Description
The plastic movement of buffer/backfill material and surrounding rock in the EDZ under an imposed load. The buffer and backfill materials can creep or move as a result of imposed loads such as the weight of the waste packages or lithostatic pressure from and creep of 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.
- 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.
Creep of certain components of the EBS and certain kinds of host rock near a repository could potentially impact upon: 1) the development and / or sealing of potential mass transport pathways through the barrier system; and 2) forces driving migration of fluids (water, liquid hydrocarbons and gases) by reducing void volumes. Material creep could therefore affect the likelihood that radionuclides and other contaminants are released from the waste packages, and if release occurs, the subsequent migration of radionuclides and other contaminants through the barrier system.
Creep of one material may influence the mechanical behaviour of an adjacent material. For example, creep of a salt host rock in the EDZ and salt backfill surrounding a waste package may affect the stresses borne by the waste package and hence the likelihood that it might deform, releasing radionuclides and other contaminants.
The thickness of a barrier might be affected by creep. For example, owing to creep a buffer might decrease in thickness in some areas, but increase in thickness in others. There might be consequent implications for buffer performance. Creeping of the surrounding rock restrains components of the EBS ensuring the sealing function of these components.
If creep causes variations in the surface areas of pores that are accessible to fluid, there may be an impact upon the ability of the material undergoing volume change to retard radionuclide migration. Changes in surface areas that are accessible to migrating radionuclides and other contaminants, should these be released from the waste packages, will tend to impact on retardation by sorption. Retardation by matrix diffusion will be influenced by any creep that changes the connectivity between fractures though which fluid advection occurs and more poorly connected pores in the material’s matrices.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.