Grid for a nuclear fuel assembly, and a strap for such a grid

Abstract

At regular intervals, the grid strap has formed therein notches for assembly with transverse straps. Between at least some pairs of notches, it has a rod-holding spring comprising two resilient strips cut out from the plane wall of the strap and integral therewith. Each strip extends transversely relative to its strap and is connected to the common portion of the strap at its two ends. In the free state, the strips project towards the inside of the cell concerned and they are interconnected in the middle by a transverse bridge which projects relative to the two strips.

1 / A grid strap for holding fuel rods, in which there are formed notches at regular intervals for assembly with transverse straps, and between at least some pairs of notches, rod-holding springs ( 22 ,  30 ), each comprising two resilient strips ( 24 ) cut out from the plane wall of the strap and integral therewith, each of which extends mainly in the flow direction and is connected to the common portion of the strap via its two ends, the strips projecting, when in the free state, towards the inside of the cell concerned and being interconnected in their middle by a transverse bridge ( 26 ) projecting relative to both strips, the two resilient strips ( 24 ) of at least some of the springs ( 22 ) touching each other in the vicinity of their roots and being spaced apart from each other in their central portions which are interconnected by the bridge ( 26 ).  
     
     
         2 / A grid strap for holding fuel rods, in which there are formed notches at regular intervals for assembly with transverse straps, and between at least some pairs of notches, rod-holding springs ( 22 ,  30 ), each comprising two resilient strips ( 24 ) cut out from the plane wall of the strap and integral therewith, each of which extends mainly in the flow direction and is connected to the common portion of the strap via its two ends, the strips projecting, when in the free state, towards the inside of the cell concerned and being interconnected in their middle by a transverse bridge ( 26 ) projecting relative to both strips, the shape of the strips and of the bridge of each spring ( 22 ,  30 ) being such that the strips are pushed back elastically into the same plane as the common portion of the strap provided with the spring by the presence of a rod.  
     
     
         3 / A strap according to  claim 1  or  2 , characterized in that the springs are of different structures depending on whether the wall in which the spring is formed lies between two cells that are both designed to be occupied by respective rods, or between two cells, one of which is designed to be occupied by a guide tube ( 20 ).  
     
     
         4 / A strap according to  claim 1 ,  2 , or  3 , characterized in that the two strips of some only of the springs ( 30 ) are substantially parallel to each other and to the flow direction.  
     
     
         5 / A strap according to  claim 2 , characterized in that the springs ( 30 ) having parallel strips are backed by a cell which has a guide tube ( 20 ) passing therethrough.  
     
     
         6 / A strap according to  claim 4  or  5 , characterized in that each of the springs. ( 30 ) having parallel strips lies, in the direction extending transversely relative to the strap, between weld zones that are substantially plane or slightly curved.  
     
     
         7 / A grid according to any one of  claims 1  to  4 , characterized in that each spring designed to be backed by a cell containing a fuel rod lies, in the direction extending transversely to the long dimension of the strap, between two bosses ( 28 ) projecting in a direction opposite to that of the spring ( 22 ).  
     
     
         8 / A strap according to  claim 7 , characterized in that the bridge ( 26 ) of a spring ( 22 ) and the bosses ( 28 ) on either side thereof and constituting abutment means, are of the same shape.  
     
     
         9 / A grid for holding fuel rods for a nuclear fuel assembly, the grid being constituted by two crossed sets of straps ( 12 ,  14 ) according to any preceding claim, and being characterized in that the upstream portion of each end of each strap includes cutouts or reinforcements of curved shape serving as bearing points for an inwardly curved belt ( 38 ), at least on the upstream side of the grid.  
     
     
         10 / A grid according to  claim 9 , characterized in that the cutouts or reinforcements of curved shape include a stud ( 44 ) engaged in a hole in the curved portion of the belt.  
     
     
         11 / A grid according to  claim 9  or  10 , characterized in that the belt carries reinforced springs, integral therewith.  
     
     
         12 / A grid according to  claim 11 , characterized in that each spring of the belt is cut out from a zone of the belt which is inwardly deformed to constitute a swelling, protecting the springs against direct external stresses and against excessive outwards displacement of the rod.