In boiling water reactors (BWR), the fuel is similar to PWR fuel except that the bundles are 'canned'; that is, there is a thin tube surrounding each bundle. This is primarily done to prevent local density variations from affecting neutronics and thermal hydraulics of the reactor core. In modern BWR fuel bundles, there are either 91, 92, or 96 fuel rods per assembly depending on the manufacturer. A range between 368 assemblies for the smallest and 800 assemblies for the largest U.S. BWR forms the reactor core. Each BWR fuel rod is back filled with helium to a pressure of about three atmospheres (300 kPa).
This model is a BWR type fuel rod with 96 fuel pellets, and was carefully modeled in-scale based on mechanical drawings of this specific fuel rod assembly.