Patent Number: 046876286
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an elevational view, partly in cross-section, of a pressurized water reactor 10 comprising a vessel 12 of generally conventional configuration including an upper dome 12a, cylindrical sidewalls 12b, and a bottom closure 12c comprising the base of the reactor 10. Within the bottom closure 12c, as schematically indicated, is so-called base-mounted instrumentation 14. The lower barrel assembly 16 comprises a generally cylindrical sidewall 17 affixed at its lower and upper ends to respective lower and upper core plates 18 and 19. Fuel rod assemblies 20 are positioned in generally vertically oriented, parallel axial relationship within the lower barrel assembly 16. A radiation reflection shield 21 is mounted interiorly of the cylindrical sidewalls 17, in conventional fashion. The inner barrel assembly 24 includes a cylindrical sidewall 26 within which are positioned a plurality of rod guides in closely spaced, parallel axial relationship; for simplicity of illustration, only two such rod guides are shown in FIG. 1, namely rod guide 28 housing a cluster of radiation control rods 30 (RCC) and a rod guide 32 housing a cluster of water displacement rods 34 (WDRC). Mounting means 36 and 37 are provided at the respective upper and lower ends of the rod guide 28 and, correspondingly, mounting means 38 and 39 are provided at the respective upper and lower ends of the rod guide 32, the lower end mounting means 37 and 39 mounting the respective rod guides 28 and 32 to the upper core plate 19, and the upper mounting means 36 and 38 mounting the respective rod guides 28 and 32 to a calandria assembly 50. The calandria assembly 50 includes a lower calandria plate 52, an upper calandria plate 54, and a plurality of parallel axial calandria tubes 56 which are positioned in alignment with corresponding apertures in the lower and upper calandria plates 52 and 54 and to which the calandria tubes 56 are mounted at their respective, opposite ends. Calandria extensions 58 project downwardly from the calandria tubes 56 and connect to corresponding mounting means 36 for the upper ends, or tops, of the RCC rod guides 28. The upper end mounting means 38 associated with the WDRC rod guides 32, in accordance with the present invention, are interconnected by flexible linkages (shown and described in detail hereafter) to the the mounting means 36 of the RCC rod guides 28. Thus, the calandria extensions 58 are associated only with the RCC rod guides 28 and not with the WDRC rod guides 32 but serve, through the flexible linkages, to provide both stiff lateral as well as resilient axial support to compensate for relative differences in positioning to the tops of the WDRC rod guides 38 without overstressing the flexible linkages. Extending upwardly beyond the upper calandria plate 54 and, more particularly, within the dome 12a of the vessel 12, there is provided a plurality of flow shrouds 60 respectively aligned with the calandria tubes 56. A corresponding plurality of head extensions 62 is aligned with the plurality of flow shrouds 60, with respective adjacent ends thereof in generally overlapping relationship. Control rod cluster (RCC) displacement mechanisms 64 and water displacement rod cluster (WDRC) displacement mechanisms 66 are associated with the respective head extensions 62, flow shrouds 60 and calandria tubes 56 which, in turn, are respectively associated with the respective clusters of radiation control rods 30 and water displacment rods 34. Particularly, the RCC and WDRC displacement mechanisms 64 and 66 connect through corresponding lines to the respective clusters of radiation control rods and water displacement rods 30 and 34, to control the respective vertical positions thereof and, particularly, to selectively lower same through corresponding openings (not shown) provided therefore in the upper core plate 19 into surrounding relationship with respectively associated fuel rod assemblies 20. In this regard, the clusters 30 and 34 have an extend of travel corresponding substantially to the longitudinal, oraxial height of the fuel rod assemblies 20. While the particular control function is not relevant to the present invention, insofar as the control over the reaction within the core is effected by the selective positioning of the respective rod clusters 30 and 34, it is believed that those skilled in the art will appreciate that moderation or control of the reaction is accomplished in accordance with the extent to which the control rod clusters 30 are inserted into the core and with the effective water displacement adjustment which is achieved by selective positioning of the water displacement rods 34. The flexible rod guide support for the inner barrel assembly of a pressurized water reactor in accordance with the invention will be discussed with concurrent reference to FIGS. 2-5, inclusive. FIG. 2 comprises a perspective, exploded and