In this second phase, the first step is the production of end plugs. For this purpose, zircaloy rods are received which, once inspected, are turned into the plugs used to close the fuel rods.
For the fuel rod fabrication process, tubes, to which the end plug has previously been welded, are used for loading the rods, i.e. inserting the pellets into the tubes.
Once loaded, the tubes are fitted with a spring, the second end plug and, after pressurisation with an inert gas, the second end plug is welded on and the fuel rod is complete. Once the rod is finished, it is subjected to a series of quality checks (ultrasonic testing, X-ray, He leakage, eddy current array probes and scanning) to verify that it meets all specification requirements.
The next step is the fabrication of a skeleton, made up of rods, nozzles and grids, which, after inspection, will serve as a frame for inserting the fuel rods.
Final assembly: Due to their different constitution, a difference is made between PWR and BWR fuel assemblies.
Generally speaking, this last operation of the process consists of inserting the fuel rods into the supporting skeleton, finally placing the nozzles and support structures.