See nuclear safety and protection and safety.

safety action:
A single action taken by a safety actuation system.

safety case:
A collection of arguments and evidence to demonstrate the safety of a facility or activity.
This will normally include a safety assessment, but would also typically include information (including supporting evidence and reasoning) on the robustness and reliability of the safety assessment and the assumptions made therein.

safety committee:
A group of experts from the operating organization convened to advise on the safety of operation of an authorized facility.

safety culture:
The assembly of characteristics and attitudes in organizations and individuals which establishes that, as an overriding priority, protection and safety issues receive the attention warranted by their significance.
For a more detailed discussion, see Ref [10]

safety function:
A specific purpose that must be accomplished for safety.
Safety Series 50-SG-D1 [61] lists 20 safety functions to be met by the design of a nuclear power plant in order to meet three general safety requirements:

  • the capability to safely shut down the reactor and maintain it in a safe shutdown condition during and after appropriate operational states and accident conditions;
  • the capability to remove residual heat from the reactor core after shutdown, and during and after appropriate operational states and accident conditions; and
  • the capability to reduce the potential for the release of radioactive materials and to ensure that any releases are within prescribed limits during and after operational states and within acceptable limits during and after design basis accidents.

This guidance is commonly condensed into a succinct expression of three main safety functions for nuclear power plants:

safety group:
The assembly of equipment designated to perform all actions required for a particular postulated initiating event to ensure that the limits specified in the design basis for anticipated operational occurrences and design basis accidents are not exceeded.

! The term group is also used (with various qualifying adjectives, e.g. maintenance group, commissioning group) in the more obvious sense of a group of people involved in a particular area of work.  Such terms may need to be defined if there is any chance of confusion with safety group.

safety indicator:
A quantity used in assessments as a measure of the radiological impact of a source or practice, or of the performance of protection and safety provisions, other than a prediction of dose or risk.
Such quantities are most commonly used in situations where predictions of dose or risk are unlikely to be reliable, e.g. long term assessments of repositories.  They are normally either:

  • illustrative calculations of dose or risk quantities, used to give an indication of the possible magnitude of doses or risks for comparison with criteria; or
  • other quantities, such as radionuclide concentrations or fluxes, that are considered to give a more reliable indication of impact, and that can be compared with other relevant data.

safety issues:
Deviations from current safety standards or practices, or weaknesses in facility design or practices identified by plant events, with a potential impact on safety because of their impact on defence in depth, safety margins or safety culture.

safety layers:
Passive systems, automatically or manually initiated safety systems, or administrative controls that are provided to ensure that the required safety functions are achieved.
Often expressed as:

  • hardware, i.e. passive and active safety systems;
  • software, including personnel and procedures as well as computer software; and
  • management control, particularly preventing defence in depth degradation (through quality assurance, preventive maintenance, surveillance testing, etc.) and reacting appropriately to experience feedback from degradations that do occur (e.g. determining root causes and taking corrective actions.

See also defence in depth.

safety standards:
Standards of safety issued pursuant to Article III(A)(6)[44] of the Statute of the International Atomic Energy Agency [27].<
Safety standards issued since 1997 in the IAEA Safety Standards Series are designated as Safety Fundamentals, Safety Requirements or Safety Guides.  Other Agency publications, such as Safety Reports and TECDOCs (most of which are issued pursuant to Article VIII of the Agency’s Statute), are not safety standards.  Some safety standards issued prior to 1997 in the IAEA Safety Series were designated Safety Standards, Codes, Regulations or Rules.  Furthermore, some publications issued in the Safety Series were not safety standards, notably those designated Safety Practices or Procedures and Data.
See the booklet "Preparation and Review of Safety Related IAEA Publications" [43].

safety system:
See plant equipment.

