Patent Number: 043269206
Section: description

Turning now to the drawings, wherein like components are designated by like reference numerals throughout the various figures, a pool type nuclear reactor generally indicated by the reference numeral 10 is illustrated in FIG. 1. In a preferred embodiment, this reactor is a liquid metal fast breeder reactor buy may be of any other type compatible with the present invention to be described hereinafter. The reactor shown in FIG. 1 includes a reactor vessel 12 which is located under a reactor deck arrangement 14 within the vertically extending cavity 16 defined by a circumferential cavity wall assembly 18. As seen in FIG. 1, vessel 12 is separated into two compartments, a top compartment containing a pool of hot sodium generally indicated at 20 and a lower compartment containing a pool of cold sodium generally indicated at 22. Some of the reactor components located within the vessel and contained within these pools include a central core 24 containing both fuel and blanket assemblies (not shown) and a technique for cooling these assemblies by passing liquid coolant, specifically the liquid sodium, across and in contact with the assemblies. This technique utilizes a pump 26, discharge piping 28 and coolant distributing means 30 which together pass sodium from the cold pool through the fuel and blanket assembly for ultimate passage into the hot pool 22. The distributing means may be constructed conventionally or in accordance with co-pending U.S. patent application Ser. No. 132,361, filed Apr. 23, 1979, and entitled "Flow Distribution System for Coolant in a Nuclear Reactor and Method", this application having been assigned to the Assignee of the present application. Other reactor components include an internal heat exchanger 32 adapted to receive the coolant from the hot pool after the latter passes through the fuel and blanket assemblies, an instrument tree 34 mounted over the core, and other components which may or may not be illustrated but which are not pertinent to the present invention. All of these reactor components including the ones recited above, with the exception of vessel 12 and cooperating support components of deck arrangement 14 and wall assembly 18, may be readily provided by those with ordinary skill in the art and, hence, will not be discussed in detail herein except where necessary for a better understanding of the present invention. During normal operation of the reactor, it is necessary to carry out periodic in-service inspections of the reactor vessel for cracks and the reactor includes suitable access ports for passing suitable equipment in the space between the reactor vessel and a surrounding guard vessel 36 which preferably is supported in place as disclosed in co-pending U.S. patent application, Ser. No. 32,285, filed Apr. 23, 1979, and entitled "Nuclear Reactor Guard Vessel Arrangement" (Att. Docket A-34365), the application being assigned to the Assignee of the present application. Referring now to FIG. 2, attention is directed to reactor vessel 12 and the way it is supported between deck arrangement 14 and cavity wall assembly 18. As seen in this figure, the vessel includes a main body 40 located within cavity 16 as best seen in FIG. 1 and an upper circumferential rim forming a support flange 42 located and interlocked between the deck arrangement and upper section of the wall assembly, as will be discussed in more detail hereinafter. For the moment, it suffices to say that the reactor vessel, that is, main body 40 and support flange 42 are constructed so as to eliminate the previously described bimetallic weld. In a preferred embodiment, these two components are formed as a single unit, specifically of stainless steel in a preferred embodiment by welding a stainless steel flange 42 to a stainless steel body 40. As seen best in FIG. 2, the support flange 42, which is shown in cross-section, includes an outer, downwardly directed shoulder 44 and an inner upwardly directed shoulder 46 located vertically above shoulder 44. In the embodiment shown and in a preferred embodiment each of these shoulders extends in a horizontal plane entirely around the vessel. Shoulder 44 is supported on a complimentary, upwardly directed shoulder 48 extending around and forming part of cavity wall assembly 18 and in this way the cavity wall assembly supports the entire vessel. At the same time, the deck arrangement 14 includes a downwardly directed, circumferential shoulder 50 which is complimentary to shoulder 46 and which is supported by the latter such that the reactor vessel and cavity wall assembly support the deck arrangement. It should be apparent from FIG. 2 that the adjacent surfaces of deck arrangement 14, support flange 42 and cavity wall assembly 18 together define two circumferential joints 52 and 54. In a preferred embodiment of the present invention, these joints are sealed at their top ends by means 56. Each of these means may be of any suitable material compatible with the reactor environment and displaying at least a limited degree of compliance so as to accomodate thermal displacement. In a preferred embodiment, each of these seals extends across and is welded on both sides of a corresponding joint 52 and 54 at the top end of the joint. Moreover, each seal means in a preferred embodiment is sufficiently thin and appropriately designed in cross-section (as shown) to provide at least a limited degree of compliance in the direction transverse to the joints in order to accomodate thermal displacement. Another technique for accomodating thermal displacement, that is, allowing for differential displacement between the three interfacing components utilizes a slide or slider