Patent Number: 053274709
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 10, a typical fuel bundle is illustrated. An upper tie plate 16, lower tie plate and inlet orifice 14 with a plurality of fuel rods F extending therebetween is shown. Only one spacer S is shown between the tie plates. The reader will realize that the vast length of the fuel bundle is not shown; typically fuel bundles are in the order of 160 inches long with a 5.25 inch by 5.25 inch cross section and containing between 5 and 9 spacers, with 7 spacers distributed at equal vertical intervals along the length of the fuel bundle being the usual arrangement. Referring to FIG. 1, a subchannel tube T is shown in its initial dimension in top plan. In FIGS. 2A and 2B, subchannel tube T is shown with rifling R. Rifling here consists of a pitch providing 90.degree. of rotation with four internal threads 14, 16, 18, and 20. The reader will realize that other pitches and numbers of threads can be used. Referring to FIGS. 3A and 3B, the subchannel tube of FIGS. 2A and 2B is configured with stops S1 and S2. These stops S1 and S2 are members against which tubes may be biased to provide spacer alignment of each of the fuel rods F passing through the spacer S. Additionally top and bottom grid notches 32, 34, 36, and 38 are made in anticipation of the receipt of grid members. Referring to FIG. 4, the top of subchannel tube T is illustrated only, it being understood that the serial steps previously outlined have occurred. Members H and V with respective confronting notches 44, 45 are made to form a grid with the formed grid G being placed into the top interior of each tube T at respective notches 32-38. Fastening--as by spot welding or braising--then occurs. A first grid is formed at the top of the spacer; a second grid is similarly formed at the bottom of the spacer. Referring to FIGS. 5A and 5B, the remainder of the process can be understood. Intersecting grid sections of members H and V are drilled out of the respective subchannel tubes T at top and bottom. In the embodiment here illustrated, a drill is used that has the size of the inside diameter of subchannel tubes T and only drills out the top or the bottom. This separate drilling of the top and separate drilling of the bottom has the result that members H and V are ground off flush with tube T. Alternately, drilling can occur with drills that have an outside diameter the same dimension as the inside diameter of the threads formed interior of the subchannel tubes T. In this case, a short protruding stub will be left from members H and V of the grid on the interior of the tube T. Referring to the section illustrated in side elevation at FIG. 5B, the side elevation of both the interior of the spacer as well as the exterior as surrounded by a band B can be understood. (Deflection tabs are not shown). The finished construction can be seen in FIG. 6 holding fuel rods F in place. Spacer S is shown at a corner section only having members H and V connected at the exterior of tubes T at the respective grooves 32-38. Loop springs 50 have been placed at selected members H and V; the placement and configurations of such springs with respect to stops S1 and S2 are well known and will not be further discussed herein. Further, it will be noted that at the periphery of the formed grid, some tubes T have been cut in half at the adjacent point to band B. FIGS. 7, 8, and 9 illustrate an alternate construction in which twisted strips of metal are inserted interior of subchannel tubes T. This construction is not preferred because such twisted strips of metal must independently attach to subchannel tubes T at both ends rather than be formed as an integral portion of tubes T. When an integral construction is utilized, the chances of small portions of an assembly separating as loose pieces interior of a reactor vessel is minimized. Referring to FIG. 7, a grid has been formed of members H and member G and joined to subchannel tubes T at grooves 32, 34, 36, and 38. As before, springs 50 have been added at selected intervals to bias fuel rods F (not shown) into stops S1 and S2. Referring to FIG. 8B, a group of metal strips 72, 74, 76, and 78 joined at the bottom grid by continuous grid member 70 have each been inserted interior of subchannel tube T. Thereafter, these members have been twisted. The particular twist here illustrated is 180.degree., it being realized that other twist angles could be used as well. Referring to FIG. 8A, top members H and top and bottom members V are placed and fastened. A grid structure having central swirling metal pieces 72-78 is formed where each of the metal pieces is fastened top and bottom to the respective subchannel tube T. Finally, and referring to FIGS. 9A and 9B, the center of such subchannel tubes T is drilled out. This leaves the respective constructions of FIGS. 9A and 9B. The reader will understand that the attachment of this spacer configuration to spacer band B and insertion of fuel rods F is well known and will not be further set forth herein.