This is a 3D model I made of the fuel rod bundle found inside nuclear reactors.

Size and shape varies depending on the reactor type and design, but each fuel bundle is an average of 12 feet tall, and a few hundred of them are placed side-by-side in a grid pattern inside the reactor, which makes up the core. The number of rods also varies between reactors.

Inside the silver metal tubes are hundreds of uranium oxide pellets stacked on top of each other, which make up the actual nuclear rods themselves, which generate tremendous heat and energy through nuclear fission. They are encased inside of a zirconium cladding.