Patent Number: 046577300
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and more particularly to FIG. 1 thereof, there is disclosed, in part, a nuclear reactor pressure vessel which conventionally comprises a vertically oriented, cylindrically tubular shell portion 10 the bottom of which is closed by means of a hemispherical shell portion 12 welded to the upstanding cylindrical shell portion 10 along the mutually engaging peripheries of the shell sections 10 and 12 as noted at 14. A core vessel or barrel 16 is disposed internally within the reactor or pressure vessel 10, and is seen to include a bottom support plate 18 upon which are supported the various components of the reactor constituting the core internals, such as, for example, the fuel element assemblies, the fuel elememt assemblies support grid structure or framework, and the like, as generally denoted at 20, all in a conventional manner. The upper end, not shown, or the core vessel or barrel 16 is conventionally provided with an annular, radially outwardly extending flange, and an upper region, also not shown, of the reactor pressure vessel 10 is correspondingly provided with an annular, radially inwardly projecting shoulder or ledge upon which the core barrel flange is seated. This structural system defined between the core vessel or barrel 16 and the reactor pressure vessel 10 constitutes the primary support means for suspendingly supporting the core vessel or barrel 16 within the reactor pressure vessel 10 in a downwardly extending, cantilevered manner. As has been noted hereinbefore, the lower end of the core vessel or barrel 16 must be laterally stabilized under the influence of a multitude of forces acting within a horizontal plane, and in addition, secondary support means should be provided for supporting the core vessel or barrel 16 relative to the reactor pressure vessel 10 under extraordinary vertical load conditions, such as, for example, those attendant earthquake shock loads or seismic vibrations, core barrel or weld fractures, coolant loop or other accidental or operational malfunctions, and the like. In accordance then with the present invention, and with particular reference now being made to FIGS. 1-4 of the drawings, there is provided four auxiliary core vessels or barrel support structures, generally indicated by the reference character 100, which are mounted upon the upper sidewall portions of the lower hemispherical shell portion 12 of the reactor or pressure vessel 10. The auxiliary support structures 100 are equiangularly disposed about the inner peripheral surface of hemispherical shell portion 12, and it is noted that only two of the four auxiliary support structures 100 are shown in FIG. 1 engaging the periphery of plate 18. As may best be appreciated from FIGS. 2 and 4, each of the auxiliary support structures 100 comprises a horizontally disposed, tangentially oriented crossbeam member 102 and a pair of vertically disposed, plate-type brackets 104 integrally formed upon opposite sides or ends of the crossbeam member 102. Each of the brackets 104 is substantially radially oriented, and in this manner, the brackets 104 are relatively divergent with respect to each other as well as with respect to crossbeam member 102 as one proceeds in a radial direction from crossbeam member 102 to the reactor vessel shell portion 12. Each of the brackets 104 is also tapered as one proceeds in the radial direction, with the thicker or larger tapered dimension being disposed within the vicinity of the lower hemispherical shell portion 12 so as to enhance the lateral stability, and optimize the stress distribution, of the brackets 104, as well as the entire support structure 100, relative to shell wall portion 12 as will become more apparent hereinafter. The angle of divergence .alpha. of each bracket 104 is seen to be approximately 19.degree., and the distal or base end of each bracket 104 is welded to the shell wall portion 12 as at 106. The brackets 104 are also seen to extend radially outwardly of the crossbeam member 102 so as to dispose the crossbeam member 102 in a radially spaced manner with respect to the interior wall surface of shell portion 12. In this manner, a substantially vertical, rectangularly configured flow channel or conduit 108 is defined by means of hemispherical shell wall portion 12, brackets 104, and crossbeam member 102 through which coolant can flow in a substantially unimpeded pattern relative to the auxiliary support structures 100, it being of course also appreciated that coolant is likewise flowing in the regions exterior to, or laterally of, the structures 100 as designated at 110. In order to further facilitate such unimpeded, non-turbulent flow of coolant through and about the structures 100, each of the upper surfaces of brackets 104 is inclined downwardly, as viewed in the direction proceeding from the shell wall portion 12 to crossbeam member 102, through an angle .beta. of approximately 45.degree. as best seen in FIG. 3, and in addition, these upper surfaces of brackets 104 may also be provided with rounded chamfered portions 112 for further promoting the aerodynamically laminar flow of the coolant relative to the support structures 100, as best seen in FIGS. 4 and 5. Crossbeam member 102 is provided with a rectangularly configured recess 114 which, as best seen from FIG. 2, is open along the front and top corresponding surfaces of crossbeam member 102. A pair of blind bores 116 are