Description

The physical, chemical and biological characteristics and properties of the shaft/ramp seals at repository closure.

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.

The characteristics of shaft/ramp seals will impact upon the potential for radionuclides and other contaminants to migrate through / from the repository, should the waste packages and any other engineered barriers have pathways through them from the disposal tunnels / rooms. The shafts / ramps provide a connection between the repository and the surface. Hence, impairment of these seals could potentially provide pathways from the repository to the biosphere. These shaft / ramp seals may also influence the rate at which fluids (such as liquid water, non-aqueous liquids or gases) may enter or leave the repository in the post-closure period. The shaft / ramp seals may therefore affect the rate at which the repository re-saturates following closure. Impairment of the shaft / ramp seals may, depending upon the natural hydraulic gradients, result in cross-flow of groundwater or other fluids (e.g. hydrocarbon liquids or gases) between different rock formations or structures in the rock sequence above the repository. Should the wastes and / or engineered barrier components evolve to produce gas, the permeability of the shaft / ramp seals may influence the pressures that are attained.

The potential ability of the shaft / ramp seals to affect fluid flow to / from repository means that they could potentially influence the chemical and biological conditions within the repository.

The presence and nature of shaft / ramp seals may also impact upon the likelihood of future human intrusion into the repository, by influencing how easy it is to gain access to the facility.

2000 List

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

2.1.05

Related References