Description

The large-scale (geological) removal and accumulation of sediments, with associated changes in topography and geological/hydrogeological conditions at the repository site. Regional erosion and sedimentation could result in localised incisions that remove large volumes of rock from a small area or broader-ranging actions that remove large volumes of surface soil and rock from a widespread area. The eroded material could be transported and deposited elsewhere (sedimentation) for example on lake bottoms and in till sheets, moraines and eskers.

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.

  • 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.

Regional erosion and sedimentation have the potential to affect repository performance and safety by:

  • changing the separation/lengths of transport pathways between the repository and the biosphere;
  • changing hydraulic gradients through and around the repository;
  • leading to changing chemical conditions in and around the repository;
  • changing the stresses on the repository; and
  • affecting the nature and spatial distributions of environmental receptors, including the biosphere, that could be impacted should radionuclides and/or other contaminants leave the repository.

Erosion would tend to reduce the separation / lengths of transport pathways between a repository and the biosphere, whereas sedimentation would have the opposite effect. Differential erosion, or sedimentation in localised topographical lows would change not only the separation/lengths of transport pathways, but also topographical gradients driving groundwater flow. Changes in the chemical environment in and around a repository could accompany erosion or sedimentation, because these processes would also change the flow path lengths between groundwater recharge zones and the repository. Erosion would tend to decrease these lengths, increasing the likelihood that relatively fresh, oxidising water could penetrate towards the repository. Conversely sedimentation would tend to increase these lengths, resulting in a greater likelihood that water/rock interactions would establish reducing conditions along the flow path following recharge. Erosion, by removing rock above the repository, would reduce stresses upon it, whereas sedimentation above the repository would increase stresses upon it. These stress changes could lead to dilation or contraction of pre-existing faults and fractures in the repository’s host rock and surrounding rock formations, affecting the ability of these faults and fractures to conduct water, other liquids and gases.

2000 List

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

1.2.07

Related References