Description
The temporal evolution of the waste package’s pH from its initial state. Included is the pH evolution of the water within the waste package due to water exchange between the waste package and its surroundings (assuming that such exchange can occur), mixing between water from different sources, and solid-water, gas-water and non-aqueous liquid-water reactions. The evolution of pH (generation or consumption of H+) is a characteristic of many chemical processes that may occur within a waste package or at the outer surface of the waste package. The rates of many chemical processes are dependent upon pH. Additionally, microbial processes may influence (and be influenced by) pH. The overall evolution of pH will reflect the couplings between these processes and may be heterogeneous within the waste package.
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 evolution of pH will influence/reflect the evolution pathways and evolution rates of waste package components. Consequently, the integrity of the waste package and the potential for radionuclides or other contaminants to be released from it may be affected. pH-dependent processes may cause a package that initially offers containment to lose its integrity. Alternatively, where a package does not offer full containment initially (e.g. because the package is vented), the ability of the package to resist migration of radionuclides or other contaminants may be affected.
Where a waste package does not provide containment, the forms in which radionuclides and other contaminants are released and migrate from it will be influenced by pH within the waste package. In such a case, the ability of the waste package components to retard the migration of radionuclides and other contaminants (e.g. by sorption) may also be affected by pH.
pH within the waste package may be coupled to chemical processes outside the waste package, where the package lacks integrity. pH at the outer surface of a waste package will be coupled to chemical processes in the surrounding natural and / or engineered barriers. These couplings may cause the pH at the outer surface of the waste package and possibly within the waste package (if the waste package lacks integrity) to also influence the chemical evolution of the surrounding barriers.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
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NEA (), Engineered Barrier Systems and the Safety of Deep Geological Repositories, State-of-the-art Report, Nuclear Energy Agency, NEA-3615, EUR 19964 EN, https://www.oecd-nea.org/rwm/reports/2003/nea3615-ebs.pdf
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IAEA (), Application of Ion Exchange Processes for the Treatment of Radioactive Waste and Management of Spent Ion Exchangers, IAEA Technical Report Series, International Atomic Energy Agency, Vienna, No. 408