Nuclear reactors utilize various materials based on their type and design. Liquid metal fast reactors, such as FFTF and EBR-II, typically employ stainless steel cladding around MOX fuel pellets and use liquid sodium as coolant. Light water reactors (LWRs), which dominate commercial power generation, include boiling water reactors (BWRs) and pressurized water reactors (PWRs), with fuel cladding primarily made of Zircaloy-2 for BWRs and Zircaloy-4 or newer alloys like ZIRLO for PWRs. Gas-cooled reactors, such as the AGR, use stainless steel cladding and graphite moderators, while pebble bed reactors may utilize graphite or carbide cladding. Understanding these materials is crucial for reactor efficiency and safety.