ALARA
Principle in radiological protection philosophy, at which dose and risk of exposure is maintained as low as reasonably achievable (ALARA) taking into account economic and social factors.
Activated substances
Substances which become radioactive ones as a result of long-term exposure by neutron flow, e.g. in nuclear reactor or accelerator.
Core
Central part of nuclear reactor containing fuel elements and any moderators.
Alpha particle
Positively charged particle evolving from atomic nucleus during radioactive decay. Alpha particles are helium nuclei and contain 2 protons and 2 neutrons.
Atom
Speck of matter, which impossible to break by chemical agents. Atoms have nucleus consisting of positively charged protons and uncharged neutrons of same mass. Positive charges of protons are balanced by some amount of negatively charged electrons moving round nucleus.
Becquerel
Unit of measurement in SI system of actual radioactivity in the material. One Bq means one decay per second and, consequently, activity of a number of radioactive materials equaling in average to one decay per second.
(Such units as GBq and TBq are frequently used in practice).
Beta particle
Particle evolving from atom during radioactive decay. Beta particles could be both electrons (negatively charged) and positrons.
Biological protection
1. Mass of absorber material (e.g. thick concrete walls) located around reactor or radioactive material to reduce exposure (especially by neutrons and gamma-rays accordingly) to a level safe for public.
2. A lot of absorber material (e.g. thick concrete walls) located around reactor or radioactive material to reduce exposure (especially by neutrons and gamma-rays accordingly) to a level safe for public.
Borosilicate glass
A specific form of fixed tough glass (like Pyrex), which is used to reduce mobility of radioactive waste prior to its storage, and to produce kitchenware and scientific glassware. Chemical composition of borosilicate glass ensures high resistibility to damages, heating and chemical action.
Decommissioning
Decommissioning of facility (e.g. reactor), and subsequent actions to ensure its safe storage, dismantling and unrestricted use of site.
Gamma-radiation
High energy electromagnetic emission from atomic nucleus, practically identical to x-rays.
Gray
Measurement unit of absorbed ionizing radiation in SI system, where 1 Gray (Gy) represents absorption of one Joule per kg of tissue.
Fission
Fission of heavy nucleus for two ones accompanied with deposition of relatively high energy and usually one or two neutrons. This process could be spontaneous, but usually is carried out due to neutron absorption by nucleus, as a result of which nucleus becomes unstable.
Dose
Energy absorbed by tissue from ionizing radiation. One Gray equals to one Joule per kg, but dose varies depending on impact of different kinds of radiation, and thus Sievert is dose equivalent unit used at establishing exposure standards.
Moderator
Material, e.g. light or heavy water or graphite, used in the reactor to moderate fast neutrons by means of collision with lighter nuclei to promote further fission.
Sievert
Unit designating biological hazard caused by radiation. One joule of beta- or gamma-radiation absorbed in kg of tissue defines 1 Sievert of biological impact; J/kg of alpha-radiation corresponds to 20 Sv impact; 1 J/kg of neutrons corresponds to 10 Sievert impact.
Isotope
Atomic form of element having specific number of neutrons. Different isotopes of element have the same number of protons, but different number of neutrons, thus different mass, e.g. U-235, U-238. Some isotopes are unstable and decay generating then isotopes of other elements.
Ion
Atom electrically charged because of neutron loss or acquisition.
Ionizing radiation
Radiation (including alpha particles), having an ability to break chemical binding, thus causing matter ionization through which it passes, and damaging living tissue.
Waste classification
Special categories established for radioactive waste to ensure that generated waste are treated and managed by the most appropriate manner ensuring public and environmental protection. General considerations being taken into account when classifying radioactive waste: how long waste will remain at hazardous level of radioactivity; what concentration of radioactive material is in waste, and do they generate heat.
The main categories of radioactive waste are: very low level waste (VLLW), low level waste (LLW), intermediate level waste (ILW) and high level waste (HLW).
Cobalt-60
Radioactive isotope used like a source, e.g. during checking welded joints and cancer treatment.
