Description

The chemical speciation and solubility processes affecting contaminant migration through the geosphere under the prevailing geosphere conditions. The concentration of an element in aqueous solution at equilibrium with a coexisting solid reflects the solubility of the solid. Factors such as temperature, gas partial pressure, ionic strength, the presence of complexing agents and pH and redox conditions affect solubility. These factors affect the chemical form and speciation of the element. Thus different solids of the same element may have different solubilities in a particular solution.

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.

The chemical speciation and solubility of radionuclides and other contaminants that originate in a repository (if their transport through the EBS is possible), will influence their partitioning between immobile solid phases and a coexisting, potentially mobile aqueous phase. Retardation of radionuclides and other contaminants by sorption will depend upon their chemical speciation within the aqueous phase and upon the surfaces of solid phases (surface complexes). The chemical speciation of these contaminants will also affect their ability to bind to potentially mobile colloids within the aqueous phase.

The nature and chemical speciation of aqueous solutes other than radionuclides and contaminants will influence the concentration of species that may form complexes with the radionuclides and other contaminants. Complexation may in turn influence the partitioning of the radionuclides and other contaminants between immobile solid phases and a coexisting, potentially mobile aqueous phases.

At equilibrium, the aqueous solubility of a solid phase containing a radionuclide or other contaminant will control the maximum aqueous concentration of the radionuclide or other contaminant.

The aqueous solubility of solid phases that do not necessarily contain radionuclides or other contaminants may nevertheless influence the pH and Eh, and the nature and concentrations of solutes in coexisting water. These parameters may in turn influence the chemical speciation of the radionuclides and other contaminants.

2000 List

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

3.2.02, 3.2.05