Wrapper duct

Protmsion in wrapper tube Rounded comer of wrapper duct tube 680.2 30.2... 

BEHAVIOUR OF MATERIALS FOR FUEL PIN CLADDING AND SUBASSEMBLY DUCT (WRAPPER)... 

Figure 5.2 shows a typical core fuel element (also called a fuel pin) and fuel assembly (also called a fuel subassembly). The core fuel element contains the core fuel, upper and lower axial blanket fuels, and a space called the fission gas plenum within a cladding tube. Then they are assembled as a fuel element bundle. The fuel assembly contains the fuel element bundle in a hexagonal assembly duct called a wrapper tube. 

Fuel rods (typically 100—300 in number) are arranged as a bundle to form the fuel assembly (FA), with a hexagonal or square cross section, which can either be open or have a flow duct (wrapper) of lateral containment of the bundle. 

Table 9.1 shows a list of FM steels which have been used as materials for fuel subassemblies in several fast reactors, some of which are still in operation. Due to their limitations in terms of high-temperature thermal creep strength as compared, for instance, to austenitic steels, the main application of FM steels was for wrappers or ducts, whose maximum operating temperature in Na-cooled fast reactors does not exceed about 550°C. However, in some cases, 12% Cr FM steels such as HT9, EP-450 and FV448, or 9% Cr EM12 steel have also been used for cladding. 

Paper/foil and paper/film laminations are used for many appHcations including candy wrappers, microwave packaging, ice cream carton lids, and reflective building insulation. Flexible laminations are multilayered composites, with each each component providing special properties. Examples include snack food bags, aseptic containers sterilized by radiation or heat, meat packages, solar screen laminations, and flexible air ducts. 

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