Low level waste		A common type of light water reactor (LWR), where water is allowed to boil in the core thus generating steam directly in the reactor vessel. (cf PWR)
Decommissioning		The most common type of light water reactor (LWR), it uses water at very high pressure in a primary circuit and steam is formed in a secondary circuit.
Disintegration		Ammonium diuranate, the penultimate uranium compound in U3O8 production, but the form in which mine product was sold until about 1970. See also Uranium oxide concentrate.
Criticality		A radioactive isotope of an element.
Fast breeder reactor		Chemical treatment of used reactor fuel to separate uranium and plutonium and possibly transuranic elements from the small quantity of fission product wastes, leaving a much reduced quantity of high-level waste (which today includes the transuarnic elements).
Spent fuel		Structured collection of fuel rods or elements, the unit of fuel in a reactor.
Thermal reactor		A fast neutron reactor (qv) configured to produce more fissile material than it consumes, using fertile material such as depleted uranium in a blanket around the core.
Half-life		Devices to absorb neutrons so that the chain reaction in a reactor core may be slowed or stopped by inserting them further, or accelerated by withdrawing them.
Light water reactor		A chemical substance that cannot be divided into simple substances by chemical means; atomic species with same number of protons.
Yellowcake		Removal of a facility (eg reactor) from service, also the subsequent actions of safe storage, dismantling and making the site available for unrestricted use.
Heavy water reactor		The splitting of a heavy nucleus into two, accompanied by the release of a relatively large amount of energy and usually one or more neutrons. It may be spontaneous but usually is due to a nucleus absorbing a neutron and thus becoming unstable.
Element		Used fuel assemblies removed from a reactor after several years use and treated as waste.
Alpha particle		The SI unit of absorbed radiation dose, one joule per kilogram of tissue.
Burnup		A reactor in which the fission chain reaction is sustained primarily by slow neutrons, and hence requiring a moderator.
Fuel assembly		The incorporation of high-level wastes into borosilicate glass, to make up about 14% of it by mass. It is designed to immobilise radionuclides in an insoluble matrix ready for disposal.
Coolant		A material such as light or heavy water or graphite used in a reactor to slow down fast neutrons by collision with lighter nuclei so as to expedite further fission.
Radionuclide		A reactor which uses heavy water as its moderator, eg Canadian CANDU (pressurised HWR or PHWR).
Tailings		natural change in the nucleus of a radioactive isotope as particles are emitted (usually with gamma rays), making it a different element.
Fission		The period required for half of the atoms of a particular radioactive isotope to decay and become an isotope of another element.
Moderator		The liquid or gas used to transfer heat from the reactor core to the steam generators or directly to the turbines.
Milling		Measure of thermal energy released by nuclear fuel relative to its mass, typically Gigawatt days per tonne (GWd/tU).
Gray		Ground rock remaining after particular ore minerals (e.g. uranium oxides) are extracted.
Reprocessing		A positively-charged particle from the nucleus of an atom, emitted during radioactive decay. Helium nuclei, with 2 protons and 2 neutrons.
Control rods		Condition of being able to sustain a nuclear chain reaction.
Pressurised water reactor		Process by which minerals are extracted from ore, usually at the mine site.
In situ leaching		The recovery by chemical leaching of minerals from porous orebodies without physical excavation. Also known as solution mining.
Gamma rays		is mildly radioactive material usually disposed of by incineration and burial.
Boiling water reactor		High energy electro-magnetic radiation from the atomic nucleus, virtually identical to X-rays.
Vitrification		A common nuclear reactor cooled and usually moderated by ordinary water.