A postulated or assumed set of conditions and/or events.
Most commonly used in analysis or assessment to represent possible future conditions and/or events to be modelled, such as possible accidents at a nuclear facility, or the possible future evolution of a repository and its surroundings.  A scenario may represent the conditions at a single point in time or a single event, or a time history of conditions and/or events.

A type of analysis aimed at eliminating from further consideration factors that are less significant for protection or safety, in order to concentrate on the more significant factors.  This is typically achieved by consideration of very pessimistic hypothetical scenarios.
Screening is usually conducted at an early stage in order to narrow the range of factors needing detailed consideration in an analysis or assessment.

Measures to prevent the loss, theft or unauthorized transfer of radiation sources or radioactive material.
This term is usually used in the context of the radiological hazard that might result from the loss or theft of sources or radioactive material; but also relates to the safeguards implications of the loss, theft or unauthorized transfer of fissile material, for which the term physical protection is also used.

! Note the difference between safety and security in Agency usage.  This should be particularly borne in mind in view of the fact that in many languages the same word may be used for both.

sensitivity analysis:
See analysis.

The use of a structure for protection from an airborne plume and/or deposited radionuclides.
An urgent protective action, used to provide shielding against external exposure and to reduce the intake of airborne radionuclides by inhalation.

The specific movement of a consignment from origin to destination. [41]

sievert (Sv):
Name for the SI unit of equivalent dose and effective dose, equal to 1 J/kg.

single failure:
A failure which results in the loss of capability of a component to perform its intended safety function(s), and any consequential failure(s) which result from it.

single failure criterion:
A criterion (or requirement) applied to a system such that it must be capable of performing its task in the presence of any single failure.

site area:
See area.

site characterization:
See characterization.

site confirmation:
The final stage of the siting process for a repository, based on detailed investigations on the preferred site which provide site specific information needed for safety assessment.  This stage includes the finalization of the repository design and the preparation and submission of a licence application to the regulatory body.
Site confirmation follows site characterization.

site personnel:
All persons working in the site area of an authorized facility, either permanently or temporarily.

The process of selecting a suitable site for a facility, including appropriate assessment and definition of the related design bases.
The siting process for a repository is particularly crucial to its long term safety; it may therefore be a particularly extensive process, and is divided into the following stages:

The interaction of an atom, molecule or particle with the solid surface at a solid–solution interface.
Used in the context of radionuclide migration to describe the interaction of radionuclides in pore- or groundwater with soil or host rock, and of radionuclides in surface water bodies with suspended and bed sediments.
A general term which includes absorption (interactions taking place largely within the pores of solids) and adsorption (interactions taking place on solid surfaces).  The processes involved can also be divided into chemisorption (chemical bonding with the substrate) and physisorption (physical attraction, e.g. by weak electrostatic forces).
In practice, sorption may sometimes be difficult to distinguish from other factors affecting migration, such as filtration or dispersion.

1.   Anything that may cause radiation exposure — such as by emitting ionizing radiation or by releasing radioactive substances or radioactive materials — and can be treated as a single entity for protection and safety purposes.
For example, materials emitting radon are sources in the environment, a sterilization gamma irradiation unit is a source for the practice of radiation preservation of food, an X ray unit may be a source for the practice of radiodiagnosis; a nuclear power plant is part of the practice of generating electricity by nuclear fission, and may be regarded as a source (e.g. with respect to discharges to the environment) or as a collection of sources (e.g. for occupational radiation protection purposes).  A complex or multiple installation situated at one location or site may, as appropriate, be considered a single source for the purposes of application of safety standards.

  • natural source: A naturally occurring source of radiation, such as the sun and stars (sources of cosmic radiation) and rocks and soil (terrestrial sources of radiation).

2.   Radioactive material used as a source of radiation.
Such as those used for medical applications or in industrial instruments.  These are, of course, sources as defined in (1), but this usage is less general.

  • disused source: A source no longer in use or intended to be used.
    The Joint Convention [13] refers to ‘disused sealed sources’, but does not define them.

