The influence of iron on water radiolysis in cement-based materials

For the time being, assessing the H2 source term generated by γ irradiated cement-based materials consists of simulating the radiolysis of the pore liquid on the only elementary reactions relating to the decomposition of alkaline water. Such incomplete description does not take into account the impurities contained in the cement and leads to underestimate the production of H2. Systematically present in cement materials, iron is likely to influence radiolysis by the disturbance induced on radical chemistry throughout the irradiation period. The faster reactivity of eaq- and OH radicals on Fe(III) and Fe(II), respectively, than on H2O2 and H2 is responsible for the lower recycling capability of the “Allen’s chain reaction”, allowing for H2 to be preserved in a closed system. A critical review of reaction data about iron complexes (hydroxo-, peroxo-) is presented in order to build up an “iron” database. Radiolysis simulations in cement porewater in the presence of Fe(OH)3 (considered as a model phase) show, as expected, an increase in the effective production of radiolytic H2 and the co-existence of exotic valence Fe(IV) with Fe(II) and (III) during the irradiation period (γ).