| Activation | The capture of a free neutron by a stable non-radioactive atom, causing it to become radioactive. See What is radioactive waste? |
| ADU | Ammonium Diuranate |
| AETP | Active Effluent Treatment Plant (at reactor site) |
| AEWTP | Active Effluent Waste Treatment Plant (at reactor site) |
| AGR | Advanced Gas-cooled Reactor |
| AWE | Previously the Atomic Weapons Establishment, now known as AWE. AWE develops nuclear warheads for the UK’s deterrent at Aldermaston and Burghfield in Berkshire |
| BAESM | BAE Systems Marine Ltd.; a company that designs, manufactures and services naval ships and submarines |
| BCD | Burst Cartridge (Can) Detection |
| Becquerel | Bq; the standard international unit of measurement of radioactivity – corresponding to one decay per second (see also kBq, GBq and TBq). |
| BEP | Box Encapsulation Plant (at Sellafield) |
| BEPO | British Experimental Pile O. Air-cooled graphite-moderated pile (at Harwell site; shut down in 1968) |
| Beta particle | Particle emitted from parent nucleus in beta decay with corresponding neutrino. Beta- decay results in electron emission with an antineutrino and Beta+ decay results in positron emission with a neutrino |
| Beta/gamma activity | Radioactivity associated with the emission of beta particles and/or gamma radiation |
| BPS | Berkeley Power Station |
| BTC | British Technology Centre (at Sellafield). Now known as National Nuclear Laboratory, Central Laboratory |
| C & M | Care and Maintenance |
| Capping material | Cement or other substance forming inactive cover over conditioned waste in a container |
| CCP | Cartridge Cooling Pond |
| CEGB | Central Electricity Generating Board |
| Characterisation | The process of assessing the composition of radioactive materials and wastes, and classifying them based on their levels of radioactivity, and physical and chemical properties |
| CHILW | Contact Handled Intermediate Level Waste |
| Clifton Marsh | Landfill site (near Preston) |
| Conditioned volume | The volume of waste after conditioning, consisting of the waste material and encapsulating matrix |
| Conditioned waste | Radioactive waste that has undergone conditioning |
| Conditioning | The process used to prepare waste for long-term storage and/or disposal by converting it into a solid and stable form, e.g. by encapsulation in cement |
| Conditioning matrix | The material used to contain and/or stabilise waste for disposal. This may be cement, glass or polymer. |
| Contamination | Radioactive particles that have accumulated on an exposed surface by contact with a radioactive material or waste. See What is radioactive waste? |
| Controlled burial | The authorised disposal of some LLW, arising principally in the non-nuclear sector, at suitable landfill sites that possess good containment characteristics. |
| Crud | Any deposits of impurity or corrosion product within a reactor, storage vessel or chemical plant. |
| CVCS | Chemical Volume and Control System (PWR station) |
| CXPP | Chapelcross Process Plant. |
| DCIC | Ductile Cast Iron Container |
| DCP | Dounreay Cementation Plant. |
| Decommissioning | The process whereby a nuclear facility, at the end of its economic life, is taken permanently out of service and its site made available for other purposes |
| Decommissioning waste | Wastes arising after the shutdown of a facility associated with the use or handling of radioactive materials. They can consist of plant or equipment, building debris and material from the clean-up of surrounding ground. |
| Depleted uranium | Uranium where the uranium 235 isotope content is below the naturally occurring 0.72% by mass. |
| DESNZ | Department for Energy Security & Net Zero |
| DFR | Dounreay Fast Reactor (shut down in 1977) |
| DIDO | Heavy-water cooled and moderated materials testing reactor (at Harwell site; shut down in 1990). |
| Disposal | The emplacement of waste in a suitable facility without intent to retrieve it. (Retrieval may be possible but, if intended, the appropriate term is storage.) |
| DMTR | Dounreay Materials Test Reactor |
| DNLEU | Depleted, Natural and Low Enriched Uranium |
