Description

The excavation of shafts, tunnels, waste emplacement galleries, silos, holes etc. of a repository, the stabilisation of these openings and installation/assembly of structural elements. This includes rock bolting, shotcrete, grouting construction of tunnel/shaft linings, drain layers and installation of services and waste handling components.

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

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 are some similarities between Construction (this FEP, 1.1.5), Operations (FEP, 1.1.6) and Closure (FEP 1.1.7). FEP 1.1.5 covers excavation and related activities, whereas FEP 1.1.6 covers activities other than excavation (e.g. emplacement of wastes in a disposal hole), excluding final closure (covered by FEP 1.1.7). FEP 1.1.5 does not cover emplacement of backfill and seals during closure, or associated activities, such as reaming of the EDZ. The sequencing of construction activities, as opposed to the activities themselves, is covered by FEP 1.1.4 (Schedule and planning).

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.

Construction of a repository results in mechanical disturbance to the host rock formation and adjacent rock formations (particularly the overlying rock formations, but also possibly deeper rock formations and adjacent rock formations). Construction methods affect the properties of the excavation damaged and disturbed zones around the repository and shafts (FEP 3.1.6). Excavation has the potential to create pathways such as excavation-disturbed zones around tunnels. If not subsequently sealed, these pathways could allow the transport of gas and/or water and contaminants, including radionuclides, in the post-closure period. Any waste package emplacement holes must be excavated in such a way that they meet the required specifications (e.g. suitably low groundwater inflows). The process of construction also disturbs the hydrogeological and geochemical environment of the host rock and its surroundings. For example, groundwater flow directions may be perturbed if pumping is required during repository construction. Geochemical conditions are also perturbed, for example by oxygen ingress due to ventilation of excavations, or the introduction of alkalis owing to the use of cement. These chemical perturbations may cause changes in the properties of engineered and natural barriers. The hydrogeological and geochemical disturbances may potentially influence the migration and retardation of radionuclides in the post-closure period and need to be treated appropriately in performance and safety assessments. Quality control (FEP 1.1.1) during construction also has the potential to influence the effectiveness of natural barriers and engineered barriers that are emplaced subsequently. Failure to carry out construction appropriately could result in impaired performance of the barrier systems in the post-closure period.

2000 List

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

1.1.02

Related References

  • IAEA (), Planning and Design Considerations for Geological Repository Programmes of Radioactive Waste, IAEA-TECDOC-1755, International Atomic Energy Agency, Vienna
  • IAEA (), Geological Disposal Facilities for Radioactive Waste, Specific Safety Guide No. SSG-14, International Atomic Energy Agency, Vienna, http://www-pub.iaea.org/MTCD/publications/PDF/Pub1483_web.pdf