Collective dose
Sum of individual doses obtained for specified period of time by certain number of people from certain radiation source exposure.
Conditioning
Process used to reduce potential hazard from radioactive waste by their transformation into stable solid form fixing waste and providing moderation to ensure that waste could be safely processed during transportation, storage and final disposal.
Container or vessel
Container used for safe transportation of spent fuel and nuclear waste of high level. Container is designed to protect population from accidental dispersion of radioactive materials and exposure in accordance with international regulations.
Cosmic radiation
Energy particles, including protons, attacking the Earth from open space.
Criticality
Condition, in which nuclear chain reaction could be sustained.
ICRP
International Commission for Radiological Protection (ICRP) is independent group of scientific experts providing consultancies and recommendations on assuring protection of public and personnel of nuclear industry from ionizing radiation. Usually, these recommendations have a basis for international, regional and national regulations on radiological protection.
Neutron
Uncharged atomic particle being in nucleus of each atom, except for hydrogen. Single fluent neutrons moving at different speeds are generated due to fission reactions. Slow (thermal) neutrons could in their turn become easily a reason of nuclei fission of “fissile” isotopes, e.g. U-235, Pu-239, U-233; and fast neutrons could cause nuclei fission of “fertile” isotope, e.g. U-238. Sometimes atomic nuclei just absorb the neutrons.
Depleted uranium
Uranium containing less than 0.7% of natural Uranium-235. As by-product of enrichment in fuel cycle, it usually contains 0.25-0.30% of Uranium-235, the rest is Uranium-238. It could be mixed with high enriched uranium (e.g. from nuclear weapon) to produce nuclear fuel.
Ore beneficiation
Process, with help of which minerals are retrieved from ore usually on exploitation site. Normal beneficiation process includes ore breakage and grinding and different chemical processes on uranium separation from waste called tailings. Beneficiation by leaching in-situ includes chemical processes on uranium separation from solution.
Enriched uranium
Uranium, in which ratio of Uranium-235 (to U-238) is increased higher than natural one (0.7%). Reactor uranium is usually enriched, approximately, up to 3.5% U-235, and U-235 content in weapon-grade uranium constitutes more than 90%.
Fuel-element cladding
Metal tubes in the core, containing oxide fuel tablets.
Optimization
Principle of radiological protection philosophy, according to which doses and risks of exposure should be maintained as low as reasonably achievable (ALARA), considering economic and social factors.
Vitrified waste
High level waste enclosed in borosilicate glass to fix radionuclides in insoluble, stable matrix appropriate for disposal.
Vitrification
Enclosure of high level waste in borosilicate glass, about 14% by mass. Vitrification is used to fix radionuclides at rest in insoluble, stable matrix appropriate for disposal.
Spent (irradiated) fuel
Fuel assemblies retrieved from reactor after several years of operation, as they are no longer considered effective to produce heat.
High level waste (HLW)
Highly radioactive fission products and transuranium elements (usually different from plutonium), being generated during reactor operation and contained in spent fuel. They could be separated by processing spent fuel and vitrified for long-term storage, or spent fuel containing them could be considered as high level radioactive waste.
Low level waste (LLW)
Low level waste (LLW) is medium radioactive material usually removed by means of incineration and disposal. They are generated from hospitals and industry, as well as nuclear-fuel cycle, and consist of paper, rags, instruments, cloth and filters containing small amount of shortest lived radioactivity.
Intermediate level waste (ILW)
Intermediate level waste (ILW) contain concentrations of radioisotopes higher than low level waste (LLW), and they will may need shielding. Basically, they are generated from nuclear industry and contain resins, chemical sediments and metal fuel cladding, as well as some activated structured materials of the core remained after reactor decommissioned. ILW could be short- and long-lived. Mainly, short-lived waste are disposed in the near-surface storage facilities, whereas long-lived waste (from spent fuel processing) are currently planned to dispose deep under the ground. Medical, industrial and scientific sectors also produce small amount of long-lived ILW as a result of using radioactive sources, such as Americium-241 and Radium-226.
