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Traditional energy systems utilize two fundamentally different types of fuel: fossil (organic) fuels and nuclear fuels.
Fossil (organic) fuels
Fossil fuels are classified by their physical (aggregate) state into three main categories: gaseous, liquid, and solid. Each of these categories is further subdivided into natural and artificial fuels.
Gaseous
Natural gaseous fuel:
Natural gas
Artificial gaseous fuels:
Generator gas
Coke oven gas
Blast furnace gas
Petroleum-derived gases
Gas from underground coal gasification
Biogas
Synthesis gas (syngas)
Liquid fuels
Natural liquid fuell:
Crude oil
Artificial liquid fuels (petroleum-derived products):
Petrol
Kerosene
Solar oil (light diesel oil)
Fuel oil (mazut)
Solid Fuels
Natural solid fuel:
Peat
Brown coal
Hard coal (bituminous coal)
Anthracite
Oil shale
Vegetable-based fuels:
Firewood
Wood residues
Fuel briquettes
Fuel pellets
Artificial solid fuels
Charcoal
Coke and semi-coke
Coal briquettes
Coal processing waste (coal enrichment by-products)
Nuclear fuel
Nuclear fuel is produced from natural uranium. Before it can be used in nuclear power plants, uranium must be enriched. After extraction, the uranium is sent to an enrichment plant where about 90% of the by-product – known as depleted uranium, is sent for storage. The remaining 10% is enriched to a concentration of a few percent (typically 3–5% for power reactors).
The enriched uranium dioxide is then sent to a specialized plant where it is processed into cylindrical pellets. These pellets are placed into hermetically sealed zirconium tubes nearly 4 meters length, forming fuel elements (TFE). For operational efficiency, several hundred fuel elements are grouped together into fuel assemblies (FA).