Mini encyclopedia
A B C D E F G H I L M N O P R S T U V W X Y Z
Alpha emission
Ionizing radiation, a flux of positively charged particles (alpha particles) ejected in radioactive decay and nuclear reactions. The penetrating power of alpha particles is low (can be stopped by a piece of paper). Internal exposure such as inhaling, ingestion (swallowing) or absorbing into the blood stream of a human body is extremely dangerous.
Alpha particle
Consists of two protons and two neutrons bound together into a particle identical to a helium nucleus.
Atom
The smallest component of an element having chemical properties of the element. The atomic structure is similar to that of the solar system. Each atom has a center (the nucleus) which contains protons and neutrons. Electrons orbit around the nucleus. The number of electrons in the atom is equal to the number of protons in the nucleus.If the nucleus of an atom were the size of the button on a baseball pitcher's cap, the electrons would be like dust particles revolving around the outside of the baseball stadium.
Back-end fuel cycle
The elements of the nuclear fuel cycle after use in a nuclear reactor, which includes transportation, storage and processing of spent nuclear fuel, waste management and disposal.
Background radiation
Ionizing radiation constantly present in the environment, emitted from a variety of natural sources.
Becquerel (Bq)
The unit of radioactivity. 1 Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The Becquerel is named after Henri Becquerel.
Beta particles
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay. There are two forms of beta decay, β− and β+, which respectively give rise to the electron and the positron.
Beta radiation
Beta radiation is a form of ionizing radiation– a flow of electrons or positrons emitted at nuclear reactions or radioactive decay. Beta radiation can penetrate living tissues to 1 cm . Both external and internal exposure is dangerous for humans. Beta radiation, as well as alpha radiation, is the most harmful in case of contact radiation, i.e. if it enters the body, hits the mucous membranes and contaminates the skin. An aluminum plate several mm thick would be sufficient protection against beta radiation.
Beyond the design-basis accident
An accident caused not by the design-basis accident initiator or followed by further safety system failures (not a single system failure) beyond design-basis accidents, wrong decisions by personnel which may cause severe damage or core melting. Effects can be mitigated by control of the accident and/or implementation of an action plan to protect the public and personnel.
From NRC: This term is used as a technical way to discuss accident sequences that are possible but were not fully considered in the design process because they were judged to be too unlikely. As the regulatory process strives to be as thorough as possible, "beyond design-basis" accident sequences are analyzed to fully understand the capability of a design.
Biological shield
Physical radiation barrier installed around a nuclear reactor core, or radiation source, that is used to protect personnel, the public and the environment from harmful effects of ionizing radiation or radioactive contamination. NPPs use concrete as the basic material for the construction of such protective barrier protection. For high-power nuclear reactors, the thickness of the biological shield can be several meters.
Burnable absorber
A material added to the core of a nuclear reactor, either in the fuel or as a separate element that is consumed during the operation of the nuclear reactor. These absorbers modify the reactivity of the nuclear reactor cores fuel to compensate for changes in such nuclear activity due to the burning of the nuclear fuel. The overall result, typically, is a lengthening of the refueling cycle or a flattening of the reactivity curve during operations which minimizes necessary changes in the control rods. These absorbers are discharged from the core, together with fuel, in the process of reloading.
Chain reaction
In a fission chain reaction, a fissile nucleus absorbs a neutron, fissions and simultaneously releases several neutrons (in the case of U-235 an average of 2.46 per fission event). These neutrons can be absorbed, in turn, by other fissile nuclei, initiate fissions and release other neutrons. Depending on the average number of reactions, the reaction is called self-attenuating, self-perpetuating or self-amplifying.
Closed fuel cycle
An example of a nuclear fuel cycle in which spent nuclear fuel discharged from a reactor is reprocessed for separation of uranium and plutonium, with the waste material and then the actinides returned back into the nuclear fuel cycle for repeated use.
Commercial operation
Operation of a nuclear plant under normal conditions to produce energy which is in compliance with the design and safety requirements that have been authorized at the start-up stage of the facility.
Commissioning
The process when an NPP's equipment and systems start demonstrating normal operations and pass an acceptance test: including preliminary performing testing, start-up and first criticality, and which is finalized by putting an NPP into commercial operation.
Confining layer
Watertight stratum in rock
Containment
Technological systems (components) designed to prevent or ensure only localized release of radioactive substances, and ionizing radiation, into the environment through an accident occuring during beyond the design-basis limits. Containment systems perform given functions under normal conditions of operation and in design-basis accidents and also localize radiation exposure in the event of beyond-design-basis accidents.
Containment vessel
Specialized design and equipment of a nuclear reactor used to prevent inadmissible quantities of radioactive substances from escaping into the environment, even in the case of a severe accident. A containment vessel and biological shield are often designed together and function as a pair to ensure safety to the public and the environment.
Control rods
A rod-shaped arrangement used to control the reactivity of a nuclear reactor. The control rod consists of neutron-absorbing material (cadmium, boron, etc.)
