Description

The processes affecting the growth and decline of microbes in the waste package. Microbes can be present in waste packages, especially those containing organic waste. Their growth requires the presence of suitable nutrients, such as cellulosic wastes, simple organic molecules containing oxygen, nitrogen and/or sulphur, and small amounts of putrescible materials. The loss of such nutrients can result in the decline of microbial populations, as can microbial poisoning. Microbial processes may decline as a result of high temperature, as a result of pH changing to a value at which the microbial population ceases to function, and due to the presence of high concentration of heavy metals or other contaminants.

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 microbial populations within a waste package, or on its outer surface, will determine the potential for biological/biochemical processes to impact a waste package’s chemical evolution and consequently the physical characteristics of waste package components (since chemical and physical processes are coupled). Formation or decay of biofilms could also affect the mass transport properties of waste package materials. Different kinds of microbe within a population may grow or decline at different rates as conditions (e.g. temperature) evolve within a waste package. The make-up of the microbial population, and hence its influence on the evolution of the waste package, may therefore also change temporally. The growth and decline of microbial populations may influence the release rates of radionuclides or other contaminants from the waste form. This growth and decline may also impact the chemical and physical forms of any such releases. The abundance and compositions of different phases that are present within the waste package at any time may be affected by whether microbial populations are growing or declining. For example, the rates of gas generation, and the gas composition, could be controlled by the proportions of different microbes in a population. These proportions will depend in turn on how the growth and decline of each kind of microbe present is affected by the evolving environment. Thus, the pressure evolution, and the pressure values attained within the waste package, could also be influenced by microbial growth and decline. This pressure evolution potentially may influence the integrity of the waste package. If the waste package does not offer full containment (either because it is vented or because it has been breached), the pressure evolution could affect the transport of radionuclides and other contaminants from the waste package. The growth and decline of microbial populations may affect the characteristics of engineered components, and potentially their performance. For example, microbes may influence corrosion of metals (‘microbially-influenced corrosion’).

2000 List

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

2.1.10, 2.1.12

Related References

  • Wolfram J H, Rogers R D and Gazsó L G (Eds) (), Microbial Degradation Processes in Radioactive Waste Repository and in Nuclear Fuel Storage Areas, Volume 11, Microbial Degradation Processes in Radioactive Waste Repository and in Nuclear Fuel Storage Areas, Springer, ISBN 978-0-7923-4488-9, http://www.springer.com/gb/book/9780792344889