrete containments subjected to internal pressure and elevated temperature Following items will be included: General evaluation of the structural capacity of the containment structure subjected to internal pressure; Analysis of full scale pressure tests; Interpretation and evaluation of measuring results from prestressing forces in Swedish containment structures. Tests on the relationship between prestressing steel stress and strain under periodically elevated temperature and long-term loading ought to be carried out as well as tests on remaining strength. The project aims at studying the problems described above. In order to solve them, data have been assembled from the Swedish nuclear power stations. Supplementary measurements and laboratory tests will be conducted