Conversion
Chemical process of U3O8 conversion to uranium hexafluoride (UF6). Conversion, i.e. uranium fluorination, is a necessary stage in the production chain preceding uranium enrichment.
Coolant
Any substance {depending on reactor type, it may be water (light or heavy), gas (carbon dioxide, helium), liquid metal (sodium, lead or cerrobase)} circulating through the core to remove the heat from fuel rods. Heat energy absorbed by the coolant is used to generate steam, supply it to the turbine and produce electric power for heating, hot water and other process-oriented purposes.
Cosmic radiation
Background ionizing radiation, consisting of primary radiation originating from space and secondary radiation resulting from primary cosmicradiation impinging on the Earth's atmosphere.
Critical mass
The smallest fissile material mass which, under fixed conditions (type of fissile material, geometry, moderated/immoderate system, etc.), initiates a self-perpetuating chain reaction.
Curie (Ci)
Name for the former unit of activity. The activity of 1 curie, symbol: Ci, is equal to the decay of 3.7·1010 (37 billion) atoms of a radionuclide per second. The activity unit curie has been replaced by the 'Becquerel'. 1 curie = 3.7·1010 Becquerels.
Decay products
Atom nuclei, stable or radioactive, generated from radioactive decay of unstable nuclei.
Decommissioning
An action plan to shut down a nuclear power plant, or any other nuclear facility, resulting in the disposal of the nuclear fuel and decontamination and dismantling of the structures (and equipment) to ensure the safety of personnel and the environment. The NPP would also be converted into an environmentally safe status allowing its release from regulatory control.
Decontamination
Elimination or reduction of radioactive contamination using chemical or physical procedures from any surface or media.
Depleted uranium
Uranium with a lower percentage of U-235 than the 0.7205% contained in natural uranium (for example, in spent fuel from the reactors using natural uranium).
Depletion
The process of reduction of a certain isotope in the isotope mix (for example, during nuclear fuel burning in the reactor).
Design-basis accident (DBA)
Design-basis accidents are postulated accidents to which a nuclear plant, its systems, structures and components must be designed and built to withstand loads during accident conditions without releasing harmful amounts of radioactive materials into the outside environment. Design basis accidents are used in the design of a nuclear power plant to establish the performance requirements for reactor structures, systems and components, including description of initial events and final states, safety systems limiting the accident effects given a single system failure or single personnel error. Any DBA is controlled by reactor safety systems with insignificant off-site consequences, but may require long shutdown for correction or repair.
Design-basis limits
Parameter and characteristic values of an NPP and its systems (components) designed for normal operation, emergency situations and accidents.
Dose of radiation
In radiation protection, a value used for assessing the risk of late effects of exposure for a human body, its organs and tissues given their radiosensitivity. There are such doses as exposure, absorbed and equivalent.
Dosimeter
Device to determine an absorbed dose or a dose generated by ionizing radiation.
Electron
Elementary particle with a negative charge.
Emergency cooling system
Designed to reduce intensity of heat release from the core and prevent the most important in-core structures from over-heating, if heat removal is not possible by standard equipment at the nuclear facility. The emergency cooling system should meet the following requirements:
- Be capable of removing residual heat from the core;
- If necessary, partly or in full, make up for the coolant leakage from the first circuit at the initial time of any accident (if the coolant is water);
- For safety enhancement, to have two- or n-fold redundancy;
- To have independent power sources to drive in-core circulation devices.
Emergency core cooling system (ECCS)
Reactor cooling system for safe removal of residual heat in the event of an interruption of the heat transfer between reactor and heat sink due to failure of a standard cooling system. Emergency cooling systems are designed so that even in the case of reactor coolant loss, the reactor is cooled and the decay heat can be removed. Through such design a very high degree of functional safety is achieved.
Enriched uranium
Uranium in which the percentage of the fissionable isotope U-235 is increased beyond the content of approximately 0.7% in naturally occurring uranium. Uranium for reactors is usually enriched to 3.5% U-235; the percentage of U- 235 in weapon grade is greater than 90%.
Enrichment
Process of increasing U-235 ratio to U-238
Environmental security
Adequate and required protection of the environment from hazardous effects of a nuclear plant under normal operation and in the event of an accident.
Experimental reactor
A nuclear reactor designed for research purposes such as obtaining data on physics and reactor technology necessary for engineering and development of similar reactors or their components.
Fast neutron reactor
A reactor with no moderator and hence utilising fast neutrons. It normally burns plutonium while producing fissile isotopes in fertile material such as depleted uranium (or thorium).
First coolant circuit
Coolant circuit together with pressurizer designed for coolant circulation in the core under normal operational conditions.
First power
The stage of putting a nuclear plant into operation when the nuclear plant starts generating power as designed, then increasing power and performing functional check of the NPP at all power levels including that designed for commercial operation.
Fission products
Nuclides generated by fission or subsequent radioactive decay of nuclides directly generated by fission.
