Simulation Study Of Temperature Field Of Nuclear Waste Repository Near-Field Granite Surrounding Rock

With the development of nuclear power and nuclear technology, problem of nuclear waste repository arises inevitably. In deep geological disposal, heat from decay of radioactive elements in nuclear waste transfers to outer engineered barrier and near-field surrounding rock to generates temperature field. Change of temperature filed of near-field surrounding rock will make thermal stress of surrounding rock changed accordingly, and this change in the high temperature condition may cause some state change of repository, so it will threaten the tightness and security of repository, impact groundwater system and radionuclide migration eventually. Research for temperature filed change of near-field surrounding rock can provide important support for repository design and important reference for study of repository physical properties such as thermal, stress, and it is significant for the monitoring and prevention of nuclear waste tank leakage accident caused by microbe activity or geologic activity.This thesis takes temperature field of nuclear waste repository near-field surrounding rock as the main research object, analyses the distribution and change of surrounding rock temperature and thermal stress in numerical simulation way. Meanwhile this thesis puts forward the idea that measuring surrounding rock temperature by distribution optical fiber sensing system, and makes simulation experiment research for this idea. The completed work and acquired recognition contains:(1) Multi-layer barrier system of nuclear waste repository is introduced, type of granite rock and style of horizontal drilling disposal are selected to make numerical simulation. thermodynamic properties of granite rock is analyzed, thermal governing equation and thermal stress equation are analyzed and derived, principle and function structure of distributed fiber optical temperature sensor system are expounded.(2) Numerical model of nuclear waste repository near-field surrounding rock which contains three drillings was established by finite element analysis software ANSYS, and numerical simulation for temperature field of near-field surrounding rock in 100 years was completed. Simulation result indicates that temperature variation is not linear relationship about time, the drillings' temperature reaches the top at about 10 years after disposal beginning, and temperature of each part of surrounding rock increases rapidly in 10 years to 20 years, and decreases slowly after getting to its' top. And the temperature field of 10 m, 15 m and 20 m in different drilling spacing are compared, finding that the spacing is smaller, the mutual influence of temperature field between the drillings is more obvious, and the relatively reasonable drilling spacing is 15 m.(3) Preliminary numerical simulation of thermal stress field is made, which is relative coupling field of temperature field. Simulation result indicates that within 100 years after disposal beginning the inner thermal stress of surrounding rock is decreasing gradually from its' larger value, and reduces an order of magnitude in 100 years. Thermal stress distribution of each layer of surrounding rock is not balanced, the inner layer is larger, the outer layer is smaller, and the middle layer is minimum.(4) Simulation results of temperature field and thermal stress field of near-field surrounding rock indicate that temperature of near-field surrounding rock has a dramatic change in the first 10 years, and thermal stress generated is relatively larger, and inner temperature is still at a high level in 10 to 30 years.(5) One idea to measure temperature distribution of nuclear waste repository near-field surrounding rock by distribution optical fiber sensing system is proposed, simulation experiment research is carried out, then the experiment data obtained and numerical simulation result are compared and analyzed, founding that numerical simulation data graph is better than experiment result in smooth degree, and experiment result graph is higher than simulation data in temperature value of each layer. Meanwhile the differences are analyzed, and research method of temperature field of nuclear waste repository near-field surrounding rock is discussed.The innovation points of this thesis contain:(1) Style of horizontal drilling disposal is selected, and numerical simulation of temperature field and thermal stress field of nuclear waste repository near-field surrounding rock which is granite type is made by ANSYS software. Several ways and angles are used to analyze temperature field and thermal stress field in detail, indicating that temperature of near-field surrounding rock has a dramatic change or high value in the first 30 years, and thermal stress generated is relatively larger.(2) The idea that distribution optical fiber sensing system can be applied in measuring surrounding rock temperature is proposed, and its' feasibility analysis and experiment research are carried out. The way combined experiment method and numerical simulation style is discussed, and it can provide one reference for relative research of temperature field of repository.The study achievements can provide important reference for analysis and research of temperature field of nuclear waste repository near-field surrounding rock, and provide important basis for research of engineering properties of nuclear waste repository rock and response laws of rock in multi-field coupling condition.