| Dragon | Experimental high temperature reactor project sited at Winfrith and funded by the Organisation for Economic Cooperation and Development (shut down in 1976). |
| DU | Depleted Uranium |
| EA | Environment Agency; the leading public body for protecting and improving the environment in England See How are sites regulated? |
| EARP | Enhanced Actinide Removal Plant (at Sellafield) |
| EAST | External Active Sludge Tanks (at Winfrith) |
| EFDA | European Fusion Development Agreement |
| Electron | Negatively charged fundamental particle in orbit about an atomic nucleus |
| Enriched uranium | Uranium where the uranium-235 isotope content is above the naturally occurring 0.72% by mass. |
| Enrichment | The process of increasing the abundance of fissionable atoms in natural uranium. |
| ENSREG | European Nuclear Safety Regulators Group |
| Euratom | European Atomic Energy Community |
| Ex situ | ‘Off the site’ (in the context of waste disposal) |
| FED | Fuel Element Debris |
| FGMSP | First Generation Magnox Storage Pond (at Sellafield). |
| FHP | Fuel Handling Plant (at Sellafield) |
| Fission | Spontaneous or induced fragmentation of heavy atoms into two (occasionally three) lighter atoms, accompanied by the release of neutrons and radiation. |
| Fission products | Atoms, often radioactive, resulting from nuclear fission. |
| Flatrol | Type of railway wagon. It is used for transporting fuel flasks. |
| Floc | A product of flocculation, a process that separates suspended contaminants from a liquid. |
| Fuel cladding | The metal casing around the fuel |
| Fuel stringer | A string of fuel element assemblies for an AGR. |
| Fusion | The process of fusing two or more atoms to form a heavier atom, releasing large amounts of energy. This is essentially the same process that occurs in the Sun. |
| GBq | Gigabecquerel, one thousand million (109) Becquerels. |
| GDA | Generic Design Assessment. |
| GDF | Geological Disposal Facility |
| GE Healthcare Ltd | A company that provides products and services for use in healthcare and life science research. This includes radioisotopes for medical and research users. |
| Geological disposal | A long-term waste management option involving the emplacement of radioactive waste in an engineered underground geological disposal facility, where the geology (rock structure) provides a barrier against the escape of radioactivity and there is no intention to retrieve the waste once the facility is closed. |
| GLEEP | Graphite Low Energy Experimental Pile. Low energy, graphite reactor (at Harwell site; shut down in 1990). |
| Government | A collective term for the central government bodies responsible for setting radioactive waste management policy within the UK. It comprises the UK Government, the Scottish Government and the devolved administrations for Wales and Northern Ireland. |
| Grout | Material (typically cement) used to immobilise radioactive waste |
| Grouting | Process of immobilising radioactive waste in cement |
| HA | High Activity |
| HAL | Highly Active Liquor |
| Half life | The time it takes for the amount of radioactivity to decrease by 50%. |
| HAW | Higher Activity Waste. |
| HEU | Highly Enriched Uranium. Uranium where the uranium-235 isotope content is 20% by mass or more. |
| Hex | Uranium Hexafluoride |
| HF | Hydrogen Fluoride |
| HLW | High Level Waste |
| HMNB | His Majesty’s Naval Base |
| HVVLLW | High Volume Very Low Level Waste |
| IAEA | International Atomic Energy Agency; An international organisation working for the safe, secure and peaceful uses of nuclear science and technology |
| IFP | Insoluble Fission Products |
| ILW | Intermediate Level Waste. |
| In situ | ‘On the site’ (in the context of waste disposal) |
| Irradiated fuel | Fuel that is being or has been used to power nuclear reactors. |
| ISO | International Organisation for Standardisation |
| Isotope | Atoms of the same element which have the same number of protons but different number of neutrons |
| IWS | Integrated Waste Strategy |
| JET | Joint European Torus – the internationally funded fusion project sited at Culham. |
| kBq | Kilobecquerel, one thousand (103) Becquerels. |
