Description

The collapse of tunnels, shafts and boreholes, including cave-ins, roof settling, spalling and rock bursts. Collapses could occur where voids remain post-closure (e.g. because galleries are not backfilled, or because backfill emplacement is not 100% efficient, resulting in there being residual headspace).

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

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 collapse of openings within a repository could potentially influence post-closure performance of the EBS and/or the surrounding geosphere barrier.

Collapses of openings could damage waste packages or other components of the EBS. Collapses could also produce pathways through the surrounding geosphere for the possible migration of fluids (such as liquid water, non-aqueous liquids and gases). These fluids could transport radionuclides and other contaminants from the repository, should there be pathways through the EBS.

Were collapses to occur, they could change the permeability distribution of materials in the repository, with a consequent effect on the patterns of fluid flow through / around it.

While collapses could potentially produce pathways for fluid migration, they might also increase the areas of exposed fresh solid surfaces. These surfaces might contact migrating radionuclides or other contaminants, should these be released from the waste packages and move through the other EBS components. The increased surface areas might engage in increased sorption and hence retardation.

2000 List

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

2.1.07