! Note that a disused source may still represent a significant radiological hazard.  It differs from a spent source in that it may still be capable of performing its function; it may be disused because it is no longer needed.

  • orphan source: A source which poses sufficient radiological hazard to warrant regulatory control, but which is not under regulatory control because it has never been so, or because it has been abandoned, lost, misplaced, stolen or otherwise transferred without proper authorization.
  • sealed source: Radioactive material that is (a) permanently sealed in a capsule, or (b) closely bonded and in a solid form.
    The Joint Convention definition [13] is identical, except that the words "excluding reactor fuel elements" are added.  The BSS definition [1] is as above [9], but continues: "The capsule or material of a sealed source shall be strong enough to maintain leaktightness under the conditions of use and wear for which the source was designed, also under foreseeable mishaps."
    The term special form radioactive material, used in the context of transport of radioactive materials, has essentially the same meaning.
  • spent source: A source that is no longer suitable for its intended purpose as a result of radioactive decay.

! Note that a spent source may still represent a radiological hazard.

source material:
Uranium containing the mixture of isotopes occurring in nature; uranium depleted in the isotope 235; thorium; any of the foregoing in the form of metal, alloy, chemical compound, or concentrate; any other material containing one or more of the foregoing in such concentration as the Board of Governors shall from time to time determine; and such other material as the Board of Governors shall from time to time determine. [57]

source term:
The amount and isotopic composition of material released (or postulated to be released) from a facility.
Used in modelling releases of radionuclides to the environment, particularly in the context of accidents at nuclear installations or releases from radioactive waste in repositories.

special form radioactive material:
Either an indispersible solid radioactive material or a sealed capsule containing radioactive material. [41]
This term is essentially identical in meaning to sealed source.

spent fuel:
1.   Nuclear fuel removed from a reactor following irradiation, which is no longer usable in its present form because of depletion of fissile material, poison build-up or radiation damage.
2.   [Nuclear fuel that has been irradiated in and permanently removed from a reactor core.] [7]
The adjective ‘spent’ suggests that spent fuel cannot be used as fuel in its present form (as, for example, in spent source). In practice, however (as in (2) above), spent fuel is commonly used to refer to fuel which has been used as fuel but will no longer be used, whether or not it could be (which might more accurately be termed ‘disused fuel’).

spent fuel management:
All activities that relate to the handling or storage of spent fuel, excluding off-site transportation.  It may also involve discharges. [13]

State of destination:
A State to which a transboundary movement is planned or takes place. [13]

State of origin:
A State from which a transboundary movement is planned to be initiated or is initiated. [13]

stochastic analysis:
See probabilistic analysis.

stochastic effect:
See health effects (of radiation).

The holding of spent fuel or of radioactive waste in a facility that provides for its containment, with the intention of retrieval. [13]

! Storage is by definition an interim measure, and the term interim storage would therefore be appropriate only to refer to short term temporary storage when contrasting this with the longer term fate of the waste.  Storage as defined above should not be described as interim storage.

See, structures, systems and components.

structures, systems and components:
A general term encompassing all of the elements (items) of a facility or activity which contribute to protection and safety, except human factors.
Structures are the passive elements: buildings, vessels, shielding, etc. A system comprises several components, assembled in such a way as to perform a specific (active) function. 

Any legal person to whom a registrant or licensee delegates duties, totally or partially, in relation to the design, manufacture, production or construction of a source.  (An importer of a source is considered a supplier of the source.) [40]

surveillance testing:
Periodic testing to verify that structures, systems and components continue to function or are in a state of readiness to perform their functions.


See structures, systems and components.

System of Radiological Protection:
The systems of protection for practices and for intervention recommended by ICRP.<
System of Radiological Protection usually refers to both systems together (or, for historical reasons, to the system for practices only); individually they should be referred to as the ‘system of protection of practices’ and the ‘system of protection for intervention’.
See ICRP 60 [48].