| LA | Low Activity |
| LAEMG | Low Active Effluent Management Group area (at Sellafield). |
| LA-LLW | Low Activity Low Level Waste |
| LAW | Lower Activity Waste |
| LETP | Liquid Effluent Treatment Plant |
| LEU | Low Enriched Uranium. Uranium enriched in U-235 to less than 20% by mass. |
| LLLETP | Low Level Liquid Effluent Treatment Plant |
| LLRF | Low Level Refuelling Facility. |
| LLW | Low Level Waste |
| LQA | Land Quality Assessment |
| LSA | Low Specific Activity. |
| LWR | Light Water Reactor. |
| m3 | Cubic metres – a measure of volume |
| MA | Medium Active |
| MAC | Miscellaneous Activated Component. |
| Magnox | An alloy of magnesium used for fuel element cladding in natural uranium fuelled gas-cooled power reactors. Also a generic name for this type of reactor. |
| MBGWS | Miscellaneous Beta Gamma Waste Store. |
| MBq | Megabecquerel, one million (106) Becquerels. |
| MCI | Miscellaneous Contaminated Items. |
| MEB | Multi-Element Bottle. Container used to hold irradiated LWR fuel in cooling ponds prior to reprocessing. |
| MEP | Magnox Encapsulation Plant (at Sellafield). |
| MMMF | Man-Made Mineral Fibre |
| MOD | Ministry of Defence; UK government ministerial department |
| MODIX | Multi-stage Oxidative Decontamination with Ion-Exchange. A process used, among other things, to clean the pressure vessels and primary circuit pipework of nuclear submarines prior to refuelling. |
| MOX | Mixed Oxide. Refers to nuclear fuel consisting of uranium oxide and plutonium oxide for use in reactors. |
| MRWS | Managing Radioactive Wastes Safely |
| mSv | milliSievert, one thousandth of a Sievert |
| MTR | Materials Testing Reactor. |
| MWP | Minor Waste Producers |
| NDA | Nuclear Decommissioning Authority. A non-departmental public body responsible for overseeing the decommissioning and cleanup of 17 of the UK’s civil public sector nuclear sites. |
| NDS | Commercial disposal service formerly operated by AEA Technology Harwell, sometimes referred to as the National Disposal Service. |
| NE | Not Estimated |
| NEA | Nuclear Energy Agency |
| Nimonic | An alloy of the elements nickel, chromium and other minor constituents. |
| NNL | National Nuclear Laboratory Limited. A Government owned science and technology services company. |
| NORM | Naturally Occurring Radioactive Material. These are materials that typically accumulate as scale on pipework during the extraction of oil and gas, and have raised levels of naturally occurring radioactivity |
| NRTE | Naval Reactor Test Establishment (at Vulcan, Dounreay) |
| NRW | Natural Resources Wales; Welsh Government Sponsored Body, responsible for making sure that the environment and natural resources of Wales are sustainably maintained, sustainably enhanced and sustainably used, now and in the future. See How are sites regulated? |
| NU | Natural Uranium |
| Nuclear fuel | Fuel used in a nuclear reactor. Most fuel is made of uranium, and produces heat when the uranium atoms split into smaller fragments. |
| Nuclear fuel cycle | The sequence of activities involved in the production and use of nuclear fuel. See How is radioactive waste produced? |
| NWS | Nuclear Waste Services |
| OECD | Organisation for Economic Co-operation and Development |
| ONR | Office for Nuclear Regulation; Organisation responsible for efficient and effective regulation of the nuclear industry, holding it to account on behalf of the public. See How are sites regulated? |
| Operational waste | Wastes arising from the day-to-day operations of a facility associated with the use or handling of radioactive materials. |
| Ore | Any naturally occurring mineral from which economically valuable constituents (e.g. metals) can be extracted. |
| Oxide | A chemical compound of oxygen and another element. For example, rust is an iron oxide which is a compound of iron and oxygen |
| Packaged volume | The volume of waste after packaging, consisting of the waste material, any encapsulating matrix, any capping grout and ullage, and the container. |
| Packaged waste | Radioactive waste that has undergone Packaging. |
