摘要(英) |
The use of nuclear power generation has become one of the major sources of electricity in the world, but the nuclear fuel waste is tricky to treat due to its radioactive characteristic that the half-life of decay is as long as hundreds of thousands of years. Additionally, the decay heat generated during the decay process will have a temperature field effect on surroundings. How to completely isolate the used nuclear fuel from the biosphere is the common goal of all advanced nuclear energy countries. At present, the treatment for used nuclear fuel is based on the concept of “Deep Geologic Disposal”, which intends to isolate migration of radioactive species in deep formations. However, it is mainly affected by Thermal, Hydro, Mechanical, and Chemical factors, called T-H-M-C coupling effect, and usually two or more factors interact, leading the unexpected function of the final disposal site.
To access the THM coupling effects, this study proposed a small-scale physical modeling and the related numerical simulation. Firstly, the small-scale test continues Lin (2017) T-H coupling test, and the test scenario was applied in terms of heating specimen first and water intrusion subsequently. This is much in accordance with the actual situation when the buffer material is subjected to the temperature change caused by the decay heat initially and then subjected to the groundwater intrusion in field. Time domain reflectometry (TDR) was used as the core method to observe the water intrusion, and different initial dry density sets (1.4 g/cm3, 1.5 g/cm3, 1.6 g/cm3) were applied in the small-scale test. Three-dimensional diagrams of apparent dielectric constant, temperature, and volumetric water content were established accordingly. Due to the high swelling pressure of the tested bentonite, it produced re-expansion after water absorption. The inside of the specimen was squeezed, causing the changes of pores and making the dry density be changed consequently. Furthermore, it was observed that the bottom of the specimen was squeezed upward because the fixed boundary, while the TDR sensor was pushed up. Since the volumetric water content of the three-dimensional diagrams needs to correspond to dry density, calculation error produced in the case of a change in dry density. Therefore, the current observations of water content variation did not meet the actual situation.
To verify the feasibility of the numerical simulation, this study adopt influence factors of dry density changes, swelling due to saturation, and the infiltration rate as function of temperature of the internal sample. The calculations of each dry density sample were performed and similar to those of the manual sampling, indicating a certain degree of confidence in the numerical simulation. Possible future demand for the case of deep geologic disposal field simulation, and the establishment of large-scale numerical simulation to be satisfied the actual situation of the disposal field |
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