Radionuclide Release from the Kbs-3 Repository-Sensitivity to the Variability of Materials and Other Properties
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RADIONUCLIDE RELEASE FROM THE KBS-3 REPOSITORY- SENSITIVITY TO THE VARIABILITY OF MATERIALS AND OTHER PROPERTIES L. ROMERO, A. ANDERSSON, L. MORENO AND I. NERETNIEKS Department of Chemical Engineering and Technology Royal Institute of Technology S-100 44 Stockholm, Sweden
ABSTRACT Radionuclides leaking from a canister spread into the backfill material surrounding the canister and then migrate through different pathways into the mobile water in the rock fractures. In order to quantify uncertainties regarding the release to the far field, a sensitive analysis is performed for the uncertainties in the parameters governing the release. For nuclides escaping through a damaged canister in a repository of the type KBS-3 [1], most nuclides migrate through the pathways appointing to the fracture intersecting the deposition hole and the disturbed zone below the tunnel. The sensitivity analysis showed that the grade of impact on the release of uncertainties in the parameters cannot be generalized for all nuclides, however, some patterns of the influence can be given. Uncertainties in the hole size and uranium solubility for nuclides embedded in the matrix have a strong influence on the release. The adsorption capacity of the bentonite surrounding the canister and the hydraulic properties of the fractured rock in the short pathways to the mobile water have to be accurately known to reduce uncertainties in the release to the far field. For nuclides with a high diffusion coefficient in the bentonite, e.g. cesium and strontium, the hydraulic properties of the fractured rock nearest to the canister have to be well known. For the iodide, on the other hand, with a very low diffusion coefficient, uncertainties in the hydraulic properties have a very small effect on the release. The uranium release with a very high inventory is not affected by uncertainties in the hydraulic properties of the rock. The released nuclide fraction through each pathway is not largely influenced by uncertainties in the transport properties of the backfill materials whereas uncertainties in the
water flow rates in the zones in the rock where the water flows, have a strong influence on the nuclide release distribution.
INTRODUCTION Radionuclides leaking from a canister in deep underground repositories in crystalline rocks will spread into the backfill material surrounding the canister and will then migrate through different pathways into the mobile water in the rock fractures. Not all nuclides move at the same rate, some nuclides move faster than others depending on the transport properties of the particular nuclide. The migration rate will be influenced by the water flow rate, the water chemistry and possible changes in the redox potential, solubility and sorption properties of the nuclides on the materials in the repository, the diffusive properties of the radionuclides, and the fracture properties of the rock nearest the canisters. There is a natural variability and often an uncertainty in many of the mentioned material properties, of possible flow rate
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