Description

The spontaneous disintegration or de-excitation of an atomic nucleus, resulting in the emission of sub-atomic particles and energy and the formation of a new progeny (or daughter) nucleus in the repository.

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.

Radioactive decay and ingrowth will produce temporal changes in the identities and quantities of the radionuclides present within the EBS and the adjacent geosphere. The overall radioactivity of the radionuclides present within the EBS and adjacent geosphere will vary temporally, reflecting radioactive decay and ingrowth.

The nature of the radionuclides that are produced by decay and ingrowth will influence their mobilities in any fluids (such as water, non-aqueous liquids or gases) that may be transported through the EBS or adjacent geosphere. The physical forms (e.g. gaseous or dissolved in aqueous solution) and chemical speciation of parent and daughter radionuclides may differ. The parent and daughter radionuclides may therefore have different mobilities, reflecting the different physical forms / chemical speciation.

Radioactive decay and ingrowth may affect the partitioning of radionuclides between immobile solid phases and potentially mobile fluid phases. For example, radioactive decay of a radionuclide that is immobilised within a mineral may damage the crystal structure of the mineral, making it easier for flowing water to leach the daughter nuclide.

In post-closure assessment, radioactive decay chains are often simplified, e.g. by neglecting the shorter-lived radionuclides in release and migration calculations but adding any dose-contribution to longer-lived parent radionuclides.

2000 List

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

3.1.01