| Packaging | The loading of waste into a container for long-term storage and/or disposal. In most but not all cases this includes conditioning. |
| PCD | Primary Circuit Decontamination. |
| PCM | Plutonium Contaminated Material. |
| PFR | Prototype Fast Reactor (at Dounreay site; shut down in 1994) |
| PIE | Post Irradiation Examination, of fuel elements etc. |
| PLUTO | Heavy-water cooled and moderated materials testing reactor (at Harwell site; shut down in 1990). |
| Plutonium | A radioactive element created in nuclear reactors. It can be separated from spent nuclear fuel by reprocessing. Plutonium is used as a nuclear fuel, in nuclear weapons and as a power source for space probes. |
| POCO | Post Operational Clean Out. Activity after final shutdown that prepares a plant for decommissioning. |
| Pond furniture | Various storage racks, skips, frames, containers and MEBs used for storing irradiated fuel in cooling ponds. |
| Pu | Plutonium. |
| PuO2 | Plutonium dioxide |
| PWR | Pressurised Water Reactor |
| PWTP | Pond Water Treatment Plant (at reactor sites) |
| R&D | Research and Development |
| Radiation | The process of emitting (radiating) energy in the form of particles or electromagnetic waves. See What is radiation? |
| Radioactive decay | The splitting of an unstable nucleus, releasing energy in the form of particles (alpha and beta), neutrons or electromagnetic energy (gamma rays) |
| Radioactivity | A property possessed by some atoms that split spontaneously, with release of energy through emission of a sub-atomic particle and/or radiation. |
| Radiopharmaceuticals | Drugs that contain radioactive materials |
| Radionuclide | A general term for an unstable nuclide that emits ionising radiation (e.g. cobalt-60). |
| Raffinate | A solution resulting from a solvent extraction process. The term is applied to the aqueous solution of fission products (liquid HLW) remaining after the extraction of uranium and plutonium in the first stage or irradiated fuel reprocessing. |
| Reprocessing | The chemical extraction of reusable uranium and plutonium from waste materials in spent nuclear fuel. |
| RHILW | Remote Handled Intermediate Level Waste. |
| RRF | Residue Recovery Facility (at Capenhurst) |
| RRMPOL | Rolls-Royce Marine Power Operations Ltd.; a company that designs, supplies and supports marine power and propulsion systems |
| RV | Resin Vault (at Trawsfynydd). |
| Safeguards | Nuclear safeguards are measures to verify that countries abide by their commitments to use nuclear material for declared peaceful purposes. |
| Safety case | A set of documents that describe the radiological hazards in terms of a facility or site and operation. It also includes the measures that prevent or mitigate against harm |
| SDP | Sodium Disposal Plant (at Dounreay) |
| SDP | Submarine Dismantling Project |
| Sealed radioactive sources | Container of enclosed radioactive material used in medicine, agriculture, industry and other industries |
| SEP | Silo Emptying Plant (at Sellafield) |
| SEPA | Scottish Environment Protection Agency; Scotland’s principal environmental regulator, protecting and improving Scotland’s environment. See How are sites regulated? |
| SETP | Segregated Effluent Treatment Plant (at Sellafield). |
| SGHWR | Steam Generating Heavy Water Reactor (at Winfrith site). Shut down in 1990. |
| Sievert | Sv; the standard international unit of measurement for ionising radiation dose |
| SIXEP | Site Ion Exchange Plant (at Sellafield) |
| SLC | Site Licence Company |
| Small users | Organisations that use radioactive materials and create radioactive wastes that are not part of the nuclear sector licensed under the Nuclear Installations Act 1965 (as amended), including hospitals, universities and industrial undertakings. |
| SMP | Sellafield MOX Plant |
| Spent fuel | Fuel that has been used in nuclear reactors that is no longer capable of efficient fission due to the loss of fissile material. |
| SPF | Sand Pressure Filter |
| SPP | Sludge Packaging Plant (at Sellafield) |
| Storage | The emplacement of waste in a suitable facility with the intent to retrieve it at a later date. |
