Office for Nuclear Regulation

Basic safeguards glossary

31 January 2020

As part of the Withdrawal Agreement, existing Euratom laws and regulations will continue to apply in the UK during the post-Brexit transition period. All arrangements currently in place will remain until ONR assumes its safeguards and nuclear material accountancy duties from 1 January 2021.

This glossary provides the technical terminology used in the Commission Regulation 302/05 and throughout the Nuclear Non-proliferation website. The IAEA Glossary website can be accessed through the link in the Related Link section of this website.

Additional Protocol
see Protocol Additional to Safeguards Agreements.
Basic Technical Characteristics (BTCs)
Design information on nuclear installations as provided for Euratom Safeguards. The BTCs include a description of the installation, the form, quantity, location and flow of nuclear material being used, the layout of the installation, containment features and procedures for nuclear material accountancy (skip to content) and control. The information is used, inter alia, to prepare the safeguards approach to the installation.
A portion of nuclear material handled as a unit for accounting purposes at a key measurement point and for which the composition and quantity are defined by a single set of specifications or measurements. The nuclear material may be in bulk form or contained in a number of separate items. Examples of batches are:
  • one fuel assembly;
  • one UF 6 cylinder;
  • a tray of pellets prepared for loading into one fuel rod;
  • several drums of UO 2 powder with the same specifications.
Book Inventory
A record of all the nuclear material held at a site and its location on the site. The book inventory consists of the results of the most recent physical inventory and of all the inventory changes that have occurred since that physical inventory was taken.
Commission Regulation (Euratom) No 302/05
Regulation 302/05 provides the current legal framework for the application of safeguards under the EURATOM Treaty.
Comprehensive Safeguards Agreements
Agreements made with the IAEA by non-nuclear weapon States (NNWS) to enable the application of safeguards on all source and special fissionable material in all peaceful nuclear activities, as required by the NPT. The model text for these agreements is published as IAEA document INFCIRC 153.
Containment involves the use of seals to provide assurance of the physical integrity of an area or item in order to prevent undetected access to or movement of nuclear material or safeguards-relevant equipment and data.
Depleted Uranium
Uranium containing less than the natural abundance of the isotope uranium-235. (Natural uranium contains about 0.7% U-235.)
Destructive Assay
The analysis of nuclear materials using methods, which involve the destruction of a sample, e.g. chemical analysis or mass spectrometry.
Effective Kilogram
A special unit used in the safeguarding of nuclear material, reflecting its strategic value. A quantity in effective kilograms is obtained by taking:
  • for plutonium, its weight in kilograms;
  • for uranium with an enrichment of 1% (0.01) and above, its weight in kilograms multiplied by the square of its enrichment;
  • for uranium with an enrichment below 1% (0.01) and above 0.5% (0.005), its weight in kilograms multiplied by 0.0001; and
  • for depleted uranium with an enrichment of 0.5% (0.005) or below, and for thorium, its weight in kilograms multiplied by 0.00005.
see Treaty establishing the European Atomic Energy Community.
European Safeguards Research and Development Association (ESARDA)
A network of European organisations involved in the implementation and development of nuclear safeguards.
Fertile Material
Nuclear material that can be converted to fissile material through the capture of a neutron. An example of a fertile material is uranium-238.
Fissile Material
Fissile materials are capable of undergoing nuclear fission (splitting of the nucleus of an atom) by slow neutrons. Examples of fissile materials are uranium 235 and plutonium 239.
High Enriched Uranium (HEU)
Uranium containing 20% or more of the isotope uranium-235. A quantity of HEU can be described in terms of either the total mass of all the uranium isotopes, kg U, or as the mass of the fissile isotope uranium-235, kg U 235. For example, 100kg U of 70% enriched HEU could also be described as 70kg U 235.
The International Atomic Energy Agency, based in Vienna, is an independent intergovernmental United Nations organisation that serves as the global focal point for nuclear co-operation.

