Study Of The Coupled Thermo-hydro-mechanical Behavior Of Buffer Bentonite Blocks Including Gaps In The High-level Radioactive Waste Repository

As the buffer material,bentonite blocks are located around the high-level waste container so that the migration of nuclide will be prevented.Under the influence of water penetration from the surrounding rock and continued heat increasing of the nuclear waste,there is a complicated thermo-hydro-mechanical coupling eflfect in the buffer material.The existence of gap between two bentonite blocks has a non-negligible influence on the thermo-hydro-mechanical coupling.Therefore,on the basis of the thermo-hydro-mechanical coupling theory considering multiphase flow transmission,the paper uses the finite element method to study the thermo-hydro-mechanical coupling effect in buffer material under different kinds of bentonite gaps.The main work and research result of the paper is as follows:(1)On the basis of the thermo-hydro-mechanical coupling theory considering multiphase flow transmission,the paper inserts the coupling theoretical equations of buffer material into the multi-physics field coupling simulation software COMSOL Multi-physics.Then the paper realises the numerical solve of the coupling equations by the advantage in multi-physics field simulation.(2)Through reading the relevant papers,the related parameters of GMZ bentonite have been collected.The paper simulates the large working thermo-hydro-mechanical coupling experiment which is simply as China-Mock-Up.Through the simulation,the paper gets the interaction of penetration,temperature and mechanical field and the development of vapor pressure,gas pressure and void ratio.Through the contrast with the experiment and the existing simulation results,the new numerical method will be seen as a feasible way to simulate thermo-hydro-mechanical coupling effect.(3)According to the difference in the properities of bentonite material and bentonite blocks,a new calculation method of continued iteration is been built to reflect the influence on the permeability coefficient by the squeezing of the gap area.(4)The paper analyzes the influence of the dry density of gap medium and gap width on the thermo-hydro-mechanical coupling effect in the buffer material including cylindrical gap.Through the simulation,it can be concluded that the existence of gap not only accelerates the decrease of suction value and the increases of saturation value,but also increases the horizontal displacement greatly.In addition,the width of gap and propeities of gap material has an obvious influence on the suction,saturation and horizontal displacement value in the buffer area,but not temperature.(5)The paper analyzes the influence of the dry density of gap medium and gap width on the thermo-hydro-mechanical coupling effect in the buffer material including radial gap.Through the simulation,it can be concluded that the existence of gap not only accelerates the decrease of suction value and the increase of saturation and temperature value,but also makes the vertical displacement come into being.In addition,the width of gap and propeities of gap material has an obvious influence on the suction,saturation,temperature and vertical displacement value in the buffer area.(6)In order to simulate the pratical thermo-hydro-mechanical coupling effect in buffer material with more accuracy,the paper builds the calculation model under the both exist of cylindrical and radial gap,and analyses the development of multi-physics field variable in different time and space.The research results of paper has a significant meaning to analyse the bentonite blocks' ability of preventing the migration of nuclide in buffer material surrounding the waste container in the high-level waste disposal repository.