REGDOC-3.6, Glossary of CNSC Terminology - Glossary - D

D (D)

See absorbed dose.


See derived activity.


See derived air concentration.

dangerous occurrence (situations dangereuses)

Any of the following situations:

  1. a conveyance carrying radioactive material is involved in an accident;
  2. a package shows evidence of damage, tampering or leakage of its contents, or its integrity is degraded in a manner that may reasonably be expected to impair its ability to comply with [the Packaging and Transport of Nuclear Substances Regulations, 2015 (PTNSR 2015)] or its certificate;
  3. radioactive material is lost, stolen or no longer in the control of a person who is required to have control of it under the [Nuclear Safety and Control Act (NSCA)];
  4. radioactive material has escaped from a containment system, a package or a conveyance during transport;
  5. fissile material is outside the confinement system during transport;
  6. the level of non-fixed contamination, as defined in the IAEA Regulations, during transport exceeds the following limits as applicable when averaged over any area of 300 cm2 of any part of the surface of the package or the conveyance:
    1. 4 Bq/cm2 for beta and gamma emitters and low toxicity alpha emitters, or
    2. 0.4 Bq/cm2 for all other alpha emitters;
  7. there is a failure to comply with the provisions of [the NSCA], the provisions of [the PTNSR 2015] or any licence or certificate that is applicable to a package that may reasonably be expected to lead to a situation in which the environment, the health and safety of persons, or national security is adversely affected.

(Source: Packaging and Transport of Nuclear Substances Regulations, 2015, section 35)

data element (élément de données)

With respect to nuclear material accounting, a unit of information in material balance area records.

date of filing (of a report) (date de dépôt [d’un rapport])

The date on which a report is received by the Commission.

day (jour)

With respect to reporting requirements, a term that varies according to the contexts described in the Interpretation Act, sections 27 and 28, and subsection 35(1).


See design-basis accident.


See design-basis earthquake.


See design-basis threat.


See dose conversion factor.


See design extension conditions.

decommissioning (déclassement)

Administrative and technical actions taken to allow the removal of some or all of the regulatory controls from a facility, location or site where nuclear substances are managed, used, possessed or stored.
Note: Decommissioning actions are the procedures, processes and work activities (such as storage with surveillance, decontamination, dismantling or clean up) that are taken to retire a facility, location or site from service with due regard for the health and safety of people and the environment. For disposal facilities, with the exception of ancillary facilities, the term “closure” instead of “decommissioning” is used. See also clean-up activities; decontamination; dismantle; storage with surveillance.

decontamination (décontamination)

The complete or partial removal of contamination by a deliberate physical, chemical or biological process.

deep geologic repository (dépôt géologique en profondeur [DGP])

See deep geological repository.

deep geological repository (DGR) (dépôt géologique en profondeur [DGP])

A facility where radioactive waste is placed in a deep, stable geological formation (usually several hundred metres or more below the surface). The facility is engineered to isolate and contain radioactive waste to provide the long-term isolation of nuclear substances from the biosphere. Also called deep geologic repository. See also isolation.

defence in depth (défense en profondeur)

A hierarchical deployment of different levels of diverse equipment and procedures to prevent the escalation of anticipated operational occurrences and to maintain the effectiveness of physical barriers placed between a radiation source or radioactive material and workers, members of the public or the environment, in operational states and, for some barriers, in accident conditions.

defined specifications (spécifications définies)

The criteria that specify the capability or performance level that a structure, system or component of a nuclear power plant (NPP) must possess or attain so that the NPP can function effectively and reliably, in accordance with its safety targets. These criteria are set out in an NPP’s version-controlled documents or licensee documents requiring notification of change. Note: This definition applies specifically to NPP reporting requirements.

degraded state (état dégradé)

The state of a structure, system or component such that it exhibits reduced performance but can still be declared available according to specified success criteria.

delayed hydride cracking (fissuration par hydruration retardée)

A crack initiation and growth mechanism that may occur when certain hydride-forming materials are exposed to hydrogen and stress. For example, in CANDU pressure tubes, the zirconium alloy of the pressure tubes is a susceptible material and is exposed to hydrogen in solution.

deleterious substance (substance nocive)