defined within the floor 118 of that portion of crossbeam member 102 which defines recess 114, and a pair of vertically oriented, plastically collapsible, cylindrical shock absorbers 120 are correspondingly disposed within bores 116. The height of the shock absorbers 120 is approximately twice the depth of the bores 116 such that the upper halves of shock absorbers 120 project above the floor 118 of crossbeam recess 114 as best seen in FIGS. 1, 3, and 5. A substantially T-shaped key 122, as best seen in FIG. 5, has its upper crosspiece 124 disposed within a rectangularly configured, upwardly extending recess 126 defined within the core barrel bottom support plate 18, while the downwardly depending stem portion 128 of key 122 is disposed within crossbeam recess 114. Key 122 is secured within core barrel bottom support plate 18 by means of bolt fasteners 130 as best seen in FIGS. 3 and 6, and in addition, a peripheral weld is defined between the key 122 and plate 18 as indicated at 132 in FIGS. 3 and 5. Key stem 128 is provided with a pair of upwardly extending blind bores 134 for accommodating the upper portions of the shock absorbers 120, and it is noted, with particular reference being made to FIGS. 3 and 5, that under normal operating conditions wherein the core barrel or vessel 16 is conventionally vertically supported upon the reactor or pressure vessel 10 by means of the aforenoted upper core barrel flange and pressure vessel ledge system, not shown, the uppermost ends of bores 134 are vertically spaced above the upper ends of shock absorbers 120. In a similar manner, and also under such normally operating conditions of the reactor facility, the undersurface 136 of key crosspiece 124 is vertically spaced above the upper horizontal surface 138 of the structure 100 within the vicinity of the juncture of the crossbeam 102 and the brackets 104, as best seen in FIG. 5. It is to be noted that the vertical spacing defined between the upper ends of shock absorbers 120 and the ceilings of key stem bores 134 is less than the vertical spacing defined between the undersurfaces 136 of key crosspiece and the upper surfaces 138 of the structure 100. In this manner, should the reactor facility experience severe vertical loading wherein, for example, the core barrel 16 undergoes a vertical movement relative to the pressure vessel 10, vertical interaction or engagement between the shock absorbers 120 and the ceilings of key stem bores 134 will initially cause plastic collapsing of the shock absorbers 120 whereby the latter perform their shock absorption function. Subsequently, of course, the core barrel 16 will come to rest, and be supported upon, the upper surfaces 138 of the structures 100, and in addition, the bottom of key stem 128 will similarly come to rest, and be supported upon floor 118 of crossbeam recess 114 in view of substantially similar vertical spacing defined between floor 118 and stem 128, and between key crosspiece 124 and structure surfaces 138. In connection with the accommodation of the aforenoted severe vertical loading, it is to be further appreciated that an additonally critically unique feature of the present invention resides in the formation of the structure brackets 104 in such a manner that the bottom portions thereof are inclined downwardly as one proceeds radially outwardly toward the hemispherical shell wall 12. These inclined bottom portions 139 are denoted in FIG. 3 as forming an angle .phi. of approximately 60.degree.. Stress analysis of brackets under vertical load conditions have revealed, for example, that in the instance of conventional cantilevered brackets, wherein, for example, bottom portions 139 of the brackets 104 would be disposed horizontally, or in other words, .phi. would be equal to 90.degree., the vertically impressed loads would generate bending stresses or moments within the brackets-reactor shell wall assemblage. Such an assemblage conventionally requires the cantilevered brackets to be massive and to require extensive weldments to be defined between the brackets and the reactor vessel wall. Still further, such bending moments tend to deleteriously affect the weldments from a fatigue point of view, thereby jeopardizing further the service integrity of the reactor facility under such operational conditions. In accordance with the present invention, the aforenoted bending moments are converted into shear and compression forces acting along the interior surface of shell wall 12 and parallel to bottom surfaces 139, respectively. As may best be appreciated from FIGS. 1 and 3, the rear surface wall 140 of key stem 122 is spaced just slightly radially inwardly, or away from, the rear wall surface 142 of crossbeam 102 which defines recess 114, and in this manner, the core vessel or barrel 16 is laterally stabilized within a horizontal plane relative to pressure vessel 10 under radially directed load forces. With additional reference being made to FIG. 4, it can be seen that when radial load forces are applied to the support structures under either normal or abnormal operating conditions, the provision of the divergent brackets 104 enables the radial load forces to be transmitted in radial directions along each bracket's radial axis or plane, and since the brackets 104 are divergent, the transmitted forces are distributed to the reactor vessel shell wall 12 in a substantially balanced manner, or in other words, oppositely directed force components, which tend to balance