Patent Number: 054886430
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear reactors. More specifically, the present invention relates to a support arrangement by way of which a shroud can be supported within a reactor pressure vessel without a need for welding, drilling, or other machining of the shroud structure. 2. Description of the Related Art As is well known, safety is a paramount concern in devices such as nuclear reactors and stringent measures muse be exercised to ensure that mechanical failures, such as which tend to be induced by the formation of cracks and the like in various and numerous structures which comprise a nuclear reactor, are eliminated. It has been discovered that various stresses which are induced in a shroud structure used to enclose the fuel assemblies, tend to produce cracks in the top guide support ring area of the core shroud assembly. For example, it could be envisioned the cracks could form in the shroud at the horizontal weld joint between the top guide support ring and the shroud. This, of course induces a safety concern in that, if the weld were to break, the shroud could shift and cause a problem with control rod insertion. SUMMARY OF THE INVENTION It is an object of the invention to provide an arrangement via which a shroud can be supported within a reactor pressure vessel (RPV) in a manner which does not induce stresses that induce cracking and the like type of deterioration of the shroud assembly, which can be connected to the shroud using only light clamping, and which does not require any welding, drilling, or other machining of the shroud assembly. It is a further object of the present invention to provide a hanger rod arrangement via which a shroud or the like type of structure can be supported within a RPV or the like type of vessel without the need to weld, drill holes and the like. It is yet a further object of the present invention to provide a hanger rod arrangement which makes use of a basic upper hanger rod and multi-segment ring combination and which is supplemented with lower hanger rods which are hung on the multi-segment ring and which engage a shoulder or the like on the structure being supported, in the event that vertical displacement of the suspended structure needs to be attenuated or prevented. In brief, according to the present invention, in order to eliminate the need to weld, drill or otherwise machine a shroud structure which is used to surround a plurality of fuel assemblies in a nuclear reactor, a plurality of upper hanger rods interconnect a structure located above the shroud to a support ring assembly which is clamped about the upper periphery of the shroud below the top guide support ring assembly. Lower hanger rods interconnect the lower edge of the shroud with the support ring. Thus, through the upper and lower hanger rods and support ring assembly, the shroud can be supported within the RPV. The upper support ring is arranged to clamp the lower ends of the upper hanger rods against an upper outer peripheral portion of the shroud while the lower ends of the lower hanger rods are clamped against a lower peripheral wall portion of the shroud by a lower support ring in a manner which ensures a good connection between the lower end of the lower hanger rods and an edge such as defined by a stepped diameter portion or the like. In a specific embodiment of the invention, the top guide support ring, together with the upper part of the shroud, is held in place by a support ring assembly that is clamped around the shroud below the top guide support ring. The support ring consists of four segments which are bolted together. The segments are formed to define a polygonal ring with 12 symmetrical sides. During installation of the shroud support ring, the ring is suspended from upper hanger rods which are spaced around the shroud. When the shroud support ring is clamped around the shroud, the upper hanger rods are clamped between the support ring and the shroud, and become an integral part of the clamping assembly. The upper end of each hanger rod has a cross bar which fits between and is supported by separator latch brackets. To prevent vertical separation between the shroud and the top guide support ring, the shroud support ring is locked against vertical movement by a plurality (e.g. twelve) lower hanger rods, which are hooked over the shroud support ring. The lower ends of the lower hanger rods lock under a recess defined by a stepped diameter of the shroud located further down on the shroud. The lower hanger rods are maintained engaged with this recess by a lower support ring which surrounds the lower hanger rods and clamps the lower ends of these rods radially inward against the side of the shroud. Before the shroud support ring is finally tightened in a clamping condition, the lengths of the upper hanging rods are adjusted using adjusting nuts provided at their upper ends, so the vertical installation gap between the lower hanger rods and the horizontal surface of the recess or the like located at the lower end of the shroud and against which the lower ends of the lower hanger rods engage, is closed. It should, however, be noted that with the present invention, in the event that the risk of vertical separation between the top guide ring and the shroud is of little or no concern, the lower hanger rods and the lower support ring can be omitted, and the installation gap is closed between the upper hanger rods and the underside of the top guide support ring. More specifically, a first aspect of the present invention resides in a nuclear reactor which features: a shroud disposed within a reactor vessel so as to surround at least one fuel assembly; and a shroud support arrangement for supporting the shroud in the reactor vessel, comprising: an upper support ring clamped about the upper periphery of the shroud; and an upper hanger rod which has a lower end engaged with the upper support ring and an upper end adapted for connection to a predetermined structure located within the reactor vessel above the shroud. A second aspect of the present invention resides in a nuclear reactor which features: a shroud disposed within a reactor vessel so as to surround at least one fuel assembly; and a shroud support arrangement for supporting the shroud in the reactor vessel, comprising: a first multi-segment ring member disposed about the upper periphery of the shroud, the first ring member having a plurality of joints which allow the size of the ring to be adjusted and selectively clamped against the shroud; a first adjustable length hanger rod which has a lower end engaged with the first ring member and an upper end adapted for connection to a predetermined structure located within the reactor vessel above the shroud. A third aspect of the invention resides in a support arrangement for supporting a shroud structure within a vessel, which features: a multi-segment ring assembly which can be selectively tightened about the shroud; a plurality of first hanger rods, the first hanger rods each having hook members at the lower ends thereof, the hook members being arranged to engage with the ring assembly and to be clamped against the external surface of the shroud when the ring assembly is selectively tightened, the upper ends of the first hanger rods being arranged to be engageable with a structure which is disposed in the vessel above the shroud. A further aspect of the present invention resides in a method of supporting a shroud in a pressure vessel of a nuclear reactor comprising the steps of: suspending a plurality of upper hanger rods on a structure disposed in the pressure vessel above the level at which the shroud is suspended; connecting the plurality of upper hanger rods to a multi-segment ring member which is disposed about the shroud by arranging hooks which are provided on the lower end of the upper hanger rods to engage with the ring member so that when the ring member is tightened, portions of the hooks are pressed into engagement with the shroud; and tightening the ring member to clamp the portions of the hooks against the shroud.