Description

The geothermal characteristics and properties of the geosphere prior to repository construction, including the temperature at repository level, the thermal conductivity and heat capacity of the various rock formations.

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.

Geothermal characteristics and properties of the geosphere prior to repository construction will influence the subsequent thermal evolution of the geosphere, during repository construction, operation and, later, post-closure. These characteristics and properties have the potential to influence the effectiveness of both the EBS and the geosphere barrier. The thermal properties of the geosphere will affect the heat transport from / to the repository, and consequently the temperature evolution of the repository. In particular, heat dissipation during the thermal phase of heat-emitting wastes will be affected. This also affects repository design (e.g. spacing of waste packages) and also pertains to alteration rates of EBS materials (e.g. illitisation of bentonite).

The temperature and thermal properties of the geosphere will influence the nature and rates of fluid-solid reactions within the EBS and geosphere. These reactions will affect the partitioning between mobile and immobile phases of radionuclides and other contaminants that originate in the repository. Rates and patterns of fluid flow from the repository through the geosphere (and vice versa) will depend in part upon the temperature gradients that occur, since the density of any mobile fluid phase (such as liquid water, non-aqueous liquid or gas) will be affected by temperature. Hence, the thermal characteristics and properties of the geosphere have the potential to influence the migration patterns and migration rates of radionuclides and other contaminants that originate in a repository.

The geothermal characteristics and properties of the geosphere will also influence how the temperatures of the rock-water system evolves in response to external influences such as glaciation, which may include heat transport to and from the repository at different stages of glaciation / deglaciation.

2000 List

A reference to the related FEP(s) within the 2000 NEA IFEP List.

2.2.10