Description

The effects of volume changes in materials used in the repository. Examples include the shrinkage/expansion of concrete, expansion of metallic components due to corrosion, the swelling of bentonite and thermal expansion / contraction.

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.

This FEP (3.2.3.1) concerns explicitly the changes in volume that materials within the repository may undergo, rather than the causes of these changes, which are covered by FEP 3.2.1 (Thermal processes), FEP 3.2.2 (Hydraulic processes), FEP 3.2.4 (Chemical processes), FEP 3.2.5 (Biological processes) and FEP 3.2.6 (Radiological processes).

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.

Changes in the volumes of materials used in the EBS and the rock immediately adjacent to the repository could impact upon: 1) the development and / or sealing of potential mass transport pathways through the barrier system; and 2) forces driving migration of fluids (such as liquid water, non-aqueous liquids and gases). Material volume changes could therefore affect the likelihood that radionuclides and other contaminants are released from a waste package, and if release occurs, the subsequent migration of the radionuclides and other contaminants through the barrier system.

Decreases in material volumes could result in the development of connected porosity (fractures, connections between matrix pores) through the materials. Increases in material volumes could result in sealing of such pathways, or creation of pathways, depending upon the interaction between the stresses generated during volume increase and the pre-existing stress field.

Changes in the volume of one material may impact upon the deformation shown by an adjacent material, and upon its mass transport properties. For example, a bentonite-bearing backfill that is emplaced dry may swell, thereby imposing a stress on the adjacent rock, leading to decreases in the apertures of fractures in the excavation disturbed zone.

If material volume changes cause 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 material volume changes that affect 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.

2.1.07