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New Rapid Evaluation for Long-Term Behavior in Deep Geological Repository by Geotechnical Centrifuge—Part 2: Numerical Simulation of Model Tests in Isothermal Condition

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Abstract

In high-level radioactive waste disposal repositories, there are long-term complex thermal, hydraulic, and mechanical (T–H–M) phenomena that involve the generation of heat from the waste, the infiltration of ground water, and swelling of the bentonite buffer. The ability to model such coupled phenomena is of particular importance to the repository design and assessments of its safety. We have developed a T–H–M-coupled analysis program that evaluates the long-term behavior around the repository (called “near-field”). We have also conducted centrifugal model tests that model the long-term T–H–M-coupled behavior in the near-field. In this study, we conduct H–M-coupled numerical simulations of the centrifugal near-field model tests. We compare numerical results with each other and with results obtained from the centrifugal model tests. From the comparison, we deduce that: (1) in the numerical simulation, water infiltration in the rock mass was in agreement with the experimental observation. (2) The constant-stress boundary condition in the centrifugal model tests may cause a larger expansion of the rock mass than in the in situ condition, but the mechanical boundary condition did not affect the buffer behavior in the deposition hole. (3) The numerical simulation broadly reproduced the measured bentonite pressure and the overpack displacement, but did not reproduce the decreasing trend of the bentonite pressure after 100 equivalent years. This indicates the effect of the time-dependent characteristics of the surrounding rock mass. Further investigations are needed to determine the effect of initial heterogeneity in the deposition hole and the time-dependent behavior of the surrounding rock mass.

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Abbreviations

B :

Strain–displacement operator matrix

c l :

Specific heat of the liquid water

C lP :

Liquid water capacity

c s :

Specific heat of the solid phase

C vP :

Isothermal vapor water capacity

C vT :

Thermal vapor water capacity

D :

Tangential stiffness tensor for the solid phase

D m :

Molecular diffusion coefficient for the vapor flow in air

D Pv :

Isothermal vapor-diffusion coefficient

D Tv :

Thermal vapor-diffusion coefficient

D v :

Effective molecular diffusion coefficient of water vapor

E :

Young’s modulus

F B :

External force vector

F p :

Nodal force vector by swelling

g :

Gravity acceleration vector

I :

Identity tensor

k :

Intrinsic permeability tensor

K D :

Bulk modulus of the solid phase

k rl :

Relative permeability function

l :

Parameter for progress of swelling

L :

Latent heat of vaporization of water

P g :

Pore gas pressure

P l :

Pore liquid pressure

P l0 :

Initial pore liquid pressure

Q B :

Source term of the water flow

q rv :

Vapor flux

Q TB :

Heat-source term

RH:

Relative humidity

R v :

Specific gas constant

s :

Suction

S g :

Gas saturation

S l :

Liquid water saturation

T :

Absolute temperature

u :

Displacement vector

β Pl :

Compressibility of water

β TD :

Drained linear thermal expansion coefficient of the medium

β Tl :

Linear thermal expansion coefficient of water

ε :

Total strain tensor

ε aw :

Accumulated swelling strain

ε smax :

Maximum swelling strain

ε v :

Volumetric strain

λ dry :

Thermal conductivity of the dried medium

λ m :

Apparent macroscopic thermal conductivity of the medium

λ sat :

Thermal conductivity of the saturated medium

μ l :

Fluid viscosity

ν :

Poisson’s ratio

(ρc)m :

Heat capacity of the unit volume of the medium

ρ l :

Liquid water density

ρ l0 :

Reference liquid water density

ρ m :

Density of the mixture

ρ s :

Density of the solid phase

ρ v :

Vapor water density

ρ vS :

Saturated vapor density

σ m :

Mean stress

τ :

Tortuosity factor

ϕ :

Porosity

χ :

Bishop’s parameter for effective stress

ω smax :

Maximum swelling strain at an unsaturated state

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Acknowledgments

We would like to thank Takashi Watanabe and Masayuki Ohnami for their assistance with numerical simulations, and Fumitaka Arai for assistance with the experiments.

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Authors and Affiliations

  1. Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 1646, Abiko, Abiko City, Chiba, 270-1194, Japan

    Masataka Sawada, Soshi Nishimoto & Tetsuji Okada

Authors
  1. Masataka Sawada
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  2. Soshi Nishimoto
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  3. Tetsuji Okada
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Correspondence to Masataka Sawada.

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Sawada, M., Nishimoto, S. & Okada, T. New Rapid Evaluation for Long-Term Behavior in Deep Geological Repository by Geotechnical Centrifuge—Part 2: Numerical Simulation of Model Tests in Isothermal Condition. Rock Mech Rock Eng 50, 159–169 (2017). https://doi.org/10.1007/s00603-016-1061-6

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