AN UPDATE OF THE ASSESSMENT METHODOLOGY FOR CIVIL AGEING MANAGEMENT: DAMAGE DEVELOPMENT IN CONCRETE STRUCTURES OF A REACTOR DUE TO AGEING MECHANISMS

For many nuclear power plants worldwide the operation period will be extended to 60 or 80 years. As the operation period increases, the importance of knowledge of ageing mechanisms increases. In the framework of LTO there is limited knowledge about ageing and structural integrity of concrete structures. Recent developments have shown that ageing of civil structures receive more attention internationally. In order to increase the knowledge in the field of civil structures, this paper focusses on investigation of ageing of civil structures and determining an ageing management strategy. Knowledge of the ageing mechanisms of civil structures and especially concrete, will lead to improvement of ageing management and assessment methods of concrete. The presented work is part of ongoing research. In the past several steps have been made. Gathering of international information on civil structures ageing issues and management thereof (see PVP2019-93029 [3]), testing of a proposed assessment methodology by application to a nuclear reactor and comparison with another PWR with a steel containment (see PVP2020-21838 [4]) and creating a list of plant specific AMPs dealing with the relevant mechanisms at the various locations in a practical manner (see PVP2021-61499 [5]). The result was a general list with possible relevant locations and what type of measures could be taken. The current steps in the research focus on material behavior of structural concrete and practical assessment in finite element modelling techniques. In a this step, the concrete material and behavior will be investigated and explained. The characteristic properties of the concrete will be summarized and the degradation mechanisms will be identified. The assessment criteria for concrete finite element modelling are defined. The overall goal of the project is to obtain more knowledge on ageing management of civil structures and especially concrete. In the current research steps the aim is to create a predictive tool with the FE modelling technique for the damage quantification in concrete due to its ageing mechanism. The results of this ongoing work are presented in this report. The characteristic properties, degradation mechanisms including modelling options are identified together with an investigation on the assessment criteria for concrete finite element modelling. The behavior of structural concrete will be explained. The conclusion represents input parameters, modelling options and assessment criteria for finite element modelling of concrete. In the future steps a practical assessment in finite modelling techniques will be introduced in order to take into consideration the degradation of the concrete. The material properties will be analyzed and adapted in an FE Model.