Alpha decay – The spontaneous emission of an alpha particle from a nucleus.

Alpha particle – Nuclear of a helium aton comrising two protons and two neutrons

Backfill – Material used to fill in and close off the void areas of an underground repository after the emplacement of radioactive waste.

Becquerel (Bq) – SI unit of measurement of radioactivity, equivalent to one disintegration per second.  A Gigabecquerel is a thousand million Bq, a Terabecquerel is a million million Bq.

BAT/Best Available Techniques / BPEO/Best Practical Environmental Option / BPM/Best Practical Means  – These are regulatory terms used to define approaches that limit discharges or impacts on the environment. While the concepts are similar, different terms are applied in different parts of the UK.

Beta decay - Spontaneous emission of a beta particle from a nucleus.

Beta particle – An electron or a positron emitted from the nuclear of an atom during radioactive decay.

Borehole - Cylindrical excavation made by a drilling device during site investigation and testing.  The borehole can also be used for the emplacement of waste in repositories and for monitoring.

Ceramic matrix – High performance ceramics, heat and corrosion resistant materials which are mixed with radioactive waste thereby immobilising it.

Conditioned waste – Radioactive waste that has been treated or processed in preparation for packaging.

Criticality – The point at which a nuclear chain reaction occurs as a result of the concentration of certain types of radioactive materials.

Decay storage  – Radioactivity decays over time, though the rate at which this happens varies greatly between different radioactive substances. Decay storage is a means of managing radioactive materials and in particular short lived LLW. Through allowing its decay in situ, the radioactivity of material can be reduced and thus it can be managed in simpler, more cost effective ways.

Decommissioning - Terms used to cover all the procedures undertaken once a nuclear installation has ceased operation.  It covers processes such as de-fuelling reactors, cleaning out and making safe an installation, dismantling and removal of structures, and waste conditioning prior to storage or disposal.

Decontamination - Complete or partial removal of contamination by a deliberate physical, chemical or biological process.

Depleted uranium – Uranium containing a lesser mass percentage of Uranium-235 than natural uranium.

Dilute and disperse – Term usually describing a form of management for radioactive waste where radioactivity is released from a facility as a gas or liquid and is diluted in the air or marine environment.

Disposal - The emplacement of waste in a suitable facility without intent to retrieve it at a later date.

Duty to Co-operate - The Duty to Co-operate is a legal duty on local planning authorities, county councils and public bodies in England to actively engage in a constructive and ongoing basis to maximise the effectiveness of Local and Marine Plans and their cross border impacts.

Encapsulation – Immobilisation of solid waste by mixing it with a matrix material within a container in order to produce a more stable waste form.

EA/Environment Agency / NRW/Natural Resource Wales - Government bodies responsible for granting environmental permits in England and Wales respectively.

Fissile materials – Materials which are capable of undergoing nuclear fission, i.e. the spontaneous or impact-induced splitting of a heavy atomic nucleus accompanied by a release of enery.  Fissile materials include Uranium-233, Uranium-235, Plutonium-239, Plutonium-241 or any combination of these radionuclides.

Fission products – Radioactive elements produced by nuclear fission through the spontaneous or impact-induced splitting of a heavy atomic nuclear accompanied by a release of energy.

Gamma emission – Emission of high energy, very short wavelength, photons from a nucleus.

Geological disposal – Burial in geological formations in a purpose-built facility with no intention to retrieve the waste once the facility is closed.

Groundwater pathway - Water, flowing underground, finds a route through the rock via cracks and fissures to flow to its destination.  Drinking water is frequently obtained by drilling into underground reservoirs on the groundwater pathway.  This is one route through which radioactivity from a geological repository could be brought back to the surface.

Grouting - Means of encapsulating radioactive waste by mixing it with, for example, cement.

Half life - The time required for half the number of nuclear of a specific radionuclide to undergo radioactive decay.

HAW /High Activity Waste – HLW /High Level Waste - classified as wastes in which the temperature may rise significantly as a result of their radioactivity, so that this factor has to be taken into account in the design of storage of disposal facilities.

Heat generating waste - Waste that generates heat as it decays, a specific attribute of HLW.  The heat decreases with time.

HEU/Highly Enriched Uranium  – Uranium in which the proportion of the isotope Uranium-235 has been increased above that at which it occurs in natural uranium.

Immobilisation - Conversion of waste into a less mobile or non-mobile form by, for example, grouting or encapsulation.

