| 摘要 |
welded at interstitially placed tube members (C) between the fuel rods to form the continuous spacer grid. The improvement constitutes forming separate upper and lower reduced section grids from separate, normally aligned, first (62) and second (63) parallel sets of grid members. One grid (62, 63) is formed for the top of the spacer; the remaining grid is formed for the bottom of the spacer (not shown). Tube members (C) placed interstitially between the fuel rods are used to interconnect the grids. The tube members (C) themselves are in turn notched; the notches (60, 61) are at the upper portion of the tube members to receive the upper grid (62, 63) and at the lower portion of the tube members to receive the lower grid (not shown). Grids are placed within the notched tube members (C) and fastened, typically by welding to the top and bottom of the tubes to form a unitary spacer structure. Thereafter, the excess material of the grid (62, 63) crossing the interior of the tube members (C) is drilled out of the tube members to eliminate excess neutron absorbing material. There results in the disclosed spacer, two interconnected grid members extending at the top and bottom of the spacer having less material than the single and continuous grid of the prior art. At the same time, the assembly of what is otherwise a difficult member to construct is simplified. Provision is made for applying the improved spacer to spacers having differing pitch between the separated fuel rods. Additionally the incorporation of so-called swirl vanes in some grid (not shown) locations is disclosed in substitution for the tube members. <IMAGE>
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