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Cladding is the outer layer of the fuel rods, standing between the coolant and the nuclear fuel. It is made of a corrosion -resistant material with low absorption cross section for thermal neutrons , usually Zircaloy or steel in modern constructions, or magnesium with small amount of aluminium and other metals for the now-obsolete Magnox reactors .
Control rod assembly for a pressurized water reactor, above fuel element Control rods are used in nuclear reactors to control the rate of fission of the nuclear fuel – uranium or plutonium . Their compositions include chemical elements such as boron , cadmium , silver , hafnium , or indium , that are capable of absorbing many neutrons without ...
The nuclear reactor core is the portion of a nuclear reactor where the nuclear reactions take place. It mainly consists of nuclear fuel and control elements. The pencil-thin nuclear fuel rods, each about 12 feet (3.7 m) long, are grouped by the hundreds in bundles called fuel assemblies.
Inside the core of a typical pressurized water reactor or boiling water reactor are fuel rods with a diameter of a large gel-type ink pen, each about 4 m long, which are grouped by the hundreds in bundles called "fuel assemblies". Inside each fuel rod, pellets of uranium, or more commonly uranium oxide, are stacked end to end.
The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end , which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in the back end , which are necessary to safely ...
Caesium-134 is found in spent nuclear fuel but is not produced by nuclear weapon explosions, as it is only formed by neutron capture on stable Cs-133, which is only produced by beta decay of Xe-133 with a half-life of 3 days. Cs-134 has a half-life of 2 years and may be a major source of gamma radiation in the first 20 years after discharge.
The fuel rods are 3.64 m long, with 3.4 m of that being the active length. The maximum allowed temperature of a fuel rod is 600 °C. [19] The fuel assemblies consist of two sets ("sub-assemblies") with 18 fuel rods and 1 carrier rod. The fuel rods are arranged along the central carrier rod, which has an outer diameter of 1.3 cm.
The fuel element or assembly is arranged in an array of cells or bundles. Each bundle consists of multiple fuel rods or pins. Each fuel rod is composed of several cylindrical fuel pellets of enriched uranium, typically as UO 2 inserted into zirconium-alloy tubes. Each reactor core can be loaded with multiple bundles of these reactor bundles.