Acceptance criteria for Maintenance of Nuclear Concrete Structures: Feasibility Study

The aim of this preliminary study is to identify and compile information regarding existing acceptance criteria that trigger maintenance actions of reinforced concrete infrastructure of nuclear facilities. This study focuses on the acceptance criteria for all aspects of safe and reliable long-term operation, i.e. structural performance, durability and ageing of reinforced concrete structures. The study covers a literature review of current standards and guidelines used in several fields of civil engineering concrete infrastructure, experience gained from relevant research projects and own practical experience, and shared expertise from international technical committees addressing all aspects of concrete structures. In order to assess the effects of age-related deterioration of reinforced concrete structures, structural condition assessment of concrete structures must be performed. This includes visual inspections, special inspections and analytical methods. The study reveals that a significant proportion of condition assessment is limited to the use of visual inspection. Since inspection based on observation is subjective, and the assessment is in great part qualitative, a lot of effort has been put into developing acceptance criteria for the assessment of reinforced concrete structures. This has resulted in extensive descriptions of condition damage and defects, including image/pictorial guides. The use of special inspection is strongly dependant on the experience and qualification of the structural inspector, and is qualitative in nature. There are no comprehensive guides with procedures to specify the need for destructive and non-destructive testing methods. Furthermore, there are no guidelines how to interpret the results of both destructive and non-destructive tests. Concrete durability performance is a function of its constituents, its quality, its location and environmental loading conditions. This makes concrete durability a unique evaluation for every structure, and even for the same structure for different structural elements. For this reason, it is based on nowadays expertise and knowledge level, and it is not possible to generalise acceptance criteria for all levels of condition assessment, and for all structures. This study also includes a list of R&D needs.