Cladding tube of a zirconium alloy especially for a nuclear reactor fuel rod and method for fabricating the cladding tube

Claim 2

A nuclear reactor fuel rod having a cladding tube formed solely of a zirconium alloy, characterized by the feature that the geometric mean of the grain diameters in the zirconium alloy is smaller than or equal to 3 μm to minimize deep cracks in the cladding tube caused by chemically active nuclear fission products liberated from nuclear fuel in the cladding tube.

Claim 3

A nuclear reactor fuel rod having a cladding tube formed solely of a zirconium alloy according to claim 1, wherein the geometric mean of the grain diameters is in the range of 2 to 2.5 μm.

Claim 4

Method of manufacturing a finished cladding tube formed solely of a zirconium from a starting tube of a zirconium alloy in which the geometric mean of the grain diameters in the zirconium alloy is greater than 3 μm, for a nuclear reactor fuel rod, in which finished cladding tube the geometric mean of the grain diameters in the zirconium alloy is smaller than or equal to 3 μm, which comprises, pilger-rolling a starting tube consisting essentially of a zirconium alloy in a plurality of pilger-rolling steps sufficient to obtain a cross section change of the tube wall of 90% or more and to reduce the geometric mean of the grain diameters in the zirconium alloy to smaller than or equal to 3 μm and produce a finished cladding tube without recrystallization anneal and free of cracks.

Claim 5

Method of manufacturing a finished cladding tube formed solely of a zirconium from a starting tube of a zirconium alloy in which the geometric mean of the grain diameters in the zirconium alloy is greater than 3 μm, for a nuclear reactor fuel rod, in which finished cladding tube the geometric mean of the grain diameters in the zirconium alloy is smaller than or equal to 3 μm, which comprises, pilger-rolling a starting tube consisting essentially of a zirconium alloy in a plurality of pilger-rolling steps sufficient to obtain a cross section change of the tube wall of 90% or more and to reduce the geometric mean of the grain diameters in the zirconium alloy to smaller than or equal to 3 μm and produce a finished cladding tube without recrystallization anneal and free of cracks.

Claim 6

Method according to claim 3, wherein the cross section change of the tube wall in the range of 90 to 98% is obtained.

Claim 7

Method according to claim 3, wherein the starting tube is stress-annealed between two pilger steps.

Claim 8

Method according to claim 5, wherein the annealing temperature for stress annealing is in the range of 400° to 500° C. and is maintained for 1 to 5 hours.