Glossary and Abbreviations


Advanced Boiling Water Reactor (General Electric, GE), boiling light water cooled & moderated.


Advanced CANDU Reactor, 700 MWe class (Atomic Energy of Canada, Limited); heavy water moderated, light water cooled, low enriched uranium fuelled


Atomic Energy of Canada, Limited


Advanced Gas-Cooled Reactor, carbon dioxide cooled, graphite moderated


Advanced High Temperature Reactor


Advanced Passive 1000 MWe class pressurized water reactor (Westinghouse)


Advanced Passive 600 MWe class pressurized water reactor (Westinghouse)


The share of the overall load in an electrical grid which remains constant for a given time frame (day, week, month or year)


The becquerel (symbol Bq) is the SI derived unit of radioactivity, defined as the activity of a quantity of radioactive material in which one nucleus decays per second. It is therefore equivalent to s-1. The older unit of radioactivity was the Curie (Ci), defined as 3.7E10 Bq or 37 GBq. In a fixed mass of radioactive material, the number of becquerels changes with time. Sometimes, amounts of radioactive material are given after adjustment for some period of time. For example, one might quote a ten-day adjusted figure, that is, the amount of radioactivity that will still be present after ten days. This de-emphasizes short-lived isotopes. SI uses the becquerel rather than its equivalent, the reciprocal second, for the unit of activity measure to eliminate any possible source of confusion regarding the meaning of the units, because errors in specifying the amount of radioactivity, no matter how far-fetched, could have such serious consequences.
Often used quantities are kBq for ground contamination and PBq for nuclear reactor inventories:
kBq = Kilobecquerel = E3 Bq = 1,000 Bq
PBq = Petabecquerel = E15 Bq = 1,000,000,000,000,000 Bq


A Station Blackout describes the complete loss of electric power to the essential and nonessential switchgear buses in a nuclear power plant


In the field of nuclear energy conversion the burnup is the amount of thermal energy that has been produced per mass unit of a fuel element. Usually it is expressed in gigawatt-days per ton of heavy-metal. In contrast to fossil fuel the fuel in nuclear reactors cannot be converted "in one go" since the fuel undergoes changes during its use in the reactor which require the fuel elements to be exchanged.


Boiling Water Reactor

Bypass, Containment Bypass

A containment bypass involves a direct release of radioactive material to the environment that bypasses the containment atmosphere. Examples include PWR steam generator tube ruptures (SGTR), which allow radionuclides to be released through the secondary system, or interfacing systems loss-of-coolant accidents (ISLOCA), which allow radionuclides to be released through a breach in a system outside the containment that interfaces with the reactor coolant system (RCS).


Canadian Deuterium-Uranium Reactor (heavy water cooled & moderated, natural uranium fuelled) (Atomic Energy of Canada, Limited)


In pathology, a carcinogen is any substance or agent that promotes cancer. Carcinogens are also often, but not necessarily, mutagens or teratogens. Carcinogens may cause cancer by altering cellular metabolism or damaging DNA directly in cells, which interferes with normal biological processes.


Core Damage: Uncovery and heatup of the reactor core to the point where prolonged oxidation and severe fuel damage is anticipated


Core disassembly with early containment failure: A scram failure scenario with failure to maintain the reactor subcritical, which leads to a disassembly of the core; resulting hydrogen combustion leads to an early containment failure


Core Damage Accident: Accident resulting in damage to the reactor core due to loss of coolant; see also CMA


Core Damage Frequency


Containment Failure: The failure of the Containment can result in a release of radionuclides into the environment


Core Melt Accident: An event or sequence of events that result in the melting of part of the fuel in the reactor core


Cogeneration (also combined heat and power or CHP) is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat.


The large concrete and steel shell around a reactor whose purpose is to contain any radioactivity that might escape from the reactor itself.

Primary Containment:  The principal structure of a reactor unit that acts as a pressure retaining barrier, after the fuel cladding and reactor coolant pressure boundary, for controlling the release of radioactive material into the environment. It includes containment structure, its access openings, penetrations and other associated components used to effect isolation of the containment atmosphere.

Secondary Containment: The structure surrounding the primary containment that acts as a further barrier to limit the release of radioactive materials and also protects the primary containment from external effects. It includes secondary containment structure and its access openings, penetrations and those systems or portions thereof, which are connected to the containment structure.

