Main Outcomes for AAR Studies on Large Scale Experiments in the ODOBA International Project

Considering the importance of the potential effects induced by internal swelling reaction (ISR) on the third barrier of confinement for nuclear power plants and the lack of knowledge on ISR development on massive structure, IRSN launched the ODOBA international project in 2016. Indeed, the knowledge on ISR relies mainly on small-scale and separate effect experiments in laboratories, or medium scale outdoor experiments. Their kinetics and the structure effect of the different parameters involved (temperature, hygrometry, mix, reinforcement…) depend on the studied scale. The ODOBA project is based on experiments on very large concrete blocks widely instrumented, located in Cadarache (France). The concrete mixes are chosen with the objective of developing ISR: either the delayed ettringite formation (DEF), or the alkali-aggregate reaction (AAR), or a possible coupling between AAR and DEF. These mixes have the particularity of being as close as possible to those used for French nuclear reactor containment buildings, but with lower alkali level than former similar experiments. Concerning the 20 tons AAR blocks poured from 2016 to 2018, the residual expansion tests on small samples extracted by coring showed a very weak development of AAR pathology, with a swelling qualified as negligible according to the recommendations in force. An overview of the state of the blocks devoted to AAR is introduced by successively presenting the formulations of the concretes, their characterizations by destructive tests and their follow-up from early age until now without ageing acceleration. The lessons learned give a better assessment of AAR development possibilities for a mix using medium alkali level and classical Potentially Reactive aggregates at very large scale.