Patent Number: 039740277
Section: description

DETAILED DESCRIPTION OF THE INVENTION As illustrated, the pressure vessel 1 has a major portion 2 of its side wall in the form of a cylinder of uniform diameter, the radiating coolant pipe connections or nozzles 3 extending, however, from the upper side wall portion 4 of thicker wall diameter and, therefore, having the larger outside diameter than the portion 2. The spherical bottom 5 of the vessel has a peripheral portion resting on a support 6. The pressure vessel has a head 8 held down on top of the pressure vessel flange 9 by a mounting ring 10, the head having a spherical top 12, closing the top of the pressure vessel. The ring 10 is secured by hinge hooks 14 which engage the ring via a declining surface 15 in a self-locking manner. The hook hinge pins 16 are anchored to the upper part 17 of the concrete biological shield 18 which forms the concrete wall surrounding the pressure vessel side wall. It is this biological shield that forms the concrete pit in which the pressure vessel 1 is supported via its support 6. The encasement of this invention is generally indicated at 19. This encasement is built in the form of a shell comprising an inner layer 20 of the segmental cylindrical segments of pressure-resistant, heat-insulating material, and an outerlayer 21 made of similar segments. These segments or blocks are shaped so that the inner layer 20 engages the pressure vessel's side wall, including its portion 2 and 4, throughout the height of this side wall. The stack of segments forming the layer 20 below the side wall portion 4 are thicker than the segments contacting the portion 4, so that the outer surface of the layer 20 forms a cylinder of uniform diameter throughout, and on this layer is stacked the segments of the layer 21. As to both layers, there are a plurality of the segments both circumferentially and vertically and the segments are separable from each other. The inner surface of the layer 21 is shaped to conform exactly to the contour of the outside of the pressure vessel's side wall. By appropriately shaped segments, this includes the side of the bottom 5 which is of smaller diameter than the portion 2. The above segments or blocks may be made from a gas-containing concrete which has a specific gravity of 1.75 g/cm.sup.3 or, in other words, of so-called Leca concrete. The total thickness of both of the layers 20 and 21 may be in the neighborhood of 400 to 500 mm. The inner and outer surfaces of the layer 21 are, of course, both cylindrical and of uniform diameters throughout their lengths. The high-tensile strength steel cylinders are shown at 23, 24 and 25 and each extend over about 1/3 of the axial height of the pressure vessel side wall. However, a finer subdivision of the cylinders may be used if considered desirable from the fabrication and handling viewpoints. These rings are stacked end to end to form a substantially complete cylindrical wall. The top one of the rings 25 is formed with cutouts 26 to provide clearance for the coolant pipes 27 and, although only one of these pipes is shown, it is to be understood that a plurality of these pipes radiate from the vessel's portion 4. This permits the ring 25 to be lifted when the pressure vessel's cover has been removed and the hooks 14 swing out of the way. After this ring 25 is removed, the segments may be removed piece by piece, using simple manipulation worked from above the vessel's pit. The segments surrounding the coolant pipes 27 and the connections or nozzles 3 must also have cutouts to provide the necessary clearance. However, after removal of the segments above the pipes, and their connections or nozzles, removal of the segments on either side of the pipes and connections provide clearance for removal of the segments below these obstructions. Removal of the segments of the layer 21 upwardly from the annular space, then permits the segments of the layer 20 to be moved radially outwardly as required to clear the portion 4 of enlarged diameter, including any other shouldered parts such as at the junction between the lower vessel portion 5 and the balance of the vessel, and be then also removed upwardly. As previously indicated, the proportions of the segments and the steel cylinders are such that they are all loose relative to each other and the pressure vessel side wall when the pressure vessel is at or close to room temperatures, such as in the area of 20.degree. to 40.degree.C. When the encasement is installed and the pressure vessel expands while the steel cylinders 23, 24 and 25 remain somewhat colder, the thermal expansion of the vessel presses its side wall against the layers of segments which are then placed in compression by the reaction of the steel cylinders, thus applying the desired compressive restraint to the pressure vessel's side wall, for rupture protection. With the encasement of the present invention, the concrete wall 18 is no longer required as a mechanical containment for the vessel and it need only be designed for biological shielding purposes. Consequently, the concrete side wall need not be provided with steel reinforcements such as have heretofore been required although it may include tension rods or cables to carry the stress from the hooks 14 to the bottom of the concrete construction. In FIG. 2 the steel rings 30 are shown surrounding the main coolant lines 27 of which two are shown in this instance. These steel rings are mounted directly on the pipes 27 and are shown as having square cross sections and interspaced from each other a distance about equal to their thickness. The thickness of the square cross section rings should be at least equal to the wall thickness of the pipes 27. These steel rings are sufficient to prevent large pieces of the pipes 27 from becoming missles in the event of a rupture of the main coolant lines 27. At the same time the holes 31 in the concrete wall through which the pipes 27 pass, need not be made with undesirably large diameters. FIG. 2 shows the joints 33 which extend in the vertical direction and which in conjunction with the joints 34 which extend in the horizontal direction, permit the removal of the segments as described. In other words, the two layers are subdivided both radially and axially with respect to the pressure vessel. The segments of the two layers should be of such size as to permit them to be transported and handled in a practical manner.