Control rod assemblies
Model of a fuel assembly of pressurized water reactor showing at the top the head of the control cluster and in the middle the guide tubes of control rods along the fuel rods that were cut for visibility. The absorber rods are suspended to a structural part called the "spider", which allows to simultaneously control the movement of the 24 pencils with a single command rod passing through the lid of the reactor vessel. The vertical displacement of the command rod is achieved thanks to mechanisms located above the lid.