Fuel assembly
A cluster of fuel rods (also called a fuel element). Fuel assemblies include a plurality of fuel pins with structural grids maintaining the fuel rods substantial parallelism and preventing contact between them. Depending on the reactor type and core structure, a cluster of fuel rods may be enclosed in a shroud forming a coolant channel of the core or inserted in the reactor with no shroud.
Fuel reloading
Handling operations performed by machinery to reload spent fuel.
Fuel rod
The basic construction element of the heterogeneous reactor core containing nuclear fuel. A self-sustaining reaction taking place in fuel rods results in the fission of heavy nuclei U-235, Pu-239 or U-233 releasing heat, which is transferred to the coolant. Fuel rods consist of a core, cladding and end caps. The type of fuel rods is determined by the reactor type and purpose and coolant parameters. Fuel rods provide reliable heat transfer from fuel to the coolant.
Gamma radiation
Highly-energy, short-wave electromagnetic radiation emitted in radioactive decay and nuclear reactions. Gamma rays spread at the velocity of light, are extremely penetrative and may best be weakened by material of high density (lead) and high atomic number. To weaken gamma radiation in nuclear reactors, a thick-walled concrete shield is used.
Gas
Hydrogen, helium, nitrogen, air, carbon dioxide, methane and some other gases may be considered as coolants and work media. The basic advantages of gas coolants and work media, compared to liquids, are higher thermal and radioactive resistance and chemical (corrosion) inactivity (for certain gases). The disadvantages are low density, heat capacity and conductivity, and as a consequence, low thermal losses; when using gas coolants, it is necessary to maintain high pressure in the circuit but with reasonable capacity to keep the circulation.
Gas centrifuge process
Process to separate isotopes (for example, U-235 from U-238) in which heavy atoms are split from the lighter atoms by centrifugal forces. The gas centrifuge consists of a cylindrical rotor with a casing that completely encloses the centrifuge. The gas centrifuge utilizes continuous processing, allowing cascading, in which multiple identical processes occur in succession. This process is applied by uranium enrichment plant for the separation of uranium isotopes using UF6 gas.
Gas diffusion technology
Isotope separation procedure using the different diffusion speeds of atoms or molecules of different weight through a porous wall for separation. The diffusion separation process is employed on an industrial scale for uranium isotope separation where UF6 is used as a process medium.
Geologic section
Visual image of the earth's interior structure created by correlation (compilation) of the data from all holes in line.
Giga (symbol: G)
is a prefix in the SI system of units denoting 109, or 1,000,000,000.
Graphite
The mineral graphite is one of the allotropes of carbon. Nuclear reactors use graphite of nuclear grade as a neutron moderator.
Graphite, nuclear grade
Graphite from which neutron absorbing substance is mainly extracted.
Gray
The SI unit of absorbed radiation dose, one joule per kilogram of tissue.
Greenhouse effect
Environmental effect resulting from the rising concentration of certain gases (carbon dioxide, methane, chlorofluocarbon etc.) in the atmosphere which in turn absorb thermal radiation from the Earth’s surface, bringing about a heating of the lower atmosphere and ultimately the global warming of the Earth.
GTS
Gas-turbine set.
Half-life
Radionuclide characteristics; a period of time required for the number of nuclei of a radionuclide to decay to half of its initial quantity.
Heat exchanger
Used for heat transfer from the coolant to other reactor units, such as a steam generator, condenser, deaerator, feed-water heaters, secondary heat exchangers etc. to perform the work cycle.
All heat exchanges may be divided into two large groups: surface and contact units.
Surface heat exchanges have a solid boundary which serves as a heat exchanging surface; in contact heat exchanges heat is directly transferred from one coolant to the other.
Heavy water
Deuterium oxide, D2O; water containing two deuterium atoms instead of two light hydrogen atoms. Natural water contains one deuterium atom per 6,500 molecules H2O. D2O is applicable as a moderator in natural-uranium-fuelled reactors.
High-Level Radioactive Waste
- High-level radioactive waste generated in processing spent nuclear fuel and containing fission products, actinide and transuranic waste.
- Spent nuclear fuel, if not reprocessed.
Highly enriched uranium
Uranium in which the percentage of fissionable isotope U-235 is at least 20% (weapon-grade uranium contains U-235 over 90%).
IAEA
International Atomic Energy Agency, Vienna . Established in 1957.
IAEA safeguards
Safeguards of the International Atomic Energy Agency (IAEA) are arrangements to account for and control the use of nuclear materials. This verification is a key element in the international system which ensures that uranium in particular is used only for peaceful purposes.
In-situ leaching
The process of uranium ore treatment, dissolving and extraction in place. Uranium ore is prepared for leaching by a complex of operations followed by the injection of leaching solution through injection wells, uranium dissolving and supply of uranium-enriched solution through production wells to the processing facility. The entire process is provided with automated monitoring to ensure optimal uranium ore processing and extraction of the valuable component.
International Nuclear Event Scale (INES)
The International Nuclear Event Scale (INES) has been introduced to classify nuclear events according to their level of danger. There are eight levels on the INES scale (zero level - plus seven).
