• equipment qualification: Generation and maintenance of evidence to ensure that the equipment will operate on demand, under specified service conditions, to meet system performance requirements.
    See Safety Series No. 50-SG-D11 [59].
    More specific terms are used for particular equipment or particular conditions; for example, seismic qualification is a form of equipment qualification that relates to conditions that could be encountered in the event of earthquakes.

quality assurance (QA):
1.   Planned and systematic actions necessary to provide adequate confidence that an item, process or service will satisfy given requirements for quality, for example, those specified in the licence.
This definition is slightly modified from that in ISO 921:1997 (Nuclear Energy: Vocabulary) [45] to say "an item, process or service" instead of "a product or service" and to add the example. A more general definition of quality assurance and definitions of related terms can be found in ISO 8402:1994 [30].
2.   A systematic programme of controls and inspections applied by any organization or body involved in the transport of radioactive material which is aimed at providing adequate confidence that the standard of safety prescribed in these Regulations is achieved in practice. [41]

quality control (QC):
Part of quality assurance intended to verify that systems and components correspond to predetermined requirements.
This definition is taken from ISO 921:1997 (Nuclear Energy: Vocabulary) [45].  A more general definition of quality control and definitions of related terms can be found in ISO 8402:1994 [30].

quality factor, Q:
A number by which the absorbed dose in a tissue or organ is multiplied to reflect the relative biological effectiveness of the radiation, the result being the dose equivalent.
Superseded by radiation weighting factor in the definition of equivalent dose by ICRP [48], but still defined, as a function of linear energy transfer, for use in calculating the dose equivalent quantities used in monitoring.  The BSS [1] also state that the mean quality factor

at 10 mm depth in the ICRU sphere can be used as a value of radiation weighting factor for radiation types for which the BSS do not specify a value (see radiation weighting factor).


Unit of absorbed dose, equal to 0.01 Gy.
Superseded by the gray (Gy).
Abbreviation of roentgen absorbed dose.


! When used in Agency publications, the term radiation normally refers only to ionizing radiation.  The IAEA has no statutory responsibilities in relation to non-ionizing radiation.

Ionizing radiation can be divided into low LET radiation and high LET radiation (as a guide to its relative biological effectiveness), or into strongly penetrating radiation and weakly penetrating radiation (as an indication of its ability to penetrate shielding or the human body).

radiation area:
See controlled area.

radiation detriment:
The total harm that would eventually be experienced by an exposed group and its descendants as a result of the group’s exposure to radiation from a source. [40]
In Publication 60 [48], ICRP defines a measure of radiation detriment, which has the dimensions of probability, and could therefore also be considered a measure of risk.

radiation level:
The corresponding dose rate expressed in millisieverts per hour. [41]

! This usage is specific to the Transport Regulations, and should otherwise be avoided.

radiation protection:
See protection (1).

radiation protection programme:
Systematic arrangements which are aimed at providing adequate consideration of radiation protection measures. [41]

radiation weighting factor, wR:
A number by which the absorbed dose in a tissue or organ is multiplied to reflect the relative biological effectiveness of the radiation in inducing stochastic effects at low doses, the result being the equivalent dose.
Values are selected by ICRP to be representative of the relevant relative biological effectiveness and are broadly compatible with the values previously recommended for quality factors in the definition of dose equivalent.  The radiation weighting factor values recommended by ICRP [48] are:

Type of radiation


Photons, all energies


Electrons and muons, all energiesa


Neutrons, energy:

< 10 keV

10 keV to 100 keV

> 100 keV to 2 MeV

> 2 MeV to 20 MeV

> 20 MeV






Protons, other than recoil protons, energy > 2 MeV


Alpha particles, fission fragments, heavy nuclei


a Excluding Auger electrons emitted from radionuclides bound to DNA, for which special microdosimetric considerations apply.

If calculation of the radiation weighting factor for neutrons requires a continuous function, the following approximation can be used, where E is the neutron energy in MeV:

For radiation types and energies not included in the table, wR can be taken to be equal to
at 10 mm depth in the ICRU sphere and can be obtained as follows:

where D is the absorbed dose, Q(L) is the quality factor in terms of the unrestricted linear energy transfer L in water, specified in ICRP Publication No. 60, and DL is the distribution of D in L.

where L is expressed in keV/µm.

