Alloy and tube for nuclear fuel assembly and method for making same

Abstract

The invention concerns a method for making tubes designed for a nuclear fuel pencil case or guide tube which consists in forming a bar in a zirconium based alloy containing equally 0.3 to 0.25 wt. % of the total iron, of chromium or vanadium, 0.8 to 1.3 wt. % of niobium, less than 2000 ppm of tin, 500 to 2000 ppm of oxygen, less than 100 ppm of carbon, 5 to 30 ppm of sulphur and less than 50 ppm of silicon. The bar is soaked in water after being heated at a temperature between 1000° C. and 1200° C. A blank is spun after being heated at a temperature between 600° C. and 800° C. The blank is cold-rolled, in at least three of four passes, to obtain a tube with intermediate heat treatments between 560° C. and 620° C. and s final heat treatment is carried out between 560° C. and 620° C. in inert atmosphere or under vacuum.

1 . Zirconium based alloy also containing, by weight, 0.03 to 0.25% in total firstly of iron and secondly at least one of the elements from the group comprising chromium and vanadium, 0.8% to 1.3% by weight of niobium, less than 2000 ppm of tin, 500 to 2000 ppm of oxygen, less than 100 ppm of carbon, 5 to 35 ppm of sulfur and less than 50 ppm of silicon.  
     
     
         2 . Sheathing tube for a nuclear fuel rod or guide tube for a nuclear fuel assembly, made from a zirconium based alloy also containing, by weight, 0.03 to 0.25% in total firstly of iron and secondly at least one of the elements from the group comprising chromium and vanadium, 0.8% to 1.3% by weight of niobium, less than 2000 ppm of tin, 500 to 2000 ppm of oxygen, less than 100 ppm of carbon, 5 to 35 ppm of sulfur and less than 50 ppm of silicon, in the re-crystallized state, at least the greater part of the iron being in the form Zr(Nb,Fe,Cr) 2  or Zr(Nb,Fe,V) 2  and in which the intermetallic compounds are of a size not exceeding 200 nm.  
     
     
         3 . Tube as claimed in  claim 2 , characterized in that the oxygen content is between 1000 and 1600 ppm.  
     
     
         4 . Tube as claimed in  claim 2  or  3 , characterized in that the content of tin is less than 300 ppm.  
     
     
         5 . Tube as claimed in  claim 2  or  3 , characterized in that the content of tin is between 300 and 1500 ppm.  
     
     
         6 . Sheet of alloy as claimed in  claim 1 .  
     
     
         7 . Method of manufacturing tubes intended for making all or the external part of a sheathing tube for a nuclear fuel rod or a guide tube for a nuclear fuel assembly, characterized in that a bar is formed of a zirconium based alloy which also contains, firstly 0.03 to 0.25% in total firstly of iron, secondly, at least one of the elements from the group comprising chromium and vanadium, 0.8 to 1.3% of niobium, less than 2000 ppm of tin, 500 to 2000 ppm of oxygen, less than 100 ppm of carbon, 5 to 35 ppm of sulfur and less than 50 ppm of silicon, 
 quenching the bar in water after heating to between 1000° and 1200° C.,    extruding a blank after heating to a temperature of between 600° C. and 800° C.,    cold-rolling said blank in at least four passes to obtain a tube, with intermediate heat treatments between 560° C. and 620° C., and    applying a final heat treatment at between 560° C. and 620° C., all the heat treatments being applied in an inert atmosphere or under vacuum.    
     
     
         8 . Method as claimed in  claim 7 , characterized in that the alloy contains at most 0.20% of iron.  
     
     
         9 . Method as claimed in  claim 7 , characterized in that the Fe/(Cr+V) ratio is between 0.5 and 30 by weight.  
     
     
         10 . Method as claimed in  claim 7 , characterized in that the Fe/(Cr+V) ratio is at least 0.5 and the content of Fe+Cr+V is at least 0.03%.  
     
     
         11 . Method as claimed in any one of  claims 7  to  10 , characterized in that the oxygen content is between 1000 and 1600 ppm.