Description
The release of contaminants in gas or vapour phase or as fine particulate or aerosol in gas or vapour from the waste form. This FEP includes the mobilisation of C-14 by incorporation into carbon dioxide or methane, incorporation of I-129 into iodine gas or methyl iodide, and incorporation of tritium (H-3) in hydrogen gas or water vapour. Gas-mediated release can also include the direct release of gases from gaseous waste forms (e.g. Kr isotopes).
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.
Gas-mediated release can arise from various gas production processes such as radon production (FEP 2.3.6.4), biochemical processes resulting in volatilisation (e.g. FEPs 2.3.4.5 and 2.3.5.2) and radiolysis resulting in hydrogen production (FEP 2.3.6.2).
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.
Radionuclides or other contaminants released from a waste form directly in gaseous form (e.g. Rn or Kr isotopes), or into a gaseous phase that contacts the waste form (e.g. isotope exchange of C-14 with C-12 and C-13 present in coexisting CO₂), will have the potential to be mobile. The mobility will depend partly upon the degree to which the gaseous phase is miscible with / soluble in any liquid phase that might also be present, and the relative densities of the gaseous and liquid phases (which will control the buoyancy of the gaseous phase). Radionuclides or other contaminants that are released into or as a gas phase may be mobilised by bulk gas movement (if there is a pressure gradient) or by gas diffusion (if there is no significant pressure gradient). If diffusion is the dominant mechanism, then the rate of release from the waste form will depend upon the concentration gradient that exists from the surface of the waste form into the gaseous phase. Sorption / desorption of the gaseous phase may influence the partitioning of radionuclides or other contaminants between the solid and gaseous phases. Gas generation processes may lead to pressurisation of the waste form, which in turn might also influence the rate of release of radionuclides and other contaminants, and the chemical / physical forms in which these releases occur.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
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IAEA (), Scientific and Technical Basis for the Geological Disposal of Radioactive Wastes, IAEA Technical Report Series, International Atomic Energy Agency, Vienna, 413, 80, http://www-pub.iaea.org/MTCD/publications/PDF/TRS413_web.pdf
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W. Rodwell, S. Norris, W. Cool, M. Cuñado, L. Johnson, M. Mäntynen, W. Müller, P. Sellin, M. Snellman, J. Talandier, T. Vieno and S. Vines (), A thematic network on gas issues in safety assessment of deep repositories for radioactive waste (GASNET), European Commission Report EUR 20620 EN, https://bookshop.europa.eu/en/a-thematic-network-on-gas-issues-in-safety-assessment-of-deep-repositories-for-radioactive-waste-gasnet--pbKINA20620/
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S. Norris (), FORGE project: updated consideration of gas generation and migration in the safety case, in R.P. Shaw (ed.) Gas generation and migration in deep geological waste repositories, Special Publications, Geological Society, London, 415, 241-258, https://www.geolsoc.org.uk/SP415