Factors in the Selection of Container Materials for the Disposal of HLW/SF
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Factors in the Selection of Container Materials for the Disposal of HLW/SF Fraser King1 Integrity Corrosion Consulting Ltd Nanaimo, BC, Canada V9T 1K2
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ABSTRACT The container is the only absolute barrier in the multi-barrier system that forms the basis of all nuclear waste disposal strategies. The selection of an appropriate container material is therefore of utmost importance. Some of the factors that underlay the choice of container material are discussed, ranging from the properties of the near-field and host rock to the desired or expected containment period. There has been a trend towards the specification of container materials that will corrode actively under repository conditions, such as copper and carbon steel. Passive materials, such as titanium and nickel alloys and the various stainless steels, have found less acceptance and the reasons for this emphasis on active materials are also discussed. In selecting an appropriate container material, it is essential to understand the nature of the corrosive environment and how it evolves over time. The evolution of environmental conditions will also cause the corrosion behaviour of the container to change with time. For repositories in saturated environments, it will be argued that passive alloys can provide long container lifetimes without some of the disadvantages of some active materials such as gas generation and other adverse impacts on other barriers. Finally, areas of future development and areas requiring additional study will be discussed. INTRODUCTION All proposed strategies for the disposal of nuclear waste involve a series of engineered (man-made) and natural barriers. The container is a key component of such strategies as it represents the only absolute barrier in the overall multi-barrier system. Until the container fails, radionuclides cannot be released to the near- and far-fields and, eventually, reach the accessible environment. Because of this and other reasons, containers and their long-term performance often come under considerable scrutiny when proposals for the disposal of spent fuel (SF) and/or high-level nuclear waste (HLW) are reviewed by regulatory authorities and the general public. Therefore, the selection of the container material is an important consideration. Various factors must be considered when selecting a container material. Here the discussion is limited to the selection of container materials for the disposal of SF/HLW. Furthermore, because ultimate failure of the container is likely to be the result of corrosion of the container material, emphasis is placed on those factors relating to the corrosion performance of the container material, rather than on factors associated with the design, fabrication, inspection, and mechanical performance. For convenience, the various factors are divided into: x Material-related factors, such as the interaction between the material and the pore and ground waters or the amount of oxidant available to support corrosion.
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Program-specific factors, such as the target container lifet
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