Description
The internal and external thermal processes that affect the buffer/backfill, seals and other engineered features, and the overall thermal evolution of the repository.
The thermal evolution of the repository will be affected by heat transfer due to gradients in temperature caused by heat conduction or convective flow which will be affected by the thermal characteristics (thermal conductivity, heat capacity) of the engineered features and the surrounding geosphere. Thermal processes include thermal expansion and contraction and consequent changes in densities of materials in the repository.
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.
- Event
- Process
Comments
The “Comments” field, when present, contains any additional explanation of the IFEP, beyond that implicit in the FEP's description and provided in the “Relevance to Performance and Safety” field. This additional explanation may include, where appropriate, the IFEPs characteristics, the circumstances under which it might be relevant and its relationship to other (especially similar) IFEPs.
Internal thermal processes are those that arise from the waste packages (FEP 2.3.1) and other components of the repository. They are distinct from external thermal processes that arise from the surrounding geosphere and are covered by FEP 4.2.1 (Thermal processes [geosphere]).
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.
Thermal processes that affect the repository could impact upon: the effectiveness of the EBS; processes by which radionuclides and other contaminants are released, should this be possible via the EBS; the rates at which such released radionuclides and other contaminants are transported; the forms (chemical species and phases) within which these released radionuclides and other contaminants are transported; and processes by which released radionuclides and other contaminants are retarded.
Thermal processes will affect the temperature evolution of the repository, which may in turn impact upon the mechanical properties of EBS components and the geosphere. There might be a consequent influence on responses to the stress regime, and the rheological properties of solids, for example whether they are brittle (potentially leading to migration pathways developing for radionuclides and other contaminants) or undergo plastic deformation.
The temperature evolution will also impact upon the rates and characteristics of biological and chemical processes within the repository and surrounding geosphere. These processes might influence the rates and characteristics of evolution shown by engineered barrier components.
Temperature-related variations in these biological and chemical processes will also impact upon the releases of radionuclides and other contaminants from the waste packages, should there be pathways through the EBS. For example, the solubilities of solid phases that contain these contaminants will be temperature-dependent.
Temperature gradients that develop within a repository and in the surrounding geosphere might help to drive the movement of fluids (such as liquid water, non-aqueous liquids and gases) and any radionuclides or other contaminants that they contain. For example, convection of groundwater might transport heat away from heat-generating waste packages.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
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Hodgkinson DP, Lever DA and Rae J (), Thermal Aspects of Radioactive Waste Burial in Hard Rock, Progress in Nuclear Energy, Elsevier, 11(2), 183-218
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Bond A and Watson S (), Understanding the Post-Closure Thermal Impact of HLW/SF Waste Packaged, An NDA RWMD Research Study, NDA RWMD, https://rwm.nda.gov.uk/publication/qrs-1384q-r2-v2-1/