Homogenization of bentonite barriers for nuclear waste





Bentonite barriers, Nuclear waste, Homogenization


The safety functions of bentonite barriers for nuclear waste depend mainly on the value of the dry density (or porosity) of the bentonite. The evolution of this variable during the transient phase of the barrier is complex. The paper presents a theoretical formulation to compute, by coupled numerical analyses, the changes in dry density that occur due to the hydration of the barrier, with special focus on the process of homogenization. A double structure constitutive model has been adopted to represent more realistically the mechanical (stress-strain) behaviour of the bentonite. Using the formulation presented, two hydration tests, with different boundary conditions, have been satisfactorily simulated. The samples exhibited a large degree of initial heterogeneity. The analyses predict correctly the final saturation of the samples, the value of the final swelling pressure and, especially, the homogenization process that takes place during the tests. The double structure model has allowed the examination of the hydration and homogenisation phenomena from a wider perspective.


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