Description

The precipitation of an element from the aqueous phase to the solid phase in the waste package, which depends on chemical conditions in the waste package (particularly pH, Eh and the concentration of complexing ions).

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.

Precipitation of radionuclides or other contaminants within solid phases that might form within the waste package will prevent the precipitated radionuclides or other contaminants from being later transported from the waste package by a mobile fluid phase (water, gas, or organic liquid) should conditions change. The aqueous concentration of a radionuclide or other contaminant at the time of precipitation could be an upper limit under the specific conditions prevailing; the radionuclide or other contaminant would be ‘solubility limited’. Precipitation of solid phases may also impact upon the barrier function of materials within the waste package. For example, the performance of a cement encapsulant, if one is present within the waste package, may be affected by precipitation of calcium carbonate. In such a case, the calcium carbonate may occlude porosity within the cement, affecting its mass transport properties and potentially influencing the ability of the cement to buffer the pH of water present.

2000 List

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

2.1.09

Related References