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.