  1. any substance that, if added to any water, would degrade or alter or form part of a process of degradation or alteration of the quality of that water so that it is rendered or is likely to be rendered deleterious to fish or fish habitat or to the use by man of fish that frequent that water, or
  2. any water that contains a substance in such quantity or concentration, or that has been so treated, processed or changed, by heat or other means, from a natural state that it would, if added to any other water, degrade or alter or form part of a process of degradation or alteration of the quality of that water so that it is rendered or is likely to be rendered deleterious to fish or fish habitat or to the use by man of fish that frequent that water, and without limiting the generality of the foregoing includes
  3. any substance or class of substances prescribed pursuant to paragraph (2)(a),
  4. any water that contains any substance or class of substances in a quantity or concentration that is equal to or in excess of a quantity or concentration prescribed in respect of that substance or class of substances pursuant to paragraph (2)(b), and
  5. any water that has been subjected to a treatment, process or changes prescribed pursuant to paragraph (2)(c).

(Source: Fisheries Act)

depleted uranium (uranium appauvri)

Uranium that contains uranium‑235 in a concentration that is less than that normally found in nature. (Source: Nuclear Substances and Radiation Devices Regulations)

Note: In the context of packaging and transport of nuclear substances, depleted uranium means uranium containing a lesser mass percentage of uranium‑235 than natural uranium.

derived activity (DA) (activité dérivée [AD])

The expected retention or excretion rate, expressed as becquerels or becquerels per day, from a single measurement of a radionuclide made at the end of a monitoring period, such that the corresponding extrapolated annual committed effective dose is equal to 1 millisievert. The DA is calculated with the assumption that the intake occurs at the mid-point in the monitoring period.

derived air concentration (DAC) (limite dérivée de concentration dans l’air [LDCA])

The concentration of a radionuclide in air that, when inhaled at a breathing rate of 1.2 m3 per hour for 2,000 hours per year, results in the intake of 1 annual limit on intake.

derived investigational level (DIL) (niveau d’enquête dérivé [NED])

With respect to a program that monitors internal dosimetry, the predetermined level of contamination that triggers an investigation and dose assessment. The DIL, measured in becquerels, is commonly set by programs for monitoring internal contamination and is one of several actions that may be taken when contamination rises above certain levels.

derived reference level (niveau de référence dérivé)

Bioassay-determined activity due to occupational sources, measured in becquerels per litre.

derived release limit (DRL) (limite de rejet dérivée [LRD])

As defined in the CSA Group publication CSA N288.1, Guidelines for calculating derived release limits for radioactive material in airborne and liquid effluents for normal operation of nuclear facilities [3]:

the release rate that would cause an individual of the most highly exposed group to receive and be committed to a dose equal to the regulatory annual dose limit due to release of a given radionuclide to air or surface water during normal operation of a nuclear facility over the period of a calendar year.

design (conception)

In the context of a reactor design review, the overall planning and philosophies that go into ensuring that every aspect of the physical design will consider safety, security and safeguards under all scenarios it may encounter during its lifecycle. See also design basis.

designated non-nuclear response force personnel (personnel désigné qui ne fait pas partie de la force d’intervention pour la sécurité nucléaire)

Nuclear security staff who are authorized under the Public Agents Firearms Regulations to possess or have access to prohibited and restricted firearms, items or devices on behalf of and under the authority of the CNSC for the purpose of carrying out their duties. These duties may encompass the storage, transport, handling, maintenance and use of firearms related to onsite nuclear response force functions. See also onsite nuclear response force.

designated officer (DO) (fonctionnaire désigné)

A person designated as a designated officer under section 37. (Source: Nuclear Safety and Control Act)

Note: The DO is considered qualified to perform duties specified under the Nuclear Safety and Control Act, on behalf of the Commission. The DO may be a CNSC employee or a person otherwise employed under an arrangement with the CNSC.

designated project (projet désigné)

One or more physical activities that

  1. are carried out in Canada or on federal lands;
  2. are designated by regulations made under paragraph 84(a) [of the Canadian Environmental Assessment Act, 2012 (CEAA 2012)] or designated in an order made by the Minister [of the Environment] under subsection 14(2) [of CEAA 2012]; and
  3. are linked to the same federal authority as specified in those regulations or that order.

