GLOSSARY Actinide: natural or artificial radionuclide, with an atomic number between 89 (actinium) and 103 (lawrencium). Some authors start the actinides series with element 90 (thorium). BNI: Basic Nuclear Installation. Installation which, due to its nature or the quantity or activity of the radioactive substances it contains, is governed by a particular regulatory system, defined by the Environment Code and the Order of 7 February 2012. Conditioning (of radioactive waste): industrial process using a blocking material to immobilise the waste in a matrix, the type and performance of which depend on the type of waste. Containment (of radioactive materials): keeping radioactive materials inside a determined space, thanks to a range of systems (or barriers) aiming to prevent the dispersion of unacceptable quantities of them outside this space. Criticality: in the field of nuclear engineering, criticality is a discipline which aims to assess and prevent the risks of an unwanted chain reaction in nuclear facilities. It is a sub-discipline of neutronics. The criticality risk is the risk of triggering an uncontrolled fission chain reaction. Disposal (or Repository): this consists in definitively placing the radioactive waste in a safe place, where its radioactivity will decrease over time. Fission products: fission products are nuclides resulting from the fission of a fissile element (a nucleus). Each nucleus of fissile material undergoing nuclear fission breaks into two (exceptionally three) pieces, which stabilise in the form of new atoms. IAEA: International Atomic Energy Agency. Intergovernmental organisation created in 1957, with the same legal structure as the United Nations Organisation (UNO), mandated to foster and promote the safe, secure and peaceful use of nuclear technologies throughout the world. Management route: refers to all the operations performed on the radioactive waste which, from production to disposal, contribute to ensuring that it is made safe, once and for all. It is adapted to certain types of radioactive wastes. PNGMDR: French National Radioactive Materials and Waste Management Plan. The State’s strategic oversight tool for the management of radioactive materials and waste. It defines the management solutions for these substances and the conditions in which they are implemented (recycling, disposal, interim storage, etc.). Processing: set of mechanical, physical or chemical operations designed to modify the characteristics of the waste. The purpose of processing is to make the waste suitable for conditioning. Radiation protection: aims to prevent or reduce the health risks linked to ionising radiation, on the basis of three broad principles, justification, optimisation and limitation of radiation doses. To apply these principles, radiation protection implements regulatory and technical means adapted specifically to three categories of persons: the public, patients and workers. Radioactive half-life: time needed for the decay of half the atomic nuclei of a radioactive nuclide. Radionuclide: radioactive atomic species defined by its mass number, its atomic number and its nuclear energy state. Reversibility: this is a prudent approach in the light of the available knowledge. Reversibility entails the ability, for a limited period of time, to recover and transfer the waste packages (recoverability), the ability to intervene in the disposal process (flexible management in stages, maintenance and surveillance) and the ability to modify the design. Safety (nuclear): the set of technical provisions and organisational measures – related to the design, construction, operation, shutdown and decommissioning of Basic Nuclear Installations, as well as the transport of radioactive substances – which are adopted with a view to preventing accidents or limiting their effects. Spent fuel: nuclear fuel having being irradiated in the core of a reactor, from which it is removed once and for all. Storage: operation consisting in placing radioactive substances for a temporary period in an above-ground or near-surface facility specially fitted out for the purpose, with the aim of subsequently retrieving them. Transmutation: following an intentional or spontaneous nuclear reaction, transformation of one element into another. The aim is to reduce the harmfulness or make for easier management of long-lived or high-level radionuclides, by transforming them into other radionuclides which are either lower level or shorter lived. WRC: retrieval and conditioning of legacy waste. 34 • Les cahiers de l’ASN • May 2024
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