What are Enrichment and Fuel Fabrication?

Dulcie Edis: You have selected alternative vehicles. I am going to assume this is an error and discuss enrichment and fuel fabrication in commercial nuclear power plant refueling assemblies. At present the USA has no facilities licensed to burn either thorium or plutonium. As such, enrichment only applies to uranium based reactors. Enrichment refers to the percentage, by weight, of the isotope U-235 in a given sample of uranium. Natural uranium is 0.720% U-235. Weapons grade uranium is 90% or more U-235 and there are a few research reactors licensed in the USA which use this material as fuel. This practice is frowned on and no more new such plants are being licensed due to the potential for theft and use as a weapon.Fuel consists of uranium dioxide UO2, uranium hydride UH3 or metallic uranium. Uranium carbide UC2 has been used in the past. Fuel assemblies are made from fuel sandwiched between plates of either Zircaloy-2 or Zircaloy-4. Canada uses Zircaloy-2.5. ! Other countries have different names for the alloy, but are essentially Zircaloy alloys. The number refers to the maximum combined percentage of tin, niobium, iron, chromium, nickel and other metals, which are added to improve mechanical properties and corrosion resistance. Sometimes thermal neutron poisons (B4C, Sm, or Dy) are added to control excess reactivity at the start of a fuel cycle. The assemblies are welded together using electron beam welding techniques.Zircalloy is used as the cladding in fuel assemblies due to its very low absorption cross-section of thermal neutrons, high hardness, ductility and corrosion resistance. At temperatures greater than 1000°C Zircaloy undergoes destructive decomposition in the presence of steam to yield zirconium oxide, zirconium hydride and hydrogen gas:Zr + 2 H2O â†' ZrO2 + 2 H2Zr + H2 â†' ZrH2This is the mechanism which caused fuel clad failure at Three Mile Island, the Limerick Plant and Fukushima 1 Nuclear Power Plant....Sh! ow more