plate 58 between the shoulders 44 and 48 and a slider plate 60 between the shoulders 46 and 50. Each of these plates is constructed of bronze or other suitable material which allows the confronting shoulders to slide relative to one another. One specific type of slide plate used is a lubricated bronze plate manufactured under the name LUBRITE by Merriman, Inc. (a division of Litton Industries). In this regard, it should be pointed out that while separate slide plates can be provided between the confronting shoulders, it should be understood that the shoulders themselves could be provided with their own coating of suitable slidable material. In addition to these various components just described for accomodating or allowing for thermal displacement, the reactor, in a preferred embodiment, includes a number of shear pins 62 interlocking the support flange with the confronting components of the deck arrangement and cavity wall assembly for resisting seismic forces. The shear pins 62 are aligned with their longitudinal axes directed toward the center of the reactor 10 and lying in horizontal planes so as not to restrain diffential thermal expansion of the cooperating components of deck arrangement 14, support flange 42, and cavity wall assembly 18. Referring to FIGS. 3 through 6, different configurations of support flange 42 and the cooperating components of deck arrangement 14 and cavity wall assembly 18 are shown. For example, the support flange shown in FIG. 3 and indicated generally by the reference numeral 42a includes a downwardly directed, outer circumferential shoulder 44a corresponding to the previously described shoulder 44 and an upwardly directed, inner circumferential shoulder 46a corresponding to previous shoulder 46. As seen in FIG. 3, shoulder 44a rests on the complimentary shoulder 48a corresponding to previously described shoulder 48 and hence forming part of assembly 18a. On the other hand, shoulder 46a is spaced below the shoulder 50a which corresponds to previous shoulder 50 and which forms part of arrangement 14a. However, these two latter mentioned shoulders do not rest adjacent one another but rather contain a hollow ring 64 constructed of a suitable material for the reactor environment and one which is designed to be sufficiently resilient to accomodate thermal expansion between the two shoulders. In a preferred embodiment, this ring is secured in place by means of a plurality of circumferentially spaced shear pins 66 extending through the bottom of the ring and into shoulder 46a and also a plurality 67 extending from the top of the ring into cooperating shoulder 50a. Additional shear pins 62a corresponding to shear pins 62 extend between support flange 42a and the interfacing component of assembly 18a. These shear pins are preferably covered with carbon steel caps 68. Finally, a shear block 70 extends entirely around a cooperating surface on deck arrangement 14a and is held in place by a plurality of bolts 72. This shear block is covered by an appropriate seal 56a which corresponds in function to previous seal 56. The shear block itself extends into a cooperating slot 74 in the top end of the support flange 42. Referring to FIG. 4, a support slange 42b is shown and includes outer and inner shoulders which cooperate with complementary shoulders forming a part of deck arrangement 14b and cavity wall assembly 18b in the same way described with respect to FIG. 2. Moreover, a slide plate is provided between each of the pairs of adjacent shoulders. The difference between this configuration and the configuration shown in FIG. 2 resides in the utilization of two circumferential skirts 80 extending vertically upward and forming part of the support flange. These skirts are welded to confronting surfaces on the deck arrangement and wall assembly, as shown, thereby eliminating the necessity for a seal corresponding to the seals 56 while providing compliance for radial displacement and restraint against upward and/or lateral displacement of the parts relative to each other. FIG . 5 illustrates still another support flange embodiment generally indicated at 42c. This support flange may be identical to flange 42 in cross-sectional configuration and hence includes corresponding outer and inner shoulders cooperating with complementary shoulders provided by deck arrangement 14c and cavity wall assembly 18c. Moreover, a slide plate may be provided between each of the cooperating pairs of shoulders. The difference between this support technique illustrated in FIG. 2 resides in the utilization of a plurality of studs and nuts 82 and 84, respectively. Some of the studs extend through the support flange including its outer shoulder and into the cavity assembly and some of the studs extend through the deck assembly and into the support flange through its inner shoulder. The adjacent parts are sealed by means of seal rings of carbon steel or other suitable material which bridge over the nuts and the tops of the studs as indicated generally at 86. Referring finally to FIG. 6, still another support flange 42d is shown between deck arrangement 14d and cavity wall assembly 18d. This support flange includes a bottom section which may be identical to the bottom section of support 42b but includes a top section having an inner, upwardly directed shoulder 50d which is slotted to receive the bottom edge of a resilient support ring 88. The top of this support ring extends in a cooperating slot formed in deck arrangement 14d, as shown. In this embodiment, a stud and nut as well as a top seal are provided in the same manner as described with respect to FIG. 5. Finally, shear pins are provided between the flange and cavity wall assembly as illustrated.