Glossary

Assembly

Also called a fuel element, this is a metal structure comprising a determined number of rods containing sintered pellets of enriched uranium. The assemblies placed in the reactor vessel form the reactor core

Biological protection

Device or material to prevent people from being exposed to ionising radiation. For example, the water in cooling pools is an excellent form of biological protection.

Centrifugation

A separation process which consists in subjecting components of a mixture to a centrifugal force according to their difference in density.

Conditioning matrix

A matrix material that encapsulates or blocks radioactive waste.

Container

Sealed container for transport, storage and/or disposal of radioactive materials.

Conversion

Find out more (link to the uranium conversion page)

Decommissioning

All the technical and regulatory operations that follow the final shutdown of a nuclear facility. Decommissioning includes the physical dismantling, decontamination of all devices and equipment and the management of associated radioactive waste.

Enrichment

Process to increase an element’s concentration of fissile isotopes. In its natural state, uranium only contains 0.7% of fissile uranium 235. To become suitable for use in a pressurised water reactor, like those at Doel and Tihange, this proportion is increased through the enrichment process to between 3% and 5%.

Energy mix

Refers to the mix of various types of primary energy used to cover the energy consumption of a country, a company, etc

Fuel sheaths

A rod-shaped, sealed metal capsule made of zircalloy (a zirconium-based alloy) that surrounds the uranium pellets and isolates them from the heat transfer fluid. The sheath is one of many safety barriers.

Fuel rods

Long tubes containing enriched uranium pellets. Together, they make up fuel assemblies

Half-life

This is the time required to reduce the quantity of radioactive isotopes to half its initial value also called the radioactive decay.

In situ leaching

Also referred to as ISL, is a process designed to dissolve metals (copper, uranium, etc.) to make them easier to put into a deposit.

Isolation barriers

Devices capable of preventing, limiting or slowing the dispersal of radioactive material.

Mox fuel

A nuclear fuel based on mixed uranium and plutonium oxide obtained during reprocessing operations.

Nuclear fuel

A material made from uranium or a mixture of uranium and plutonium that is used to make the assemblies that form the core of a nuclear reactor.

Nuclear fuel cycle

It includes three key stages:

  • from the procurement of raw materials to the fabrication of nuclear fuel, also known as the front end of the cycle;
  • use in the reactor vessel;
  • management of spent fuel and irradiated fissile materials, also known as the back end of the cycle.

The fuel cycle is said to be closed if it includes the reprocessing of spent fuel assemblies and the recycling of fissile material recovered through reprocessing. If there is no reprocessing, it is called an open cycle.

Plutonium (Pu)

Artificial and radioactive heavy metal element. Plutonium 239, the fissile isotope, is produced in nuclear reactors through the irradiation of a uranium 238 core.

Post-operational phase

Period of 5 years between the shutdown of the reactor and the beginning of the dismantling.

Radioactive period

Also called half-life: the time it takes for the number of atoms of a radioactive element to decay by half. No external physical action is capable of altering the half-life of a radioactive element, except transmutation (transformation of one radioactive element into another).

Radioactive waste

Radioactive substances for which no further use is planned or intended

  • Category A waste: has a short half-life and has low or medium levels of radioactivity;
  • Category B waste: has a long half-life and has low or medium levels of radioactivity;
  • Category C water: has a long half-life and has high levels of radioactivity.

https://www.ondraf.be/sortes-de-dechets-radioactifs#:~:text=Pour%20leur%20gestion%20%C3%A0%20court%20terme%20(et%20notamment%20pour%20leur,Les%20d%C3%A9chets%20de%20haute%20activit%C3%A9

Radioactive waste conditioning

The process of immobilising radioactive waste in a matrix suitable for transport, storage or disposal.

Radioactive waste disposal

An operation that consists of placing radioactive substances in a facility (on the surface or underground) specially designed as a final disposal site to store them for very long periods of time.

Recycling

Reprocessing of spent fuel allows nearly 96% of the raw materials to be recovered, which can then be used again in reactor cores.

Reprocessing

An operation to separate recyclable materials from the final radioactive waste.

Storage

This is an interim stage in the nuclear waste management process. It consists of temporarily putting processed waste in special storage facilities to ensure that it remains isolated for a given period of time in order to protect humans and the environment. Storage is a temporary solution.

SWU

For a separative work unit. This is a work measurement unit often used in enrichment contracts. It is also used to determine the production capacity of an enrichment plant

Uranium hexafluoride

Before being enriched, uranium in the form of yellowcake is first converted into a gas called uranium hexafluoride UF₆.

Vitrification

This is an operation that consists of enclosing concentrated solutions of highly radioactive products in a glass matrix.

Yellow cake

A uranium concentrate with the chemical formula U3O8 (triuranium octoxide).

Zircaloy-4

Alloy used in the fabrication of fuel assemblies composed of more than 98% zirconium. The other components are tin, chromium and hafnium.

Zirconium

Metal highly resistant to corrosion at high temperature. It is used as an alloy to fabricate nuclear fuel assemblies.