It includes any physical activity that is incidental to those physical activities. (Source: Canadian Environmental Assessment Act, 2012)

design authority (autorité en matière de conception)

The entity that has overall responsibility for the design process, or the responsibility for approving design changes and for ensuring that the requisite knowledge is maintained.

design basis (dimensionnement)

The range of conditions and events taken explicitly into account in the design of a nuclear facility, according to established criteria, such that the facility can withstand this range without exceeding authorized limits. Note: Design extension conditions are not part of the design basis.

design-basis accident (DBA) (accident de dimensionnement [AD])

Accident conditions for which a nuclear facility is designed according to established design criteria and for which damage to the fuel and the release of radioactive material are kept within authorized limits. DBA is a plant state.

design-basis earthquake (DBE) (séisme de référence [SR])

As defined in the CSA Group publication CSA N289.1‑08, General requirements for seismic design and qualification of CANDU nuclear power plants [4] referenced in the nuclear power plant licence:

an engineering representation of potentially severe effects at the site due to earthquake ground motions having a selected probability of exceedance of 1x10‑4 per year, or such probability level as determined by the regulatory authority.


  1. DBE ground motions are usually referred to as an “earthquake”, and can take the form of a response spectrum, or time history of acceleration, velocity, or displacement.
  2. The DBE is used for the seismic qualification of certain structures, systems, and components. It is used as an input for nuclear power plant seismic design, analysis, and testing to produce a design that is adequate for the specified seismic hazard.
  3. The DBE for some older plants was based on an estimated probability of exceedance of 1x10‑3 per year or was established deterministically (i.e., without probabilistic measures).
design-basis threat (DBT) (menace de référence)

The characteristics of a potential adversary in respect of which countermeasures are incorporated into the design and evaluation of a physical protection system. (Source: Nuclear Security Regulations)

design envelope (enveloppe de conception)

The range of conditions and events (including design extension conditions) that are explicitly taken into account in the design of a nuclear facility, such that significant radioactive releases would be practically eliminated by the planned operation of process and control systems, safety systems, safety support systems and complementary design features.

design extension conditions (DEC) (conditions additionnelles de dimensionnement [CAD])

A subset of beyond-design-basis accidents that are considered in the design process of the facility in accordance with best-estimate methodology to keep releases of radioactive material within acceptable limits. Design extension conditions could include severe accident conditions. DEC is a plant state.

desktop review (examen des documents ou examen documentaire)

See compliance assessment.

detailed decommissioning plan (plan détaillé de déclassement)

A plan setting out the detailed work program, safety and environmental protection procedures, and management systems that will be followed in the decommissioning of a licensed activity/facility. Note: Detailed decommissioning plans should evolve from the preliminary decommissioning plan.

deterministic effect (effet déterministe)

A health effect of radiation for which a threshold level of dose generally exists above which the severity of the effect is greater for a higher dose.

deterministic safety analysis (analyse déterministe de la sûreté)

An analysis of a nuclear facility’s responses to an event, performed using predetermined rules and assumptions (such as those concerning the initial facility operational state, availability and performance of the facility systems and operator actions). Deterministic safety analysis can use either conservative or best-estimate methods.

dewatering water (eau d’assèchement)

Groundwater intercepted by pumps to prevent it from flowing into open pits or into the underground workings of a mine.


See deep geological repository.

diagnostic nuclear medicine (médecine nucléaire diagnostique)

The administration of unsealed sources (nuclear substances) to humans for diagnostic purposes related to their healthcare. Diagnostic nuclear medicine includes the processing of radiopharmaceuticals and laboratory studies that are part of the diagnostic studies.


See derived investigational level.

direct bioassay (essai biologique direct)

See bioassay.

direct effect (effet direct)

An effect in which the cause–effect relationship has no intermediary effects.

direct (in vivo) radiobioassay (essai biologique direct [mesures in vivo])

See bioassay.

direct regulatory activities (activités de réglementation directes)

Those activities, such as assessing applications, issuing licences and certificates, granting approvals and authorizations, verifying and enforcing compliance and providing information, products and services, that are required for the Commission to fulfill its regulatory responsibilities. (Source: Canadian Nuclear Safety Commission Cost Recovery Fees Regulations)

direct trip parameter (paramètre de déclenchement direct)

A process or neutronic parameter that is used to trigger a shutdown action and that is a direct measure of the challenge to derived acceptance criteria or a direct measure of the event taking place.

direct visual surveillance (surveillance visuelle directe)

Direct observation by a person who is physically present at the place that is under observation. (Source: Nuclear Security Regulations)

disconnect (déconnecté)

A condition in which the sealed source assembly is inadvertently released from the control cable.

discretization (discrétisation)

A method of approximation of the true mathematical function to be integrated.

dismantling (démantèlement)

With respect to radiation devices, means to take apart a device to repair, replace or remove faulty components that may include the nuclear substance of that device (part of the licensed activity of servicing, installation and dismantling of devices containing radioisotopes).


