Language selection


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

main control room (MCR) (salle de commande principale [SCP])

A room where operations personnel can centrally monitor and control facility systems.

maintenance (entretien)

The organized activities, both administrative and technical, to keep Class II prescribed equipment and radiation devices, as well as structures, systems and components, in good operating condition. Note: For reactor facilities, maintenance includes repair aspects.

malevolent act (acte malveillant)

An illegal action or an action that is committed with the intent of causing wrongful harm.

management (gestion)

In relation to nuclear fuel waste, long‑term management by means of storage or disposal, including handling, treatment, conditioning or transport for the purpose of storage or disposal. (Source: Nuclear Fuel Waste Act)


A functional area that groups 3 of the 14 safety and control areas (SCAs) within the CNSC SCA Framework: management system, human performance management and operating performance. Other functional areas are “core control processes” and “facility and equipment”.

management measures (mesures de gestion)

With respect to nuclear criticality safety, functions performed by a licensee, generally on a continuing basis, on nuclear criticality safety controls, to ensure the controls are available and reliable to perform their functions when needed. Management measures include configuration management, maintenance, training and qualifications, procedures, audits and assessments, event investigations, records management, and other quality assurance elements.

management system (système de gestion)

[With respect to packaging and transport of nuclear substances, h]as the same meaning as in the IAEA Regulations. (Source: Packaging and Transport of Nuclear Substances Regulations, 2015)

Note: In the IAEA Regulations, a management system means a set of interrelated or interacting elements (system) for establishing policies and objectives and enabling the objectives to be achieved in an efficient and effective manner.


The framework of processes, procedures and practices used to ensure that an organization can fulfill all tasks required to achieve its objectives safely and consistently.

management system SCA (DSR Système de gestion)

A safety and control area (SCA) that covers the framework that establishes the processes and programs required to ensure an organization achieves its safety objectives, continuously monitors its performance against these objectives, and fosters a healthy safety culture. This SCA is one of the 14 within the CNSC SCA Framework.

MAPS (normes de performance minimales permises)

See minimum allowable performance standards.

material balance area (MBA) (zone de bilan matières [ZBM])

An area within a facility or a location outside a facility where both of the following conditions apply:

  • the quantity of nuclear material in each transfer to and from the area can be determined
  • the physical inventory of nuclear material within the area can be determined when necessary, in accordance with specified procedures, so that the material balance can be established for IAEA safeguards purposes
material balance period (période de bilan matières)

The time between two consecutive physical inventory takings.

material category (catégorie d’élément des matières nucléaires)

With respect to nuclear material accounting, any one of the following:

  • any of these element material categories – natural uranium, depleted uranium, enriched uranium, thorium and plutonium
  • any of these isotope material categories – uranium‑235, uranium‑233 and plutonium‑239
material description code (MDC) (code de description de matière [CDM])

With respect to nuclear material accounting, a four-character code used to describe nuclear material batches by physical form, chemical composition, containment or type of container, and by irradiation status and quality.

material unaccounted for (MUF) (différence d’inventaire)

See inventory difference.


See material balance area.

MB Code (code MB)

See measurement basis code.

MBq (MBq)

megabecquerel, that is, 106 becquerels; see becquerel.


See main control room.


See material description code.

measurement basis code (MB Code) (measurement identification code) (code de type de mesure [code de base de mesure])

The data element for the method used to measure or determine the weight or mass data of a nuclear material element and isotope. The MB Code indicates whether weight data was determined in the current material balance area (MBA) or another MBA and whether the data was new or previously reported.

measurement uncertainty (incertitude relative à la mesure)

The amount by which a measured value may vary from the actual physical value of a parameter at the time of measurement.

medical linear accelerator (accélérateur linéaire médical)

An accelerator that produces a collimated beam of high-energy photons (X‑rays) that are used to deliver controlled doses of radiation for therapeutic purposes.

medical review officer (MRO) (médecin examinateur[ME])

With respect to fitness for duty, a person who is a licensed physician and board-certified as a medical review officer responsible for receiving and reviewing laboratory results generated by an employer’s drug testing program and evaluating medical explanations for certain drug test results.

medically treated injury (accident nécessitant des soins médicaux)

An injury or illness beyond a first aid injury, where there have been no lost days that are the direct result of an occupational injury or illness incident.

megabecquerel (mégabecquerel)

106 becquerels; see becquerel.

member (commissaire)

A member of the Commission appointed under section 10 of the Act. (Source: Canadian Nuclear Safety Commission By‑laws)

Métis (Métis)

See Aboriginal peoples of Canada or Indigenous peoples.

