Radiolytic Hydrogen Production Associated With Cement Hydrates

Water radiolysis is one of the consequences of the interaction between a cementitious matrix and low or intermediate-level radioactive wastes that are encapsulated within this matrix. Thus, for safety assessment, the hydrogen released from the cementitious packages must be limited and quantified. Up to now, the hydrogen production was thought to arise solely from the water trapped in the cement porous network. However, recent experimental and theoretical indication suggest that the cement paste itself can play a significant role in H2 production. Calcium silicate hydrate (C-S-H) is the main hydrate (70%) of Portland cement. This present work is focused on the interactions between water and C-S-H, a nanocrystallized product with a layered chemical structure. The aim of this study is to understand the radiolytic mechanisms of the hydrogen production in hydrated C-S-H. Therefore, after characterization by several techniques (nitrogen gas adsorption-desorption, X-ray diffraction, thermogravimetric analysis, infrared and Raman spectroscopies, small-angle X-ray scattering), C-S-H with different chemical composition and cured at different controlled relative humidities were submitted to gamma radiation and heavy ions beams to determine their H2 radiolytic yield, G(H2). The results show the H2 production is strongly modified in highly confined system in comparison to the bulk water. The electron paramagnetic resonance (EPR) spectroscopy experiments using trapping molecules are in progress to reveal the reaction mechanisms involved. The present work would help us to understand the radiation effects in confined media and particularly in cements.