[en] A PWR fuel rod is a mechanical structure composed of a thin tube and welded end plugs. A plenum coil spring and stacked UO₂ pellets are inside it. It suffers from a high inside temperature caused by the heat of the pellets and an external high pressure of the reactor system. The important functions of a fuel cladding tube are to maintain mechanical strength and to provide a primary barrier of the radioactive materials through their lives in a reactor. It should also satisfy the neutron economy so that a material is confined to be zirconium based alloys nowadays. The thickness reduction due to fretting wear is considerably concerned recently to achieve a failure-free fuel. These requirements affect the determination of a cladding tube thickness. Nevertheless, it is thought that studies on a cladding thickness have rarely been done. It may be attributed to the fact that the dimensions of a fuel rod are conventionally predetermined in general from the previous experiences in the nuclear industry. The fuel designers have usually focused on the enhancement of fuel performance and duty with maintaining the dimensions. In short, it may be unnecessary to deeply consider the dimension change of a fuel cladding. However, the necessity should arise if a completely new concept fuel rod is attempted. A recently studied dual-cooled fuel could be a good example. A bigger diameter should be used in that fuel since it should provide an internal flow passage in addition to a conventional outer passage. If the diameter increases, the thickness may well increase correspondingly from a simple mechanical viewpoint