Numerical simulation is essential for the understanding of the coupled thermal, hydraulic, mechanical, and chemical processes related to the disposal of radioactive high-level waste (HLW) and their effects on the long-term performance. The correct implementation of the physical-chemical processes in the numerical codes, the handling of the complicated problem, and the interpretation of the simulation results become more important due to the complexity of such systems. Within a Chinese-German co-operation program between BRIUG and BGR, a comparative coupled THM modelling exercise based on the Chinese disposal concept has been jointly performed using the numerical codes GeoSys/RockFlow and ANSYS. In the Chinese vitrified high level radioactive waste disposal concept, seven different materials (waste, carbon steel overpack, gaps filled with air and water, bentonite in the disposal hole, backfill in the tunnel, and granite rock) with in total more than 80 thermal, hydraulic, mechanical and petrophysical parameters have been considered. Three phases including excavation, emplacement of the waste package, and post closure were simulated. The coupling effects have been analysed step by step from single process modelling to coupled TM and THM modelling. The results from the two codes are comparable. The modelling results may serve as a basis for further construction design.
The Federal Institute for Geosciences and Natural Resources (BGR), which performs geo-scientific investigations of potential repository sites in Germany, has developed numerical codes to understand the coupled THMC processes related to the disposal of radioactive waste. One numerical fully THMC-coupled code is GeoSys/RockFlow, which has been developed jointly by BGR together with the Helmholtz Centre for Environmental Research (UFZ). This code is intensively verified within the framework of a benchmarking project and widely used in different international projects, e.g. DECOVALEX.
In 2004, BGR (Germany) and Beijing Research Institute of Uranium Geology (BRIUG, China) signed a Memorandum of Understanding for the Chinese-German cooperation covering bilateral experience exchange in the field of methodological study of site characterization, study of the mechanical and hydraulic properties of the granite from Beishan site, and study of migration of radionuclide in fractured granite.
During the current work phase, a comparative coupled THM modelling exercise based on the Chinese disposal concept in fractured rock has been performed. Taking the Chinese vitrified high level radioactive waste disposal concept into consideration, the BGR team simulated the evolution of temperature, humidity, and stress in the technical and geological barriers using the code GeoSys/RockFlow, while the BRIUG team used the commercial code ANSYS for the same purpose. Due to the complexity of the system and processes considered, the feasibility and handling of the codes have been analysed.
The modelling results may serve as a basis for further construction design.
Site characterisation for high level waste disposal is intensively being investigated by BRIUG. In Northwestern China the Beishan area in the Gansu Province has been considered as a potential area. Investigations including regional geological settings, crust stability, geological characterisation, hydrogeological and methodological studies are currently at work.
