GB2025567A - Closure apparatus for pressure vessel. - Google Patents

Abstract

Closure apparatus for a penetration (4) in a prestressed concrete pressure vessel (5) has a sealing cover (3) and a supporting cover (2). The penetration (4) has a first liner (6) with a flange (7) sealed against a flange (11) of the sealing cover (3) by annular seals (12) accommodated in grooves (12), this arrangement constituting a primary sealing zone (14; 31). A second liner (18) surrounds the first liner (6), is mounted on a fork (16) secured to the first liner and is connected to an annular supporting surface (19). This surface (19) co-operates with a bearing surface (20) on the supporting cover (2) to form a secondary sealing zone (21) at which forces are transmitted from the supporting cover (2) to the pressure vessel (5). <IMAGE>

Description

SPECIFICATION Closure apparatus consisting of a supporting cover and a sealing cover for a large vessel opening The invention concerns closure apparatus consisting of a supporting cover and a sealing cover for a large vessel opening in a prestressed concrete pressure vessel clad with a liner, wherein both covers are held against the prestressed concrete pressure vessel by means of tendons and the sealing cover, which is provided with a flange, is supported on the supporting cover under the load of the internal pressure of the vessel.

From German published application No. 1784369 a closure apparatus for a manhole opening in the wall of a prestressed concrete pressure vessel is known which consists of two superposed components. The first member consists of prestressed concrete and the second is formed from an arcuate metal plate with the aid of which a leakage-proof sealing of the manhole cover should be achievable.

The two closure members have no direct contact with each other, i.e. the prestressed concrete member exerts no pressure (to increase the sealing effect) on the metal plate.

In German published application No. 17 84 625 there is described a similarly removable cover for a prestressed concrete vessel in which peripheral pressure pieces are arranged around a central closure member. The former are pressed radially against the central closure member by peripheral strips so that radial gaps remain between the strips.

The central closure member consists of several mutually superposed discs which are firmly pressed against each other by means of tension members or tendons arranged in the longitudinal direction of the vessel.

A further closure apparatus for a vessel opening is disclosed in German published application No. 25 10 021. It is constructed as a plug and both between the plug and the opening as well as between the plug and objects passing out from the vessel opening through the plug, welded lid seals are provided.

It is furthermore known for pressure vessels comprising of a steel vessel and a concrete shell surrounding the steel vessel to close the pressure vessel by means of a concrete cover as well as a steel cover arranged beneath the latter. Such a closure apparatus is described in German published application No. 22 19 412. Usually, the steel cover is connected with the concrete cover and is removable together with the latter. If there are only a few openings, (e.g. for control rod drives) through both of the covers, then the steel cover may be separated from the concrete cover also by an assembly method of separation.

The state of the art also includes a closure apparatus comprising a plurality of closure components in which the closure components are separated from each other as to function and are constructed as a sealing cover and a supporting cover. The two covers are restrained by tendons working in the longitudinal direction of the vessel.

Sealing is effected partly by a welded lip seal which bridges the gap between a flange arranged on the sealing cover and a flange provided on the liner of the penetration, and partly through annular seals arranged between the two flanges mentioned above.

By utilising prestressed concrete covers to close large pressure vessel penetrations, satisfactory safety against bursting may be achieved. However, it has proved difficult to construct such a closure apparatus in a sufficiently leakproof manner because at the location of contact between the closure apparatus and the pressure vessel unavoidable differential deformations arise. These have their root cause in that the closure apparatus deforms in a rotationally symmetrical manner but the pressure vessel opening or penetration does not deform in a rotationally symmetrical manner.

The task of the present invention is to achieve an improved sealing effect in a closure apparatus for large vessel openings of the above-mentioned type of construction.

According to the invention, this task is solved in that to seal the closure apparatus a primary and a second sealing zone are provided, wherein the primary sealing zone is constructed, in a manner known per se, from annular seals between the flange of the sealing cover and a flange applied to the liner of the penetration and the secondary sealing zone is realised by the co-operation of an annular bearing surface arranged on the supporting cover with a supporting surface which is rigidly connected with a second liner that coaxially surrounds the upper part of the liner of the penetration and which is supported on the concrete surrounding the prestressed concrete pressure vessel, the second liner being arranged at the free end of a fork member inserted into the liner of the penetration, and wherein the transmission of forces from the supporting cover to the prestressed concrete pressure vessel takes place in the region of the secondary sealing zone between the annular bearing surface and the annular supporting surface.

Thus in the closure apparatus according to the invention, an improved sealing effect is achieved in that the actual (primary) sealing zone is separated from the region of the transmission of forces from the supporting cover to the pressure vessel, i.e.

differential deformations cannot arise at this sealing zone or only to a considerabiy diminished extent.

