Creative Commons CC-BY-NC licence https://creativecommons.org/licenses/by-nc/4.0/ Mock-up wall for non-destructive testing and evaluation of thick reinforced concrete structures in nuclear power plants F. Al-Neshawy (1) , T. Ojala (1) , M. Ferreira (2) , J. Puttonen (1) 1) Aalto University School of Engineering, Department of Civil Engineering, Finland 2) VTT - Technical Research Centre of Finland, Finland Abstract The reinforced concrete structures in nuclear power plants (NPP) are deteriorated due to aging and environmental stressors during the lifetime of the power plant. To assess construction quality and the long-term performance of reinforced concrete structures, different non-destructive testing (NDT) and evaluation (NDE) methods are used. Some of the challenges for assessing the performance of these structures are that (i) the assessment could be performed only during the annual overhauls when testing is time- limited, (ii) the accuracy and reliability of the available NDT testing devices, (iii) uncertainty of the international uniformity of the methods used for NDT tests, and (iv) the creditability of results and analyses. To increase the reliability of condition evaluation, a mock-up wall representing a NPP containment concrete wall is constructed for the critical investigation of NDT&E methods and techniques. The mock-up wall contains simulated defects, which are representing typical defects in concrete structures such as dimensional errors, finishing errors, honeycombing, cracking, delamination due to structure stresses or deterioration mechanisms, embedded foreign objects in the concrete, voids adjacent to liner, and voids in grouted tendon ducts for the post-tensioned structures. This paper introduces modern NDT techniques that are suitable for assessing the condition of the mock-up wall under the real environmental conditions. The mock-up wall for NPP thick-walled reinforced concrete structures will enable the assessment of NDT&E methods and experts experience, and provides an important and very much need education environment for NDE experts. Keywords: NDE, concrete, thick-walled, defects, deterioration, reinforcement. 1. Introduction Non-destructive testing of concrete structures provides information about the condition of the structure including its components and materials. With modern NDT techniques, we are able to investigate relatively small details or to scan large surface areas to map reinforcing and cable ducts. For example acoustic techniques make it possible to describe the concrete structure and its mechanical properties. By combining NDT techniques, we obtain a comprehensive picture of the internal structure of the wall and the condition of large volumes of reinforced concrete in its undisturbed state. [1] The aim of this paper is discuss the use of available modern NDT methods for measuring the performance of thick-walled concrete structure. The objectives of the investigation were to test a thick-walled concrete mock-up with NDT techniques in order to: a) identify embedded simulated defects