Non Destructive Evaluation of concrete material properties for nuclear power plant survey: results in the laboratory and on the VeRCoRS mock-up

Abstract

Pre-stressed concrete nuclear power plant containment vessel is the third barrier in case of an accident so that quantifying concrete properties with Non Destructive Evaluation (NDE) is a continuing goal. This includes the mapping of the following concrete properties: elastic modulus, water saturation, permeability. In addition, those measurements have to be challenged with the level of stress (which will be modified during an accident) possibly coupled with thermal induced damage. In the ANR French project 'Non Destructive Evaluation of containment nuclear plant structures' (ENDE) eight partners have carried out laboratory and in situ NDE measurements with the aim to compare and combine them to reach quantitative useful information about concrete conditions. In this paper we present a synthesis of the mains results obtained with classical and non-classical NDE methods. This includes electromagnetic techniques such as radar, capacitive measurements, resistivity measurements and ultrasonic measurements (impact echo, ultrasonic pulse velocity - in reflexion and transmission mode for longitudinal and transverse waves, surface waves, diffuse waves, coda wave interferometry, nonlinear acoustics, etc.). The laboratory experiments have been conducted on slabs 0.5 m x 0.25 m x 0.12 m, for one concrete mix formulated to be representative of nuclear containment walls, in different conditions: - sound concrete without any stress for different water saturations,- heat damage of partially saturated slab (at 80°C, 150°C, 200°C),- sound concrete under stress (up to 30% of the compressive strength),- heat damage concrete under stress.A series of NDE method combinations (using data fusion approach) is performed to solve the problem of multiple sensitivity issues. This laboratory work is then transposed on the VeRCoRS mock-up which is a 1/3 scaled concrete power plant (a Õ 16 m x h 30 m cylinder, with 0.40 m thick walls) heavily instrumented (700 sensors, 2 km of fiber optic). In this paper we present results obtained before, during and after a decennial test simulation which consists in increasing the internal pressure with air, maintaining its level to 4 bars during 2 hours and then decreasing back to the atmospheric pressure level.To conclude industrial and research perspectives are presented.