Description

The degradation of the metallic component(s) of the repository by interaction with its environment, specifically, by reactions involving water in liquid or vapour form and / or gases (e.g. oxygen in the air), and/or by reaction with solutes within the water (e.g. sulphide). Metallic components may include rebar in concrete, mesh to prevent rock fall, liners or rock bolts. Corrosion of repository metals can occur by a number of processes such as generalised (or uniform), localised and galvanic corrosion processes. Galvanic corrosion occurs when two different metals are in electric contact. Metal corrosion may result in the consumption of oxygen, or the generation of hydrogen.

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.

Corrosion may impact upon the effectiveness of the EBS, and / or upon the effectiveness of the geosphere barrier surrounding the repository.

Corrosion of rebars in certain cementitious barriers may lead to these barriers losing mechanical integrity. Such corrosion may reduce the overall strength of a barrier owing to the rebars losing strength. Alternatively, corrosion may cause the metallic components to expand, thereby cracking the cementitious barrier.

Corrosion of rock bolts may allow deformation of the rock surrounding excavated cavities. Possibly, there could be rock collapse if cavities remain, for example where galleries are not backfilled, or where headspace remains above backfill. Such deformation may in turn impact upon the integrity and performance of the EBS.

Corrosion of metals, whether present for structural reasons, or present in equipment / facilities that are not removed on closure (e.g. ventilation ducts or rails), may influence gas pressures within the repository. Aerobic corrosion of Fe-bearing metal components will consume oxygen that has been trapped within the repository at the time of closure. Later anaerobic corrosion of Fe-bearing metal components will generate H₂ gas and consume water. The evolution of gas pressure caused by corrosion may affect the mechanical properties of the engineered and natural barriers. Potentially, existing fractures could dilate, or new fractures could form. The evolution of gas pressure due to corrosion may also impact upon the movement of fluids (such as water, non-aqueous liquids and gases) to and from the repository and within the repository. Such fluid movement may influence the transport of radionuclides and other contaminants originating in the wastes, should these be released from the waste packages. In this case, the partitioning of the radionuclides and other contaminants between immobile solid phase and mobile fluids may be affected by the evolution of redox conditions caused by corrosion (i.e. evolution from oxidising to reducing conditions caused by consumption of O₂ and generation of H₂).

Radionuclides and other contaminants may sorb to, or co-precipitate with, the products of corrosion, such as Fe-oxyhydroxides. Thus, corrosion may help to retard or immobilise radionuclides and other contaminants.

2000 List

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

2.1.09