The IAEA assists its Member States in planning for and using nuclear science and technology for peaceful purposes. It develops nuclear safety standards and, based on these standards, promotes the achievement and maintenance of high levels of safety in applications of nuclear science. The IAEA also verifies, through its inspection system, that States comply with their commitments under the Non-Proliferation Treaty and other non-proliferation agreements to use nuclear material and facilities for peaceful purposes only.
The Institute of Nuclear Materials Management (INMM)
A US-based organisation that works to support the development of all aspects of nuclear materials management.
Inventory Change Report (ICR)
A report that describes changes in inventory of nuclear material in a material balance area. ICRs are usually provided on a monthly basis.
Key Measurement Point (KMP)
A location where nuclear material appears in such a form that it may be measured to determine material flow or inventory. KMPs include, but are not limited to, the inputs and outputs (including measured discards) and storages in material balance areas.
Low Enriched Uranium
Uranium containing less than 20% of the isotope uranium-235 but more than that which occurs in natural uranium. (Natural uranium contains about 0.7% U-235.)
Material Balance Area (MBA)
An area inside or outside of a facility such that:
  • the quantity of nuclear material in each transfer into or out of each MBA can be determined; and
  • the physical inventory of nuclear material in each MBA can be determined when necessary, in accordance with specified procedures, in order that the material balance for safeguards purposes can be established.
Material Balance Report (MBR)

A report of the nuclear material in a material balance area or facility, which shows aggregated transactions for the material balance period (e.g. year) in comparing the physical inventory with the book inventory.

Nuclear Materials Balance (also known as Material Unaccounted For (MUF) or Inventory Difference (ID))
The difference between the physical inventory and the book inventory. The difference can be either positive (apparent gain of material) or negative (apparent loss of material). MUF is caused primarily by measurement uncertainties. Whilst any actual loss of material would be included in the MUF, the existence of a negative MUF does not necessarily indicate a real loss of material. The MUF values for any accountancy period are assessed for their acceptability in relation to the activities, which occurred over that period. Note that the Euratom convention for MUF (physical inventory - book inventory) is the opposite of the IAEA convention.
Measured Discards

Nuclear material which has been measured, or estimated on the basis of measurements, and disposed of in such a way that it is not suitable for further nuclear use. An example of a measured discard is a discharge to the environment.

Natural Uranium
Uranium as it occurs in nature, consisting of about 99.3% uranium-238, 0.7% uranium-235 and very small quantities of uranium-234.
Non-destructive Assay (NDA)
The measurement of the nuclear material content of an item without producing significant physical or chemical changes in the item. NDA usually involves measurement of the radioactivity of the item for comparison with a calibration based on similar items whose nuclear material contents are very accurately known.
Non-Proliferation Treaty (NPT)
See Treaty on the Non-Proliferation of Nuclear Weapons.
Nuclear Facility (or Installation)
Under IAEA safeguards, a nuclear facility (or installation) is defined as:
  • a reactor, a critical facility, a conversion plant, a fabrication plant, a reprocessing plant, an isotope separation plant or a separate storage installation; or
  • any location where nuclear material in amounts greater than one effective kilogram is customarily used.
Nuclear Fuel Cycle
A system of nuclear facilities interconnected by flows of nuclear material. For example, the UK nuclear fuel cycle includes conversion plants, enrichment plants, fuel fabrication plants, reactors and reprocessing plants.
Nuclear Material
Any source material or special fissionable material.
Nuclear Materials Accountancy
A system to register material quantities and locations, track items and quantities through transfers and processes, record measurement data, and provide information for reporting and analysis. Accounts of nuclear materials are kept for security, safety, environmental and international safeguards reasons.
Physical Inventory (Taking)
The process of quantifying the amount of nuclear material present using techniques such as visual verification, sampling and analysis, weighing and other measurements (e.g. NDA). During the physical inventory taking exercise the material is transferred to locations within the facilities where measurements can be made.
Physical Inventory Listing (PIL)
A report listing all batches of nuclear material separately and specifying material identification and batch data for each batch.
Protocol Additional to Safeguards Agreements (Additional Protocol)
Agreements with the IAEA made by States that specify the additional authority necessary for the IAEA to fully implement its obligations under comprehensive safeguards agreements pursuant to the NPT. Additional protocols contain measures to improve the efficiency and strengthen the effectiveness of the IAEA safeguards system. The main features of the additional protocol are the requirements that States provide:
  • information beyond that required for nuclear materials accountancy, e.g. on nuclear fuel cycle-related R&D, specified manufacturing activities (e.g. centrifuge manufacture) and exports and imports of certain non-nuclear material and equipment; and
  • extended access to the IAEA to check this reporting.
Retained Waste
Stored waste containing nuclear material deemed unrecoverable by existing technology but retained in a form from which it is retrievable. The nuclear material content of retained waste is recorded on accounts separate from the main safeguarded inventory.
Nuclear safeguards are measures to verify that civil nuclear materials are properly accounted for and are not diverted to undeclared uses. The measures include nuclear materials accountancy, containment and surveillance.
Source Material
Uranium containing the mixture of isotopes occurring in nature; uranium depleted in the isotope 235; thorium; any of the foregoing in the form of metal, alloy, chemical compound, or concentrate; any other material containing one of more of the foregoing in such concentration as the IAEA Board of Governors shall from time to time determine; and such other material as the Board of Governors shall from time to time determine. The Euratom definition of source material is identical.
Special Fissionable Material (or Special Fissile Material)
Plutonium-239; uranium-233; uranium enriched in the isotopes 235 or 233; any material containing one or more of the foregoing; and such other fissionable material as the IAEA Board of Governors shall from time to time determine. The term special fissionable material does not include source material. The Euratom definition of special fissile material is identical, apart from the addition of ores/ore wastes to the exclusions.
The use of equipment, usually optical equipment such as video cameras, to confirm information on the movement of nuclear material or detect tampering with containment or safeguards relevant equipment, samples and data.
The amount of nuclear material processed through facilities, usually expressed over a time period (e.g. a semi-annual accountancy period).
Treaty establishing the European Atomic Energy Community (EURATOM Treaty)
The EURATOM Treaty, which entered into force on 1 January 1958. The UK became subject to the Treaty upon joining the European Community in 1973.

