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To evaluate the stress level and damage of a reinforced concrete containmentwall and its reaction to pressure variations, we implemented successiveultrasonic experiments on the exterior surface of the containment wall in thegusset area for three consecutive years. During each experiment, the pressureinside the containment wall increased gradually from 0 MPa to 0.43 MPa and thendecreased back to 0 Mpa.From the analysis of the ultrasonic coda waves obtainedin the multiple scattering regime, we performed Coda Wave Interferometry tocalculate the apparent velocity changes in the structure (denoted by $dV/V_a$)and Coda Wave Decorrelation (DC) measurements to produce 3D cartographies ofstress and crack distribution. From three source-receiver pairs, located at thetop, middle and bottom of the experimental region, we observe that coda wavesdilate, shrink and remain almost unchanged, respectively. This corresponds tothe decreasing, increasing and invariant pressure inside the concrete. Thecomparison of three years' results demonstrates that the variation of $dV/V_a$and DC under the same pressure test increases through the years, whichindicates the progressive deterioration and aging of the concrete. From a largecollection of source-receiver pairs at different times, the spatial-temporalvariations of $dV/V_a$ and DC are then used to produce a map of the structuralvelocity and scattering changes, respectively. We observe a decreasing velocityon the top part and an increasing in the middle one, which is in line with the$dV/V_a$ analysis. The reconstructed scattering changes (or structural changes)highlight the active region during the inflation-deflation procedure,corresponding to the opening and closing (and sometimes the development) ofcracks. The larger magnitude in 2019 than in 2017 indicates the increasingdamage in the concrete.

Ultrasonic monitoring of stress and cracks of the 1/3 scale mock-up of nuclear reactor concrete containment structure