partially broken away view of rod guides and respectively associated top plates, in conjunction with a flexible linkage in accordance with a first embodiment of the present invention. FIG. 3 comprising a top plan view of an exemplary assemblage of a top plate of a first (WDRC) type, as interdigitized with associated top plates of a second (RCC) type disposed in surrounding, mating relationship therewith and, further, as interconnected by a flexible linkage, all in accordance with the aforesaid first embodiment of the invention. FIGS. 4 and 5 comprise elevational, cross-sectional views taken along the lines 4--4 and 5--5, respectively, in FIG. 3. The rod guide 32 for the WDRC rod cluster 34 and the rod guide 28 for the RCC rod cluster 30, as best seen in FIG. 2, have first and second, different configurations, and have respectively associated therewith top plates 38 and 36 corresponding to the respective mounting means 38 and 36 diagramatically illustrated in FIG. 1. Each of the rod guides 28 and 30 is formed of sheet metal and each of the respective top plates 36 and 38 is machined to achieve the configurations as illustrated. The peripheries of the top plates 36 and 38 generally correspond to the peripheries of the respective rod guides 28 and 30, as viewed in cross-section taken in a plane transverse to the vertical axes thereof and thus parallel to the plane of FIG. 3. The top plates 36 and 38 furthermore have interior channels 70 and 72, respectively, the profiles or boundaries of which correspond to the configuration, again in cross-section, of the corresponding RCC rod clusters 30 and WDRC rod clusters 34, the latter being illustrated in simplified schematic form in FIGS. 6 and 7, respectively. In FIG. 6, the RCC rod cluster 80, shown in a simplified perspective view, includes a spider 82 comprising a pair of orthogonally related cross arms 82a and 82b interconnected by a central hub 83, a plurality of RCC rodlets or rods 84 depending from the arms 82a and 82b. Particularly, each of the arms 82a and 82b carries four (4) such rods 84. Correspondingly, as best seen in FIG. 3, the interior channel 70 of the top plate 36 has a profile corresponding to the RCC rod cluster 30, permitting the latter to be lowered axially through the channel 70 thereof under control of the control rod displacement mechanism 64 (FIG. 1) which connects through drive line 86 to the central hub 83 of spider 82 of the RCC rod cluster 30. The interior channel 72 of the WDRC top plate 38 likewise has a profile corresponding to the periphery, again in cross-section, of the WDRC rod cluster 34 (FIG. 1), the latter being shown in a simplified schematic plan view in FIG. 7. The WDRC rod cluster 34 similarly includes a spider 90 having a plurality of radially extending arms 92 connected to a central hub 93; further, alternate ones of the arms 92 include transverse cross arms 92a. A plurality of WDRC rods 94 then are appropriately connected to the arms 92a and depend therefrom in parallel axial relationship. From FIG. 3, it will be apparent that the respective rod guides 28 and 30 and the associated top plates 36 and 38 are configured so as to permit relatively dense packaging thereof and, more particularly, the assemblage thereof as interdigitized matrices. Particularly, the top plate 38 of the WDRC rod guides 30 is surrounded by a symmetrical, associated sub-array of four RCC top plates 36; further, each of the RCC top plates 36 in turn is configured to engage an associated sub-array of four WDRC top plates 38. While the symmetrical configuration of the respective rod clusters and thus of the corresponding rod guides and associated top plates is a preferred embodiment, alternative configurations are also contemplated as within the scope of the invention, the principal requirement being that interdigitized matrices of the respective rod guides and top plates may be established in a tightly packaged array. The top plates 36 and 38 are now described in detail, with concurrent reference to FIGS. 2-5, common reference numerals being employed to identify the common elements of the symmetrical portions of the respective, individual structures. The WDRC top 38 plate is of a generally annular configuration with a generally square periphery and includes four (4) major arms 100, each each pair of two (2) adjacent arms 100 extending in perpendicular relationship and the totality of four (4) such pairs defining four (4) major exterior vertices, or corners. A diagonal minor arm 102 spans each such vertex and integrally interconnects the pair of associated, adjacent major arms 100. Inwardly transverse, or lateral, extensions 104 are formed at intermediate positions along the length of each of the major arms 100 displaced from the opposite ends thereof, and integrally join a central, link connection vertical stub 106. An outwardly transverse, or lateral wedge-fit extension 106a is formed on the stub 106, extending beyond the outer sidewall