Description
The temporal evolution of the repository’s redox state, as represented by parameters such as the redox potential relative to the standard hydrogen electrode (Eh).
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 redox evolution of the repository will be coupled to the physical evolution of the EBS and the surrounding geosphere barrier. For example, aerobic corrosion of a steel waste container immediately after repository closure will consume oxygen present initially in the repository and at the same time potentially decrease the mechanical strength of the container. Thus, the redox evolution may impact upon the development or sealing of potential pathways through which fluids (such as liquid water, non-aqueous liquids or gases) may move. If mobile, such fluids may in turn transport radionuclides and other contaminants, should these be released from the waste containers.
The redox evolution is coupled to the temporal changes in the identities and proportions of solid phases and fluid phases (which may include one or more of liquid water, non-aqueous liquids and gases), and temporal changes in the chemistries of these phases. Reactions that influence redox conditions in one barrier component may influence the chemical evolution of an adjacent barrier if fluid is able to move between the components, or at the interface between the components. For example, oxidation of trace sulphide minerals in a backfill may remove dissolved oxygen from the pore fluid, which then cannot oxidise a steel barrier component with which it later comes into contact.
The redox evolution will affect the chemical speciation of certain redox-sensitive radionuclides and other contaminants directly. Redox evolution may influence indirectly the chemical speciation of non-redox-sensitive radionuclides and other contaminants that may combine with redox-sensitive species. These redox-related effects may influence the abilities of radionuclides and other contaminants to precipitate / co-precipitate, re-dissolve, sorb and diffuse, and partition among different potentially mobile fluid phases (such as liquid water, non-aqueous liquids and gases).
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.