Abstract: A fuel assembly, a fuel rod and a cladding tube for a fuel rod for a nuclear reactor are disclosed. The cladding tube includes a tubular substrate defining an inner space for housing nuclear fuel pellets, and a surface layer applied on the tubular substrate. The tubular substrate is made of a zirconium base alloy and has a first thermal expansion coefficient. The surface layer has an alloy which consists of a major part of main elements comprising Cr and at least one of Nb and Fe, a minor part of zirconium, and possibly a residual part of interstitial elements. The alloy of the surface layer has a second thermal expansion coefficient. The concentrations of the main elements are selected so that the second thermal expansion coefficient is greater than the first thermal expansion coefficient from 20 to at least 1300° C.