GB2144898A

GB2144898A - Nuclear power plant

Info

Publication number: GB2144898A
Application number: GB08409249A
Authority: GB
Inventors: Francis Chi-Ping Han
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1983-08-11
Filing date: 1984-04-10
Publication date: 1985-03-13
Also published as: FR2550600B1; CA1218863A; JPS6044665A; FR2550600A1; GB2144898B

Abstract

The heat-transport-system building 16 of the nuclear power plant is in communication with one or more auxiliary buildings 17 through a leak-tight joint across the seismic gap 19 between the buildings. This joint is welding sealed leak-tight by a gap liner which includes flexible corner assemblies 21. Along the walls defining each corner of the heat- transport-system building and of an auxiliary building each flexible assembly includes a pair of members which may be described as box-like open at the bottom or of generally U-shaped transverse cross section. The outer arm of each U is joined to the metal which lines the associated wall; the inner arm is disconnected from the wall. At each corner there are two sets of these members, one set along the walls defining the corner of the heat- transport-system building and the other along the wall defining the corner of an auxiliary building. When the walls at the joint are displaced, each member of an assembly is deflected or deformed relieving the strain produced by the displacement so that the seal between the assembly and the walls remains leak-tight. <IMAGE>

Description

SPECIFICATION Nuclear power plant This invention relates to structures which are required to be leak-tight or pressure-tight to fluids, particularly gases and, particularly, to nuclear-reactor power plants including structures on which the condition of leak-tightness is imposed.

A nuclear-reactor power plant includes a containment for a nuclear reactor and a plurality of auxiliary buildings and heat-transportsystem buildings which have facilities for monitoring the reactor and for converting the energy generated by the reactor into electrical power. The heat-transport-system buildings and the auxiliary buildings have walls of reinforced concrete. Where these walls are required to be leak-tight or pressure-tight, they are lined with a pressure-tight metal, usually carbon steel.

Typically a nuclear power plant includes in addition to the containment an auxiliary building and a heat-transport-system building which carry pipes for sampling the coolant and are referred to as a pipeway and sampling pipeway. Where the coolant is a highly reactive liquid such as sodium, the pipeway and the sampling pipeway must be maintained leak-tight to guard against the consequences of a spill of the liquid particularly as the liquid is radioactive. It is also necessary that nitrogen at a controlled pressure be maintained within the pipeway and the containment. The pipeway (auxiliary building) is separated from the sampling pipeway (heat-transport-system building) by a seismic gap. There is a passage between the pipeway and the sampling pipeway across this gap whose boundaries must be maintained leak-tight.The spacing between the walls of the pipeway and the walls of the sampling pipeway is variable.

Typically the spacing between the pipeway wall and the wall of the sampling pipeway at the seismic gap is between 5. and 7.5 cm.

The expansion and contraction of the gap between the buildings may vary between 0.7 mm and 25 mm. It is essential that the joint along the boundaries of the passage between the pipeway and the sampling pipeway be leak-tight regardless of changes in the spacing between the walls of these buildings at the passage.

In accordance with the teaching of the prior art an attempt was made to maintain this joint leak-tight by providing along the boundaries of the passage across the seismic gap a thin steel plate of angular transverse cross-section.

Typically the internal angle of the plate was about 60 with one leg of the angle welded to the metal with which the floor, walls and ceiling of the pipeway are lined and the other arm welded to the metal with which the floor, walls and ceiling of the sampling pipeway are lined. It was anticipated that this angle plate would fold or straighten out without rupturing or cracking to accommodate for changes of the seismic gap caused by the varying displacement of the structures defining the gap.

This anticipation was not realized. Under the strain caused by the structural motion, there were cracks at all four corners of the boundary of the passage.

It is the principal object of this invention to provide a leak-tight gap liner at the passage across a seismic gap between buildings particularly of a nuclear reactor power plant which gap liner shall maintain the power plant reliably leak-tight.