With respect to decommissioning, means to take apart, disassemble and tear down the structures, systems and components of a facility, location or site for the purposes of decommissioning.

dismounting (démontage)

See install.

disorderly crowd (foule désordonnée)

A group of people in a recognizable area, with behaviours classified as one of five types: casual, cohesive, expressive, demonstration and aggressive. Note: Each type requires careful consideration on how to manage it. The tactics range from simple crowd monitoring to the presence of uniformed officers interacting with individuals in the crowd, to the deployment of an offsite public order unit. Deployment and the tactics used are judgment calls based on the overall strategies determined by the commander to manage crowds at all levels of order, using the least amount of force.

disposal (évacuation or élimination)

The placement of radioactive waste without the intention of retrieval.

diversity (diversité)

The presence of two or more redundant systems or components to perform an identified function, where the different systems or components have different attributes so as to reduce the possibility of common-cause failure.

division (division)

The designation applied to a given system or set of components that enables the establishment and maintenance of physical, electrical and functional independence from other redundant sets of components.

DO (fonctionnaire désigné)

See designated officer.

dose acceptance criteria (critères d’acceptation des doses)

With respect to safety analysis, bounds for radiation doses that are established to protect workers and the public from the release of nuclear substances from a reactor facility during normal operation, anticipated operational occurrences and design-basis accidents.

dose conversion factor (DCF) (facteur de conversion de la dose [FCD])

The committed effective dose in sieverts, per unit activity in becquerels, delivered by a given radionuclide of a given form.

dose information (renseignements sur les doses)

The occupational radiation doses of monitored workers on record with the National Dose Registry (NDR). This dose information includes annual summaries, discrete dose details, cumulative dose totals, dose histories, dose type, pregnant worker dose information, and exposure to radon progeny. Note: Dose information excludes other information in the worker’s NDR record, such as the worker’s name, date of birth, pregnancy declaration date, social insurance number, employer and job category.

dose limit (limite de dose)

A maximum allowable radiation dose (effective dose or equivalent dose), as specified in the Radiation Protection Regulations, which is in place to minimize the risk of adverse health effects due to radiation exposure.

dose of record(dose enregistrée)

Data about an individual’s radiation dose that has been measured by a licensed dosimetry service and submitted to the National Dose Registry.

dosimeter (dosimètre)

A device for measuring a dose of radiation that is worn or carried by an individual. (Sources: Nuclear Substances and Radiation Devices Regulations; Radiation Protection Regulations)

Note:Among common types are thermoluminescent and optically stimulated luminescent dosimeters.

dosimetry period – one‑year (période de dosimétrie d’un an)

See one‑year dosimetry period.

dosimetry period – five‑year (période de dosimétrie de cinq ans)

See five‑year dosimetry period.

dosimetry service (services de dosimétrie)

A prescribed facility for the measurement and monitoring of doses of radiation. (Source: Nuclear Safety and Control Act)

dosimetry types (types de dosimétrie)

The methods used for measuring radiation dose in or excreted from a body or in radioactive atmospheres.

  • External dosimetry is usually employed for photon (that is, X and gamma) radiation, but may also be used for beta and neutron radiation sources outside of the body.
  • Internal dosimetry involves bioassay in the form of either in vitro monitoring, in vivo monitoring, or a combination of the two.
  • Radioactive atmosphere is usually measured by air monitoring techniques. Typical measurements are for radon progeny and radioactive dusts in uranium mines.
double contingency principle (principe de contingence double)

A characteristic or attribute of a process that has incorporated sufficient safety factors so that at least two unlikely, independent and concurrent changes in process conditions are required before a nuclear criticality accident is possible.

drill (exercice de simulation)

See emergency drill.

drive cable (câble de commande)

See control cable.

drive mechanism (mécanisme de commande)

See remote control.


See derived release limit.

dry mouth (bouche sèche)

The inability of a donor to provide a sufficient amount or volume of oral fluid (that is, saliva) to permit a valid oral fluid drug test.


designated supervising physician

dual-use item (article à double usage)

See nuclear and nuclear-related dual-use items.

duty area (fonction)

One of a job incumbent’s main areas of activity or a grouping of closely related tasks.

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