Patent Number: 054886430
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective partially cut-away view of a boiling water reactor of the type to which the present invention is applicable. This BWR (boiling water reactor) includes, merely by way of example, a head 40 which is secured to the top of the reactor vessel 41, a vent and head spray 42, a steam dryer lifting lug 43, a steam drier assembly 44, a steam outlet 45, a steam separator assembly 46, a feedwater inlet 47, a core spray inlet 48, a feedwater sparger 49, a low pressure coolant injection inlet 50, a core spray line 51, a core sprayer sparger 52, a top guide 53, jet pump assemblies 54, a core shroud 55, fuel assemblies 56, a jet pump/recirculation water inlet 57, a core plate 58, control rods 59 (enclosed in elongate tubular guide thimbles), a recirculation water outlet 60, a vessel support skirt 61, a shield wall 62, control rod drive mechanisms 63, control rod drive hydraulic lines 64, and an in-core flux monitor 65. FIG. 2 is plan view of the above type of reactor showing the manner in which the shroud 55 is arranged with respect to the inner periphery of the reactor pressure vessel wall 66 and the disposition of elements such as the separator lift rods 68, the core spay pipes 70, a separator guide bracket 70 and the like. This view also shows the tops of upper hanger rods 100 which form a vital part of the present invention and which will be discussed later in connection with FIGS. 4 to 7. FIG. 3 is a plan view showing a shroud support ring 200 disposed about the upper periphery of the shroud 55. As will be appreciated from this figure, the shroud support ring 200 comprises an assembly of four, three-sided members 200A which are interconnected to form a twelve sided polygonal ring member. In this instance the four segments or members 200A of the assembly are bolted together at four ring clamp sites or joints 200B which allow the shroud support ring 200 to be tightened against the outer peripheral surface of the shroud 55 at a location below the top guide ring 56. In order to improve the rigidity and strength of the joint 200B, a gusset or reinforcing plate arrangement 200BG is disposed in the illustrated manner. Note that these reinforcing plate arrangements 200BG are not shown in the plan view of FIG. 3 for the sake of illustrative clarity. FIGS. 4 to 7 show details of the upper hanger rods 100 and associated lower hanger rods 300, and the manner in which they cooperate with the upper shroud support ring 300 and a lower support ring 400. As shown, the upper hanger rods 100 each comprise a shaft 100A having a G clamp-like member or portion 100B at the lower end and a U-shaped bracket or cross-bar member 100C at the upper end. The U-shaped cross-bars 100C are connected to the shafts 100A by way of adjust nuts 100D. The U-shaped cross-bars 100C are each arranged to fit between two adjacent separator latch brackets 46A and are dimensioned to cooperate with these brackets 46A in a manner which allows a rigid supportive connection to be established. The G clamp-like members 100B at the lower ends of the shafts 100B are arranged to receive the upper support ring 200 in the illustrated manner. As will be appreciated, in the event that an upper hanger rod 100 is disposed at a ring clamp site 200B, the G clamp-like member 100B projects out to essentially the same level as the end portions of the flanges 200F which are formed at each end of the segments 200A. This, as will be appreciated from FIG. 7, allows the bolt 200D which interconnects the two flanges 200F to pass through the essentially rectangular shaped aperture. The vertical wall portion 100Bw of each of the G clamp-like members 100B is arranged to have its rear edge surface trapped against the outer peripheral surface of shroud 55 by the upper support ring 200 and to be clamped in this position upon tightening of the bolts 200D which interconnect each of the segments 200A of the upper support ring 200. The upper ends of the lower hanger rods 100 are formed with a double hook arrangement 300A (see FIGS. 6A and 6B) which hangs over the upper edge of the upper support ring 200. In the instance that an upper and lower hanger rod are disposed in vertical alignment with one another, the double hook arrangements 300A are arranged to seat on either side of the G clamp-like member 100B of the corresponding upper hanger rod 100. In the instances wherein the lower hanger rods are disposed at a joint, the double hook portion is arranged to straddle the joint and to be retained by the bolt 200D of the joint which passes behind the arrangement in a manner which traps the double hook portion in position. The lower ends of each of the lower hanger rod shafts 300B are each formed with an enlarged head or boss portion 300C which fits in part under a stepped diameter shoulder or edge portion 55A formed on the shroud 55. The lower edge of the lower support ring 400 rests on the top of the boss portion 300C in the manner illustrated in FIGS. 6A and 7. Further, as will be apparent from FIG. 7, the lower support ring 400 is arranged to clamp the lower end portion of the shafts 300B of each of the lower hanger rods 300 against the external periphery of the shroud 55 and prevents the boss 300C at the end of each of the shafts 300B from moving laterally and outward away from the shroud 55 and thus ensures that the required supportive connection between the shroud and the lower hanger rods is maintained. FIGS. 8 and 9 are side elevational views showing the manner in which the U-shaped cross-bars 100C of the upper hanger rods 100 fit in between and are supported by the separator latch brackets 46A. In these figures, numeral 80 denotes a core spray pipe, numeral 82 denotes a shroud lift lug, and numeral 84 denotes a separator guide bracket. During installation of the above described shroud support ring arrangement, the upper support ring 200 is suspended by the upper hanger rods 100 which are spaced around the shroud 55. When the shroud support ring 200 is clamped around the shroud 55, the upper hanging rods 100 are clamped between the support ring 200 and the shroud 55, and become an integral part of the clamping assembly. The cross-bar 100C at the upper end of upper end of each hanger rod fits between and is supported by separator latch brackets 46A. Vertical separation of the shroud and the top guide support ring, is prevented due to the shroud support ring 200 being locked against vertical movement by the lower hanger rods (twelve in this case), which are hung on the shroud support ring 200. Before the shroud support ring 200 is finally tightened in a clamping condition, the lengths of the upper hanging rods 100 are adjusted using the adjusting nuts 100D provided at their upper ends. This allows the vertical installation gap, located between the boss portions 300C at the end of the lower hanger rods 300 and the horizontal surface of the stepped diameter or edge portion 55A of the shroud 55, to be closed. It should be noted that in the event that the risk of vertical separation between the top guide ring and the shroud 55 is of little or no concern, the lower hanger rods 300 and the lower support ring 400 can be omitted, and the installation gap can be closed between the upper hanger rods 100 and the underside of the top guide support ring through adjustment of the upper hanger rod lengths. Although the present invention has been described with reference to only one embodiment, it will be noted that the various changes and modifications which can be made without departing from the scope of the invention will be essentially self-evident and as such is limited only by the appended claims.