surface, or periphery, of the major arm 100. A link connection threaded bore 107 is formed in each vertical stub 106. The RCC top plate 36 (best seen in FIG. 3) includes a corresponding plurality of four (4) equiangularly displaced major arms 110, the interior peripheral edges of each pair of adjacent arms 110 defining an interior vertex which receives therein a corresponding exterior vertex, or corner, of the top plate 38, as defined by a pair of adjacent major arms 100 thereof. The top plate 36 further includes a diagonal minor arm 112 extending across the geometrical interior vertex defined by the major arms 110, the exterior vertical surface of the arm 112 corresponding to the interior vertical surface of the diagonal minor arm 102 of the top plate 38. Transverse, or lateral extensions 114 extend symmetrically from both sides of the major arms 110, each extension 114 corresponding in size and configuration to the corresponding lateral extension 104 of a top plate 38 associated with the corresponding arm 100. As best seen in FIG. 2, the transverse lateral extensions 114 on the respective peripheral edges of a pair of adjacent major arms 110 which define a given interior vertex are continuous with the diagonal minor arm 112, and furthermore the extensions 114 and the included diagonal minor arm 112 have a common planar upper surface, corresponding to the planar upper surface of the major arms 110, but are forshortened in vertical height relative to that of the major arms 110 such that the lower surfaces thereof define an undercut interior peripheral region, or channel, 118. The outer end of each major arm 110 furthermore includes a wedge-fit extension 116 generally aligned with the major axis of the corresponding major arm 110. A stop pin bore 115 is formed in each of the transverse lateral extensions 114 of each arm 110 in a position so as to be aligned with the stop pin bore 105 in the corresponding inward lateral extension 104 of a corresponding arm 100 when the top plates 36 and 38 are assembled, as in FIG. 3. Further, a link connection threaded bore 117 is formed in the integral juncture 110' of adjacent major arms 110 surrounding the interior channel 70 and defining the interior vertex. A groove 120 further is formed in the associated transverse extensions 114 and the included diagonal minor arm 112, extending along the respectively associated peripheral edges of the associated pair of adjacent major arms 110 and communicating with a counter bore 121 which is coaxial with the threaded bore 117. The assembled relationship of the top plates 36 and 38 is best understood from the top plan view of FIG. 3, taken in conjunction with the vertical cross-sectional views of FIGS. 4 and 5, the latter taken along the lines 4--4 and 5--5 in FIG. 3, respectively. As seen in FIG. 4, each diagonal minor arm 102 of the top plate 38 is received within the corresponding diagonal portion of the channel 118 defined by the diagonal minor arm 112 and the integral juncture 110' of an adjacent pair of major arms 110, the diagonal minor arm 112 thus being superposed on diagonal minor arm 102. As seen in FIG. 5, the transverse lateral extensions 114 are superposed on the respective midside, inward lateral extensions 104 of a given major arm 100 of the top plate 38. As best seen from FIG. 3, the free ends of the major arms 110 of two adjacent top plates 36 which bound, or are contiguous with, a common major arm 100 of a top plate 38 are juxtaposed in closely spaced relationship, the respective, aligned wedgefit extensions 116 thereof closely engaging the respective surfaces of the corresponding outward, transverse wedge-fit extension 106a of that associated major arm 100. Stop pins 125 then are positioned in the aligned stop pin bores 105 and 115. Finally, a flexible linkage 130 is received within the channels 120 of the group of top plates surrounding a given top plate 38, which then is bolted in position. Particularly, bolts 132 are received through the apertures 131 in the corners, or vertices, of the linkage 130 and securely threaded into the corresponding, threaded bores 117 and, further, bolts 134 are received through the apertures 133 in the side arms of the linkage 130 and securely threaded into the corresponding threaded bores 107 in the link connector vertical stubs 106. Respective matrices of top plates 36 and 38 thus are interdigitized by virtue of the respective structural components defining the mating, interior and exterior vertices thereof and including the channels 118 and the superposed lateral, or transverse, extensions 114 and 104. Further, the top plates are laterally interlocked (i.e., in a plane perpendicular to the axis of the assembly 24) by the flexible linkages 130 in a two dimensional, concatenated relationship in which each of the top plates 38 is linked rigidly in the lateral direction to four respectively surrounding top plates 36--and, in turn, each of the top plates 36 is laterally interlocked at its four interior vertices to associated exterior vertices of four top plates 38 which are interdigitized therewith. It will be appreciated that whereas the interdigitized relationship exists throughout the majority of the array, as is apparent, the outer edges, or the periphery, of the array necessarily will be defined by one or more peripheral edges of either one or the other of the top plates 36 and 38--typically, the top plates 36. Mounting of the concatenated and interdigitized matrices of top plates 36 and 38, for securing the top ends of the rod guides 28 and 30 in position within the upper end of the inner barrel assembly 24, is achieved by connections provided between the lower calandria plate 52 and the RCC top plates 36. FIG. 8 is an enlarged view of the portion of a lower calandria plate 52 and of a broken-away portion of the upper calandria plate 54, illustrating more clearly the association of the calandria tubes 56 and the calandria plates 52 and 54. More specifically, the calandria tubes 56a which are connected at their lower ends to corresponding calandria extensions 58 are associated with the RCC rod clusters and the associated top plates 36. Calandria tubes 56b, on the other hand, are associated with the WDRC rod clusters and the corresponding top plates 38. Provided in the lower calandria plates 52, intermediate the various calandria tubes 56, are flow holes 59 through which the core output flow, exiting upwardly from the inner barrel assembly 24, proceeds through the calandria assembly 50. Corresponding flow holes (not shown) are provided in the upper calandria plate 54. FIG. 9 is a top plan view of a portion of the lower calandria plate 52, illustrating (in solid cross-section) the assemblage of calandria tubes 56a and 56b associated with the array of top plates 36 and 38 shown in FIG. 3. FIG. 10 is a cross-sectional view illustrating the connection of a top plate 36 to the calandria bottom plate 52 by a calandria extension 58. Particularly, the calandria extension 58, of circular cross-section, is received within the corresponding circular cross-sectional channel 70 of an RCC top plate 36, thus establishing lateral stability of the RCC top plate 36; each top plate 36 receives a corresponding calandria extension 58 in its channel 70. Accordingly, the RCC top plates 36 are supported directly, and the interdigitized and concatenated top plates 38 thus are supported through, the top plates 36, against lateral movement by the plurality of calandria extensions 58 and ultimately by the lower calandria plate 52. FIGS. 9 and 10, taken concurrently, illustrate leaf springs 140 which resiliently load the top surfaces of the top plates 36 of the RCC rod guides 28, and which generate sufficient lateral frictional force such that fluctuating steady state loads applied to the guides do not cause slippage; the springs 140 also compensate for effects of differential thermal expansion and minimize adverse effects of resulting forces due to such thermal expansions. More particularly, the leaf springs 140 are attached to the lower surface of the lower calandria plate 52 by suitable bolts 142; as seen better in FIG. 9, the leaf springs 140 comprise two parallel pairs 140-1, 140-2 and 140-3, 140-4, for a total of four (4) springs, the first pair of springs 140-1 and 140-2 being aligned with the second pair of springs 140-3 and 140-4 and thus displaced from one another by 180.degree. about the generally circular cross-section of the RCC calandria tube 56a. Moreover, with respect to the matrix of RCC top plates 36 and the corresponding RCC calandria tubes 56a, the leaf springs 140 are rotated by 90.degree. for successive RCC calandria tubes 56a of a given row, the leaf springs 140 for the respective, column-related calandria tubes 56a of successive, adjacent parallel rows being offset by 90.degree.. From FIG. 10, the two related pairs of leaf springs 140 extending from a given calandria extension 58 associated with a given top plate 36, at their outer free ends, engage the corresponding end extremities of the upper surfaces of the adjacent, aligned major arms 100 of the aligned and next adjacent RCC top plates 36 (only one of which is shown) at corresponding positions close to the outer, free ends thereof. Further, due to the symmetrical and regular array of calandria tubes 56 and associated extensions 58 with respect to the top plate 36 and the alternating parallel and transverse orientation of the leaf springs 140, it will be apparent that each top plate 36 is engaged by a symmetrically loaded force by corresponding leaf springs at the outer extremities of the aligned, or 180.degree. displaced, major arms 100 so as to maintain a symmetrical or balanced loading force thereon. The requirements which must be satisfied by the flexible rod guide support structure of the invention, as outlined briefly above, the adverse environmental conditions (e.g., vibration, and both axial and lateral displacement forces) which exist within the inner barrel assembly 24 and the manner in which the flexible rod guide support structure of the present invention accommodates these conditions and satisfies those requirements, as now may be better appreciated, will be discussed, again with reference to FIG. 1. Further, as before noted, the flexible support structure of the invention must, itself, not introduce sources of vibration and most significantly must not be susceptible to excessive wear which, over time, would cause the mounting assembly to loosen and eventually permit vibrations to ensue. Particularly, the concatenated and interdigitized matrices of the RCC top plates 36 and WDRC top plates 38 effectively present a single, relatively stiff structure of mutually, or interdependently, supported top plates at the interface of the inner barrel assembly 24 and the lower calandria plate 52, which nevertheless permits a limited extent of relative motion between the rod guides 28 and 32 by out-of-plane bending of the flexible linkages 130. The flexible support structure of the invention furthermore facilitates assembling the rod guides with the calandria extensions 58--which assembly, as before noted, is accomplished by having the RCC top plates 36 receive the calandria extensions 58 within the respective cylindrical internal channels 70 therein. The extent of relative movement between adjacent top plates 36 and 38, as permitted by in-plane tensile elongation of the flexible linkages 130, however, is limited by the stop pins 125 which provide an ultimate load capacity for very large loads. Thus, under very large loads, the stop pins 125 prevent excessive loading of any of the flexible linkages 130 and ensure that loads from the WDRC rod guides 30 are transmitted through the concatenated and interdigitized RCC top plates 36 into the calandria bottom plate 52. The stop pins 25 serve a further function in providing rough positioning of the interdigitized top plates 36 and 38 prior to attachment thereto of the flexible linkages 130. As previously noted, the leaf springs 140 serve to react normal operational fluctuating loads laterally, by the frictional forces generated by their engagement with the top surfaces of the RCC top plates 36. The leaf springs may be of the type known as 17.times.17 fuel assembly springs, which are typically employed in conjunction with the fuel rod assemblies 20 in the lower barrel assembly 16. As employed in accordance with the present disclosure, the leaf springs 140 may be designed to react nominally a force of 388 lbs. at each RCC guide top plate 36, assuming a coefficient of 0.3 without slippage. More specifically, the nominal force applied to each RCC top plate 36 is 1,294 lbs. with a range of 918 lbs. to 1,528 lbs. Accordingly, assuming a coefficient of friction of 0.3, the lateral force can be nominally as great as 388 lbs. before any movement of a given top plate 36 would occur. Differential lateral forces across the array thus may be compensated for and reacted to independently by the corresponding leaf springs 140. The concatenated design particularly precludes impact wear from occurring between the rod guide top plates 36 and 38 and the calandria extensions 58. To the extent that such wear does occur, and particularly relative to the calandria extensions 58, the extent and effect of such wear is believed not significant relative to rod guide alignment or the structural capability of the extensions 58 to react to seismic loads. To the extent that wear relative to a particular extension 58 occurs, in like fashion, the associated leaf springs 140 will continue to maintain both axial and lateral alignment, and to react forces tending to cause lateral lateral displacement, thus limiting the excitation and ultimately wear on the RCC guides 34 and WDRC guides 30 and the respective rodlet clusters 92 and 84. The concatenated relationship of the interdigitized matrices of the array affords the further significant benefits of distributing force effects via the flexible linkages and compensating for differential axial expansion and lateral forces acting on the array, throughout the entirety of the interdigitized rod guide top plates 36 and 38, and thus minimizing wear potential with respect to any given calandria extension 58 and its respectively associated top plate 36, and of the interface between any given rod guide and its associated rodlet cluster. Thus, the potential of wear due both to axial sliding forces arising, for example, from core plate vibration and as well due to lateral forces resulting from differential thermal and other effects is greatly decreased, and the structure is self-compensating even as to any specific, individual connection with a given calandria extension 58 which has worn due, for example, to initial mechanical misalignment. As can be appreciated from FIG. 10, only minimal axial space is required to accommodate the array of top plates 36 and 38 and the flexible linkages 130 therein, along with the leaf springs 140; this enables use of the flexible rod guide support structure of the invention without requiring any modification of the vessel 10 to accommodate an axially elongated inner barrel assembly 24. As is clear from FIG. 9, taken further in the context of FIGS. 1 and 8, the flexible support structure of the invention does not interfere with the required free passage of core outlet flow through the openings 59 provided therefor in the lower calandria plate 52 (i.e., at which the support structure of the invention presents an interface, as before noted). While it is preferred to employ a flexible linkage 130 of generally square configuration, alternative configurations are also available and fall within the scope of the invention. For example, two or more individual linkages 130 may be stacked to obtain selectively variable stiffness across the tops of the concatenated support plates. Further, it will be appreciated that each square linkage 130 comprises effectively a unitary assemblage of four individual flexible support linkages of two perpendicular arms each, namely the pair of adjacent linkage arms extending from and including a vertex having a screw hole 131, and through and including the enlarged portions containing the screw holes 133. Thus, four (4) separate linkages so configured could be employed in the alternative to a unitary linkage 130 as shown; while this would simplify manufacture, it would increase the number of parts and connectors required for assembly. The cross-section of the arms of the linkage 130, whether of unitary structure or of individual two-arm linkages as described, may be varied to achieve the desired stiffness. Moreover, rather than being symmetrical, the arms of each individual linkage, or the corresponding arms of an unitary assemblage may have an L-shape (i.e., of equal length arms) or other configuration, in accordance with the configurations of the associated top plates and the related connection positions thereon. Furthermore, the linkages, while contemplated to have exterior right angle vertices as in the case of the square linkage 130, may have alternative angular vertices, for example as shown in FIGS. 11 and 12. More particularly, FIG. 11 is a schematic and somewhat simplified top plan view of an alternative arrangement of an RCC top plate 36' and a WDRC top plate 38' having an associated flexible linkage 130', FIG. 12 comprising an elevational cross-sectional view along the lins 12--12 in FIG. 11. The flexible linkage 130' is of star-shaped configuration and is connected to the respective top plates 36' and 38' in somewhat of a reverse orientation of parts, relative to the embodiment of FIGS. 2-10. Particularly, the adjacent major arms 100' of the WDRC top plate 38' again form an exterior vertex crossed by a diagonal minor arm 102' which is received by a channel 118' such that a diagonal minor arm 112' of the RCC top support 36' is superposed in part on the diagonal minor arm 102' of the WDRC top plate 38' in interdigitized relationship. The diagonal arm 102' in this instance is extended vertically relatively to the height of the major arms 100', in a manner somewhat analogous to the vertical stub extension 106 of the top plate 38 as seen in FIG. 2. A groove 120' extends downwardly through the top surface of the major arms 110' and a star-shaped flexible linkage 130' then is received within the grooves. The central aperture 133' of the linkage 130' thus is disposed in alignment with the link connection threaded bore 107' in the diagonal minor arm 102', and the corner apertures 131' of the linkage 130' are disposed in alignment with the respective link connection threaded bores 117', in this instance formed in the extremities of the major arms 110' of the RCC top plate 36'. Although for simplicity of illustration, corresponding bolts are not shown in FIG. 11, FIG. 12 illustrates a bolt 134' connecting the center aperture 133' of the flexible linkage 130' to the diagonal minor arm 102' of the WDRC top plate 38'. Similar bolts of course would connect the corner apertures of the linkage 130' to the extremities of the major arms 110' of the RCC top plate 36. Thus, each exterior vertex of the WDRC top plate 38' is received in mating engagement within an interior vertex of the RCC top plate 36', as in the first embodiment of the invention, and the same are concatenated by a flexible linkage interconnecting the major arms of one thereof with the major arms of the other, the link connection positions being reversed effectively in the embodiment of FIGS. 11 and 12, relatively to those of the first embodiment. Accordingly, it will be apparent to those of skill in the art that numerous modifications and adaptations of the invention may be achieved and accordingly it is intended by the appended claims to cover all such modifications and adaptations as fall within the true spirit and scope of the invention.