An Assessment Methodology for Civil Ageing Management and Concrete for LTO/CSO Based on International Standards and Engineering Judgement
Authors: de Haan - de Wilde F. H. E. , de Bont C. G. M. 
Published: October 2020

For many nuclear power plants worldwide the operation period will be extended to 60 or 80 years in the coming 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 (for example concrete degradation in bunker building Doel and buried piping attention in topical peer review EU). In order to increase the knowledge in the field of civil structures, this work 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.

As a first step international information was gathered on civil structures ageing issues and management thereof (see PVP2019-93029). In addition a very high level assessment methodology was proposed.

The goal of the project is to obtain more knowledge on ageing management of civil structures and especially concrete. It will lead to an assessment method for civil ageing management and ageing management programs dealing with the relevant mechanisms at the various locations in a practical manner.

The results of this ongoing work are presented in this report. The initial proposed assessment methodology has been tested by application to the HFR research reactor. The resulting list of relevant AMPs has been verified with the outcome for another PWR with a steel containment. With this experience the assessment methodology is improved. In addition each civil SSC in the scope of the Continued Safe Operation program is linked to the relevant AMP(s). The improved, but not finalized assessment method of ageing management for civil structures can be seen in figure 2.

The proposed assessment method for ageing of civil structures has been tested, compared and improved. The results indicated that the method can be used to obtain a list of plant specific AMPs. The comparison of the list of relevant AMPs for a steel containment PWR, showed similar results. What is added to the assessment method is the link to the TLAAs for civil structures. The detailing to a level of practical work instructions for the maintenance of the plant has to be made in the near future.

In the near future the step will be made from a high level of IGALL AMP to a practical AMP that will deal with the relevant mechanisms at the various locations. Therefore further steps are in studying of relevant degradation mechanisms, relevant AMPs (like AMP305 [9],AMP306 [10]) and applicable literature (e.g.[21]) in combination with the practical knowledge from operation of a reactor. The international developments on ageing management of concrete will be included. It is foreseen that the future report will contain information on concrete degradation mechanisms relevant for nuclear reactors. If findings requires calculations the assessment method will be verified with the finite element modelling techniques.