MeV (MeV)

megaelectron volt

microsievert (µSv) (microsievert [µSv])

One‑millionth of a sievert.

mill (usine de concentration)

A facility at which ore is processed and treated for the recovery of uranium concentrate, including any tailings-handling and water treatment system associated with the facility. (Source: Uranium Mines and Mills Regulations)

millisievert (mSv) (millisievert [mSv])

One‑thousandth of a sievert.

mine (mine)

An excavation site and a removal site. (Source: Uranium Mines and Mills Regulations)

Note: A mine includes both these sites.

mineralized waste rock (stériles minéralisés)

Rock with the potential to release hazardous and/or nuclear substances that could significantly harm human health or the environment. Mineralized waste rock may be further segregated based on radiological content, contaminants of concern (such as nickel or arsenic), and acid-generating potential. Also called special waste rock.

mine waste (résidu minier)

Waste that includes tailings and mineralized waste rock but not overburden or clean rock.

minimum accident of concern (accident préoccupant le moins grave)

With respect to nuclear criticality safety, an accident resulting in a dose to free air of 0.20 gray in the first minute at a distance of 2 metres from the reacting material.

minimum allowable performance standards (MAPS) (normes de performance minimales permises)

The set of operating limits or the range of conditions, established for components or subsystems, which define the minimum acceptable states for those components or subsystems credited in a safety analysis.

minimum measurable concentration (MMC) (concentration minimale mesurable [CCM])

The smallest amount (activity or mass) of a radionuclide (or analyte) in a sample that will be detected with a probability β of non‑detection while accepting a probability α of erroneously deciding that a positive (non‑zero) quantity of analyte is present in an appropriate blank. MMC is measured in becquerels per litre.

minimum shift complement (effectif minimal par quart)

See minimum staff complement.

minimum staff complement (effectif minimal par quart)

The minimum number of qualified workers who must be present at all times to ensure the safe operation of a nuclear facility and its adequate emergency response capability. Note: Also called minimum shift complement. While shift and staff have similar meanings, shift is used in power reactor operating licences.

minimum testing level (MTL) (niveau minimal d’essai [NME])

The smallest amount of radioactive material that a dosimetry service must be able to measure as part of an independent testing program.

Minister (ministre)

The Minister of Natural Resources or such member of the Queen’s Privy Council for Canada as the Governor in Council may designate as the Minister for the purposes of this Act. (Source: Nuclear Safety and Control Act)

misconnect (mauvaise connexion)

For exposure devices, a condition in which a remote control can be attached to an exposure container without attaching the control cable to the sealed source assembly.

missile generation (formation de missiles)

The hazard associated with the sudden high-speed propulsion of debris.

mission time (temps de mission)

The duration within which a system or component is required to operate or be available to operate and fulfill its function following an event.

mitigation (mesures d’atténuation)

Measures aimed at eliminating, reducing or controlling the adverse effects of a licensed activity, substance, equipment or facility. Mitigation may include restitution for any damage caused by such effects, such as through replacement, restoration or compensation.


Measures aimed at limiting the scale of core damage, preventing interaction of the molten material with containment structures, maintaining containment integrity, and minimizing off-site releases, in the event of an accident.

mitigative control (contrôle atténuateur)

A control intended to reduce the consequences of an accident sequence, not to prevent it. When a mitigative control works as intended, the results of the sequence are called the mitigated consequences.


See minimum measurable concentration.


Micro modular reactor; see reactor facility.

modelling parameters (paramètres de modélisation)

With respect to environmental risk assessment, numerical values used to characterize properties of contaminants (such as an octanol-water partitioning coefficient) and environmental media (such as an organic matter fraction of soil) that are used in models to predict the environmental fate and transport of contaminants.

modelling uncertainties (incertitudes relatives à la modélisation)

Uncertainties associated with the models and correlations embedded in a computer code and that represent the physics of the problem, the solution scheme, data libraries and inherent deficiencies of the computer program.

moderation (modération)

The process of decreasing the energy of neutrons through successive collisions with moderator nuclei without appreciable competing capture.

moderator (modérateur)

A material used to slow down or “moderate” neutrons produced by the nuclear fuel. The moderator reduces neutron energy by scattering without appreciable capture. Materials of prime concern are those containing light nuclei with large scattering cross-sections and relatively low absorption cross-sections.

moderator control area (zone de contrôle des modérateurs)

An area defined by a nuclear criticality safety evaluation in which moderators are limited and controlled for nuclear criticality safety.

moderator control engineered barrier (barrière artificielle de contrôle du modérateur)

A physical feature of a system specifically identified and used to limit or control the introduction of moderators for nuclear criticality safety. Some examples of typical moderator control engineered barriers are secondary roofs, false ceilings, secondary walls, vapour barriers, raised floors or structure, normally closed apertures, and seals.

modified Kusnetz method (méthode de Kusnetz modifiée)

A method of determining and expressing atmospheric concentrations of radon progeny in terms of latent alpha energy. This method requires the use of an alpha counter equipped with an electronic scaler to measure the emission of alpha particles.

monitoring (contrôle)

See condition monitoring.

mood-altering substance (substance psychoactive)

Any product that, whether legally or illegally used, results in cognitive or physical limitations that negatively impact performance on the job.


See medical review officer.


material safety data sheet (associated with Workplace Hazardous Materials Information System)


main steam isolation valve


See minimum testing level.


metric tonne of uranium


monitor unit

MUF (différence d’inventaire)

material unaccounted for; see inventory difference

Page details

Date modified: