New Rapid Evaluation for LongTerm Behavior in Dee

Authors: Soshi Nishimoto Masataka Sawada Tetsuji Okada

Publish Date: 2016/04/21

Volume: 49, Issue: 8, Pages: 3323-3341

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Abstract

The objective of this study is to evaluate the longterm geomechanical behavior of a geological repository for highlevel radioactive waste disposal using the centrifugal nearfield model test The model consisted of a sedimentary rock mass bentonite buffer and model overpack and was enclosed within a pressure vessel Tests were conducted with a centrifugal force field of 30 G under isotropic stressconstraint conditions with confining pressures of 5–10 MPa and injection of pore water up through a time period equivalent to about 165 years in the field Our results showed that the measured values and the temporal changes in the displacement of the overpack the soil pressure of the bentonite and the strain of the rock mass were clearly dependent on the confining pressure These data were not convergent during the test Our data experimentally revealed that longterm behavior in the near field was changed by the geomechanical interaction between the deformation stress of the bedrock/disposal hole and the swelling behavior of the bentonite bufferWe are grateful to Yukihisa Tanaka and Koichi Shin for their fruitful discussions The manuscript was improved by the perceptive comments of  anonymous reviewers We would like to thank Fumitaka Arai Akira Sekiguchi and Kohei Hirano for their test supportIn Eq 8 the first term is the effective stress the second term is the thermal stress the third term is the pore pressure and the fourth term is the body force Here C ijkl is the elastic modulus u the displacement T the temperature T 0 the reference temperature χ the saturation function ρ the density of the bedrock ρ f the weight per unit volume of water barrho s= ρ−χδ ij ρ f δ i3 the weight per unit volume of saturated bedrock g the gravitational acceleration h the hydraulic head and b i the body force In addition δ ij is the Kronecker delta and β is equal to α 3λ + 2μ where α is the coefficient of expansion and λ and μ are Lamé’s constantsIn Eq 9 the first term is the migration of groundwater by the differential head Darcy’s law the second term the groundwater migration by the thermal gradient the third term the density variations of pore fluid by the change of head the fourth term the change of groundwater storage the fifth term the change in effective porosity due to the deformation and the sixth term the density variation of the pore fluid due to the change of temperature Here kθ is the hydraulic conductivity θ the volume water content D T the coefficient for migration of water by the thermal gradient n the porosity and ψ the pressure headIn Eq 10 the first term is the time variation of energy the second term the change in energy due to convection the third term the change in energy due to heat conduction the fourth term the heat migration due to the vapor the fifth term the variation of internal energy due to the change of pore pressure and the sixth term the variation of internal energy due to the deformation of the solid phase Here V fi is the groundwater velocity L the latent heat of vapor per unit volume and D Pν the vapor diffusion coefficient

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