Cladding tube for nuclear fuel rod, method and apparatus for manufacturing a cladding tube

Abstract

A cladding tube for nuclear fuel made from metal and including concave dimples on its external surface. A nuclear fuel assembly includes at least a plurality of nuclear fuel rods provided with such cladding tubes. The cladding tube is advantageously manufactured by pilgrim rolling, the dimples being formed during the pilgrim rolling.

1 - 20 . (canceled) 
     
     
         21 . A cladding tube for a nuclear fuel rod, the cladding tube being made from a metal, the cladding tube comprising dimples on an external surface. 
     
     
         22 . The cladding tube according to  claim 21  wherein the cladding tube comprises an internal surface, the internal surface being smooth. 
     
     
         23 . The cladding tube according to  claim 21  wherein the cladding tube has an external diameter between 6 and 20 mm. 
     
     
         24 . The cladding tube according to  claim 21  wherein the cladding tube has a wall thickness between 0.4 and 1.5 mm. 
     
     
         25 . The cladding tube according to  claim 24  wherein each dimple has a depth between 10% and 60% of the wall thickness of the cladding tube. 
     
     
         26 . The cladding tube according to  claim 21  wherein each dimple has a contour in a shape of an ellipse or a circle. 
     
     
         27 . The cladding tube according to  claim 26  wherein the contour of each dimple has a maximum dimension greater than 0.8 mm. 
     
     
         28 . The cladding tube according to  claim 21  wherein the cladding tube is made from a zirconium-based alloy. 
     
     
         29 . The cladding tube according to  claim 21  wherein the dimples are obtained by punching. 
     
     
         30 . A nuclear fuel assembly comprising: a bundle of nuclear fuel rods, each of the fuel rods comprising a cladding tube filled with a stack of nuclear fuel pellets, wherein the cladding tube of at least one of the fuel rods is the cladding tube according to  claim 21 . 
     
     
         31 . A method of manufacture by pilgrim rolling of a metal cladding tube from a tubular blank, the method comprising the following steps: progressively deforming a blank by rolling between a mandrel inserted inside the blank and two dies disposed about the mandrel;
 reciprocally moving the two dies along the mandrel; and advancing the blank along the mandrel between reciprocating movements of the dies, wherein dimples are formed on an external surface of the blank during the rolling of the blank.   
     
     
         32 . The method according to  claim 31  wherein the dimples are formed with the aid of at least one punch disposed on one of the dies. 
     
     
         33 . The method according to  claim 32  wherein the diameter of the blank is reduced during the pilgrim rolling. 
     
     
         34 . The method according to  claim 31  wherein the dimples are formed at a front end of the mandrel with respect to a direction of advancing the blank along the mandrel during the pilgrim rolling. 
     
     
         35 . The method according to  claim 31  wherein the blank is turned about an axis of the mandrel between reciprocating movements of the dies. 
     
     
         36 . The method according to  claim 31  wherein the metal cladding tube has a smooth internal surface. 
     
     
         37 . A pilgrim rolling apparatus for the manufacture of a metal tube from a tubular blank, the pilgrim rolling apparatus comprising: at least two dies; and a mandrel received between the dies mounted to carry out reciprocating movements along the mandrel for rolling a blank fitted onto the mandrel between the mandrel and the dies, wherein at least one of the dies has at least one punch to form dimples on an external surface of the blank fitted on the mandrel during the reciprocating movements of the dies. 
     
     
         38 . The apparatus according to  claim 37  wherein each die comprises a peripheral groove, the grooves of the dies forming a passage for the mandrel between the dies, each punch being disposed at a base of the groove of the corresponding die. 
     
     
         39 . The apparatus according to  claim 38  wherein the mandrel is of convergent shape along an axis of the mandrel, the or each punch being disposed in a calibration region of the groove of the corresponding die defining the passage for the mandrel when the dies are advanced and surround an end of the mandrel with a smaller diameter. 
     
     
         40 . The apparatus according to  claim 37  wherein each die comprises at least one punch.