Description
The spontaneous disintegration or de-excitation of an atomic nucleus, resulting in the emission of sub-atomic particles and energy and the formation of a new progeny (or daughter
) nucleus in the waste package.
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
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.
Radionuclide decay and ingrowth will affect: 1. the radioactivity at any location within the waste package; 2. the rates at which radionuclides and other contaminants are released from solid matrices in the waste package; and 3. the chemical and physical forms in which the releases occur. In the long-term, radioactive decay reduces the total activity of the radionuclides in the waste package, but at the same time changes the proportions of radionuclides present, until and unless secular or transient equilibrium is achieved between parent and daughter radionuclides. Where a precursor radionuclide decays to a progeny radionuclide, this causes the ingrowth of progeny in the waste package. The chemical and physical properties of a daughter nuclide may differ from its parent. A daughter isotope may have a different mobility to its parent (e.g. Ra-226 is more soluble in water than its parent, Th-230). Radiation damage to a solid material in which a daughter isotope is formed may make the daughter more likely to be released from the solid than its parent. Recoil (movement of a relatively high-energy daughter isotope) may enhance release of the daughter isotope. In post-closure assessment, radioactive decay chains are often simplified, e.g. by assuming that the shorter-lived radionuclides decay instantaneously in release and migration calculations but adding any dose-contribution to longer-lived parent radionuclides.
2000 List
A reference to the related FEP(s) within the 2000 NEA IFEP List.
Related References
-
IAEA (), Development of Specifications for Radioactive Waste Packages, IAEA-TECDOC-1515, International Atomic Energy Agency, ISBN 92–0–109206–7, ISSN 1011–4289, 55, http://www-pub.iaea.org/books/IAEABooks/7571/Development-of-Specifications-for-Radioactive-Waste-Packages