Research On Experiment And Simulation Of Nuclear Waste Repository In Roadway Liner Under Thermal-mechanical Couping

With the rapid development of China's economy,the use of nuclear energy more and more widely,but also produced a lot of nuclear waste.The safe disposal of nuclear waste has also become the focus of research around the world.The construction of an underground repository for geological treatment has been considered by the world as the most reasonable approach.Cement-based materials as an important material for the construction of nuclear waste disposal repository,in the design and construction of underground roadway lining of nuclear waste,not only to play the role of roadway support,but also have lower permeability as nuclear waste and rock between the artificial barrier.When the repository is running,on the one hand,the lining of the roadway is subjected to the stress of the ground.On the other hand,the radioactive elements in the nuclear waste will release a lot of heat during the disposal process,so that the lining stress is generated.This roadway lining is affected by the interaction of the temperature field and the stress field,resulting in a very complex thermodynamic coupling problem.Which affects the permanence and stability of the repository.Therefore,it is necessary to study the thermo-mechanical coupling characteristics of the cement-based materials used in the lining of the nuclear waste disposal.In this paper,the characteristics of the test and finite element simulation are used to study the characteristics of the cement-based materials in the tunnel,and the main contents of the research and analysis are as follows:(1)The theoretical study of temperature field and stress field of cement-based materials is deduced by heat conduction theory and the basic equations are deduced.(2)The water-cement ratio of 0.4,0.45 and 0.5 mortar samples was prepared.The thermal parameters of the three groups were obtained,including density,thermal conductivity,specific heat capacity and expansion coefficient.Through uniaxialcompression test and conventional triaxial test can get the three groups of the mechanical parameters,including elastic modulus,Poisson 's ratio,cohesion and internal friction angle.And the influence and variation of different water cement ratio on its t thermodynamic parameters were compared and analyzed.It can be concluded that with the increase of water-cement ratio,the sample density,thermal conductivity,specific heat capacity,elastic modulus,Poisson's ratio and cohesion are all decreased,which were negatively correlated with the water cement ratio;Only the expansion coefficient was positively correlated with the water-cement ratio;The internal friction angle was basically unchanged,all at 39 degrees.(3)Through the finite element software Abaqus numerical simulation,the establishment of nuclear waste disposal library model,select a reasonable thermal-mechanical coupling analysis method.The thermodynamic parameters of the three water-cement ratio were compared into the model,the variation law of temperature field and coupling field of different water-cement ratio roadway lining were simulated and analyzed.The results show that the change of water-cement ratio has little effect on the temperature field,and it has a great influence on the coupling field.The initial stress value,the rate of stress increase with time,the peak value of stress and the stress value after the treatment for 100 years of the tunnel lining with water cement ratio of 0.4 were smaller than those of the other two.Reducing the water-cement ratio can reduce the temperature stress which is more conducive to the safety and stability of roadway liner.This study provides a reference for the conceptual design of nuclear waste repository.