Description
The physical, chemical, and biological characteristics and properties of any overpack at the time of emplacement in the repository. An overpack is a container that is used to secure or shield one or more inner containers and in some disposal concepts is used for disposal (as well as transport and storage).
Category
Categorisation as a Feature, Event and/or Process.
Features
are physical components of the disposal system and environment being assessed. Examples include waste packaging, backfill, surface soils. Features typically interact with one another via processes and in some cases events.Events
are dynamic interactions among features that occur over time periods that are short compared to the safety assessment timeframe such as a gas explosion or meteorite impact.- "Processes" are issues or dynamic interactions among features that generally occur over a significant proportion of the safety assessment timeframe and may occur over the whole of this timeframe. Events and processes may be coupled to one another (i.e. may influence one another).
The classification of a FEP as an event or process depends upon the assessment context, because the classification is undertaken with reference to an assessment timeframe. In this generic IFEP List, many IFEPs are classified as both Events and Processes; users will need to decide which of these classifications is relevant to their context and its timeframes.
- Feature
Relevance to Performance and Safety
The “Relevance to Performance and Safety” field contains an explanation of how the IFEP might influence the performance and safety of the disposal system under consideration through its impact on the evolution of the repository system and on the release, migration and/or uptake of repository-derived contaminants.
Overpack characteristics and properties are relevant to the performance and safety of repositories that contain waste packages with overpacks; not all repository concepts include such waste packages. The overpack, if present, protects an inner container and contributes to containment of radionuclides and other contaminants within a waste package. The physical, chemical and biological characteristics and properties of an overpack will determine its evolution during the post-closure period, whether its integrity is lost during this period, and if so when the integrity loss occurs. The characteristics and properties of the overpack also control how it interacts with the container inside it and with the barriers (whether engineered or natural) that surround the overpack. The overpack will contribute to the mechanical strength of the overall waste package. The chemical and biological characteristics and properties of the overpack will also determine its ability to buffer the chemical conditions of the environment within and around a waste package. For example, corrosion of an iron overpack may contribute to maintaining reducing conditions. This ability to buffer conditions may help to influence the mobility of radionuclides and other contaminants after any breach in the waste package. As they are released from a breached waste package, certain radionuclides and other contaminants may be retarded by sorption on, or co-precipitation with, alteration products of the overpack (e.g. iron oxides). A safety / performance assessment needs to consider the potential for an overpack to react with surrounding barriers in ways that influence the performance of these barriers. For example, iron released from an iron-containing overpack may react with smectite in a surrounding bentonite buffer, thereby influencing its swelling pressure.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
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IAEA (), Containers for Packaging of Solid Low and Intermediate Level Radioactive Wastes, IAEA Technical Report Series TRS-355, International Atomic Energy Agency, Vienna
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IAEA (), Characterisation of Radioactive Waste Forms and Packages, IAEA Technical Report Series TRS-383, International Atomic Energy Agency, Vienna