Investigation of Consequences of Concrete Alkali Aggregate Reaction on Nuclear Structures

Several degradation mechanisms of concrete structures shall be investigated to define Ageing Management Programs (AMPs) of Nuclear Power Plants (NPPs). With many NPPs considering life extension and long-term operation, understanding and mitigating the consequences of Alkali-Aggregate Reaction (AAR) has become paramount.

After identifying the need to assess the consequences of AAR and to find a way to take into account these consequences in the assessment of structures, CNSC staff established an extensive research program to cover the analytical and experimental sides of assessing existing concrete structures. The goal of the research program was to provide technical support for developing an independent regulatory position regarding the condition assessment and the acceptance criteria for concrete structures subjected to the AAR phenomenon. The main results show that, compared with the reference shear wall, the ductility of the AAR-affected shear wall was significantly lower, and the ultimate capacity was slightly higher. The results of the experimental program were further used as input data for the numerical simulation benchmarks performed during Phases II and III of the three-phase Assessment of Structures Subjected to Concrete Pathologies (ASCET) international project of the Nuclear Energy Agency (NEA). It was shown that the peak strength of the walls was predictable, but losses of ductility were difficult to model.

This paper will first present the holistic approach undertaken to assess the properties of concrete specimens subjected to accelerated environmental conditions at the material and structural levels as well as the numerical simulations performed. The results of the benchmarks of the ASCET project will be discussed further. A brief conclusion will sum-up the overall pertinent outcomes.