Half-life period
Period of time required to ensure that half of atoms of certain radioactive isotope is decayed and became the isotope of other element.
Plutonium
Transuranium element being generated in nuclear reactor at neutron capture. It has several isotopes, some of which are capable for fission, but some are subject to spontaneous fission emitting the neutrons. Weapon-grade plutonium is produced in special reactors to obtain >90% of Pu-239, and reactor plutonium contains about 30% of non-fissile isotopes. Approximately, one third of light-water reactor energy comes from Pu-239 fission, and this is main useful isotope, which could be renewed at spent fuel processing.
Natural uranium
Uranium discovered in the nature containing 99.3% of U-238, 0.7% of U-235 and small amount of U-234. Natural uranium could be used as fuel in heavy-water reactors as moderator.
Decay product
Atomic nucleus, stable or radioactive, being received during radioactive decay of unstable nucleus. Sometimes it is called daughter nucleus.
Fission products
Daughter nuclei made either due to fission of heavy elements, like uranium, or as a result of decay of primary daughter nuclei. They are usually highly radioactive.
Fuel production
Production of reactor fuel, usually in the form of ceramic tablets enclosed into metal tubes, which subsequently are gathered in fuel assemblies.
Proton
Positively charged particle presented in each atom nucleus.
Radiation
Release and spreading of energy by means of electromagnetic waves or particles (equal to ionizing radiation).
Radium
Radioactive decay product of uranium, frequently detected in uranium ore. It has several radioactive isotopes. Radium-226 generates Radon-222 at decay.
Radioactivity
Spontaneous decay of unstable atomic nucleus, at which radiation is emitting.
Radioactive waste
Radioactive materials generated by a number of industrial sectors using radioisotopes, e.g. by nuclear industry, medical sector and other industrial sectors, which are not allowed to use so far and which require appropriate storage and disposal.
Radioactive decay
Self-existing transformation of nucleus, at which particles or gamma-radiation is emitting, or x-radiation is releasing after atomic electron capture, or self-existing nucleus fission is occurring.
Decay
Decay of atomic nuclei resulting in release of alpha- or beta-particles (usually accompanied with gamma-radiation). Moreover, material radioactivity is decreasing exponentially while nuclei are decaying and more stable nuclei are forming.
Coolant
Liquid or gas used to transfer heat from the reactor core to steam-generators or directly to turbines.
Fuel assembly
Structured set of fuel rods or elements, fuel element in reactor.
Transmutation
Atom transformation of one element into atoms of another one by means of neutron attacking causing neutron capture.
Transuranium element
Very heavy element generated artificially at neutron capture and probably with subsequent beta-decay. It has higher atomic number than uranium (92). All transuranium elements are radioactive. The most known transuranium elements are neptunium, plutonium, americium and curium.
Control rods
Devices absorbing neutrons so that chain reaction in reactor could be moderated or stopped by moving down the rods or could be accelerated by moving them up.
Uranium (U)
The heaviest natural element (atomic number is 92). It is metal of medium radioactivity, having two fissile isotopes (U-235 and U-233) and two isotopes (U-238 and U-234), which could be used as atomic raw materials. Uranium is basic fuel in nuclear power industry.
Background radiation
Natural ionizing radiation, by which each person is exposed. It origins in Earth crust (including radon) and comes from space.
Storage facility
Permanent site for radioactive waste disposal.
Electron
Negatively charged atomic particle.
Nuclear fuel
Fissile material passed required production processes and formed so that it could be loaded into reactor.
Nuclear waste
Radioactive materials generated at different stages of nuclear-fuel cycle, including exploitation, enrichment, production of fuel, reactor operation, fuel processing and reactor decommissioning, which could not be subsequently used as deemed.
Nuclear reactor
Device, in which chain reaction of nuclear fission is taking place under controlled conditions so that heat generation or neutron beams could be used. All commercial reactors are thermal ones and operate on thermal neutrons using moderator for neutron deceleration.