[en] A cladding tube or a control rod itself is constituted with a composite such as of a carbon fibers. Tar or resin is impregnated into a cylindrical rod-like member made of carbon fibers, which are then carbonized, to form a cladding tube, and neutron absorbers such as of boron or hafnium are charged therein. Alternatively, tar or resin is impregnated in the cylindrical or columnar rod-like member made of mixed fibers of carbon and boron, which are carbonized. Such a composite is light in weight and tough, has excellent abrasion resistance, has no worry of causing cracks by irradiation, to extend the life of the control rod and reduce the life cycle cost. Further, the composite which contains boron requires no cladding tube, causes no public pollution. (N.H.)