[en] In a channel box made of zirconium base-alloy in a fuel assembly, β processed layer having a thickness of several microns or a clad layer having a thickness of several tens microns is formed on the surface of portions opposing to stainless steel, such as a contact portion with an upper lattice plate, a corner adjacent with an instrumentation tube and a contact portion with a control rod handle. That is, the surfaces of predetermined regions are heated by electron beams or lasers at the final stage of the products to form a β - processed layer. Alternatively, powders of nickel or chromium are coated on the surface of predetermined regions and heated by electron beams or lasers at the final stage of the products to form a corrosion resistant clad layer. With such procedures, local corrosion especially at the vicinity of portions opposing to stainless steel, such as contact portion with the upper lattice plate can be prevented effectively. Accordingly, integrity of the channel box against high burnup degree can be improved. (I.N.)