Condition assessment of concrete structures at nuclear power plants by state of the art non-destructive testing

The approach combining Non Destructive Examination (NDE) with Finite Element Analysis (FEA) methods is both workable and necessary in order to accurately determine and predict the condition of Nuclear Power Plant (NPP) containment structures. This approach was introduced in the European 5th Framework Project with acronym CONMOD [1]. The current paper presents some of the work performed after the CONMOD project combining the on-site investigation at nuclear power plant (NPP) stations in Sweden and Finland. Several non-destructive techniques were chosen for the investigations described in this paper. The MASW (Multi Channel Analysis of Surface Waves) and Impact Echo (IE) techniques have been used for evaluation of thickness and stiffness of concrete and also for location of possible defects. The above-mentioned techniques have been applied under investigations of concrete containments. Additionally reinforcement corrosion was investigated in cooling water channels by means of the Galvanostatic Pulse technique allowing determination of corrosion rate. Further, following the CONMOD concept, the coupling between the non-destructive measurements on site and finite element method is established. As the result of this coupling, the information about the status of concrete structures in nuclear power plants is obtained. In the ongoing research & development project CONSAFESYS (Concrete Containment Condition Status & Ageing Examination System) the qualification and validation of investigative methods and diagnostic tools and analysis for reactor containments are further developed. One unique benefit with the CONSAFESYS project is the possibility of introducing artificial defects and anomalies into a decommissioned reactor containment structure.