Description

The processes affecting the growth and decline of microbes in the repository. Growth requires the presence of energy sources and suitable nutrients in the repository, such as simple organic molecules containing oxygen, nitrogen and/or sulphur, and organics derived from wastes. The loss of such energy sources and / or nutrients can result in the decline of microbial populations, as can microbial poisoning. Poisoning of microbial processes can occur due to changes in temperature and chemical conditions in the repository but extremophiles can survive and thrive outside the range at which most microbes flourish.

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.

The growth and decline of microbes in the repository may influence the evolution of the EBS and the adjacent geosphere, and potentially the performance of the EBS and natural barrier. Growth and decline of microbes in the repository may also change the migration rates through these barriers of radionuclides and other contaminants originating in the waste, should they be released from a waste package.

Microbial growth and decline may cause temporal and spatial variations in the chemical environment within the repository that may impact upon the transport and retardation of radionuclides and other contaminants within the repository. The changing chemical environment may result in changes in the complexation of the radionuclides and other contaminants, which could in turn affect their partitioning between immobile solid phases and potentially mobile fluid phases (such as liquid water, non-aqueous liquids and gases). For example, the changing chemical conditions might impact upon processes such as sorption and solid precipitation / co-precipitation.

Microbial growth and decline may also cause changes in the nature and proportions of solid and fluid phases that are present. For example, gas may be produced or consumed during microbial growth, while microbial decay may be accompanied by precipitation of solid carbonate phases.

A result of microbial growth and decline affecting the chemical conditions in the repository and the natures and proportions of solid and fluid phases present may be variations in the forces driving fluid flow. Gas pressure gradients may be affected. Chemical gradients driving diffusion may also be influenced.

Growth of certain microorganisms may concentrate radionuclides and other contaminants within their structures. Conversely, decay of such microorganisms following their death may release these radionuclides and other contaminants to a potentially mobile fluid phase.

2000 List

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

2.1.10