Combined Cycle Gas Turbines

Combined cycle is a term used when a power producing engine or plant employs more than one thermodynamic cycle. Heat engines are only able to use a portion of the energy their fuel generates (usually less than 30%). The remaining heat from combustion is generally wasted. Combining two or more "cycles" such as the Brayton cycle and Rankine cycle results in improved overall efficiency. In a combined cycle power plant (CCPP) or combined cycle gas turbine (CCGT) plant a gas turbine generator generates electricity and the waste heat from the gas turbine is used to make steam to generate additional electricity via a steam turbine; this last step enhances the efficiency of electricity generation. Most new gas power plants are of this type. In a thermal power plant, high-temperature heat as input to the power plant, usually from burning of fuel, is converted to electricity as one of the outputs and low-temperature heat as another output. As a rule, in order to achieve high efficiency, the temperature of the input heat should be as high as possible and the temperature of the output heat as low as possible (see Carnot efficiency). This is achieved by combining the Rankine (steam) and Brayton (gas) thermodynamic cycles. Such an arrangement used for marine propulsion is called COmbined Gas (turbine) And Steam (turbine) (COGAS).


Core Power Excursion: The nuclear power excursion refers to a multiple increase of reactor power within fractions of a second


The state of a nuclear chain-reacting medium when the chain reaction is just self-sustaining (critical)

Criticality Accident

Accident at a reprocessing plant, where a chain reaction becomes self-sustaining due to the reaching of the critical mass


The decommissioning of nuclear facilities is sometimes referred to as nuclear decommissioning, to mark the difference between “conventional” decommissioning and dismantling projects. In fact, the main difference to the dismantling of a “conventional“ facility is the possible presence of radioactive or fissile material in a nuclear facility, which requires special precautions. Decommissioning involves many administrative and technical actions, whose purpose, after a facility has been taken out of service, is to allow its release from regulatory control and relieve the licensee of his responsibility for its nuclear safety.


Emergency Operating Procedures


European Pressurized Reactor (Areva NP), pressurized light water cooled & moderated


ECMWF 40-year re-analysis of the global atmosphere and surface conditions for the period September, 1957 - August, 2002, by ECMWF. Here you find the description of the ERA-40 data set.


ECMWF re-analysis of the global atmosphere and surface conditions which will cover the period from 1989 to 2013. It has higher horizontal and vertical resolution, better data assimilation and a more recent model system than the ERA-40. Here you can find the description of the ERA-interim data set.


Economic Simplified Boiling Water Reactor; General Electric designation for an advanced boiling light water cooled & moderated reactor


The Espoo-Convention regulates licensing procedures for technical plants which can lead to cross-boarder environmental impacts.


European Atomic Energy Community

Fast Breeder Reactor

The fast breeder or fast breeder reactor (FBR) is a fast neutron reactor designed to breed fuel by producing more fissile material than it consumes. The FBR is one possible type of breeder reactor.


Fast Neutron Reactor

Fuel Cell

A fuel cell is an electrochemical energy conversion device. Fuel cells differ from batteries insofar as they are designed for continuous replenishment of the reactants consumed; they produce electricity from an external supply of fuel and oxygen as opposed to the limited internal energy storage capacity of a battery. Additionally, while the electrodes within a battery react and change as a battery is charged or discharged, a fuel cell's electrodes are catalytic and relatively stable. Typical reactants used in a fuel cell are hydrogen on the anode side and oxygen on the cathode side (a hydrogen cell). Usually, reactants flow in and reaction products flow out. Virtually continuous long-term operation is feasible as long as these flows are maintained.


Gas-cooled Reactor


Gas-cooled Fast Reactor


Generic Severe Accident: extrapolated from the literature and used as an accident scenario in the flexRISK project


Gas Turbine Modular Helium Reactor, a gas cooled, graphite moderated reactor (General Atomics)


Giga-Watt: 1 GW = 1,000 Megawatt


Giga-Watt electrical power


Modular High temperature gas cooled Reactor – optimized for Hydrogen production


High-Temperature Engineering Test Reactor


International Atomic Energy Agency


International Energy Agency


International Nuclear Event Scale


International Nuclear Safety Advisory Group of the IAEA


An Interfacing Systems Loss-Of-Coolant Accident (ISLOCA) is a breach in a system that interfaces with the reactor coolant system (RCS) and could cause a loss of coolant accident, if the breach is not isolated from the RCS. Such a breach could be caused if valves fail to isolate the RCS from an interfacing system not designed for the high RCS pressures. When portions of an interfacing system are located outside the containment, particular concern arises because an unisolated system breach outside containment can result in a release of radionuclides that bypasses the containment.


