Foreign matter filter for fuel assembly in pressurized water reactor

Abstract

A foreign matter filter provided between a DFBN and a lower grid has two adjacent thin straps assembled into a lattice. The straps are equipped on the front and back sides with axially continuous protrusions.

1 . A foreign matter filter provided between a lower nozzle DFBN and a lower grid in a nuclear reactor, 
 wherein two adjacent thin straps are assembled into a lattice-like form.    
   
   
       2 . A foreign matter filter according to  claim 1 , wherein axially continuous protrusions are provided on inner straps in the vicinity of intersections of said straps.  
   
   
       3 . A foreign matter filter according to  claim 2 , wherein a slot for protrusion formation is provided in the height (axial) direction on the inner strap intersection side, and wherein the forward end portions of the protrusions are formed by inner straps provided with separated cantilever-like protrusions that are axially continuous.  
   
   
       4 . A foreign matter filter according to  claim 3 , wherein the forward ends of the protrusions are connected by welding in order to restrain vibration of the cantilever-like protrusions.  
   
   
       5 . A foreign matter filter according to  claim 2 , wherein the forward end portions of the protrusions of the inner straps are fitted into cutouts or the like in the outer surfaces of inserts to mechanically retain the foreign matter filter at a desired axial position.  
   
   
       6 . A foreign matter filter according to  claim 1 , wherein, in order that foreign matter may easily enter portions other than the periphery of fuel rods, the space regions of the strap intersections are set to be large, and wherein vane type protrusions are provided so that still smaller foreign matter can be trapped.  
   
   
       7 . A foreign matter filter according to  claim 1 , wherein the space regions of the strap intersections are set to be large so that foreign matter may easily enter portions other than the periphery of the fuel rods, and wherein the foreign matter filter is provided directly below the lower grid, with each of the large space regions being divided into two by the straps of the lower grid so that even small foreign matter can also be trapped.  
   
   
       8 . A foreign matter filter according to  claim 1 , wherein the foreign matter filter is provided between the lower nozzle DFBN and the lower grid, and wherein protrusions continuous in the axial direction of the straps of each lattice row are provided on the front and back sides.  
   
   
       9 . A foreign matter filter according to  claim 1 , wherein, between the lower nozzle DFBN and the lower grid, protrusions are provided alternately on the front and backsides in the axial direction of the straps of each lattice row, and wherein the protrusions have a rounded and a 45° straight dimple configurations.  
   
   
       10 . A foreign matter filter according to  claim 1 , further comprising outer straps, which are provided with protrusions that are flat or continuous in the axial direction of the straps.  
   
   
       11 . A foreign matter filter according to  claim 1 , further comprising outer straps, which are provided with protrusions continuously extending axially from an upper region toward a lower region.  
   
   
       12 . (canceled)  
   
   
       13 . A foreign matter filter, wherein several cells in a nuclear reactor are in a spring-like form, and wherein grooves are formed in fuel rod lower end taps where engagement is effected for fixation.