Ion
An atom or molecule which has lost or gained one or more electrons. A charged particle forms when atoms, molecules etc. lose or attach electrons. Ions may be charged positively (when loosing electrons) or negatively (when gaining electrons).
Ionizing radiation
Radiation resulting in ionization of atoms and molecules in the media and breaking chemical bonds. Includes gamma, X-rays, positron and electron, proton, neutron and alpha-particle beams.
Irradiation
Process of interaction of ionizing radiation with the medium, including the human body.
Isotopes
are any of the different types of atoms of the same chemical element, each having a different atomic mass (mass number). Isotopes of an element have nuclei with the same number of protons but different numbers of neutrons. Some isotopes are unstable and decay giving life to isotopes of other elements.
ITER (International Thermonuclear Experimental Reactor)
The ITER is intended to demonstrate that it is physically and technically possible to simulate on Earth the energy generation of the sun and to obtain energy by nuclear fusion. The ITERis an experimental fusion Tokamak-based plant. It is an international project under the auspice of the IAEA and supposed to be the prototype model of the world's first DEMO nuclear plant.
Leaching
Chemical process of diluting one or several components from solid substances using chemical solutions.
License
Permit issued to an applicant by a regulatory body for certain activities related to power plant siting, design, construction, commissioning and operation and decommissioning of a nuclear power plant or another nuclear facility.
Light water
Normal water (H20) different from heavy water (D2O) which is used as a coolant and moderator in some nuclear reactors.
Low active waste
Low active waste which due to the low content of radionuclides, does not require special protection when handled. Such waste is usually incinerated or otherwise disposed.
Low enriched uranium
Uranium enriched less than 20 % in U-235 by weight.
MCP
Main circulating pump.
Megawatt
A million times the power unit of a watt (W), symbol: MW. 1 MW = 1,000 kW = 1,000,000 W.MW(e) relates to electric capacity of a generator; MW(t) to thermal capacity of a reactor or a heat source (for example, total heat capacity of the reactor is usually three times as much as its electric capacity).
Micro
Prefix in the SI and other systems of units denoting a factor of 10−6 (one millionth).
Symbol, µ
MOX
Mixed (commonly, U and Pu-based) nuclear oxide fuel.
Natural background
Natural radiation consisting of space and ionizing radiation, naturally distributed natural radionuclides (on the surface of the Earth, in air, water, foodstuffs, human body etc.).
Natural irradiation
Originates from natural radiation sources.
Natural uranium
Naturally occurring uranium with isotope U-235 of approximately 0.7%. Can be used to fuel heavy-water moderated reactors
Natural uranium concentrate (U3O8)
Feedstock to produce uranium hexafluoride (UF6) followed by fuel manufacturing for NPPs.
Network-connected coolant
Heat transmitter, from a nuclear power plant, to intermediate and end users.
Neutron
Uncharged elementary particle present in nucleus of each atom of safe hydrogen. Single mobile neutrons moving at different velocities originate from fission reaction.
Neutron moderator
Material used to "decelerate" fast neutrons (0.5-10 MeV) to low energies (less than 1 eV) - the fission of the U-235 nuclei resultsing in a better yield at low neutron energy. Amongst others, light water, heavy water and graphite are used as moderators.
NHPP
Combined nuclear heat and power plant.
NPP construction
Construction of NPP structures and installations, including a package of construction works, installation of equipment, by-work, transportation and other.
NPP normal operation
Normal NPP operation as specified by the design of operational limits and conditions.
NPP pilot operation
Period of NPP operation from start-up of power testing until its putting into commercial operation.
NPP quality control
Planned and regularly performed work aimed at controlling all operations during the stages of siting, design, construction, commissioning, operation and decommissioning of an NPP or its units, construction and manufacturing of NPP facilities and equipment and compliance of such operations’ results within the specified requirements.
NPP safe operation
In the event of an incident outside normal circumstances the NPP’s safe operation function will limit radiation exposure to personnel, the public and the environment within a certain range. The concept of NPP safe operation includes technical, nuclear, radioactive and environmental safety.
NPP safe operation limits
Design parameters of NPP operation departure outside of which an accident may result.
NPP safety – basic rules and standards
- General safety rules;
- Nuclear safety rules;
- Radiation safety criteria;
- Sanitary regulations of NPP design and operation;
- Requirements to NPP location and output given environmental and safety restrictions.
NPP security
Management and engineering control to protect fissile/radioactive materials and other inventories at a nuclear plant and to prevent unauthorized access to the nuclear plant and its key areas.
Nuclear accident
An accident caused by damage to fuel rods exceeding limits of nuclear plant safe operation and/or irradiation of personnel beyond authorized limits. Induced by any of the following:
- Failure in control of the nuclear chain reaction in a reactor core;
- Criticality arising during reloading, transportation and storage of fuel rods;
- Disturbance in heat dissipation from fuel rods;
- Other reasons causing damage to fuel rods.
Nuclear electric power plant (NEPP)
Facilities and equipment for generating electricity by converting power produced by the nuclear reactor.
