Description

The dissolution, precipitation and crystallisation of contaminants in the repository under prevailing repository conditions.

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.

This FEP concerns only the effects of dissolution, precipitation and crystallisation on the water-mediated transport of contaminants. These events/processes are influenced by the more general chemical events / processes covered by FEP 3.2.3 (Chemical processes [Repository].

Dissolution is the process by which constituents of a solid, non-aqueous liquid or gas dissolve into liquid water. Precipitation occurs when chemical species in solution produce a solid and are thereby removed from the solution.

Crystallisation is the process of producing a crystalline solid phase of an element, molecule or mineral from water. Solids that are initially precipitated from an aqueous solution may be amorphous or poorly crystalline and then subsequently become more crystalline as they age.

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.

Dissolution of radionuclides and other contaminants in water may allow them to be transported in the aqueous phase, via diffusion or advection, through the EBS and adjacent geosphere. These radionuclides or other contaminants may originate in the wastes, should they be released from a waste package.

Precipitation of solid phases from an aqueous phase may immobilise radionuclides and other contaminants. The radionuclides or other contaminants may co-precipitate with more abundant solutes, as trace or minor constituents of a solid phase. Alternatively, the radionuclides and other contaminants may be essential constituents of a solid phase.

Crystallisation of solid phases that have already precipitated (e.g. progressive crystallisation of initially poorly crystalline Fe-oxyhydroxides) may affect the solubility of radionuclides and other contaminants contained within their structures. That is, crystallisation may influence the likelihood that radionuclides and other contaminants may be dissolved by an aqueous phase and thereby rendered mobile.

Dissolution, precipitation and crystallisation may affect the spatial distributions of radionuclides and other contaminants within the EBS and adjacent geosphere. This influence may then have implications for the subsequent mobilities of the radionuclides and other contaminants, and their resulting fluxes of out of the repository, should conditions change.

2000 List

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

3.2.01