Inherently Safe Reactor concept


Large early release: A large early release is a radioactivity release from the containment which is both large and early. Large is defined as involving the rapid, unscrubbed release of airborne fission products to the environment. Early is defined as occurring before the effective implementation of the off-site emergency response and protective actions.


Low-enriched Uranium


Leukemia (or leukaemia) is a cancer of the blood or bone marrow characterized by an abnormal proliferation of blood cells, usually white blood cells (leukocytes). It is part of the broad group of diseases called hematological neoplasms.


Lead-cooled Fast Reactor

Light Water Reactor

A light water reactor or LWR is a thermal nuclear reactor that uses ordinary water, also called light water, as its neutron moderator. This differentiates it from a heavy water reactor, which uses heavy water as a neutron moderator. In practice all LWRs are also water cooled


The power consumed at a given point


Loss-of-Coolant-Accident: Loss of Coolant Accidents are accidents, in which cooling water would be lost from the primary cooling system as a result of a pipe rupture or blockage. A LOCA could lead to the overheating of the core and a meltdown.


Large Release Frequency


IAEA PRIS abbreviation for RBMK Reactor


Gas-cooled reactor


Mixed oxide, or MOX fuel, is a blend of plutonium and natural uranium, reprocessed uranium, or depleted uranium which behaves similarly (though not identically) to the low enriched uranium feed for which most nuclear reactors were designed. MOX fuel is an alternative to low enriched uranium (LEU) fuel used in the light water reactors that predominate nuclear power generation. An attraction of MOX fuel is that it is a way of disposing of surplus weapons-grade plutonium, which otherwise would have to be handled as a difficult-to-store nuclear waste product, and a nuclear proliferation risk


Molten Salt-cooled Reactor


Megawatt: 1 MW = 1,000,000 Watt


Megawatt electrical power


Megawatt thermal


Nuclear Energy Agency


Facility for enrichment of fuel


Nuclear Power Plant

Nuclear Reprocessing

Nuclear reprocessing separates any usable elements (e.g., uranium and plutonium) from fission products and other materials in spent nuclear reactor fuels. Usually the goal is to recycle the reprocessed uranium or place these elements in new mixed oxide fuel (MOX), but some reprocessing is done to obtain plutonium for weapons. It is the process that partially closes the loop in the nuclear fuel cycle


Accident in a reprocessing facility caused by the explosion of red oil. A red-oil explosion is an explosion that can result from the presence of organic materials with nitric acid (NOx) and high temperature; the rapid exothermic nitration of the organic material can lead to a "red-oil explosion."


Russian Safety Regulations for NPPs 1988 (Soviet Union)


Pebble Bed Modular Reactor, a gas cooled, graphite moderated reactor using low enriched pebble bed fuel (PBMR Pty., Ltd., South Africa)


Pressurized Heavy Water Reactor


Nuclear proliferation is the spread of nuclear weapons production technology and knowledge to nations that do not already have such capabilities.


Reactor Coolant System: The system used to remove energy from the reactor core and transfer that energy either directly or indirectly to the steam turbine


Probabilistic Safety Assessment

PUREX Process

PUREX is a nuclear reprocessing method which is the de facto standard aqueous method based on liquid-liquid extraction for the recovery of uranium and plutonium from used nuclear fuel. This process can be used to recover weapon-grade materials as well as reprocessed uranium from spent nuclear reactor fuel, and as such, its component chemicals are monitored. PUREX is an acronym standing for Plutonium and Uranium Recovery by Extraction. The PUREX process is a liquid-liquid extraction method used to reprocess spent nuclear fuel, in order to extract uranium and plutonium, independent of each other, from the fission products.


