NDT assessment of a thick-walled reinforced concrete mock-up of NPP concrete structures

Abstract

Different materials within the Nuclear Power Plants (NPP) concrete structure can undergo ageing process which causes defects in the materials and can lose, partially or totally, their designed function. The typical defects include corrosion of reinforcement steel, delamination, cracks, malfunction of post-tensioning or steel composite systems etc. The testing methods to detect the defects of concrete structures are (i) destructive examinations and (ii) non-destructive testing (NDT). The challenges for assessing the performance of the NPP concrete structures using (NDT) methods include (i) the limited access time (only during the annual overhauls) and (ii) the accuracy and reliability of the available NDT testing devices. To overcome these challenges, a mock-up wall representing a section of the concrete containment of the NPP was built. Simulated defects and errors were embedded inside the wall such as dimensional errors, honeycombing, delamination, and voids in the post-tensioned grouted tendon ducts. Different NDT techniques and combinations were used for assessing the simulated defects of the mock-up wall. These techniques included basic NDT methods as rebound hammer, ultrasonic pulse velocity (UPV) and concrete cover meter and advanced NDT as Ground Penetrating Radar (GPR) and ultrasonic pulse echo (MIRA and MONOLITH). The results of basic NDT techniques as concrete cover meter, rebound hammer and UPV presented the basic characteristic properties of the concrete mock-up wall as concrete cover depth, compressive strength, and quality of concrete. The use of advanced NDT as GPR and MIRA and MONOLITH enabled us to detect and locate the embedded defect and the construction faults inside the mock-up wall. We conclude that the construction of the with simulated defects offers the possibility to investigate accuracy and reliably of the available NDT methods and increases the field experts’ skills providing also an important and very much needed educational platform for future NDE experts.