The performance of reinforced concrete containment structures is analysed with respect to their ability to prevent a fluid from percolating through the wall. For strategic structures (nuclear reactors, dams but also underground waste and energy storage reservoirs,..) the leaks break down into two flows, one of which passes through the porous networks of the cement matrix and the other passes through newly generated or pre-existing cracks. Conventionally, the fluids used to test the tightness are either liquid water or a neutral gas. In reality, the percolating fluid is more complex, in particular in the case of a nuclear incident where the percolating fluid (containing the radionuclides) consists of a mixture of air and hot water vapour.
The present project aims to pursue towards the quantitative experimental analysis and numerical multi-physics modelling of the two-phase (hot steam and air) flow and condensation processes during injection into fractured concrete material, building up on previously obtained results during the French national project MaCEnA.
Indeed, during this project, first ever experiments of in-situ quantitative visualisation of vapour condensation in cracked concrete through high-speed neutron radiography have been performed revealing a complex interplay between pressure and sorption flow phenomena and a significantly different behaviour between dry and saturated sample. Several experiments carried out at the scale of a structural element (reinforced concrete slabs) show that the air-vapour leakage rate tends to be lower than the leakage rate in dry air. Only very few experiments on laboratory scale on the injection of vapour in a porous media exists in the literature and the effect of a macro cracks have not been studied yet.
Since samples with intermediate saturation states cannot be easily obtained, this project will rely on numerical simulations of fluids in solids in order to investigate the intermediate saturation rate effects (after a throughout calibration of multi-physics models on the experimental results obtained in extreme cases i.e. dry and saturated samples). The global aim is to establish a direct physical link between the material microstructural content (porosity, intrinsic heterogeneities and saturation state) and the pre-inserted fracture network (openings, roughness and tortuosity) with fluid flow that will allow to reach a step further in well predicting the structural reliability and durability of pressurised concrete structures.
Matthieu Briffaut (Project PI)