The rods that hold pellets of uranium are called fuel rods. They are a critical component of nuclear reactors, responsible for containing the nuclear fuel and facilitating the nuclear fission process.

Here's a breakdown of the structure and function:

* Fuel Pellets: These are small, cylindrical pellets made of uranium dioxide (UO2), which serves as the nuclear fuel.

* Fuel Rod Cladding: The pellets are encased in a sealed tube called the cladding. This cladding is typically made of a zirconium alloy, chosen for its resistance to corrosion and high melting point.

* Assembly: Multiple fuel rods are bundled together to form a fuel assembly. These assemblies are then inserted into the reactor core.

Key functions of fuel rods:

* Contain the fuel: The cladding prevents the release of radioactive materials into the reactor coolant.

* Allow heat transfer: The cladding conducts heat from the fuel pellets to the reactor coolant, enabling energy extraction.

* Maintain fuel integrity: The cladding helps to maintain the structural integrity of the fuel pellets under high temperatures and pressures.

It's important to note that fuel rods are designed to withstand extreme conditions within the reactor core. They are carefully engineered to ensure safety and prevent the release of radioactive materials.