Patent Number: 044951477
Section: description

Referring now to the figures of the drawing and first particularly to FIG. 1 thereof, it is seen that the heat-retarding closure system is disposed in the nozzle space area of a pressurized-water nuclear reactor, the nozzle contour of which is indicated with reference numeral 1 and the heat-retarding partition 2 of which has pressure relief openings 3 closed by closure elements 4 in the form of heat-retarding cassette inserts. FIG. 1 shows only one such cassette insert 4; FIG. 9, on the other hand, shows larger sectors with several cassette inserts, which will be discussed later. FIG. 2 shows that the front side of a peripheral shearing edge 4a of the closure element 4 constructed as a heat-retarding cassette insert rests against an outer, sealing blowout skin 5. The blowout skin 5 is gastightly welded to the periphery of the pressure relief opening 3 bounded from the inside IS to the outside AS by walls 6 of conical or truncated-pyramid shape. For this purpose the blowout foil 5 is provided with a flanged rim 5a abutting a bent-off rim 2a1 of the outer face 2a of the partition 2, the inner face of which is marked with reference numeral 2b. The partition 2 is formed as an all-metal insulation with mutually spaced, roughly plane-parallel retarding foils indicated at reference numeral 2.1, forming the air-filled retarding walls 2.2 between them and the inner and outer faces 2b, 2a. The bounding or boundary wall 6 of the pressure relief opening 3 is formed by a metal foil having flanged rim areas 6a on the outside AS and 6b on the inside IS which abut the outer face wall 2a and inner face wall 2b, respectively, and are welded gastightly to these walls. The wall thickness (in the pressure difference direction) of the blowout skin 5 constructed as metal foil is such that when the permissible pressure difference between the inside IS and outside AS is reached or exceeded, the cassette insert 4 shears off the blowout skin with the peripheral shearing edge 4a and is itself pushed out of its seat. It then drops to the outside, but since it is of lightweight construction, it cannot damage adjacent walls or components. In the embodiment example shown, the blowout skin is 0.4 mm thick, for example; behind it is the pressure foil 4.1 which has the shearing edge 4a. Stacked behind it, in turn, are a number of retarding foils 4.2 which are mutually spaced and form retarding cells 4.3, the number of which depends on the thickness of the retarding stack or of the partition. The conical casing or wall 6 is made of austenitic steel sheet about 1 mm thick. In the construction shown in FIG. 2, the foils 4.2 are compressed, starting at the pressure side (which is equal to the inside IS) of the system, when the afore-mentioned differential pressure occurs. The foil 4.20 which is smallest in area, is located on the pressure side. This prevents the foils 4.2 from cocking or canting. After the foils have been pushed together, the load acts upon the 1-mm thick pressure or intermediate foil 4.1. This stiffer insert now brings the pressure load to bear as forward thrust on the 0.4 mm thick blowout foil 5, which is tightly welded to the frame of the surrounding retarding system, and shears it off. This is followed by the complete insert being pushed out; the overflow section is open for the medium to flow out. In the embodiment example according to FIG. 2, therefore, the cassette insert 4 is an all-metal structure, the retarding foils 4.20, 4.2 and 4.1 each being doubly chamfered in V-shape at their outer rim with the outside leg of their bevels each contacting the bottom surface of the respectively adjacent retarding foil in convection-retarding fashion. In the second embodiment example according to FIG. 3, the cassette insert 4 contains mineral fibers 8 as retarding material, and the partition 2 also contains mineral fibers 7 instead of retarding foils. The blowout skin 5' in the second embodiment is a glass blowout pane clamped and sealed in the partition area surrounding the cassette insert 4. The seat of the blowout insert 4 is again formed by the limiting wall 6 which is tapered from the inside IS to the outside AS. Furthermore, at the inner periphery of the limiting wall 6 another correspondingly tapered insert 9 is inserted. The outside of a shoulder 9a of the insert 9 