Method, use and device concerning cladding tubes for nuclear fuel and a fuel assembly for a nuclear pressure water reactor

Abstract

A method of producing a cladding tube for nuclear fuel for a nuclear pressure water reactor includes forming a tube which at least principally consists of a cylindrical tube component of a zirconium-based alloy, where the alloying element, except for zirconium, which has the highest content in the alloy is niobium, wherein the niobium content in weight percent is between about 0.5 and about 2.4 and wherein no alloying element, except for zirconium and niobium, in the alloy, has a content which exceeds about 0.2 weight percent. The cladding tube is then annealed such that the tube component is partly but not completely recrystallized. The degree of recrystallization in the tube component is higher than about 40% and lower than about 95%. A fuel assembly for a nuclear pressure water reactor also has a plurality of such cladding tubes.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. patent application Ser. No. 10 / 533,467, filed on Apr. 29, 2005, the contents of which are incorporated herein by reference in their entirety. This application is also entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Application No. PCT / SE2003 / 001685 filed on Oct. 30, 2003 and Swedish Patent Application No. 0203198.7 filed on Oct. 30, 2002.FIELD OF THE INVENTION[0002]The present invention concerns cladding tubes for nuclear fuel for a nuclear pressure water reactor. More precisely, the invention concerns such cladding tubes which are formed of a Zr-based alloy which contains Nb. The invention concerns, inter alia, a method. According to the method, a tube is formed which at least principally consists of a cylindrical tube component of a Zr-based alloy, where the alloying element, except for Zr, which has the highest content in the alloy i...

AI Technical Summary

Benefits of technology

[0012]An object of the present invention is therefore to achieve a method of producing a cladding tube, of a Zr-based alloy which includes between 0.5 weight percent and 2.4 weight percent Nb and which has an improved resistance against damages than prior cladding tubes of this kind of alloys.

[0014]A cladding tube produced according to this method has appeared to have a good resistance against damages caused by PCI at the same time as the risk for the formation of radial hydrides is low. Thereby, the risk for cracks is reduced. The cladding tube has at the same time also a high ductility, a low creep rate and a low tendency to growth caused by neutron radiation. Further objects and advantages of the invention will become clear from the following.

[0015]Since the tube component is pRXA (and not completely recrystallized), it has become clear that hydrides which are formed tend to extend in mainly a tangential direction while the risk for radial hydrides is low. Thereby, an improved resistance against crack formation is obtained. The reason why radial hydrides are avoided is probably that certain tensions which originate from the production of the tube are maintained since the tube component is not completely recrystallized. These tensions have a consequence that the tendency for radial hydrides is reduced.

[0016]It can be noted that previously known cladding tubes of this kind of alloys have undergone a final anneal such that the cladding tube has become completely recrystallized (see for example the above mentioned U.S. Pat. No. 5,648,995). Such an RXA is advantageous in certain respects (for acting against creep and growth caused by neutron radiation and for achieving resistance against PCI damages). However, the inventors of the present invention have found that these advantages to a large extent can be obtained also if the cladding tube is only finally annealed for achieving pRXA. It has thus thereby become clear that an improved resistance against damages may be obtained through this final anneal.

[0030]According to an advantageous embodiment, the alloy contains between 50 ppm and 600 ppm Fe. By keeping the content of Fe low, the creep properties are further improved. The Fe-content may for example be lower than 250 ppm. It should be noted that these low Fe-contents are only preferred embodiments of the invention. According to another embodiment, also a higher Fe-content may be permitted. The alloy may also contain a certain amount of S, for example between 20 ppm 5 and 600 ppm S, or between 100 ppm 5 and 600 ppm S. Such an amount of S can improve the corrosion resistance of the alloy and the creep properties.

Problems solved by technology

It has however become clear that also for tubes of this kind there is a risk of damages.

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