Description

The hydraulic erosion of the buffer/backfill due to water flowing through the repository, for example through intersecting hydraulically active fractures. If the rate of throughflow exceeds the rate of uptake by the buffer/backfill, then active flow channels or pipes may develop in the buffer/backfill.

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

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 density of buffer or backfill would be reduced by piping or hydraulic erosion, were it to occur. The loss of density may impair the buffer’s function. In this case, there could be enhanced transport of solutes to / from the waste container, potentially leading to its degradation and ultimately loss of its containment function. Were this to occur, transport of radionuclides and other contaminants from the waste container might occur through the buffer. Loss of buffer density could also impair its ability to insulate the waste container from the effects of rock movements.

Loss of backfill density by piping / hydraulic erosion could potentially lead to pathways forming for the transport of radionuclides and other contaminants, should there be release pathways to the backfill through the other engineered barriers.

Were it to proceed sufficiently, piping / hydraulic erosion of the backfill could potentially lead to any mechanical support function of the backfill being impaired.

2000 List

A reference to the related FEP(s) within the 2000 NEA IFEP List.

2.1.08