Description
The chemical speciation and solubility processes affecting contaminant migration through the waste package under repository conditions. The concentration of an element in aqueous solution (at equilibrium) reflects the solubility of the solid compounds which contain the element. Factors such as temperature, gas partial pressure, ionic strength, the presence of complexing agents and pH and Eh 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.
- Feature
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 solubility and chemical speciation of a radionuclide or other contaminant will influence its partitioning between solid and liquid phases within the waste package and thereby affect the concentration of the contaminant in the fluid phase and hence its potential mobility. Solubility and chemical speciation of any contaminant are related. The solubility of a contaminant will tend to be increased if it forms chemical complexes with ligands in the liquid phase. Chemical speciation will also influence the rates at which solid precipitation and dissolution reactions occur (i.e. the rate at which solubility equilibrium is attained). Hence, chemical speciation has the potential to influence the rates at which radionuclides or other contaminants are released from the waste. If the chemical system within the waste package achieves equilibrium, then the solubility of a solid phase that contains a radionuclide or other contaminant will control the concentration of the contaminant in the liquid phase. The chemical speciation of a radionuclide or other contaminant in a fluid phase will not only influence the solubility of the contaminant, but also its ability to sorb to the surfaces of solid phases within the waste package and to diffuse through these solid phases.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
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Salah S and Wang L (), Speciation and solubility calculations for waste relevant radionuclides in Boom Clay, SCK-CEN External Report SCK-CEN-ER-198, SCK-CEN, 14/Ssa/P-16, http://publications.sckcen.be/dspace/bitstream/10038/8429/1/er_198.pdf
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Wanner H (), Solubility data in radioactive waste disposal, Pure and Applied Chemistry, Iupac, 79(5), 875-882