Description

The transport of colloids and interaction of contaminants with colloids migrating through the geosphere under prevailing geosphere conditions. Colloids are particles with a maximum dimension typically less than 10 μm and are usually considered to have at least one dimension in the range 1 nm to 1 μm. Colloids are particles that can exist within a liquid without settling out.

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.

Colloidal transport of radionuclides and other contaminants that leave a repository (if their transport through the EBS is possible) may occur at a different rate to the transport of these contaminants in solution. Colloidal transport may also influence the pathways followed by the radionuclides and other contaminants. Colloids may be filtered by low-permeability media such as clays. Additionally, colloids may sorb to immobile solid surfaces, thus immobilising or retarding radionuclides or other contaminants that are in colloidal form or bound to colloids. If chemical conditions in the groundwater change, colloids may flocculate and sediment, thereby reducing the mobility of the radionuclides or other contaminants.

Colloid transport may also influence the dispersion of radionuclides and other contaminants within flowing groundwater. The dispersivity of colloids depends not only on the pore sizes and geometries, but also on the sizes and charges of the colloids. Thus, the dispersion of radionuclides and other contaminants that are transported in colloidal form or bound to colloids will depend partly upon the sizes and size distributions of the colloids.

2000 List

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

3.2.04