Description
The processes associated with high-temperature water and/or related fluids, including processes such as heat-driven groundwater flow and hydrothermal alteration of minerals in the rocks through which the high temperature groundwater flows. These processes are often complex and strongly coupled; for example, mineral precipitation and/or alteration could cause fracture infilling, thereby impeding groundwater flow, and potentially modifying groundwater salinity, resulting in the occurrence of a new set of mineral alteration reactions, and so forth. Groundwater temperature is influenced by large-scale geological and hydrogeological properties of the rock, such as the location of geothermal heat sources, thermal conductivity, location of recharge and discharge areas and hydraulic conductivity.
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.
Alteration of rocks by reactions involving hydrothermal fluids may be considered to be “hydrothermal metamorphism” by some researchers. There is therefore potential overlap between Hydrothermal activity (this FEP, 1.2.7) and Metamorphism (FEP 1.2.6).
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.
Hydrothermal activity has the potential to influence the performance and safety of a repository by:
- affecting the rates of water flow through and around the repository;
- potentially causing multi-phase fluid flow (owing to boiling and / or degassing if pressures and temperatures decrease along flow paths) with consequent partitioning of radionuclides between liquid and gaseous phases;
- influencing the chemical conditions in the repository and the surrounding rocks; and
- by causing fluid-rock reactions that affect the contaminant transport / retardation properties of the engineered barriers, the host rocks of the repository and the surrounding rock formations.
Temperature gradients may result in convection of groundwater. Elevated temperatures will also cause reactions between the water and the engineered and natural barriers to be more rapid than at lower temperatures. Hydrothermal fluids will typically transport a wide range of dissolved chemicals and gases and may therefore influence the chemical conditions in the repository. The hydrothermal fluids may dissolve or precipitate minerals as pressures and temperatures vary along flow paths. The hydrothermal fluids also have the potential to react with and alter the solid phase assemblages in wastes, engineered barriers and rocks. The mineral dissolution, precipitation and alteration reactions that may occur should hydrothermal fluids circulate through a repository or the surrounding geosphere could potentially affect the physical and chemical properties of the wastes, engineered barriers and rocks.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
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Metcalfe R and Watson SP (), Technical Issues Associated with Deep Repositories for Radioactive Waste in Different Geological Environments, Environment Agency Science Report SC060054/SR1, Environment Agency, Rio House, Waterside Drive, Aztec West, Almondsbury, Bristol, BS32 4UD, 213, http://www.gov.uk/government/uploads/system/uploads/attachment_data/file/291763/scho0809bqvu-e-e.pdf