Double Wall Containment Building Leak-Tightness Prediction: Strategy and Application

EDF operates a fleet of 56 nuclear reactors. For 24 of these reactors, the concrete containment building is a double wall structure. The inner wall is prestressed and has no metallic liner. Every ten years, the leak-tightness of the inner wall is verified by performing a pressure test. The leakage rate has to remain below a given threshold. As time passes, the leakage rate is getting closer to this threshold, so important coating programs are underway to keep the leakage rate within the regulatory limits. Therefore, it is important for EDF to be able to forecast the evolution of leakage, which depends on the concrete saturation and the level of prestress. The prestress decrease is related to creep and shrinkage of concrete and tendons relaxation (this last factor is considered negligible at ambient temperature). To tackle this issue, EDF has launched an important research program around the VERCORS mock-up, which is a containment building at scale 1/3 and has used this research program to improve its ability to predict the evolution of leak-tightness with time. In this paper, the different tools of the digital twin are presented, as well as an example of the use of the models originally developed on the VERCORS mock-up to help the choice of coating strategy for the third pressure test of an industrial containment building.