Production process for nuclear fuel element

In a process for producing a nuclear fuel element having a gap between a metal cladding tube and nuclear fuel pellets upon production of to smaller than 100μm, nuclear fuel pellets are contained in the metal cladding tube to assemble them into a nuclear fuel element, then the nuclear fuel element is kept in steams at a temperature of 300 to 500degC and at an atmospheric pressure of 1 to 110 (gage pressure), to form an oxide membrane on the outer surface of the metal cladding tube. At the same time, the outer diameter of the metal cladding tube is shrinked. Thus, a nuclear fuel element with a narrow gap can be obtained, thereby enabling to degrease the releasing amount of FP gases and PCI and also reduce the corrosion on the outer surface of the cladding tube. (T.M.)