Conference Proceedings Paper
MODELLING THE RADIOLYTIC CORROSION OF NUCLEAR FUEL INSIDE A FAILED WASTE CONTAINER
3rd Canadian Nuclear Waste Management Decommissioning and Environmental Restoration - 2016 Sept. 11-14
N. Liu (Western University)
L. Wu (Canadian Nuclear Laboratories)
Z. Qin (Western University)
D. Shoesmith (Western University)
The international concept for the disposal of high level nuclear waste involves multiple barriers including the fuel bundles, durable metal containers, clay buffer and seals, and a deep geologic environment. A key barrier in the Canadian concept is the corrosion resistant container which consists of an outer copper barrier and an inner carbon steel vessel. While designed not to fail, it is judicious to examine the consequences of container failure when the used fuel bundles could be exposed to groundwater leading to their radiolytic corrosion and the release of radionuclides to the groundwater.
If failure occurs two corrosion fronts will be established; one on the fuel driven by the alpha radiolysis of water and a second one on the inside of the steel vessel leading to the dissolution of Fe2+ and the production of H2.
Both 1-dimensional and 2-dimensional models have been developed to determine the influence of redox conditions within the failed container on the fuel corrosion/radionuclide release process. These models take into account water radiolysis, the reaction of radiolytic H2O2with the fuel both directly and via galvanic coupling to fission product phases in the fuel, the reaction with H2 (from steel corrosion and water radiolysis) catalyzed on the fuel surface and the scavenging of radiolytic H2O2 by reaction with Fe2+.
The models are described by 1-dimensional diffusion reaction equations and solved numerically using COMSOL Multiphysics, a commercial simulation package based on the finite element model. The 1-dimensional model attempts to calculate corrosion rates on the exposed surface of fuel pellets while the 2-dimensional model attempts to determine the corrosion behaviour within the cracks in the fuel pellet. Despite extensive international efforts the available database is limited. The sensitivity to various reactions in the model will be evaluated and the necessary improvements identified.
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