EDF operates 28 natural draft cooling towers in nuclear power plants. The ageing of their atmospheric cooling tower shells is periodically monitored. Proactive maintenance strategies require ranking the towers according to the risk of failure and the observed damage. The ranking includes all sorts of monitoring data acquired at the plant: foundation settlements, material properties, quantified crack patterns, shell deformation and meteorological data... This combined ranking rely on two pillars: a ranking of the towers based on their shell surface faults observed on-site and another ranking based on their safety margin in terms of structural behavior. The aim of this paper is to present the second pillar of the ranking.

The objective of the methodology is to calculate for each tower a failure quantitative risk index based on failure analysis of reinforced concrete. It includes three modules: a mechanical module which is the core module, an ageing module considering the carbonation and corrosion and a decisional module allowing ranking towers. Putting all towers on a ranking scale based on their global risk index allowing decision-maker to optimize their cooling tower maintenance program.

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