Description

The diffusion of contaminants through the repository. Diffusive migration is driven by chemical potential gradients, can be affected by thermal gradients, and can thus be in any direction. It can occur in moving or stagnant repository water.

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.

Diffusion has the potential to transport radionuclides and other contaminants that are dissolved in water, through the EBS and adjacent geosphere. As they are transported, the concentrations of the radionuclides and other contaminants will decrease.

Diffusion will lead to the “spreading” of the radionuclides and other contaminants through the water, and thereby decrease the aqueous concentrations of dissolved radionuclides and other contaminants. Diffusion may affect the size(s) and location(s) of the area(s) across which radionuclides and other contaminants may leave the repository.

Diffusion will influence chemical gradients that are established in the repository, including gradients in the concentrations of radionuclides and other contaminants. This may in turn impact upon diffusive fluxes of these contaminants within the repository and between the repository and the surrounding geosphere.

If there are also pathways through the surrounding geosphere, via which solutes could be transported from the repository to the biosphere, diffusion in the repository could impact the doses of radionuclides and other contaminants that are eventually received by biosphere receptors.

2000 List

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

3.2.07