Numerical assessment of the barrier integrity for a generic nuclear waste repository in crystalline rock

A crystalline host rock for the deep geological disposal of heat generating nuclear waste is one of the options discussed in Germany. Since a sufficiently large undisturbed rock zone to provide the essential safety function for containment of the waste cannot be assumed, a concept for disposal in multiple smaller unfractured rock zones has been developed and investigated in the joint research project CHRISTA-II. Regulation then requires the proof of integrity under thermo-hydro-mechanical (THM) load introduced by the repository. This contribution presents a modeling approach for the THM system evolution that allows for the assessment of the safety function of the geological barrier in crystalline rock, considering German regulatory requirements. Moreover with the proposed modeling approach, the quantification of the potential safety reserves at the repository can be quantified. Modeling results show that for the selected model conditions, the repository units have less safety reserves regarding tensile failure as compared to dilatant or thermal induced failure.