The secondary sealing zone which is disposed in the region of transmission of forces (thus in the region where the unavoidable deformations arise) only requires to have a sealing effect which corresponds to the quality required to prevent or limit throughflow.

The limitation to throughflow realised by the annular bearing surface and the supporting surface and the primary sealing zone provide the closure apparatus with the required redundancy. The cylindrical component of the liner of the penetration lying between the primary sealing zone and the fork member is exposed to only relatively low stresses because of the infrequently arising axial loads.

Because between the flange of the sealing cover and the flange of the liner of the cavity the forces to be transmitted are only those required for pressing together the annular seals, the two flanges and the bolts for bolting the sealing cover to the liner of the penetration need only be of very small dimensions.

The pressure is taken up by the supporting cover made of concrete which is designed in the same way as the prestressed concrete pressure vessel and which ensures the desired safety against bursting.

During assembly or dismantling of the closure apparatus, the primary sealing zone does not present any particular difficulties. In the course of dismantiing the heavy suppoerting cover the sealing cover made of metal remains in the penetration so that a sealing closure of the pressure vessel is ensured.

The fork member inserted in the liner of the penetration is advantageously arranged at the end of a gap which is between the liner of the penetration and the concrete surrounding the prestressed concrete pressure vessel, where the length of the gap is to be dimensioned so that the deformations in the concrete are either not transmitted to the primary sealing zone or have an effect on it only to a very small extent. Thus the deformations do not have any influence on the primary sealing zone.

Expediently, the space between the individual seals in the primary sealing zone should be monitored for leakage and to this end control ducts are arranged in the relevant region. The said space may also be subjected via a duct to sealing (packing) gas, which measure may be additional to the leakage control. If the prestressed concrete pressure vessel serves to accommodate a helium-cooled nuclear reactor, then preferably pure helium is used as the sealing gas.

Advantageously a welded lip seal may be arranged around the periphery of the sealing cover flange which seal is welded to the flange of the liner of the penetration.

The concept of sealing of the closure apparatus according to the invention is compatible without limitations with smaller penetrations in both closure parts; i.e. one or more smaller openings may be provided in the closure apparatus.

It is advantageous so to construct the secondary sealing zone that on failure of the primary sealing zone a throughflow cross-section of predetermsined magnitude is released or cleared in the secondary sealing zone.

The drawings schematically show two preferred embodiments of the closure apparatus according to the invention. In both cases the object is the closure of a pressure vessel penetration in which a fan or blower for a steam generator may be installed. This latter is a part of a nuclear reactor plant.

In the Figures: Figure 1 is a first closure apparatus in vertical section, and Figure2 is an enlarged detail of a second closure apparatus according to the invention.

Figure 1 shows a closure apparatus 1 consisting of a supporting cover 2 and a sealing cover 3 for a penetration 4 disposed in a prestressed concrete pressure vessel 5. The penetration 4 is clad with a metallic liner 6 which has a flange 7 at its upper end.

A nuclear reactor (not shown) is installed within the prestressed concrete pressure vessel 5. Afan or compressor 8 for a steam generator is accommodated in the penetration 4. Vertical tensioning tendons 9 are led through the prestressed concrete vessel 5 and are connected via coupling members (not shown) with further tensioning tendon sections 9a. The latter, as well as the coupling members, are arranged in the supporting cover 2 which is made of concrete. The supporting cover is in the shape of a short cylinder and is surrounded both on its outer periphery as well as on its lower end face with a metallic sheath or sleeve 10.

The sealing cover 3 which is made of metal has a flange 11 on its periphery which lies against the flange 7 of the liner 6 and on its end face facing the flange 7 has a plurality of annular grooves in which annular seals 12 are arranged. To achieve the required sealing effect, the flange 11 and the flange 7 are pressed together by means of cylindrical bolts 13. This region represents the primary sealing zone 14. It is at the upper end of a gap 15 which extends downwardly between the liner 6 of the penetration 4 and the surrounding concrete of the prestressed concrete pressure vessel 5 over a predetermined "damping length" in order to keep the liner closure free of stress caused by creep of the surrounding concrete.

At the lower end of the gap 15 there is provided a fork member 16 set in the liner6 at the free end 17 of which is arranged a second liner 18 which coaxially surrounds the upper part of the liner 6. An annular supporting surface 19 is rigidly connected with the liner 18 and is supported on the surrounding concrete (containment) of the prestressed concrete pressure vessel 5. The annular supporting surface 19 co-operates with an annular bearing surface 20 arranged on the metallic sheath 10 of the supporting cover 3; i.e. the transmission of force from the supporting cover 2 to the prestressed concrete pressure vessel 5 ensues in this region.