Incineration - Waste treatment process of buring combustible waste which reduces its volume although also produces radioactive residues.

ILW /Intermediate Level Waste – classified in CM2919 as wastes with radioactivity levels exceeding the upper boundaries for LLW but which do not require heating to be taken into account in the design of storage or disposal facilities.

Ionising radiation – Radiation that produces ionisation in matter, for example alpha particles, gamma rays, x-rays and neutrons.

Long-lived waste - Radioactive waste that contains radionuclides that have a half-life of more than 30 years.

LALLW/Low Activity Low Level Waste - A sub-set of LLW which is below a certain threshold of radioactivity.

LLW /Low Level Waste – classified as waste containing radioactive materials other than those acceptable for disposal with ordinary refuse, but not exceeding 4GBq per tonne of alpha or 12 GBq per tonne of beta/gamma activity.

LLWR /Low Level Waste Repository - term sometimes used for the facility sited near the village of Drigg in West Cumbria at which some forms of LLW are accepted for burial.  Not all of the UK’s LLW can be disposed of a the LLWR because of its unsuitability in terms of radioactivity, or its physical or chemical properties, such as liquid content or flammability.

Multi-barrier concept - Natural or engineered barrier consisting of two or more components used to insolate radioactive waste, and prevent radionuclide migration, from a repository.

Neutrons - Electrically neutral sub-atomic particles.

Non-nuclear LLW – A range of processes and industries outside the nuclear industry produce LLW. These include hospitals, research facilities, military uses and certain industries. There is a separate Government strategy to manage non-nuclear LLW.

NORM/Naturally Occurring Radioactive Material – NORM consists of materials, usually industrial wastes or by-products, which contain naturally occurring radioactive materials which have been concentrated by the nature of certain industrial processes. Within the UK a range of industries including oil and gas, produce such NORM wastes. There is a separate Government strategy for the management of NORM.

NDA/Nuclear Decommissioning Authority – A Non Departmental Public Body established by the Energy Act 2004, and fully funded by Government, responsible for decommissioning 19 civil nuclear sites formerly owned by BNFL and the UKAEA.

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 – All nuclear fuel related operations associated with the production of nuclear energy, inluding: the mining and milling of ores, enrichment, manufacture of fuel, operation of nuclear reactors, spent fuel reprocessing, and all related radioactive waste management activities.

Nuclide - An atom specified by its atomic number, atomic mass and energy state.

ONR/Office for Nuclear Regulation - Independently regulates nuclear safety and security at 37 nuclear licensed sites in the UK. They also regulate transport and ensure that safeguards obligations for the UK are met. In addition, they oversee the decommissioning of nuclear sites and cooperate with international regulators on safety and security issues of common concern, including associated research

Out of scope wastes – Material that is so low in radioactivity that the risks to humans and the environment can be classed as negligible.

Overpacking - Secondary, or additional, outer container for one or more waste packages, used for handling, transport, storage and/or disposal.

PBO/Parent Body Organisation – A commercial organisation contracted by the NDA to take ownership of Site License Companies at NDA sites, and provide senior management.

Partitioning - The separating out, by physical and chemical methods, of radioactive elements contained in a waste stream to permit their further treatment.

Plutonium - A radioactive element occurring in small quantities in uranium ores but mainly produced artificially by neutron bombardment of uranium for use in nuclear fuel and in nuclear weapons, and as a power source for space probes.  It can be separated from spent nuclear fuel by reprocessing.

Radioactivity - The property possessed by some atoms of splitting spontaneously, with release of energy through emission of a charged particle and/or gamma radioation.  Radioactive decay describes the way in which a radioactive material loses activity naturally as a result of this process.  The rate at which atoms disintegrate is measured in becquerels.

Reprocessing - The chemical extraction of reusable uranium and plutonium from waste materials in spent nuclear fuel.

SLC/Site License Company – The body which is licenced by ONR to operate a nuclear site.

Storage - The emplacement of waste in a suitable facility with the intent to retrieve it at a later date.

Uranium - A radioactive element that occurs in nature.  Uranium is used for nuclear fuel and in nuclear weapons.

VLLW/Very Low Level Waste – This is a sub-category of LLW, consisting of the same sorts of materials, but is the least radioactive and does not require specially designed containment. It is divided into Low Volume (‘dustbin loads’) coming mainly from hospitals and universities, and High Volume (‘bulk disposal’) from nuclear sites


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