A measurement of, or adjustment to, an instrument, component or system to ensure that its accuracy or response is acceptable.

  • model calibration: The process whereby model predictions are compared with field observations and/or experimental measurements from the system being modelled, and the model adjusted if necessary to achieve a best fit to the measured/observed data.

! This usage of the term is not universally accepted.  The terms model validation and model verification are more commonly used to describe related processes in relation to models.

See container.

Any person, organization or government undertaking the carriage of radioactive material by any means of transport.  The term includes both carriers for hire or reward (known as common or contract carriers in some countries) and carriers on own account (known as private carriers in some countries). [41]


  • direct cause: The latent weakness which allows or causes the observed cause of an initiating event to happen, including the reasons for the latent weakness.
    Corrective actions designed to address direct causes are sometimes termed repairs.
  • latent weakness: An undetected degradation in an element of a safety layer.
    Such a degradation could lead to that element failing to perform as expected if it were requested to work.
  • observed cause: The failure, action, omission or condition which directly leads to an initiating event.
  • root cause: The fundamental cause of an initiating event which, if corrected, will prevent its recurrence, i.e. the failure to detect and correct the relevant latent weakness(es) and the reasons for that failure.
    Corrective actions designed to address root causes are sometimes termed remedies.

See authorization.

An arrangement of interconnected components within a system that initiates a single output.  A channel loses its identity where single output signals are combined with signals from other channels, e.g., from a monitoring channel, or a safety actuation channel.
The above definition is specific to a particular area of nuclear safety.  The term channel is also used, in its normal senses (and therefore normally without specific definition), in a variety of contexts.

1.   Determination of the nature and activity of radionuclides present in a specified place.
For example, determination of the radionuclides present in a bioassay sample or in an area contaminated with radioactive material (as a first step in planning cleanup).  For the latter example, care should be taken to avoid confusion with the existing, and different, definition of the term site characterization.
2.   Determination of the character of something.
This is the dictionary definition, and would not need to be included in an individual glossary.  It is included here only to distinguish the normal usage from the more restricted one indicated in (1).

chronic exposure:
See exposure situations.

Any measures that may be carried out to reduce the radiation exposure from existing contamination through actions applied to the contamination itself (the source) or to the exposure pathways to humans.


1.   Removal of radioactive materials or radioactive objects within authorized practices from any further regulatory control by the regulatory body.
Removal from control in this context refers to control applied for radiation protection purposes.
Conceptually, clearance — removing certain materials or objects within authorized practices from further control — is closely linked to exemption — determining that controls do not need to be applied to certain sources and practices.
Various terms are used in different States to describe this concept, e.g. ‘free release’.
A number of issues related to the concept of clearance and its relationship to other concepts are currently under review.
2.   The net effect of the biological processes by which radionuclides are removed from a tissue, organ or area of the body.
The clearance rate is the rate at which this occurs.

closure [43]:
1.   Administrative and technical actions directed at a repository at the end of its operating lifetime — e.g. covering of the disposed waste (for a near surface repository) or backfilling and/or sealing (for a geological repository and the passages leading to it) — and termination and completion of activities in any associated structures.
For other facilities, the term decommissioning is used.
2.   The completion of all operations at some time after the emplacement of spent fuel or radioactive waste in a disposal facility. This includes the final engineering or other work required to bring the facility to a condition that will be safe in the long term. [13]

A feature of protection system design such that two or more overlapping or simultaneous output signals from several channels are necessary in order to produce a protective action signal by the logic.

collective dose:
See dose concepts.

The process during which systems and components of facilities and activities, having been constructed, are made operational and verified to be in accordance with the design and to have met the required performance criteria.
Commissioning may include both non-nuclear/non-radioactive and nuclear/radioactive testing.

common cause failure:
See failure.

competent authority:
Any national or international regulatory body or authority designated or otherwise recognized as such for any purpose in connection with these Regulations. [41]

! This term should be used only with reference to the Transport Regulations.  Otherwise, the more general term regulatory body should be used.

See structures, systems and components.

condition indicator:
See indicator.

See waste management, radioactive (1).

A barrier which surrounds the main parts of a facility containing radioactive materials and which is designed to prevent or mitigate the uncontrolled release of radioactive material to the environment in operational states or design basis accidents.
Confinement is similar in meaning to containment, but is typically used to refer to the barriers immediately surrounding the radioactive material, whereas containment refers to the additional layers of defence intended to prevent the radioactive materials reaching the environment if the confinement is breached.  Hence, for example, in a nuclear power plant confinement may be provided by the reactor pressure vessel, whereas containment may be provided by the building housing the reactor.  In a repository, confinement may be provided by the waste form and its container, whereas containment may be provided by the surrounding host rock.

! This is not the meaning of confinement implied in use of the term confinement system in the Transport Regulations.

Any package or packages, or load of radioactive material, presented by a consignor for transport. [41]

Any person, organization or government which prepares a consignment for transport, and is named as consignor in the transport documents. [41]

The process of manufacturing and assembling the components of a facility, the carrying out of civil works, the installation of components and equipment and the performance of associated tests.

container, waste:
The vessel into which the waste form is placed for handling, transport, storage and/or eventual disposal; also the outer barrier protecting the waste from external intrusions.
The waste container is a component of the waste package.
For example, molten HLW glass would be poured into a specially designed container (canister) where it would cool and solidify.

