Description

The chemical/geochemical processes that affect the seals and other engineered repository features (excluding the waste packages), and the overall chemical/geochemical evolution of the repository. This includes the effects of chemical/geochemical influences on repository components by the waste packages, adjacent repository components and the surrounding geosphere.

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

Comments

The “Comments” field, when present, contains any additional explanation of the IFEP, beyond that implicit in the FEP's description and provided in the “Relevance to Performance and Safety” field. This additional explanation may include, where appropriate, the IFEPs characteristics, the circumstances under which it might be relevant and its relationship to other (especially similar) IFEPs.

Chemical processes [repository] (this FEP 3.2.4) concerns the chemical events / processes that impact upon the properties of repository components and on the overall chemical conditions in the repository. The influences of these FEP Subgroup 3.3 (Contaminant Migration [repository]).

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 processes in the repository will influence the chemical, biological and physical evolution of the EBS and the surrounding geosphere. Some chemical processes may lead to the formation or enhancement of pathways through the EBS and surrounding geosphere, through which fluids (such as liquid water, non-aqueous liquids and gases) may migrate. These fluids may transport radionuclides and other contaminants, should these be released by the waste packages. Other chemical processes may cause the complete or partial sealing of pre-existing pathways through the EBS and surrounding geosphere.

Chemical processes will influence the chemical conditions (e.g. redox, pH, cation and anion concentrations) within the repository and surrounding geosphere. These conditions may in turn influence the behaviour of radionuclides and other contaminants from the wastes (should the waste packages release contaminants). For example, chemical processes may influence the solubilities and aqueous chemical speciation of these solutes, thereby influencing their mobilities.

Chemical processes may impact upon the thermal conditions in the repository. Some chemical reactions are endothermic (consume heat), whereas others are exothermic (produce heat).

Chemical processes may lead to density gradients that in the fluid phase(s) that may in turn contribute to driving advection. These gradients may develop as a result of dissolution or precipitation processes, or as a consequence of certain chemical reactions generating or consuming heat (exothermic and endothermic reactions respectively).

2000 List

A reference to the related FEP(s) within the 2000 NEA IFEP List.

2.1.09, 2.1.12

Related References