Study On Solute Transport Based On The Deep Geological Disposal Of HLW

Comparing with other solute transport,solute transport in geological disposal system of HLW is characterized as complex way and law of transport,long distance,and so on. Therefore,based on the "multi-barrier system" design of HLW and analysis of safety assessment,the interaction between groundwater and the buffer in engineering barrier,and nuclide transport in geological barrier are primary researched when the groundwater comes back to the repository.The main works and conclusions are as follows:Firstly,on the basis of considering groundwater scenario as basic scenario of safety assessment and T-H-M-C processes,the interactions between saline water and buffer and the interactions between the fresh groundwater and buffer are simulated with EOS1 and EOS2 respectively.The simulated results of saline water show that salt accumulation in buffer material is not so significant,if properties of buffer material and saline water are nearly similar with those which are given in this paper;and the latter results show that precipitate of calcite will change the porosity of bentonite,but the effect on the other cation resulting from this change is not evident,moreover the impact on simulated system caused by Ca²⁺ is more obvious than the other cations.These simulated results are the corresponding reference for study on the interaction of groundwater and the buffer materials and the basis of further research of coupled T-H-M-C processes in near-field.Secondly,in order to resolve solute transport in the fractured media of far field, conceptual and mathematical models of solute transport in single fracture are built according to the double media theory,and analytic solutions with injection of exponential disintegration are deduced by Laplace transform.Relative concentrations of Th-229,Cs-135 and Se-79 in fracture and matrix are calculated respectively based on the analytic Solution,and their transport distance in fracture and diffusion depth in matrix are researched in detail.The results show that the retardation coefficient is negatively related with transport distance and diffusion depth of these nuclides.Moreover,many parameters,such as aperture,hydraulic gradient,will influence on these nuclide transport in fractured media,these influences are analyzed,and the results indicate that transport distance and relative concentration of these nuclides will increase with increase of aperture or hydraulic gradient.For the same nuclides,the change of hydraulic gradient has more influence on relative concentration when the hydraulic gradient is getting smaller.While the aperture is small(5.89×10^-5 m),the half life of the nuclides will affect relative concentration in fractured media by comparison the relative concentration of Se-79 and Cs-135.Because of the complex of fractured media,the fractured media is described by one dimensional multi-way solute model,and the transport of above-mentioned nuclides in fractured media is simulated with this model,the results show that the transport of Th-229 is the lowest while the Se-79 is the farthest,and the relative concentration of these nuclides in fracture will getting stable about 3×10⁷ years.In addition,these results are compared with the results which are calculated in single fracture,the comparison indicates that the correct description of fractured media is the sticking point of successfully numerical simulation.Finally,the nuclides which are researched widely in domestic by experiments,such as Cs-134,Co-57 and Tc-99,are chosen,and their transport in granite is simulated with one dimensional multi-way model.The results show that the transport of Cs-134 is the farthest and Tc-99 is the lowest under the same condition,which is the tentative gist of safety assessment of HLW geological disposal.