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.


the conversion operations involve transforming yellow cake into uranium hexafluoride by giving it the required purity to produce the nuclear fuel.

Energy mix

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


process involving increasing an items fissile material content.

Final storage

location where waste is deposited for the final time.

Fuel rods

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


High Activity Disposal Experimental Site: underground research laboratory operated by EURIDICE.


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

Interim storage

an intermediate stage in the nuclear waste management process. It involves placing the conditioned waste in a facility that will ensure, for a set period, that they are kept away from contact with humans and the environment.

lb = Pound

a unit of mass equivalent to exactly 0.453… kg which is used in the USA, the UK and Canada.


mixed oxides. Nuclear fuel based on a mix of uranium and plutonium oxides from reprocessing.

Nuclear fuel cycle: three key stages

supply through to production of the nuclear fuel, its irradiation in the reactor core and management of the spent fuel.

Plutonium (Pu)

The fissile isotope plutonium 239 is a uranium 238 product that arises in nuclear reactors.


the PRACLAY experiment is studying the effect radioactive waste's heat emissions have on Boom clay.

Radioactive waste

  • 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.


reuse, in a reactor, of nuclear materials from spent fuel reprocessing.


spent fuel processing with a view to separating the recyclable materials from the final waste.


a separative work unit – this is a unit that is used in enrichment contracts.


enrichment process involving turning at high speed a gaseous mixture of isotypes so as to use the centrifugal force to alter the composition of this mixture.


operation involving immobilising in a glass die concentrated solutions of highly radioactive materials.

Yellow cake

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