Description
The thermal processes that affect the host rock and other rock units, and the overall thermal evolution of the geosphere. Included is heat transfer due to natural gradients in temperature. Thermal processes include thermal expansion and contraction and consequent changes in densities of solid and fluids in the geosphere.
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.
Geosphere thermal processes (this FEP 4.2.1) are those that arise from natural heat flow. They are distinct from internal thermal processes that arise from processes within the repository, such as radiogenic heat generation, which is covered by FEP 3.2.1 (Thermal processes [repository]).
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.
The thermal processes that affect the host rock and other rock units, and the overall thermal evolution of the geosphere will influence the temperature gradients that develop in and around the repository during operation and later, in the post-closure period. Thermal processes have the potential to influence the effectiveness of both the EBS and the geosphere barrier. The mechanical properties of the EBS and geosphere barrier depend partly on temperature. Chemical reactions that affect EBS components, the repository host rock and surrounding rocks, and the fluids present (such as liquid water, non-aqueous liquids or gases) are temperature-dependent. Thermal gradients will influence fluid density gradients and fluid viscosity, thereby affecting fluxes and flow patterns of fluid (such as water, non-aqueous liquids or gases). Fluid- and solid-phase transitions may also occur due to changing temperature. For example, as temperature changes along a flow path the proportions of water and any gaseous phase present may vary. If pressure – temperature – water chemistry conditions are suitable gas (e.g. methane) hydrates may form. These may retain certain radionuclides that could then be released again should the hydrates subsequently become unstable. Hydrate formation could potentially reduce the permeability of the EBS. In evaporite rocks thermal processes may affect mineralogy, for example there may be thermal degradation of carnallite. Thermomigration of water and solutes may also occur.
Partitioning of radionuclides and other contaminants originating in the repository between mobile and immobile phases will depend partly upon temperature.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.