The supporting surface 19 and the bearing surface 20 together constitute a secondary sealing zone 21 which only requires to be of the quality necessary for limiting throughflow. This region, in which differential deformations occur, is thus required to resist only relatively low sealing demands. In contrast, the primary sealing zone, which must meet the highest requirements, remains uninfluenced by differential deformations because it is separated from the region of force transmission or from the zone of equalisation or compensation for the differential deformption. The connecting part between the liner 6 and the liner 18, nameiy the fork member 16, is arranged so deeply within the penetration 4 that it is no longer influenced or exposed to differential deformations.

A smaller opening 22 is provided in the closure apparatus 1 to enable a shielding plug to be accommodated therein. It is provided with metallic cladding 23 which widens at the top and at the bottom into flanges. To these flange-like widened parts 24 there is secured by means of expansible bolts a cover 25 the requisite sealing of which is provided by means of annular seals 26. The lower of the two covers 25 is pivotally constructed.

Figure 2 shows an enlarged detail of another closure apparatus 30 according to the invention and in particular here only the region of the primary sealing zone is represented. Insofar as the individual components agree with those of Figure 1, here the same reference numbers have been used. The primary sealing zone 31 is constituted by the flange 7 of,the liner 6 of the penetration, the flange 11 of the sealing cover 3 and the annular seals 12 arranged between the two flanges, the seals being disposed in annular grooves 32 of the flange 11. By means of a plurality of cylindrical bolts 33 the two flanges 7 and 11 are pressed against each other. Compensating plates or strips 34 may be provided between the sealing cover 3 and the supporting cover 2.

Additional sealing of the closure apparatus 30 is achieved with the aid of a welded lip seal 35 which is welded both to the flange 11 of the sealing cover 3 and to the flange 7 of the liner 6 of the penetration. A control duct 36 is provided to monitor the space between the annular seals for leakage. By means of a further duct 37, the space between the outer annular seal 12 and the welded lip seal 35 is subjected to pure helium as sealing gas.

Claims (11)

1. Closure apparatus consisting of a supporting cover and a sealing cover for a large penetration in a prestressed concrete pressure vessel that is provided with a liner, wherein the two covers are restrained against the prestressed concrete pressure vessel in use by means of tensioning tendons and the sealing cover is provided with a flange and is supported against the supporting cover under the load of the internal pressure of the vessel and wherein a primary sealing zone and a secondary sealing zone are provided to seal the closure apparatus, the primary sealing zone being constituted by annular seals provided between the flange of the sealing cover and a flange provided on the liner of the penetration, while the secondary sealing zone is constituted by the co-operation between an annular bearing surface arranged on the supporting cover and an annular supporting surface, which latter is rigidly connected with a second liner that coaxially surrounds the upper part of the penetration liner and is supported on the surrounding concrete or containrepent of the prestressed concrete pressure vessel, the second liner being mounted at the free end of a fork member mounted in the penetration liner, the arrangement being such that the transmission of forces from the supporting cover to the prestressed concrete pressure vessel takes place in the region of the secondary sealing zone between the annular bearing surface and the annular supporting surface.

2. Closure apparatus according to claim 1, wherein the fork member is arranged at the end of a gap between the penetration liner and the surrounding concrete or containment of the prestressed concrete pressure vessel, the length of the gap being so dimensioned that in use deformations in the concrete have no or very little effect at the primary sealing zone.

3. Closure apparatus according to claim 1 or 2, wherein the spaces between the individual seals in the primary sealing zone are monitored for leakage via control ducts.

4. Closure apparatus according to any preceding claim, wherein the spaces between the individual seals in the primary sealing zone are subjected via a duct to sealing (packing) gas.

5. Closure apparatus according to any preceding claim, wherein a welded lip seal is arranged at the periphery of the flange of the sealing cover and is welded to the flange of the penetration liner.

6. Closure apparatus according to any preceding claim, wherein the covers are provided with at least one smaller opening.

7. Closure apparatus according to any preceding claim, wherein the secondary sealing zone is so constructed that on failure of the primary sealing zone a throughflow cross-section of predetermined magnitude is left free in the secondary sealing zone.

8. A closure apparatus according to claim 4, for use in a helium-cooled nuclear reactor, wherein the sealing gas is pure helium.

9. A closure apparatus according to any preceding claim wherein the penetration accommodates a compressor/blower for a steam generator.

10. Closure apparatus substantially as herein described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

11. A nuclear power plant including a closure apparatus according to any preceding claim.