Patent Number: 039390381
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT The pressurized-water coolant nuclear reactor 1 shown by FIG. 1, includes a substantially cylindrical side wall 2 and a hemispherical bottom wall 3, the two walls being integral with each other, the side wall having pressurized water coolant connections 4 and a detachable cover 6 normally clamped firmly against the upper end of the side wall 2. The cover 6 carries various tubular connections 7 for the control rod drives. The core 5 may be conventional and consists of various individual fuel elements enclosed by the core vessel 10. These fuel elements are supported via a core frame 11 which rests on a flange 12 of the core vessel 10 (see FIG. 2), while the core vessel itself is suspended by its upper end via an annular flange 13, shown in FIG. 1, which rests on an internal shoulder 14 provided by the pressure vessel at its upper end. It can be appreciated that the core vessel, including its associated parts, is of substantial weight. It is the function of the core vessel intercept arrangement 17 to prevent this core vessel from accidentally falling through the entire distance beneath it and above the pressure vessel's bottom wall 3. The construction 17, as shown in FIG. 1, does not include all of the features of the present invention, its illustration in this figure being only to indicate in a general manner the location where the core vessel's intercept device is required. Referring now to FIGS. 2 and 3, which do show the details of the present invention, the detailed construction is as follows: The entire construction is made of metal having adequate ductility to avoid rupture when stressed beyond its elastic limit by the performance of its intended functions. The various parts may be interconnected, where required, by welding. The central column 18 comprises eight radially arranged, vertically elongated plates 18 inwardly interconnected by three vertically-interspaced short tubes 20, 20' and 20". Eight tubes in each instance form upper and lower strut systems, these being shown at 22 and 23, respectively, with each set of upper and lower tubes welded to one of the plates 19 at vertically interspaced locations. The annular series of columns are formed by plates 25 which are also radially arranged with respect to the center line of the construction and which are registered in each instance with one of the plates 19, the upper and lower strut members 22 and 23 converging and being welded at relatively closely interspaced upper and lower locations to the plates forming the annular series of vertical columns. The bottoms of the plates or columns 25 rest on the hemispherical bottom 3 near its periphery and close to its vertical side wall 2. The vertical columns 25 are aligned with the periphery of the core vessel 10 and they are connected with each other by a ring 26 arranged in a horizontal plane between the upper and lower tubular struts 22 and 23 of the strut sets. The tops of the columns or plates 25 carry a centering ring 27 which extends into the flange 12 of the core vessel 10, in interspaced but closely adjacent peripheral relationship with the flange 12. The plates 19 and 25 and upper portions 30 and 31 are reduced in cross-sectional areas by cutting the plates so they taper upwardly. The reduction in cross-sectional area is designed relative to the elastic limit of the plate metal and the anticipated falling force of the core vessel, so that these upper portions are deformed beyond their elastic limit by the falling core vessel to provide a shock-absorbing effect by the gradual dissipation of the falling energy of the core vessel as the parts plastically deform in a ductile manner. The spherical bottom 3 has an upwardly extending sleeve 33 welded to it with a cover 34 in which a slot is formed and in which is inserted the head 35 of a long tension bolt 36 which extends upwardly and through the intermediate tube 20' to which the blades 19 are welded, where the tension rod is provided with a screw-threaded engagement with a nut 37 engaging the top of this tube 20' and which pulls downwardly on the central column so that via the struts 22 and 23 the annular series of plates 25 are pulled downwardly against the arcuate sides of the bottom of the hemispherical vessel. The arrangement is such that between the bottom of the central column construction and the upper surface of the pressure vessel's bottom wall 3 a small space remains such as in the area of 20 mm space. This spacing is between the lower edge 40 of the central column, which comprises an annular ring to which the bottom edges of the plate 19 are welded. It is also to be noted that there is a slight space between the top level of the intercept framework and the bottom of the core vessel. Such spacing provides for thermal expansion and contraction but, incidentally, provides room for the core vessel to fall and gain momentum or kinetic energy, which is however absorbed gradually by the ductile deformation of the parts. All of the parts are symmetrically distributed about the vertical centerline of the pressure vessel's hemispherical bottom and the pressure vessel itself. Therefore, with all of the parts symmetrical as the framework deforms, there is little tendency for the core vessel to move laterally or angularly in its short descent. Lateral shifting is prevented by the ring 27 which is peripherally interspaced from the core vessel's flange 11 for only a distance required for thermal expansion and contraction movements.