Description
The sorption/desorption processes affecting the migration of contaminants through the geosphere under prevailing geosphere conditions. Sorption describes the physico-chemical interaction where dissolved species adhere to a solid phase. Desorption is the opposite. Two sorption-desorption processes are commonly considered: ion-exchange processes involving an electrostatic or ionic attraction between charged dissolved species and oppositely charged surfaces; and chemisorption involving the formation of a chemical bond. Neutral species and (usually) anions are generally not strongly sorbed.
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.
Sorption and desorption of radionuclides and other contaminants that originate in a repository (if they are transported through the EBS), will influence their partitioning between immobile solid phases and a coexisting, potentially mobile aqueous phase. The greater the degree of sorption of radionuclides and other contaminants, the greater will be the degree to which their migration through the geosphere is retarded. Changing chemical conditions (pH, Eh, concentrations of ligands etc.) will influence the extent to which sorption occurs. Radionuclides or other contaminants that sorb strongly under a particular set of prevailing chemical conditions may desorb if the conditions change.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.