| Supercompaction | A general term that describes the reduction in bulk volume by the application of high external force. It differs from routine compaction methods by using hydraulic equipment capable of exerting forces of 1,000-2,000 tonnes, and the original container (metal drum or box) is supercompacted along with its contents. Waste is often precompacted into steel drums or boxes prior to supercompaction of the drum or box. |
| SWR | SIXEP Waste Retrieval |
| TBq | Terabecquerel, one million million (1012) Becquerels. |
| Tc | Technetium, an element atomic number 43. |
| te | Tonnes |
| tHM | Tonnes of heavy metal. A unit of mass used to quantify uranium, plutonium and thorium including mixtures of these elements. |
| Thorium | Thorium is a naturally occurring radioactive element that can be mined, extracted and processed to make fuel for certain reactors. |
| Thorp | Thermal Oxide Reprocessing Plant (at Sellafield site) |
| THTR | Thorium High Temperature Reactor |
| TILWSP | Transportable Intermediate Level Waste Solidification Plant. |
| Treatment | A process that changes the state or form of radioactive waste to facilitate its future management. It may or may not serve to put the waste into its finally conditioned form. |
| Tritiated | Containing tritium |
| Tritium | An isotope of hydrogen (H-3) having a radioactive half-life of about 12 years. |
| TSSBN | Trident Ship Submersible Ballistic Nuclear. A nuclear powered submarine with Trident ballistic nuclear missiles. |
| tU | Tonnes of Uranium – a measure of mass. |
| U-235 | Uranium-235 is the main fissile isotope of uranium. Natural Uranium typically contains 0.72% by weight of U-235. |
| U3O8 | Triuranium octoxide |
| UF4 | Uranium tetrafluoride |
| UF6 | Uranium hexafluoride |
| Ullage | The space remaining withina container above the conditioned waste matrix and any capping material. |
| Unirradiated fuel | Fuel that has not yet been used to power nuclear reactors. |
| United Kingdom Atomic Energy Authority (UKAEA) | A public body that manages the UK fusion research programme and operates the Joint European Torus (JET). Originally formed in 1954 to carry out nuclear research for the UK Government. |
| UO2 | Uranium dioxide |
| UO3 | Uranium trioxide |
| Uranium | A radioactive element that occurs in nature. Uranium is used for nuclear fuel and in nuclear weapons. |
| Vitrification | The process of converting materials into a glass or glass-like form. Vitrification is the process used at Sellafield to convert liquid HLW from spent fuel reprocessing into a borosilicate glass. |
| VLLW | Very Low Level Waste |
| Vulcan | The Naval Reactor Test Establishment (NRTE), located adjacent to the Dounreay site on the north coast of Scotland. |
| WAC | Waste Acceptance Criteria |
| WAGR | Windscale Advanced Gas-cooled Reactor (shut down in 1981) |
| WAMAC | Waste Monitoring and Compaction facility (at Sellafield site) |
| Waste hierarchy | The waste hierarchy sets out the priority order for managing waste materials based on their environmental impacts |
| Waste package | A containerand its content of conditioned radioactive waste. |
| WCH | Waste Characterisation form. The WCH is part of the LLWR’s waste acceptance procedure. It has replaced the Waste Stream Characterisation Document (WSCD). |
| WEP | Wastes Encapsulation Plant (at Sellafield) |
| WETP | Winfrith East Treatment Plant |
| WPEP | Waste Packaging and Encapsulation Plant (at Sellafield) |
| WRACS | Waste Receipt Assay Characterisation and Supercompaction facility (At Dounreay) |
| WRAT | Waste Requiring Additional Treatment |
| WSDS | Waste Stream Data Sheets |
| WTC | Waste Treatment Complex (at Sellafield) |
| WVP | Waste Vitrification Plant (at Sellafield) |
| Yellowcake | Concentrated uranium oxide obtained through the milling of uranium ore in the form of a yellow powder. It is the raw material for making nuclear fuel. |
| ZEBRA | Zero Energy Breeder Reactor Assembly. ZEBRA was a fast reactor that operated from 1962 to 1982 at Winfrith. |
| Zenith reactor | A research reactor at Winfrith that has been decommissioned. |
| Zircaloy | An alloy of the element zirconium used for the cladding of nuclear fuel – particularly in water reactors. |