Method of manufacturing tubes of zirconium alloys with improved corrosion resistance for thermal nuclear reactors

Claim 1

A method of making cladding tubes of a zirconium alloy containing 1-5 percent by weight of alloying elements including Sn, Fe, Cr and Ni and the rest essentially Zr, for the purpose of improving the corrosion resistance to general corrosion in media typical of water cooled thermal nuclear reactors at high pressure and high temperature, comprising annealing the material after extrusion and between cold rollings in the α-phase range at a temperature within the interval 625°-790° C., at a combination of temperature and time which essentially gives complete equilibrium between zirconium matrix and precipitated secondary phase particles at which the temperature/time is defined by an annealing parameter ##EQU1## where t is the annealing time is hours, T is the absolute temperature, R is the general gas constant in cal mold · degree, which at equilibrium shall exceed a critical value A c =2.3·10 -14 , where said critical value means the following examples of shortest annealing times within the temperature interval 625°-790° C., ______________________________________ Annealing temperature (°C.) Annealing time (h) ______________________________________ 790 0.5 725 3.9 675 22.2 650 56.5 625 151.3 ______________________________________ cooling the tubes at a maximum rate of 3° C./minute and thereby obtaining a maximum volume fraction of the secondary phase particles.

Claim 2

A method of making cladding tubes of a zirconium alloy containing 1-5 percent by weight of alloying elements including Sn, Fe, Cr and Ni and the rest essentially Zr, for the purpose of improving the corrosion resistance to general corrosion in media typical of water cooled thermal nuclear reactors at high pressure and high temperature, comprising annealing the material after extrusion and between cold rollings in the α-phase range at a temperature within the interval 625°-790° C., at a combination of temperature and time which essentially gives complete equilibrium between zirconium matrix and precipitated secondary phase particles at which the temperature/time is defined by an annealing parameter ##EQU1## where t is the annealing time is hours, T is the absolute temperature, R is the general gas constant in cal mold · degree, which at equilibrium shall exceed a critical value A c =2.3·10 -14 , where said critical value means the following examples of shortest annealing times within the temperature interval 625°-790° C., ______________________________________ Annealing temperature (°C.) Annealing time (h) ______________________________________ 790 0.5 725 3.9 675 22.2 650 56.5 625 151.3 ______________________________________ cooling the tubes at a maximum rate of 3° C./minute and thereby obtaining a maximum volume fraction of the secondary phase particles.