Description
The characteristics and properties of the waste immobilisation matrix/matrices at the time of emplacement in the repository.
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.
- Feature
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.
An immobilisation matrix minimises the rate of release of contaminants from a breached or vented waste package. Another purpose may be to minimise free space within a waste container, thereby helping to provide structural integrity (e.g. so that a waste container can withstand the weight of other containers stacked on top of it). The physical and chemical characteristics of the immobilisation matrix, including its geometry (dimensions and shape, which affect surface area / volume ratios and void space), influence how contaminant release is limited. For example, a borosilicate glass matrix may immobilise radionuclides principally owing to being chemically stable and impermeable. In contrast, a cementitious matrix may immobilise contaminants because of its chemical reactivity, by buffering pH at alkaline values, under which conditions many contaminants are poorly soluble. The physical and chemical characteristics of the immobilisation matrix will also influence the form in which any radionuclides or other contaminants might be released from a waste form and subsequently transported from a waste container following container breach. For example, reactions between water, CO₂ and a cementitious matrix may prevent C-14 from being transported from encapsulated activated metals in the form of gaseous CO₂. The physical and chemical characteristics and properties of an immobilisation matrix will influence how it interacts with other waste form components (whether metallic, organic or non-metallic and inorganic) and with the waste container. Depending upon the physical and chemical characteristics of the immobilisation matrix, these latter interactions may influence the integrity of the containers. For example, the alkaline environment maintained by a cementitious matrix may decrease the corrosion rate of an iron or steel container. On the other hand, the possibility that a bituminous immobilisation matrix may expand due to radiolysis, thereby impacting upon the container, may need to be considered by a safety assessment.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
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Abdel Rahman R O, Rakhimov R Z, Rakhimova N R and Ojovan M I (), Cementitious Materials for Nuclear Waste Immobilization, Wiley, ISBN: 978-1-118-51197-8, http://eu.wiley.com/WileyCDA/WileyTitle/productCd-1118511972.html
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Ojavan M (), Handbook of Advanced Radioactive Waste Conditioning Technologies, Woodhead Publishing, ISBN 9781845696269, http://store.elsevier.com/product.jsp?isbn=9780857090959
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Ojavan M I and Lee W (), An Introduction to Nuclear Waste Immobilisation, Elsevier, ISBN 9780080993928, http://store.elsevier.com/product.jsp?lid=0&iid=73&sid=0&isbn=9780080993935