Twenty years of in-service-inspection of concrete structures in Belgian NPPs

The 7 Belgian power reactors were built in the years 1969-1985 and are located in 2 sites Doel and Tihange. Every reactor building has a primary containment (steel or pre-stressed concrete) and an outer containment in reinforced concrete. Belgian NPPs have to comply with the requirements of US regulations, and more specifically with ASME for the containments and ACI-349 for seismic category 1 structures. Moreover, it has been decided to perform a full in-service-inspection (ISI) program for structures that are not themselves safety related but whose damage could be dangerous for other safety related structures. For a convenient organisation of inspection campaigns, concrete structures have been categorised into 4 domains. Primary containments are in a specific domain. Indeed their ISI program is fully determined by codes. Domain A is for the structures that can be inspected only during an outage of the plant: internal structures of the reactor building, water in-take galleries... Domain B is for structures or part of structures located is in the controlled area (one year of inspection periodicity). Domain C is for structures that can be inspected without special operational contingencies (3 years of inspection periodicity). Inspection procedures have then been written. They take into account the specificities of each site and of each structure. Moreover the feedback experience cumulated over 20 years of reactor operations has been used to focus inspectors' attention on specific substructures where damage can be expected first