1.   Exhibiting radioactivity.
This is the scientific definition, and should not be confused with the regulatory definition (2).
2.   Designated in national law or by a regulatory body as being subject to regulatory control because of its radioactivity.

radioactive contents:
The radioactive material together with any contaminated or activated solids, liquids, and gases within the packaging. [41]

radioactive material:
1.   Material designated in national law or by a regulatory body as being subject to regulatory control because of its radioactivity.
Some States use the term radioactive substance for this regulatory purpose.  However, the term radioactive substance is also sometimes used to indicate that the scientific use of radioactive (see radioactive (1)) is intended, rather than the regulatory meaning of radioactive (see radioactive (2)) suggested by the term radioactive material.  It is therefore essential that any such distinctions in meaning are clarified.
2.   Any material containing radionuclides where both the activity concentration and the total activity in the consignment exceed the values specified in paras 401–406. [41]

radioactive substance:
See radioactive material (1).

radioactive waste management:
See waste management, radioactive.

radioactive waste:
See waste.

radioactive waste management:
See waste management, radioactive.

radioactive waste management facility:
See waste management facility, radioactive.

The phenomenon whereby atoms undergo spontaneous random disintegration, usually accompanied by the emission of radiation.
In Agency publications, radioactivity should be used only to refer to the phenomenon.  To refer to an amount of a radioactive substance, use activity.

radiological protection:
See radiation protection.

1.   Any combination of isotopes of the element radon.
2.   Radon-222.
When contrasted with thoron (radon-220).

For a nuclear chain-reacting medium:

where Keff is the ratio between the number of fissions in two succeeding generations of the chain reaction.
A measure of the deviation from criticality of a nuclear chain-reacting medium, such that positive values correspond to a supercritical state and negative values correspond to a subcritical state.

  • shutdown reactivity: The reactivity when all control devices are introducing their maximum negative reactivity.

Provision of alternative (identical or diverse) structures, systems or components, so that any one can perform the required function regardless of the state of operation or failure of any other.

Reference Man:
An idealized adult caucasian human male defined by the ICRP for the purpose of radiation protection assessment. [40]
See Ref. [60], but note that this is currently under revision.

See registration.

A form of authorization for practices of low or moderate risks whereby the legal person responsible for the practice has, as appropriate, prepared and submitted a safety assessment of the facilities and equipment to the Regulatory Authority.  The practice or use is authorized with conditions or limitations as appropriate.  The requirements for safety assessment and the conditions or limitations applied to the practice should be less severe than those for licensing. [40]
Typical practices that are amenable to registration are those for which: (a) safety can largely be ensured by the design of the facilities and equipment; (b) the operating procedures are simple to follow; (c) the safety training requirements are minimal; and (d) there is a history of few problems with safety in operations.  Registration is best suited to those practices for which operations do not vary significantly.
The holder of a current registration is termed a registrant.  Other derivative terms should not be needed; a registration is a product of the authorization process, and a practice with a current registration is an authorized practice.

Regulatory Authority:
An authority or authorities designated or otherwise recognized by a government for regulatory purposes in connection with protection and safety. [40]
The term Regulatory Authority may be used (with initial capitals) when consistency with the BSS is necessary.  However, in general, the term regulatory body is preferred.

regulatory body:
1.   An authority or a system of authorities designated by the government of a State as having legal authority for conducting the regulatory process, including issuing authorizations, and thereby regulating nuclear, radiation, radioactive waste and transport safety.
The national competent authority for the regulation of radioactive material transport safety [41] is included in this description, as is the Regulatory Authority for radiation protection and safety [1].
2.   [For each Contracting Party any body or bodies given the legal authority by that Contracting Party to grant licences and to regulate the siting, design, construction, commissioning, operation or decommissioning of nuclear installations.] [6]
3.   [Any body or bodies given the legal authority by the Contracting Party to regulate any aspect of the safety of spent fuel or radioactive waste management including the granting of licences.] [7]

regulatory inspection:
See inspection.

See cleanup.

relative biological effectiveness (RBE):
A relative measure of the effectiveness of different radiation types at inducing a specified health effect, expressed as the inverse ratio of the absorbed doses of two different radiation types that would produce the same degree of a defined biological endpoint.