The safeguards section of the Treaty (Chapter VII) requires the European Commission to satisfy itself that:
  • ores, source materials and special fissile materials are not diverted from their intended uses as declared by the users; and
  • the provisions relating to supply and any particular safeguarding obligations assumed by the Community under an agreement concluded with a third State or an international organisation are complied with.
Treaty on the Non-Proliferation of Nuclear Weapons (NPT)
Under the NPT, the nuclear weapon States (NWS -China, France, Russia, UK and US) undertake not to transfer to any recipient whatsoever nuclear weapons or any other nuclear explosive devices or control over them, and not to support manufacture or acquisition of such weapons or devices by any non-nuclear weapons States (NNWS). [Article I]

NNWS party to the NPT undertake not to receive any nuclear weapons or other nuclear explosive devices, nor to accept assistance in this respect. [Article II]

The NNWS party to the NPT also undertake to accept IAEA safeguards on all source and special fissionable material in all their peaceful nuclear activities. This undertaking is set out in agreements to be signed with the IAEA, which are known as comprehensive safeguards agreements. The NNWS undertake further to provide source and special fissionable material and relevant equipment to any other NNWS only if the material is covered by IAEA safeguards. [Article III]

The NPT does not affect the right of its parties to develop and use nuclear energy for peaceful purposes. All parties to the NPT undertake to facilitate and have the right to participate in the fullest possible exchange of equipment, materials and information on peaceful uses of nuclear energy. [Article IV]

Each of the parties to the NPT undertake to pursue negotiations on effective measures relating to an early cessation of the nuclear arms race, to nuclear disarmament and to general and complete disarmament under international control. [Article VI]

The NPT was opened for signature on 1 July 1968, and entered into force on 5 th March 1970. At its 1995 Review and Extension Conference, it was agreed that the Treaty would continue in force indefinitely.

Only three States ( India, Israel and Pakistan) have not signed the NPT.
Voluntary Offer Safeguards Agreements
safeguards agreements made with the IAEA by the nuclear weapon States (NWS), i.e. China, France, Russia, UK and US. The NPT does not require the NWS to conclude safeguards agreements, but they have all voluntarily offered parts or the whole of their civilian nuclear fuel cycle for the application of IAEA safeguards, in order to allay concerns expressed by non-nuclear weapons States (NNWS) that their nuclear industry could otherwise be at a commercial disadvantage. The UK/Euratom/IAEA voluntary offer safeguards agreement came into force in 1978.