Description
An “excavation disturbed zone” is the zone of rock around caverns, tunnels, shafts or other underground opening that is mechanically damaged (fractured), hydraulically disturbed (e.g. dewatered) or chemically perturbed. An “excavation damaged zone” is the part of an “excavated disturbed zone” characterised by mechanical damage. Mechanical damage and hydraulic or chemical disturbances may extend for different distances in the rock, so that an “excavation damaged zone” and “disturbed zone” may be extend for different distances.
The extent and properties depend on factors such as the nature of the host rock, the excavation method, and the location and effectiveness of seals and grouts around the rooms and tunnels. The extent of damage will decrease with increasing distance from the excavation wall and generally there will be a transition from the excavation damaged zone to the excavation disturbed zone to the undisturbed host rock. The zones are likely to have different properties to the undisturbed host rock, e.g. opening of fractures or change of hydraulic properties due to stress relief.
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.
- Feature
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.
FEPs affecting the undisturbed host rock are considered under Geosphere Factors (FEP 4). While a desaturated state can be a characteristic of the excavation damaged and disturbed zone (this FEP 3.1.6) the process of desaturation is covered by FEP 3.2.2.1.
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 physical, chemical and biological properties of excavation damaged and disturbed zones will influence their potential to provide migration pathways for radionuclides and other contaminants, should these leave the repository via EBS.
The porosity and permeability of the excavation damaged and disturbed zones will influence their ability to conduct fluids (such as liquid water, non-aqueous liquids or gases) to and from the repository. Initially, at the time of closure, the excavation damaged and disturbed zone will be at least partly desaturated and will provide a pathway via which resaturation of the repository and EBS could occur. This in turn may influence the rates at which certain engineered barriers attain their long-term design properties (e.g. swelling pressure of a bentonite buffer). The potential ability of the excavation damaged and disturbed zones to affect fluid flow to / from repository also means that they could potentially influence the chemical and biological conditions within the repository.
The chemical and biological properties of the excavation damaged and disturbed zones may influence the chemical forms, and consequently mobilities, of any radionuclides and other contaminants that might be conducted along them.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
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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
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Bastiaens W, Bernier F and Li X-L (), SELFRAC: Experiments and conclusions on fracturing, self-healing and self-sealing processes in clays, Physics and Chemistry of the Earth, Elsevier, 32, 8-14, https://doi.org/10.1016/j.pce.2006.04.026
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Olsson M, Markström I, Pettersson A and Sträng M (), Examination of the Excavation Damaged Zone in the TASS tunnel, Äspö HRL, Research Report, SKB, R-09-39, 116, http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/41/073/41073201.pdf
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Rübel A, Buhmann D, Kindlein J and Lauke T (), Performance Assessment of sealing systems - conceptual and integrated modelling of plugs and seals, Report, Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH, GRS-415, 76, http://www.grs.de/sites/default/files/pdf/grs-415.pdf