Description

The geochemical processes that affect the host rock and other rock units, and the overall geochemical evolution of the geosphere. Included, are changes in the chemistry of recharge water (e.g. due to glaciation / deglaciation introducing fresh meltwater into the sub-surface), chemical variations in groundwater due to mixing between chemically distinct groundwater bodies, mixing or chemical reactions between different fluid phases (e.g. between liquid water and organic gases) and chemical reactions between fluid phases, including liquid water, and minerals in the rock.

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.

Geochemical processes in the geosphere may influence the effectiveness of both the EBS and the geosphere barrier. Chemical processes in the geosphere will affect the chemical conditions in and around the EBS and the evolution of the EBS components. For example, carbonation of cementitious barriers will be influenced by the dissolved carbonate content of groundwater flowing through / around the repository. Dissolution of salt rock by groundwater can reduce the host rock thickness. Chemical processes within the geosphere will affect the chemical conditions around the waste forms should there be pathways through the EBS for fluids and solutes to enter the repository from the geosphere. In this case there will be a consequent impact upon the release rates of radionuclides and other contaminants from the waste, and the chemical forms in which the release occurs. Chemical reactions between rocks and fluids that contact them (such as water, non-aqueous liquids or gases) may influence both the chemical and solid phase (mineralogical) composition of the rock, and the chemical composition of the water. These chemical reactions may also influence the proportions of different fluid phases present. Chemical reactions among different fluid phases (e.g. exsolution or dissolution of gas) may also influence the chemical composition of the fluid phase and the reactions between the fluid and EBS components or rocks (e.g. CO₂ exsolution may lead to an increase in pH of the water and precipitation of carbonate minerals). These processes will affect the partitioning of radionuclides and other contaminants between the mobile fluid phase and immobile solid phase. Chemical buffering reactions within the geosphere barrier will affect the stability of chemical conditions in the sub-surface, including the environment immediately around the repository and further afield. For example, the redox buffering capacity of the rocks will influence the depth to which infiltrating oxidising water can penetrate.

2000 List

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

2.2.08