The probability that a system will meet its minimum performance requirements when called upon to do so.
See also availability.

The non-urgent removal or extended exclusion of people from a contaminated area to avoid chronic exposure.
Relocation is a longer term protective action.  It may be a continuation of the urgent protective action of evacuation.
Relocation is considered to be permanent relocation (sometimes termed resettlement) if it continues for more than a year or two and return is not foreseeable; otherwise it is temporary relocation.

Unit of dose equivalent and effective dose equivalent, equal to 0.01 Sv.
Superseded by sievert (Sv).
Abbreviation of roentgen equivalent man.

remedial action:
Action taken when a specified action level is exceeded, to reduce radiation doses that might otherwise be received, in an intervention situation involving chronic exposure. [40]
Remedial actions could also be termed longer term protective action, but longer term protective actions are not necessarily remedial actions.

See root cause.

See direct cause.

A nuclear facility where waste is emplaced for disposal.

  • geological repository: A facility for radioactive waste disposal located underground (usually several hundred metres or more below the surface) in a stable geological formation to provide long term isolation of radionuclides from the biosphere.
  • near surface repository: A facility for radioactive waste disposal located at or within a few tens of metres of the Earth’s surface.

A process or operation, the purpose of which is to extract radioactive isotopes from spent fuel for further use.

Required by (national or international) law or regulations, or by Agency Safety Fundamentals or Safety Requirements.
In Agency publications, required (and other terms derived from the verb require) should only be used in this sense.  The more general sense of something that is necessary should be expressed using other words.

residual heat:
The sum of the heat originating from radioactive decay and shutdown fission and the heat stored in reactor related structures and in heat transport media.

See cleanup.

Depending on the context, the term risk may be used to represent a quantitative measure (as, for example, in definitions (1) and (2)) or as a qualitative concept (as in definition (3)).
1.   A multiattribute quantity expressing hazard, danger or chance of harmful or injurious consequences associated with actual or potential exposures.  It relates to quantities such as the probability that specific deleterious consequences may arise and the magnitude and character of such consequences. [40]
In mathematical terms, this can be expressed generally as a set of triplets,
where Si is an identification or description of a scenario i, pi is the probability of that scenario and Xi is a measure of the consequence of the scenario.  The concept of risk is sometimes also considered to include uncertainty in the probabilities pi of the scenarios.
2.   The mathematical mean (expectation value) of an appropriate measure of a specified (usually unwelcome) consequence:

where pi is the probability of occurrence of scenario or event sequence i and Ci is a measure of the consequence of that scenario or event sequence.
Typical consequence measures Ci include core damage frequency, the estimated number or probability of health effects, etc.
If the number of scenarios or event sequences is large, the summation is replaced by an integral.
The summing of risks associated with scenarios or event sequences with widely differing values of Ci is controversial.  In such cases the use of the term ‘expectation value’, although mathematically correct, is misleading and should be avoided if possible.
Methods for treating uncertainty in the values of pi and Ci and particularly whether such uncertainty is represented as an element of risk itself or as uncertainty in estimates of risk, vary.
3.   The probability of a specified health effect occurring in a person or group as a result of exposure to radiation.
The health effect(s) in question must be stated — e.g. risk of fatal cancer, risk of serious hereditary effects, or overall radiation detriment — as there is no generally accepted ‘default’.
Commonly expressed as the product of the probability that exposure will occur and the probability that the exposure, assuming that it occurs, will cause the specified health effect.  The latter probability is sometimes termed the conditional risk.

  • annual risk: The probability that a specified health effect will occur at some time in the future in an individual as a result of radiation exposure received or committed in a given year, taking account of the probability of exposure occurring in that year.

! This is not the probability of the health effect occurring in the year in question; it is the lifetime risk resulting from the annual dose for that year.

risk coefficient, g:
The lifetime risk or radiation detriment assumed to result from exposure to unit equivalent dose or effective dose.

risk factor:
Sometimes used as a synonym for risk coefficient.  However, this is different from the normal medical use of the term risk factor to indicate a factor that influences an individual’s risk, and therefore should be avoided.

roentgen (R):
Unit of exposure, equal to 2.58 ' 10-4 C/kg (exactly).
Superseded by SI unit C/kg.