each other, are transmitted to the shell wall 12. In order to provide a similarly stabilized state for the core barrel 16 relative to pressure vessel 10 under tangentially directed load forces, shims 144, having a substantially inverted L-shaped configuration, are secured to radially extending shoulder portions 146 of crossbeam member 102 by means of a plurality of bolt fasteners 148 as best seen in FIGS. 4 and 5, the dependent legs of shims 144 extending along the interior sidewalls 150 which define crossbeam recess 114. The corresponding sidewalls of key stem 122 are interposed between the shims 144 thereby achieving the desired lateral stabilization. When tangential loads are thus impressed upon the support structures 100 during normal or abnormal operating conditions, the divergency of the brackets 104, as determined by the angle .alpha. is again seen to comprise a crtically important feature of the present invention for reasons similar to those noted hereinbefore in connection with the disposition of bracket bottom portions 139 as defined by the angle .phi.. In particular, if the angle .alpha. were 0.degree., only bending moments would be generated within the brackets 104 relative to shell wall 12, and in effect, the brackets would be simple cantilevered structures with stress fatigue problems similar to those previously discussed in connection with conventional vertical cantilevered brackets, that is, with respect to vertical loading. In accordance with the present invention, however, as a result of the provision of the divergent brackets 104, as determined by the angle .alpha., tangentially directed load forces, and the bending moments generated thereby, are converted into a composite of bending moments, shear forces, and radial compression forces acting along the axes or planes of the brackets 104. Such stress and moment distribution patterns can be effectively accommodated through means of the support structures 100 and the hemispherical shell wall 12 in a substantially improved manner than would normally be possible with simple cantilevered bracket structures. Continuing still further, it is well known in connection with stress analysis techniques that with respect to brackets mounted upon a base wall, such as, for example, the brackets 104 mounted upon shell wall 12, the effective center of gravity will be located at a point upon the junction or boundary of the bracket and the base wall which is at the midway point of the junction or boundary line length or distance. In particular, the center of gravity of each bracket 104 is shown in FIG. 3 as being at 152 which is located midway between the opposite ends 154 and 156 of each bracket 104 defining the length or distance of the junction line or boundary 158 defined between brackets 104 and shell wall 12. It is to be appreciated that tangential loads will be transmitted between the key stem 128 and the support structure 100 at a point located centrally of the common height or depth distance defined between the key stem 128 and the shims 144, such being illustrated at 160 in FIG. 3. If a moment arm, therefore, exists between the center of load 160 and the center of gravity 152, vertical bending moments will be induced within the brackets 104 of the support structures 100 under the influence of the aforenoted tangentially directed forces. It is further well known that the moment arm is determined by the distance defined between a plane passing through the center of gravity 152 and extending perpendicular to shell wall 12, and another plane, parallel to the first plane, passing through the center of load 160. Consequently, if this distance can be eliminated, the moment arm is then eliminated and the vertical bending or twisting moments are correspondingly eliminated. This is precisely what has been achieved by means of the present invention, and such has been achieved by means of, in effect, centralizing the center of load 160 with respect to the brackets 104 such that both the center of load 160 and the center of gravity 152 will both be disposed within the aforenoted plane passing through the center of gravity 152 and extending perpendicular to shell wall 12. In particular, this result has been achieved through the provision of the upper inclined portions 162 of brackets 104 as determined by the angle of inclination .beta.. If the angle .beta. were 0.degree., then the upper inclined portions 162 of brackets 104 would be eliminated and the length of junction line or boundary 158 defined between brackets 104 and shell wall 12 would be correspondingly shortened. The center of gravity 152 would then be correspondingly moved downwardly through a proportional distance toward the lower end 156 of bracket 104, and therefore, a moment arm would be created between the center of gravity 152 and the center of load 160. Consequently, it is seen that the provision of the upper inclined surfaces 162 of brackets 104 serves the additionally important function of eliminating the vertical bending or twisting moments which would normally be generated by means of the tangentially directed load forces developed between the core barrel 16 and the reactor vessel 10 as determined by the interaction developed between the key 122 and the support structure 100. The tangential load forces may then be adequately accommodated by means of the structural brackets 104 and the shell wall 12 in the manner noted hereinabove. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.