Description
The sorption/desorption processes affecting the migration of contaminants through the repository under prevailing repository 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.
- 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 may affect the degree to which radionuclides and other contaminants are mobilised within the EBS and adjacent geosphere, if they can leave a waste package.
Sorption and desorption may influence the partitioning of radionuclides and other contaminants between the potentially mobile aqueous phase and immobile solid phases. Sorption and desorption may also influence the partitioning of radionuclides and other contaminants between aqueous species and colloids, which may also be present within the potentially mobile aqueous phase.
Sorption and desorption may have an impact upon other processes that contribute to the mobilisation / retardation of radionuclides and other contaminants within the EBS and adjacent geosphere. Sorption and desorption may impact upon diffusion of the radionuclides and other contaminants. For example, sorption of these contaminants on the surfaces of solids within a fracture may limit the diffusion of the contaminants into the matrices of the materials bordering the fracture. The spatial distributions of radionuclides and other contaminants within the EBS and adjacent geosphere may be affected. This influence may then have implications for the subsequent mobilities of the radionuclides and other contaminants, and their resulting fluxes of out of the repository, should conditions change.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.