Nuclear fuel
Nuclear reactors can be fueled with either natural uranium of 0.7 % in U-235, or uranium enriched in U-235 up to 2%, 3%, 4% or more. The most common type of reactor fuel is UO2, sintered uranium dioxide pellets encased in a zirconium alloy tube (fuel rod).
Nuclear fuel cycle
The nuclear fuel cycle is a series of industrial processes which involves the production of electricity from the uranium in nuclear power reactors. It includes uranium mining and milling (processing), enrichment in U-235, production of nuclear fuel, fuel elements and assemblies, spent fuel reprocessing and radioactive waste disposal.
Nuclear heat plant (NHP)
Nuclear power plant generating power for heating and hot water supply.
Nuclear power industry
Sector of the power industry using nuclear energy to generate heat and electricity. In 2007 the production of nuclear power plants worldwide accounted for 16% of electric power. According to the World Nuclear Association, by the end of summer 2007, 438 nuclear reactors were in operation worldwide, 34 reactors were under construction, 81 were under development, 223 projects were under consideration and 117 projects were listed as potential. The nuclear sector is substantial in France , Belgium , Finland , Sweden , Bulgaria and Switzerland where natural energy resources are scarce These countries’ NPPs generate from a quarter to one half of their total power.
Nuclear power plant (NPP)
Facility for producing electric or heat power for operating one or several nuclear power reactors and a complex of systems, equipment and installation with the required personnel. Normally, the term NPP means any facility – a nuclear power plant, a nuclear heating plant, a nuclear power and a heat plant - unless noted otherwise.
Nuclear Process-Oriented Plant
Nuclear power plant for generating power and electric power for manufacturing and processing.
Nuclear reaction
The process in which two nuclei or nuclear particles collide to produce products different from initial particles. Hydrogen nuclei, single helium nuclei (alpha-particles), protons, neutrons and electrons (beta-particles) may exist autonomously. Such nuclei, or elementary particles, moving in space and approaching nuclei at a distance of approximately one nucleus size across may collide and react with nuclei. At that, particles may be captured with nuclei or collide and change their direction by releasing kinetic energy.
Nuclear safety
A feature of nuclear installations and nuclear power plants, to prevent a nuclear accident with a certain degree of probability.
Nuclear safety of the reactor facility (RF)
Properties of the nuclear reactor ensuring shutdown, by itself, and cooling in any incident.
Nuclear unit
The reactor of a nuclear power plant with auxiliary equipment.
Nuclear waste disposal facility
Facility designed for disposal of solid or solidified radioactive waste.
Nuclide
A nuclide is a type of atom characterized by its proton number, neutron number and its energy condition.
Open nuclear fuel cycle
Nuclear fuel cycle in which spent nuclear fuel is not reprocessed but considered as radioactive waste.
Operation
Activities and operations aimed at safe achievement of an objective for which a nuclear plant has been built, including power operation, start-up, lay-offs, testing, maintenance, repairs, fuel reloading, operational monitoring and other related activities.
Operational staff of an NPP
Personnel operating an NPP.
Operator
A company designated by a governmental higher-level agency to operate themselves, or engage other companies to operate, a nuclear facility at all stages, including siting, engineering, construction, commissioning, operation and decommissioning, and holding a license from governmental supervision/control for such operation.
Passive nuclear safety
Safety feature of a nuclear reactor that does not require operator’s actions or electronic feedback in order to shut down safely in the event of a particular type of emergency (usually overheating resulting from a loss of coolant or loss of coolant flow). Passive safety systems ensure cooling of the core within 24 hours for any design-basis accident with no operator interference (and in case of power supply failure).
Plutonium (Pu)
Nuclear element with atomic charge of 94, with the most commonly referred isotope having a mass of 239 and a half-life of 24.4 thousand years. Pu-239 is generated by U-238 irradiation with neutrons. It is one of the three main fissile nuclides used as fuel in the nuclear power industry. It accumulates in spent irradiated nuclear fuel and afterwards can be extracted by methods of chemical treatment.
Positron
Elementary particle with the mass of an electron, but positively charged. It is the "anti-electron" generated during pair creation and emitted during beta plus decay.
Production of nuclear fuel
Production of fuel assemblies for use in nuclear power plants. Typically, fuel pellets containing a mix of actinides (Uranium or MOX ) are packed into tubes made of zirconium alloy (zircaloy) - fuel rods. Approximately 200 fuel rods are normally compiled into fuel elements, ready for use, at a nuclear plant.
Protective safety systems (elements)
Special facilities designed for prevention or limitation of damage to the nuclear fuel, the cladding of the fuel rods and the equipment and pipes containing radioactive materials.
Proton
Elementary particle with a positive electrical elementary charge and a mass of 1.67262158 · 10- 24 g , which is equal to about 1836 times the electron mass. The number of protons in the atomic nucleus is determined by the chemical element allocated to this atom. Proton forms the nucleus of the light hydrogen isotope (protium).
