Description
The chemical speciation and solubility processes affecting the release of contaminants from the waste form under repository conditions. “Chemical speciation” refers the form of elements within an aqueous solution or non-aqueous solution, for example as simple ions or in combination with other elements, forming complexes that may be neutral or negatively charged or positively charged. “Solubility” refers to the limiting quantity of a solid phase that may dissolve in a fluid phase. Factors such as temperature, gas partial pressure, ionic strength, the presence of complexing agents and pH and Eh conditions affect solubility.
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.
Chemical speciation and solubility will influence the potential for a radionuclide or other contaminant to be released from the waste form and then transported in a coexisting liquid phase. The solubility of a contaminant is its equilibrium concentration in a liquid phase that contacts the waste form. Chemical speciation will influence how solubility changes as a function of pressure, temperature and chemical conditions (e.g. pH, redox, salinity). Chemical speciation will influence the rate of contaminant release from the waste form under any given set of non-equilibrium conditions. The chemical speciation of the radionuclides or other contaminants will also influence their partitioning between the liquid and any gaseous phase that might be present.
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