Description
The formation in the repository materials of a molecular entity by loose association involving two or more component molecular entities (ionic or uncharged), or the corresponding chemical species. Complexation is promoted through the presence of complexing agents (organics, inorganic ligands and microbes). Sources of these agents include organics in the waste package and inflowing 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.
The formation of chemical complexes potentially influences the mobility and retardation of radionuclides and other contaminants/impurities that originate in the wastes, should they be released from a waste package. Combination of a radionuclide or other contaminants with a ligand may influence its solubility or sorption. Complexation may also influence the partitioning of radionuclides and other contaminants between different potentially mobile fluids (such as liquid water, non-aqueous liquids and gases).
Complexation of the dissolved chemical components in the water that occupies the pores pace within the EBS, or the surrounding geosphere, will affect the nature and quantities of solids that may precipitate or dissolve in these materials. Complexation of chemical components composing solid engineered barriers, or the surrounding geosphere, may cause the enhanced dissolution of these engineered barriers or the geosphere.
Spatial variations and temporal changes in chemical complexes that occur in solution, due to processes such as changes in temperature or mixing between chemically distinct waters (e.g. between natural groundwater and cement-conditioned porewater) may cause dissolution or precipitation of solid phases within the EBS or surrounding geosphere.
These dissolution and / or precipitation processes may impact upon the creation / enhancement or partial / complete sealing of pathways through the engineered and natural barriers for the possible migration of fluids (such as water, non-aqueous liquids or gases). These fluids could in turn transport radionuclides and other contaminants.
The chemical complexation of aqueous solutes may influence the rates at which solid phases dissolve and precipitate. If dissolution or precipitation reactions are slow (kinetically inhibited), an aqueous solution may not be at equilibrium with coexisting solid phases, or may be supersaturated with respect to solid phases that do not occur (i.e. on thermodynamic grounds a solid phase ought to precipitate, but for kinetic reasons it does not do so). Depending upon the chemical complexation, at a given pressure and temperature, the aqueous concentration of a dissolved constituent may exceed the solubility of a solid phase that, if present and at equilibrium with the water, would control the aqueous concentration of the solute. Alternatively, the aqueous concentration of a solute may be lower than would be expected, based on the occurrence of solid phase and the assumption of solubility limitation.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.