Modeling of the oxic stage in a HLW disposal cell in an argillaceous host rock
Résumé
Determining the redox conditions in the near field of deep underground radioactive waste disposal cells is a key question regarding the performance of metallic components (e.g. waste overpack), which may undergo drastic corrosion processes in oxic conditions. This oxic transient is supposed to be short due notably to the oxygen consumption by corrosion and pyrite oxidation. However, the observed precipitation of Fe(III)-minerals as well as localized corrosion patterns on steel coupons placed during 6 years in a borehole drilled in the Toarcian argillite of Tournemire (France) may suggest that in-situ oxic conditions lasted several years, which is not consistent with reactive transport simulations performed with usual hypotheses (perfect contact between materials, high pyrite accessibility, water saturated conditions). Multicomponent reactive transport simulations considering gas diffusion were performed with the code HYTEC and reproduce correctly the observations made in Tournemire while considering imperfect interfaces and resaturation processes. The model was then applied to a disposal cell for highlevel waste (HLW) representative of the design developed in France, putting into evidence the possibility of a redox contrast between the front and back of a disposal cell in an argillaceous medium, as well as a duration of the