NDT Matrix - A tool for selecting non-destructive testing methods for NPP concrete structures

As concrete structures in nuclear power plants (NPP) are exposed to various environmental conditions, concrete is affected by different deterioration processes during the life time of the power plant. To ensure the integrity and load bearing capacity of the concrete components, especially with regard to the extension of the life time of NPPs, the use of non-destructive testing (NDT) methods are essential for examining the quality of concrete and its reinforcement. However, current NDT techniques are faced with several challenges: (i) NDT inspection may primarily be performed only during the annual overhauls when testing is time-limited, (ii) the accuracy and reliability of NDT testing devices, (iii) uncertainty of the international uniformity of the methods used for NDT tests, and (iv) the creditability of results and analyses. An effective inspection of concrete components is only possible if the deterioration processes are identified and robust NDT testing techniques are available. This paper describes the tool developed for selecting suitable NDT methods for NPP structures made of reinforced concrete based on the age and expected degradation mechanisms of the structures under concern. The paper also assesses critically the NDT techniques that fulfil the needs of the safety evaluation of NPPs in Finland and are currently available for testing of NPP concrete structures.The tool comprises (i) the building materials used in structural components, (ii) ageing defects affecting NPP concrete structures, (iii) available NDT techniques and (iv) inspection schedule for concrete structures recommended for Finnish NPPs.