Public (radioactive) safety
The protection of present and future generations from any harmful effects of ionizing radiation.
Radiation
Radiation describes any process in which energy emitted by one body travels through a medium or through space, ultimately to be absorbed by another body. Non-physicists often associate the word with ionizing radiation (e.g., as occurring in nuclear weapons, nuclear reactors, and radioactive substances), but it can also refer to electromagnetic radiation (i.e., radio waves, infrared light, visible light, ultraviolet light, and X-rays). What all "radiation" processes have in common is that the amount of energy is transferred.
Radioactive decay
A random process in which an unstable atomic nucleus emits particles, gamma-radiation or electromagnetic radiation or a spontaneous fission takes place. This decay results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide.
Radioactive waste
Liquid/solid by-products and radioactive materials generated at all stages of the nuclear fuel cycle which represent sources of ionizing radiation and require special handling. This waste is classified into low-active waste, medium active waste and low active waste.
Radioactive waste disposal
Safe storage of radioactive waste at storage facilities, or in special locations, excluding any removal of waste and their exposure to the environment.
Radioactive waste management
All process steps in nuclear engineering required for the further treatment of the spent fuel from a reactor: interim storage, reprocessing with return of usable fission material, conditioning of spent fuel elements and direct ultimate storag and treatment and ultimate radioactive waste disposal.
Radioactivity
Property of certain substances to convert, without external effect, by emitting ionizing particles and radiation. Radioactivity was discovered for uranium by Becquerel in 1896, while working on phosphorescent materials. These materials glow in the dark after exposure to light, and he thought that the glow produced might be connected with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent minerals on it. All results were negative until he used uranium salts. The result with these compounds was a deep blackening of the plate. These radiations were called Becquerel Rays. If the substances, or to be more precise the radionuclides, occur in nature, one refers to natural radioactivity; if they are a product of nuclear conversions in nuclear reactors or accelerators, one refers to artificial radioactivity. It was found that some substances emit charged alpha and beta particles and neutral gamma particles. Scientists discovered that alpha-particles represent helium nuclei, beta-particles – electrons and positrons; gamma-particles – electromagnetic quanta. Certain substances, for instance, radium, were identified as very intensive sources of radiation.
Radiometer
Instrument designed for measuring radionuclide’s activity in a source or sample (in a certain amount of liquid, gas, aerosol and on contaminated surface); radiant flux density.
Radionuclide
An atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits a gamma ray(s) and/or subatomic particles. These particles constitute ionizing radiation. Radionuclides may occur naturally, but can also be artificially produced. Radionuclides are often referred to by chemists and physicists as radioactive isotopes or radioisotopes.
Radium
Radium occurs naturally together with uranium, which decays to radium via a chain of alpha and beta emissions.Radium (Ra) has 25 different known isotopes, four of which are found in nature, with 226Ra being the most common. It is extremely radioactive. Its most stable isotope, 226Ra, has a half-life of 1602 years and decays into radon gas.
Radon (Rn)
Inert radioactive gas which is produced from the radioactive decay of uranium and thorium. Due to the very long half-lives, the Earth's crust contains, since its formation, among other substances, the radionuclides uranium 238, uranium 235 and thorium 232. Radon 222 (half-life 3.8 days) is generated as a decay product of radium 226, which results from the radioactive decay of uranium 238. Radon is released wherever uranium and thorium are present in the ground and enters the atmosphere or houses.
RBMK
Single-loop water-cooled graphite-moderated reactor.
Reactor
System used to initiate, maintain and control a nuclear fission reaction. The energy released from continuous fission of the atoms of the fuel is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive turbines which produce electricity.
There are several components common to most types of reactors:
Fuel. Usually pellets of uranium oxide (UO2) arranged in tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core.
Moderator. This is a material which slows down the neutrons released from fission so that they cause more fission. It is usually water, but may be heavy water or graphite.
Control rods. These are typically made with neutron-absorbing material, such as cadmium, hafnium or boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt it. Control rods can also be utilized that contain nuclear fuel and are used to add reactivity to a nuclear reactor that is lost during operations.
Coolant. A liquid or gas circulating through the core so as to transfer the heat from it. In light water reactors the water moderator functions also as primary coolant. Except in BWRs, there is a secondary coolant circuit where the steam is made.
Pressure vessel or pressure tubes. Usually a robust steel vessel containing the reactor core and moderator/coolant, but it may also be a series of tubes holding the fuel and conveying the coolant through the moderator.
Steam generator. Part of the cooling system where the heat from the reactor is used to make steam for the turbine.
Containment. The structure around the reactor core which is designed to protect it from outside intrusion and to protect those outside from the effects of radiation in the case of any malfunction inside. It is, typically, a metre-thick concrete and steel structure.
Reactor facility
Complex of equipment and systems, of a nuclear power plant, designed for the conversion of nuclear power to heat power, including the reactor itself and its auxiliary systems required for normal operation, emergency cooling, emergency protection and safety maintenance provided that other systems ensure necessary auxiliary and support functions.