Pressurized Water Reactor


Measure of how nocuous a radio nuclide is to health. The type and energy of rays, absorption in the organism, residence time in the body, etc. influence the degree of radiotoxicity of a radio nuclide


High Power Channel-type Reactor (Reactor Bolshoi Moschnosti Kanalynyi)


In case of a nuclear accident in Europe, the Real-time On-line Decision Support system for off-site emergency management in Europe (RODOS) provides consistent and comprehensive information on the present and future radiological situation, the extent and the benefits and drawbacks of emergency actions and countermeasures, and methodological support for taking decisions on emergency response strategies. Main users of the system are those responsible at local, regional, national and supra-national levels for off-site emergency management. The application of the system for training and exercises was a further important consideration in its development.


Reprocessing Plant


Reactor pressure vessel failure with early containment failure: A severe accident was considered through its progression in the core until failure of the reactor pressure vessel, followed by ex-vessel accident progression causing an early containment failure (i.e. direct containment heating, hydrogen combustion in containment or steam explosion)


Research Reactor


Reaktor Sicherheitskommission; Reactor Safety Commission


Severe accident with early containment failure: A severe accident was considered through its progression in and outside the vessel, resulting in an early containment failure (i.e. direct containment heating, hydrogen combustion in containment or steam explosion)


Super Critical Water-cooled Reactor, a type of pressurized water reactor


Sodium-cooled Fast Reactor


Steam Generator Tube Rupture: Damage at the steam generator resulting in a primary to secondary side leakage

Spent fuel storage

Interim or planned final storage facility for spent fuel from NPPs

Source Receptor Sensitivity SRS

The Source Receptor Sensitivity describes the sensitivity of a “receptor” element y to a “source” x. Lagrangian Particle Dispersion Model: model that computes the trajectories of a large amount of particles representing infinitessimally small air particles to describe the transport and diffusion of traces in the atmosphere.


Secure Transportable Autonomous Reactor for Hydrogen Production

Steam Generator

A boiler in which hot coolant from a reactor raises steam to turn a turbine generator

Steam Reformer Production

Steam reforming, hydrogen reforming or catalytic oxidation, is a method of producing hydrogen from hydrocarbons. On an industrial scale, it is the dominant method for producing hydrogen. Small-scale steam reforming units are currently subject to scientific research, as way to provide hydrogen to fuel cells.


Siedewasserreaktor (German: boiling water reactor), 1000 MWe class (Areva NP)


Treaty establishing a European Atomic Energy Community, or EURATOM. It was established on March 25, 1957, signed the same day as the more famous Treaty of Rome, instituting the European Economic Community (EEC). The European Atomic Energy Community is a separate entity, but membership and organization is fully integrated with the European Union.


Transmutation is the conversion of one object into another. Transmutation of chemical elements occurs through nuclear reactions. This is called nuclear transmutation. Natural transmutation is when radioactive elements spontaneously decay over a long period of time and transform into other more stable elements. Artificial transmutation occurs in machinery that has enough energy to cause changes in nuclear structure of the elements. The machines that can cause artificial transmutation include the particle accelerator and tokamak reactor.


Natural Uranium fuelled, Gas cooled, Graphite moderated reactor

Uranium Hexafluoride

Uranium hexafluoride, or UF6, is a compound used in the uranium enrichment process that produces fuel for nuclear reactors and nuclear weapons. It forms solid grey crystals at standard temperature and pressure (STP), is highly toxic, reacts violently with water and is corrosive to most metals. It reacts mildly with aluminum, forming a thin surface layer of AlF3 that resists further reaction.


Very High Temperature Reactor, a type of gas cooled, graphite moderated reactor


pressurized light water cooled & moderated reactor (Russian acronym for type of pressurized water reactor, PWR), (Voda-Vodyanoi Energetichesky Reaktor)


Western European Nuclear Regulators Association


World Health Organization


World Nuclear Association

World Energy Council

World Energy council (WEC) has Member Committees in over 90 countries, including most of the largest energy-producing and energy consuming countries. Established in 1923; the organisation covers all types of energy, including coal, oil, natural gas, nuclear, hydro, and renewables, and is UN-accredited, non-governmental, non-commercial and non-aligned. WEC is a UK-registered charity headquartered in London.


Yellowcakes (also known as urania) are uranium concentrates obtained from leach solutions. They represent an intermediate step in the processing of uranium ores. Yellowcake concentrates are prepared by various extraction and refining methods, depending on the types of ores. Typically yellowcakes are obtained through the milling and chemical processing of uranium ore forming a coarse powder which is insoluble in water and contains about 80% uranium oxide, and which melts at approximately 2878°C.