Patent Number: 048760633
Section: claims

1. An improved fuel assembly including a lower tie-plate, an upper tie-plate, a square sectioned channel connecting said lower and upper tie-plate in fluid tight relation whereby fluid entering said lower tie-plate is discharged out said upper tie-plate, fuel rods each containing fissionable material therewithin, said fuel rods being held at said upper and lower tie-plates in a 9 by 9 array of rows and columns with all fuel rods having the same diameter; a plurality of spacers placed between said fuel rods for maintaining said fuel rods in spaced apart relation between said upper and lower tie-plates; said fuel rods in said 9 by 9 array having three said fuel rods removed from the middle row and two said fuel rods removed from each row on either side of said middle row to create a vacated interstitial volume defined by the absence of said removed fuel rods, the removal of said fuel rods at each row on either side displaced towards adjacent corners of said 9 by 9 array; a pair of water rods for placement in the vacated interstitial volume, said water rods each including vertically extending cylindrical wall portions extending across approximately 270.degree. of arc around a generally cylindrical form of said water rods and a truncating vertically extending cord wall being disposed in a flat planar vertically extending disposition between the two ends of said cylindrical wall portion of said water rods whereby said cord wall of said water rods imparts a generally "D" cross-section to said water rod, said water rods each being placed in back-to-back relation in said fuel bundle at said vacated spatial interval, said rods confronted at their respective flat cord walls whereby said vacated interstitial volume is filled with said water to provide improved water moderation of said nuclear reaction at said fuel bundle.  a pair of water rods for placement in the vacated interstitial volume created by the removal of said fuel rods, said water rods each including a vertically extending wall portion of said water rods extending to approximately 270.degree. of arc around a generally cylindrical exterior; and  a truncating vertically extending chord wall in a flat disposition closing said cylindrical wall portion of said said water rods whereby said cord wall of said water rod imparts a generally "D" cross-section to said water rods, said water rods being placed in back-to-back relationship in said fuel bundle at said vacated spatial interval with said two flat cord walls confronting one another whereby said vacated interstitial volume is filled with water rods to provide water moderation of a nuclear reaction in said bundle. 2. The invention of claim 1 and wherein said water rods are welded to transition pieces at the bottom, said transition pieces are welded to smaller diameter circular rods. Said rods have end plugs which fit in holes in the lower tie plates. 3. The invention of claim 2 and wherein said water rods are welded to transition pieces at the top, said transition pieces are welded to smaller diameter circular rods. Said rods have end plugs which fit in holes in the upper tie-plates. 4. The invention of claims 2 and 3 and wherein one of said water rods includes spacer tabs, said spacer tabs positioned for support of said spacers along the outside surface of said water rod. 5. In a fuel assembly including a lower tie-plate, an upper tie-plate, a square section channel connecting said lower and upper tie plates; fuel rods each containing fissionable material therewithin, said fuel rods being in a 9 by 9 array of rows and columns with all said fuel rods having the same diameter and, a plurality of spacers between said fuel rods for maintaining said fuel rods in spaced apart relation between said upper and lower tie-plates, the improvement to said fuel bundle including said fuel rods in said 9 by 9 array having three rods removed from the middle row and two rods removed from each row on either side of the middle row, the removal at either side row being displaced towards adjacent corners of said 9 by 9 array, said removed rods creating a vacated interstitial volume;