Reactor pressure vessel
A thick-walled gastight vessel intended for enclosing a reactor core, and other facilities, and for safe cooling of the nuclear fuel.
Reactor start-up
The stage of putting a nuclear plant into operation, including the first fuel loading, attaining the first criticality and performance of necessary physical testing at a capacity when heat from the reactor sinks due to natural heat losses (thermal dissipation).
Reactor, boiling water (BWR)
Nuclear reactor with water as a coolant and as a moderator, boiling in the core. The resulting steam is generally used directly to drive a turbine. There is just a single circuit in a BWR.
Reactor, fast
The fast reactor has no moderator and relies on fast neutrons alone to cause fission. A fast reactor uses plutonium or relatively highly-enriched uranium (about 20% U-235) as its basic fuel. At the same time the number of neutrons produced per fission is 25% more than from uranium, and this means that there are enough (after losses) not only to maintain the chain reaction but also to convert U- 238 in a "fertile blanket" around the core into fissile plutonium. No moderator is used in the breeder reactor since fast neutrons are more efficient in transmuting non-fissile U- 238 in this "blanket" to Pu-239.
Reactor, heavy-water
Heavy water moderated reactor. In Canadian natural uranium fueled reactors (CANDU) heavy water serves as a moderator and coolant.
Reactor, pressurized water (PWR)
Reactors that use ordinary water, under high, pressure as a coolant to remove heat generated by the nuclear chain reaction from nuclear fuel, and as the moderator to thermalize the neutron flux so that it interacts with the nuclear fuel to maintain the chain reaction. The primary coolant loop is kept under high pressure to prevent the water from reaching firm boiling but, meanwhile, maintaining it at 300°C . The hot primary coolant is pumped into a heat exchanger called a steam generator where heat is transferred to the lower pressure secondary circuit which evaporates to pressurized steam. The pressurized steam is fed through a steam turbine which drives an electric generator. In Western countries it is called a BWR, in Russia a VVER, and is also classified as a boiling water reactor.
Redundancy
The use of two or more similar systems in parallel, so that the failure of one would not affect plant operation. They are of special importance in systems such as instrumentation, shutdown control and emergency cooling (upon which safety depends).
Reflector
Material layer immediately around the core of a nuclear reactor. The reflector scatters neutrons, which otherwise would escape, back to the core. The reflected neutrons, in turn, can initiate fissions and therefore improve the neutron balance of the reactor.
Reprocessing
Application of chemical processes to separate valuable substances - the still existing uranium and newly generated fissile material plutonium - from the fission products, the radioactive waste, in the spent nuclear fuel after its use in the reactor. The recovered uranium and the plutonium can be reused as fuel in a nuclear power plant following appropriate further chemical treatment.
Research reactor
Nuclear reactor used for basic and applied research.
Roentgen
Former unit of ion dose, symbol: R. The ion dose of 1 roentgen is equal to the generation of an electrostatic charge unit by gamma or x-radiation in 1 cm3 dry air under normal conditions (1.293 mg air). The new unit of the ion dose is coulomb divided by kilogram (C/kg). 1 R = 258 µC/kg; 1 C/kg approx. 3 876 R.
Safe operation conditions
Designed minimum requirements for the quantity, characteristics, performability and maintenance conditions of the safety-relevant systems (elements) which ensure limits of safety operations and/or safety limits.
Safety assurance systems (elements)
Technical systems (components) designed for servicing all safety systems with power and work media and providing conditions for their functioning.
Safety control systems (elements)
Systems (elements) designed to initiate operation of the safety systems and control and monitor their performance.
Safety criteria (limits)
Parameters and/or characteristics of the incident effects provided for by normative technical documents and/or governmental supervision authorities whose compliance ensures NPP safety.
Safety culture
Required qualification and psychological awareness of employees enabling them to realize safety of a nuclear facility as a priority and perform all operations affecting the facility's safety with due attention and control of the safety parameters.
Safety standards
National regulations to ensure safety of personnel, the public and the environment.
Safety systems (features)
Systems (features) are designed for performance safety; they include reactor protection, containment, maintenance and control systems.
Sanitary protection zone
An area around the source of ionizing radiation in which a public dose under the conditions of normal operation of the source of ionizing radiation may exceed maximum permissible exposure.
Secondary nuclear fuel
Includes Pu-239 and U-233 originating from U-238 and Th-232 when absorbing neutrons. The secondary nuclear fuel is a potential source of nuclear energy.
Separative work unit (SWU)
The work to be effected for uranium enrichment is measured in separation work units. The work separation unit shows the quantity of work necessary for attaining the required percentage of enrichment. The number of SWUs is directly related to the quantity of power consumed by the enrichment facility.
Sievert
Unit of the equivalent and effective dose (by multiplying the absorbed dose by a quality factor) taking into account biological effectiveness of various forms of ionizing radiation; 1 Sv is equal to a quantity of ionizing radiation releasing 1 J in 1 kg of tissue.
Solidification of radioactive waste
Treatment of liquid radioactive waste to convert into dry solid substances and radionuclide fixation in a solid phase.
