Description

The natural or man-made features within the geosphere that may not be detected during the site investigation (e.g. fracture zones, faults, brine pockets, old mine workings and boreholes). The nature of the geological environment will indicate the likelihood that certain types of undetected features may be present and the site investigation may be able to place bounds on the maximum size or minimum proximity to such features.

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.

Depending upon their characteristics, undetected features could be either beneficial or detrimental with respect to long-term performance and safety in the post-closure period. Features that are undetected prior to repository construction may cause design changes to be made to the repository. Certain undetected features could act as pathways via which fluids (such as water, non-aqueous liquids or gases) could flow through the geosphere, potentially transporting radionuclides and other contaminants originating in the repository. Other kinds of undetected feature could act to prevent or retard the flow of these fluids, and radionuclides or other contaminants carried by the fluids. For example, faults and fracture zones may, depending upon their specific properties, behave either as fluid flow conduits or barriers. Depending upon their properties, those undetected features that could act as conduits for fluids may retard the migration of radionuclides and other contaminants. For example, the natures of the minerals that line undetected faults will influence the extent to which radionuclides may be retarded by sorption.

2000 List

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

2.2.12