AECL
Atomic Energy of Canada Limited is a Crown corporation set up by the Government of Canada in 1952 to develop peaceful uses of nuclear energy. AECL develops, markets, sells and builds CANDU power reactors and provides engineering, consulting, custom-manufacturing and field services to nuclear utilities.
ALARA
Acronym for As Low as Reasonably Achievable: one of the three basic criteria recommended by the International Commission on Radiological Protection to minimize radiation risks.
Alpha Radiation
A positively charged particle made up of two neutrons and two protons. It is the least penetrating of the three common forms of radiation, and can be stopped by a sheet of paper.
Atom
The basic building block of all matter. An atom has a nucleus made up of positively charged protons and neutral neutrons surrounded by orbiting electrons whose negative charge balances that of the protons in the nucleus.
Atomic Number
The number assigned to each element on the basis of the number of protons found in the element's nucleus.
Atomic Weight (Atomic Mass)
Approximately the sum of the number of protons and neutrons found in the nucleus of an atom.
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Background Radiation
The naturally-occurring nuclear radiation coming from outer space as cosmic radiation, or from naturally occurring radioactive elements such as uranium and radium in the materials of the earth.
Becquerel (Bq)
The unit of radioactive decay equal to 1 disintegration per second. 37 billion becquerels is equal to 1 curie (Ci). There are 30,000 disintegrations per second taking place inside a household smoke detector.
Beta Radiation
An electron (or a particle of equal weight to an electron but with a positive electrical charge) that is emitted from a radionuclide. It is less damaging than the same dose of alpha radiation but more penetrating. Beta radiation can be stopped by a thin sheet of metal or plastic.
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Calandria
A calandria in a CANDU reactor contains the core of the nuclear steam supply system. It is a large cylindrical vessel, filled with several hundred tonnes of heavy water. Hundreds of fuel channels run through the calandria, parallel to the cylindrical axis, each holding 12 or 13 fuel bundles, depending on the design.
CANDU Reactor*
The Canadian nuclear power reactor design is called CANDU, an acronym for Canada Deuterium Uranium. CANDU is a unique design that uses natural uranium fuel and a heavy water moderator. One of the unique features of CANDU is its ability to refuel while operating at full power.
Chain Reaction
A reaction that initiates its own repetition. In a fission reaction, free neutrons are produced which fly off and strike other nuclei, causing them to split and send off yet more free neutrons. The fission will continue as long as there are enough free neutrons carrying the right amount of energy.
Chernobyl
A town in northern Ukraine where a nuclear power station was built using one of two Russian power reactor designs. In April 1986, a severe nuclear accident occurred in one of the four units, killing 35 people.
CNSC
The Canadian nuclear industry is monitored and regulated by the Canadian Nuclear Safety Commission, an independent agency of the Government of Canada. The CNSC's name has recently been changed from the Atomic Energy Control Board.
Containment
Most reactors are enclosed in a thick, concrete, domed building, called the containment. In the event of a release of radioactive material into the reactor building, the containment traps the emissions and prevents their escape. In a Canadian CANDU reactor, the core is partly housed in a concrete or steel tank called the shield tank. This entire structure is enclosed in a second containment about one metre thick.
Contamination
Radioactive material deposited or dispersed into materials or places where it does not belong.
Control Rods
A rod containing neutron-absorbing materials, such as boron or cadmium. Control rods are moved in and out of the core of the reactor to control the rate of the nuclear reaction.
Coolant
The liquid or gas used to transfer the heat of nuclear fission to a heat exchanger in which steam is produced to drive the electrical generator. The cooled liquid or gas is then returned to the reactor. CANDU reactors use heavy water as the coolant.
Core
The central region of a nuclear reactor, containing the fuel assemblies, coolant and moderator, in which the fission chain reaction takes place.
Critical Mass
The minimum amount of fuel needed in the core of a nuclear reactor in order to start a self-sustaining chain reaction. When a reactor starts up, it is said to "go critical".
Curie (Ci)
A unit used to measure the rate of radioactive decay. One curie equals 37 billion disintegrations per second, or approximately the radioactivity of one gram of radium.
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Decay (Radioactive)
The change of one radioactive nuclide into a different nuclide by the spontaneous emission of alpha, beta, or gamma radiation, or by electron capture. The end product is a less energetic, more stable nucleus. Each decay process has a definite half-life.
Decontamination
The removal of radioactive contaminants by cleaning and washing with water and/or chemicals.
Deuterium
A stable, naturally-occurring hydrogen isotope. It is used as a moderator in the form of deuterium oxide or heavy water.
Dose
A general term denoting the quantity of radiation or energy absorbed in a specific mass.
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Electromagnetic Radiation
Electric or magnetic waves that travel at the speed of light. Examples: light, heat, radio waves, microwaves, gamma radiation, x-rays.
Electron
An elementary particle carrying one unit of negative electrical charge. Electrons surround the atom's positively charged nucleus and determine the atom's chemical properties.
Enrichment
The physical process of increasing the concentration of the uranium-235 isotope relative to the predominant uranium-238 isotope in natural uranium.
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Fission
The break-up of the nucleus of an atom into two major fragments, plus smaller fragments and free neutrons, when the nucleus is struck by a fast-moving free neutron.
Fuel Bundle
The package of natural uranium fuel elements for insertion into a CANDU reactor. The uranium is contained in zirconium alloy tubes or elements and the elements are held together by welding them to zirconium alloy plates. Each bundle is a half a metre long and weighs about 20 kg.