Spent nuclear fuel (SNF)
Spent nuclear fuel (SNF) is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant) to the point where it is no longer useful in sustaining a nuclear reaction. The nuclear fuel discharged from a reactor after irradiation and not recyclable by the reactor. After being discharged, the spent fuel is placed for interim storage in a pond.
Standards of environmental control
Stipulated compulsory rehabilitation of the environment, i.e. required decontamination of the territory and restoration of plough-lands and water treatment in ponds.
Steam generator
Heat exchanger generating non-radioactive steam in the second coolant circuit using heat from the first circuit. A higher temperature coolant is usually called primary and a lower temperature coolant absorbing heat - secondary.
Storage facility
A facility or a dedicated site for the safe storage and disposal of radioactive waste.
TACIS
Technical Assistance for the Commonwealth of Independent States under which a number of projects, aimed at enhancing the safety of NPPs, have been and are being performed.
Tail piece
The back part of a fuel assembly.
Th-232
Naturally occurring thorium is composed of one isotope: 232 Th. The half-life is 1.4·1010 years. Thorium, which is not a fissile material itself, when irradiated in the nuclear reactor, absorbs slow neutrons and generates fissile isotope 233U to continue the chain reaction.
Thermal reactor
A breeding reactor in which the fission chain reaction is maintained by thermal neutrons.
Thermonuclear fusion
The process of interaction (fusion) of two light nuclei at high temperatures to form a heavier nucleus and release energy.
Thermonuclear reactor
A reactor with controlled thermonuclear fusion to generate power.
Thorium (Тh)
A chemical radioactive element (metal) with the atomic number 90 and the atomic weight of the most common and stable isotope Th-232. There are only eight naturally occurring, short-lived Th isotopes. Natural thorium reserves are several times more abundant than uranium reserves.
Transmutation
Conversion of atoms of one chemical element to another by neutron bombardment resulting in neutron capture followed by radioactive decay of a generated isotope and generation of another chemical element.
Transuranium element
Radioactive element generated artificially when capturing neutrons by nucleus of a chemical element the atomic number of which is greater than 92, that of uranium, followed by the decay and emission of charged particles. The best known transuranium elements are neptunium, plutonium, americium and curium.
Turbine
The prime engine, which has a rotor (a shaft with blades attached), transforming energy of the working fluid (steam, gas, water) to mechanical work.
U-233
An artificially produced uranium isotope with the half-life 1.6?105 resulting from Th-232 transmutation after capturing a neutron; a fissile nuclide.
U-235
Naturally occurring uranium isotope with the atomic mass 235 and the half-life 7.1?108; the only naturally occurring fissile material.
U-238
Naturally occurring uranium isotope with the atomic mass 238 and the half-life 4.5?109 years; can be used as breeder to produce Pu-239.
Underground mining
Conventional underground mining of various ores, including uranium ore.
Uranium (U)
Slightly radioactive metal (the atomic number is 92) that occurs throughout the Earth's crust. It is about 500 times more abundant than gold and about as common as tin. The naturally occurring isotopes are fissionable uranium-235, uranium-238, which cannot be fissioned with thermal neutrons, and uranium-234, a decay product of radioactive decay of uranium-238. The first two are of practical importance in nuclear power production.
Uranium concentrate
Product of uranium ore hydrometallurgical treatment containing up to 70-90% of uranium by weight in the form of mixed oxides with a general chemical formula U3O8.
Uranium dioxide (U02)
Chemical uranium-oxygen compound used as basis for nuclear fuel.
Uranium hexafluoride (UF6)
A chemical compound of uranium and fluoride. It is the only highly volatile uranium compound (when heating up to 56Со, uranium hexafluoride converts from solid substance into gas which is used as feedstock for uranium enrichment).
Uranium, reprocessed
Uranium recovered from spent nuclear fuel (SNF) in the process of radiochemical treatment to be recycled in the nuclear fuel cycle (reprocessed fuel).
VVER
The Russian acronym VVER stands for water-cooled, water-moderated energy reactor. This describes the pressurized water reactor design with fuel rods immersed in non-boiling water. The whole reactor is encased in a massive steel pressure shell.
Waste processing
Processing operations to change the aggregative state and/or physical and chemical properties of radioactive waste making them suitable for transportation, storage and/or disposal.
Waste, radioactive, storage
Disposal of radioactive waste in specially designed storage facilities for the safe containment, of the waste, with the monitoring and possible removal of the waste for processing, transportation and/or final disposal at a later stage.
X-radiation
Penetrating short-wave electromagnetic ionizing radiation. X-rays have a wave length in the range of 10-7 to 10- 12 m generated by accelerating (slowing-down) charged particles.
Yellow cake
Ammonium diuranate (NH4)2U2O7, produced at a pre-final stage of natural uranium concentrate (U3O8).
Zircaloy
Zirconium-tin alloy; a structural material, in nuclear engineering, for the tubes containing nuclear fuel (fuel rods).
