The influence of temperature and hydration on the long term stability of the buffer material

The influence of temperature and hydration on the long term stability of the buffer material was studied during two experimental studies - "Mock-Up-CZ" experiment and "Long-term stability of engineering barriers" project. The objectives of these studies is to identify mineralogical, chemical and geochemical changes and describe transformation processes in the bentonite materials due to heating and interaction with various saturation media (with different chemical composition) under controlled laboratory and in situ conditions. The Rokle bentonite suitability for its use in the Czech deep repository of high-level radioactive waste was investigated. Mineralogical changes in the bentonites were evaluated by X-ray diffraction. The material of the barrier of the Mock-Up-CZ experiment is a mixture of non­activated Rokle bentonite (85 vol.%), quartz sand (10 vol.%) and graphite (5 vol.%). The barrier has been subjected to thermal stress (up to 90 řC) and synthetic granitic water for 45 months. No sample from 70 analysed samples taken at different depth levels and distances from the source of the heat and/or water showed measurable transformation of original smectites. Newly formed gypsum bordered by illite aureole was detected in the upper part of the experimental set-up (backfill samples), i.e. in the..