forms the seat for the glass pane 5'. The outer rim area of the insert 9 is welded gastightly to the limiting wall 6 at reference numeral 10. A tightening screw 11 is anchored and welded gastightly to the shoulder 9a. The tightening screw 11 has an outwardly-projecting end 11a onto which the holding plate 12 with appropriate through holes is laid around the outer rim 13 of the glass pane 5'; the sealing strip 14 is formed of a heat-retarding, asbestos-base sealing material. The holding plate 12 is pressed against the sealing strip 14 and the rim 13 by the nut 11b with a washer 11c, pressing these parts in sealing-fashion against the shoulder 9a. The actual blowout insert 4 has an outer metal foil encapsulation with the sheet metal faces 15a, 15b and an enveloping sheet metal part 16. On the outside AS and inside IS the enveloping sheet has a peripheral, projecting rim 16a, 16b each. Each rim is welded gastightly to the sheet metal faces 15a, 15b, respectively. For this purpose the sheet metal faces 15a, 15b have a folded outer rim. In this embodiment example, the peripheral, projecting rim 16b is provided with an acutely beveled bursting edge 16b1, as shown more clearly in the detailed view of the circle A according to FIG. 7. Thus a break-determining edge is formed which, when tripped, pushes against the glass pane 5', causing it to burst due to the shear stress, whereupon the cassette insert 4 is pushed out again. FIG. 4 shows a third embodiment example which is a modification as compared to FIG. 3 inasmuch as the sealing strip 14 does not envelop the rim 13 of the glass pane 5' in U-shape, but is in contact with it on one side only. Otherwise, the construction is identical with that of FIG. 3. The fourth embodiment example according to FIG. 5 again agrees with that of FIG. 3, except for the fact that both the partition 2 and the closure element 4 have a metal foil insulation and that the shearing edge of the pressure foil 4.1 is constructed like the shearing edge 4a of FIG. 2. In the fifth embodiment example according to FIG. 6, a metal foil insulation for the partition 2 and the closure element 4 according to FIG. 2 are also provided, but deviating from the embodiment example according to FIG. 5, instead of glass a metallic blowout panel 5 is provided to close the pressure relief openings 3 which is formed in this case by the tapered sheet metal seat 9. The construction of the shearing edge 16b1 (see FIG. 7) is identical with that according to FIGS. 3 and 4. The edge is again formed by a projection rim of the enveloping sheet metal part 16. In the partial view of FIG. 8, there may be seen the outer supporting shield 17 and the inner shield 18 of the biological shield for a nuclear reactor pressure vessel 19 with a nozzle 1. An annular gap 20 is disposed between the supporting shield 17 and inner shield 18, serving among other things to cool the shield and to relieve a possible overpressure. This can be relieved through an overflow canal with a spill valve disposed in the supporting shield 17 at the lower end thereof which is not shown. The ring box girder 21, anchored in the supporting shield 17, forms bearing surfaces for the support lugs 23 of the pressure vessel 19 with the brackets 22, which are distributed over the circumference of the pressure vessel 19. The in-service inspection door 24 which permits access to the annular space 25 between pressure vessel 19 and inner shield 18, forms part of the partition 2 in the nozzle space area. FIG. 9 shows, in a fragmentary view, the development of the partition in the nozzle space area with the nozzle leadthrough openings 26, the in-service inspection doors 24 and the closure elements 4, identified by diagonal lines and constructed as blowout elements. Of the eight nozzle leadthroughs 26 only two are shown; the development therefore covers slightly more than 45.degree.. Above the in-service inspection doors 24, partition recesses 27 are located, where the brackets 22 (see FIG. 8) project into the partition area. The particular advantage of the closure system is that the partition can be built completely by the building block system (see joints 28 between individual partition components) and assembled for trial outside of the reactor building. If all dimensions are correct, installation in the inner shield area (FIG. 8) can take place successively.