Patent Number: 
Section: description

FIG. 1 is a schematic, partial cross section, illustration of a boiling water reactor 100 including a reactor pressure vessel (RPV) 102. RPV 102 has a generally cylindrical shape and is closed at one end by a bottom head 106 and at its other end by removable top head (not shown). A top guide 108 is spaced above a core plate 110 within RPV 102. A shroud 112 surrounds core plate 110 and is supported by a shroud support structure 114. An annulus 116 is formed between shroud 112 and the wall of RPV 102. A baffle plate 118, which has a ring shape, extends around RPV 102 between shroud support structure 114 and the wall of RPV 102. RPV 102, of course, is filled with water. RPV 102 is shown in FIG. 1 as being shut down with many components removed. For example, and in operation, many fuel bundles and control rods (not shown) are located in the area between top guide 108 and core plate 110. In addition, and in operation, steam separators and dryers and many other components (not shown) are located in the area above top guide 108. Top guide 108 is a latticed structure including several top guide beams 126 defining top guide openings 128. Core plate 110 includes several recessed surfaces 130 which are substantially aligned with top guide openings 128 to facilitate positioning the fuel bundles between top guide 108 and core plate 110. Fuel bundles are inserted into the area between top guide 108 and core plate 110 by utilizing top guide openings 128 and recessed surfaces 130. Particularly, each fuel bundle is inserted through a top guide opening 128, and is supported horizontally by core plate 110 and top guide beams 126. The fuel is supported vertically at the core plate by structure not shown. FIG. 2 is a perspective view of a forged upper shroud section 200, with a portion cut away, in accordance with one embodiment of the present invention. Upper shroud section 200 may be machined from a single piece rectangular cross-section ring forging and includes a circular flange 202 and a cylindrical shell 204. Openings and slots 206 are machined into flange 202 to align and support the shroud head. A groove 208 is machined along an inside surface 210 of cylinder section 200, and groove 208 may be used to support top guide grid (not shown). An end 212 of cylinder section 200 is machined with a weld prep for attachment to the core section of the shroud 213. FIG. 3 is a view of forged upper shroud section 200 through line Axe2x80x94A shown in FIG. 2. The thickness of section 200 is governed by the nominal inside diameter of the shroud and the outside diameter of flange 202. The height of section 200 is limited by the size of available ring forgings. The height is also governed by the need to locate the attachment weld of upper shroud section 200 in an area with acceptable fluence levels. The thickness of flange 202 is selected to provide adequate strength to carry the loads from the shroud head. Flange 202 is also stiffened by the use of an integral gusset 214 which spans between flange 202 and cylinder shell or section 204. The thickness of shroud cylinder section 204 is selected to carry the loads from the shroud head and the radial loads from the top guide grid. The above described upper shroud section is fabricated from a single piece forging and therefore, fewer welds are required with such upper shroud section as compared to known upper shroud section. In addition, the present upper shroud section provides the same flow barrier as the welded upper sections, provides a flange to which the shroud head may be bolted and supported, provides a groove to which the top guide grid may be attached without the need for a ledge or flange, and the number to total shroud welds is reduced because of the single piece design. Reducing the number of welds minimizes cracking which can occur in shroud welds and also reduces the number of welds which must be inspected during the construction and life of the shroud. From the preceding description of various embodiments of the present invention, it is evident that the objects of the invention are attained. Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims.