Description
The mechanical processes that affect the seals and other engineered repository features (excluding the waste packages), and the overall mechanical evolution of the repository. Included are the effects of hydraulic and mechanical loads imposed on repository components by adjacent repository components, the waste packages and the surrounding geosphere.
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.
There is some overlap between the scope of FEP 3.2.3 (this FEP, Mechanical processes [repository]) and FEP 3.2.1 (Thermal processes) 3.2.2 (Hydraulic processes), FEP 3.2.4 (Chemical processes), FEP 3.2.5 (Biological processes) and FEP 3.2.6 (Radiological processes). FEPs 3.2.1-3.2.6 may all result in variations in mechanical loads on materials within the repository. Mechanical processes (this FEP, 3.2.3) covers the mechanical effects of the loads that are caused by the processes covered by these other FEPs.
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.
Mechanical processes may influence the effectiveness of the engineered barriers and any barrier function ascribed to the rock immediately surrounding the repository. These processes may produce or seal pathways through the barriers through which fluids (such as liquid water, non-aqueous liquids and gases) may potentially migrate. Mechanical processes may also produce forces that drive these fluids. Hence mechanical processes could influence the likelihood that radionuclides and other contaminants are released from the waste packages, and if release occurs, the subsequent migration of the radionuclides and other contaminants through the barrier system.
Mechanical processes may also affect retardation of radionuclides and other contaminants (sorption and matrix diffusion) along pathways through the barriers. Changes in the surface areas of solid phases that contact advecting fluid may affect sorption. Changes in the connectivity between fracture porosity and matrix porosity may influence the potential for retardation of radionuclides and other contaminants by matrix diffusion.
Depending upon the magnitude and orientation of the stresses affecting the barriers, brittle deformation could result in the formation of fractures through the barriers or widening of existing fractures. Alternatively, existing fractures may close.
Plastic deformation could cause the redistribution of barrier materials, with consequences for barrier performance. For example, bentonite within a buffer may be re-distributed, leading to changes in its thickness.
Mechanical processes may also impact upon the stability of openings. These processes may influence the requirement for, and nature of, seals, linings and other engineered structures/ materials within the repository. This may have further implications for safety.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
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Hudson J and Harrison J (), Engineering Rock Mechanics, 1st Edition: An Introduction to the Principles, Elsevier, 458, https://www.elsevier.com/books/engineering-rock-mechanics/hudson/978-0-08-043864-1