The aim of this study is to develop backfilling concepts with capabilities to attenuate near-field effects of mined repositories in argillaceous host rocks by examining the characteristics and the performance of a clay host rock and potentially favourable engineered barriers and assessing system components which contribute to their durability.
The main topics are :
- study of near field clay and materials used in HLW underground repository;
- study of selected representative emplacement configurations of HLW-repository;
- proposal of a concept and recommendations for future works.
The main results are :
- the HLW canister, used as reference, cannot be considered as a preventive barrier due to its collapse at an outside pressure of 2.5 MPa and to the sensitivity of austenitic steel at the stress-corrosion cracking;
- sulfate resistant concrete (SRPC or C3A = 0 %) can be used as backfilling material or as lining if it is sufficiently matured before being solicited by the thermal loading generated by the HLW packages;
- excavated Boom clay can be used as buffer material but future research is necessary to determine the appropriate processing to be used and the eventual adjuvant(s) to be considered;
- a program called "TEMPRES" is now available to compute temperature, pore-water pressure and stresses around heating sources in clay host rock, its validation is not yet fully performed but the first results obtained by modelling the BACCHUS test are promising;
- a program called "SOURCE" was developed to approximate the pore water pressure response at digging and drilling works performed in a isotropic medium where the pore fluid flow can be related to the pore water pressure by the Darcy's law.
The proposed concept is a first attempt to attenuate the near-field effects of HLW in argillaceous rocks by using engineered barriers taking into account their properties but also possible placement procedures.