! Note that the term waste canister is considered to be a specific term for a container for spent fuel or vitrified high level waste.

Methods or physical structures designed to prevent the dispersion of radioactive substances.
Although approximately synonymous with confinement, containment is normally used to refer to methods or structures that prevent radioactive substances being dispersed in the environment if confinement fails.  See confinement for a more extensive discussion.

containment system:
The assembly of components of the packaging specified by the designer as intended to retain the radioactive material during transport. [41]

1.   Radioactive substances on surfaces, or within solids, liquids or gases (including the human body), where their presence is unintended or undesirable, or the process giving rise to their presence in such places.
Also used less formally to refer to a quantity, namely the activity present on a surface (or on unit area of a surface).

! Translation of the term contamination into some other languages may introduce a connotation that is not present in English.  The English language term contamination refers only to the presence of activity, and gives no indication of the magnitude of the hazard involved.

2.   The presence of a radioactive substance on a surface in quantities in excess of 0.4 Bq/cm2 for beta and gamma emitters and low toxicity alpha emitters, or 0.04 Bq/cm2 for all other alpha emitters. [41]
This is a regulatory definition of contamination, specific to the Transport Regulations.  Levels below 0.4 Bq/cm2 or 0.04 Bq/cm2 would be considered contamination according to the scientific definition (1).

1.   The function or power of directing or regulating.

It should be noted that the usual meaning of the English word control in safety related contexts is somewhat ‘stronger’ (more active) than that of similar words in some other languages.  For example, ‘control’ typically implies not only checking or monitoring something, but also making sure that corrective or enforcement measures are taken if the results of the checking or monitoring indicate an unsatisfactory situation.

2.   A standard of comparison used to check the inferences deduced from an experiment.
In protection and safety, a control is most commonly a sample or a group of people that has not been exposed to radiation from a particular source; the occurrence of particular effects in a sample or group of people that has been exposed is compared with that in the control to provide some indication of the effects that may be attributable to the exposure.  For example, a case-control study is a common type of epidemiological study in which the incidence of health effects (the ‘cases’) in a population that has been exposed to radiation from a particular source is compared with the incidence in a similar population (the ‘control’) that has not been exposed, to investigate whether exposure due to that source may be causing health effects.

corrective maintenance:
See maintenance.

An action aimed at alleviating the radiological consequences of an accident.
Countermeasures are forms of intervention. They may be protective actions or remedial actions, and these more specific terms should be used where possible.

  • agricultural countermeasure: Action taken to reduce contamination of food, agricultural or forestry products before they reach consumers. [40]
    Note that restrictions on the sale, movement or use of contaminated food, agricultural or forestry products (i.e. measures to prevent them reaching consumers) are countermeasures, but are not considered to be agricultural countermeasures.

critical (adj.):

! In view of the number of special meanings attached to this word, particular care should be taken when using the adjective ‘critical’ in its more common English senses (i.e. to mean extremely important, or as a derivative of the verb ‘criticize’).

1.   Having a reactivity of zero.
Also used, more loosely, when the reactivity is greater than zero.  See criticality.

2.   Relating to the highest doses or risks attributable to a specified source.
As in, for example,
critical group, critical pathway or critical radionuclide.

3.   Capable of sustaining a nuclear chain reaction.
As in, for example, critical mass.

  • critical assembly: An assembly containing fissile material intended to sustain a controlled fission chain reaction at a low power level, used to investigate reactor core geometry and composition.
  • critical group: A group of members of the public which is reasonably homogeneous with respect to its exposure for a given radiation source and given exposure pathway and is typical of individuals receiving the highest effective dose or equivalent dose (as applicable) by the given exposure pathway from the given source. [40]
    The reference to a given exposure pathway implies that there will be a number of critical groups for a given source.  Some non-Agency documents, notably those of ICRP [46], use a definition of critical group that makes no such reference to a given exposure pathway, implying that there is only one critical group for a given source, namely the one with the highest total exposure from all exposure pathways.  Some draft Agency Safety Guides also recommend this approach to the critical group concept.
    Application of the term to potential exposures, such as those that may occur in the future as a result of radioactive waste disposal, is complicated by the facts that both the dose (if it occurs) and the probability of receiving the dose are relevant, and that these two parameters are essentially independent of one another.  Hence, a group can be homogeneous with respect to dose but not risk, and, more importantly, vice versa.  A commonly adopted solution is to define a critical group — often a hypothetical critical group — that is reasonably homogeneous with respect to risk, and is typical of those people who might be subject to the highest risk.
  • hypothetical critical group: A group of hypothetical individuals which is reasonably homogeneous with respect to the risk to which its members are subject from a given radiation source and is representative of individuals likely to be most at risk from the given source.

The state of a nuclear chain-reacting medium when the chain reaction is just self-sustaining (or critical), i.e. when the reactivity is zero.
Often used, slightly more loosely, to refer to states in which the reactivity is greater than zero.

curie (Ci):
Unit of activity, equal to 3.7 * 1010 Bq (exactly).
Superseded by the becquerel (Bq).  Activity values may be given in Ci (with the equivalent in Bq in parentheses) if they are being quoted from a reference which uses that unit.
Originally, the activity of a gram of radium.  Occasionally still referred to as ‘gram equivalent radium’.