Nuclear fuel is the core material used in reactors to produce energy through nuclear fission. The most common fuel is uranium, particularly the isotope uranium-235, which is either used in its natural form or enriched to increase its fissile content. Another important fuel is plutonium-239, typically derived from reprocessed spent fuel. The most widely used fuel form is uranium oxide (UOX), while mixed oxide fuel (MOX), which combines plutonium and uranium, is used in some reactors to recycle plutonium. High-assay low-enriched uranium (HALEU), enriched to between 5% and 20% U-235, is gaining attention for use in next-generation reactors.

The nuclear fuel cycle involves a series of industrial processes that prepare fuel for use in reactors and manage it afterward. The front end of the cycle includes mining uranium ore, milling it into concentrate, converting it into a gas, enriching it to increase the proportion of U-235, and fabricating it into fuel assemblies. The back end deals with managing spent fuel, which may be stored, reprocessed to extract usable materials, or disposed of in geological repositories.

Nuclear fuel is produced in several countries with advanced nuclear industries. The United States, France, Russia, China, and the United Kingdom all operate major fuel cycle facilities. For example, the Springfields site in the UK fabricates fuel for both domestic and international reactors. Russia and France are also leaders in enrichment and reprocessing technologies, while Canada and Kazakhstan are major suppliers of natural uranium.