With this object in view, the present invention resides in a seal structure between walls separated by a gap whose width changes responsive to thermal conditions, seismic events, or the like, there being openings in said walls defining a passage across said gap, said structure comprising gap liners, composed of a material substantially impervious to fluids, spanning said gap and sealed to the boundaries of said passage to form, across said gap, a joint substantially leak-tight to fluids, said gap liners having flexible assembly means in regions of said gap, characterized in that said assembly means has at each of said regions, at least one member having an outer leg connected to said boundary of said passage and an inner leg spaced from said boundary, whereby, on displacement of the walls at said gap, said member is deformed but said inner and outer legs remain sealed to said boundaries thereby maintaining said joint leak-tight while relieving the strain on said liner.

The strain induced in the angle plates, particularly at the corners, is three dimensional. The flexible transition member according to the invention is capable of moving freely in three dimensions and can be accommodated in the limited space available for installation.

The corner sections and the transition sections are formed of angle plates from whose lateral ends members extend which are of generally transverse U-cross section and may be described as box-like members open at one end. The straight transition sections are long narrow box-like members. Preferably, there are at each corner four transition sections, one each along the surfaces in one plane of the two opposite walls at the seismic gap; e.g., the vertical surfaces, and one each along the surfaces of these walls which are at right angles to the first-mentioned surfaces; e.g., the horizontal surfaces. The straight transition sections convert the large deflection of the angle plates which occurs in prior-art apparatus into deflection at right angles to this large deflection of the legs of the box-like members or U-section members.The legs of the members of the center bent or arcuate section accommodate a large magnitude of motion of the buildings at the gap with small strain at the seal-welded joint across the seismic gap.

A brief description of how this is accomplished follows.

The leg of the U of each member of a flexible corner assembly which is towards the interior of the building along whose wall it extends, herein called the outer leg, is sealed to the wall; i.e., to the wall liner, of its associated building. The other leg of the same U-section member is disconnected from the same wall. The transition members take up the strain in the angle plate, when the width of the joint is changed, by converting the stress, which would tend to deflect the angle plate, into a stress on the transition member at right angles to the stress on the angle plates. This stress deflects or deforms the Usection member without materially affecting the angle plate. The center bent portion of the assembly at each corner is a member which is bent so that it approaches the shape of an arc parallel to the arc tangent to the walls at the corner.This member connects the transition sections. This center portion has at its ends members of generally U transverse section.

The invention will become more readily apparent from the following description of a preferred embodiment thereof shown, by way of the example only, in the accompanying drawings, in which: Fig. 1 is a fragmentary plan view of a nuclear power plant in accordance with this invention; Fig. 2 is a view in side elevation of the passage between the sampling pipeway and a pipeway at the seismic gap, looking towards the pipeway from the sampling pipeway of the plant shown in Fig. 1; Fig. 3 is a view in side elevation enlarged of the portion of Fig. 2 in circle Ill; Fig. 4 is a view in section taken in the direction IV-IV of Fig. 3; Fig. 5 is a view in end elevation taken in the direction V-V of Fig. 3; Fig. 6 is a view in section taken along line VI-VI of Fig. 5;; Fig. 7 is a fragmental view in perspective showing a flexible corner assembly which constitutes an important feature of this invention; Fig. 8 is a fragmental diagrammatic view showing the manner in which an assembly, in accordance with the teachings of the prior art, sealing the passage at a seismic gap, changes as the width of the gap is increased; and Fig. 9 is a similar fragmental diagrammatic view for a passage at a seismic gap sealed by an assembly in accordance with this invention.

The drawings show a nuclear-reactor power plant 11 (Fig. 1) including a nuclear reactor 13 in a containment 15 and an auxiliary building 16. Among the other buildings of the plant 11 is a sampling pipeway (heat-transport-system building) 17 which is separated from the pipeway in auxiliary building 16 by seismic gap 19. There is a rectangular passage 22 (Fig. 2) between the sampling pipeway 17 and the pipeway 16 and a gap liner 21 spans the gap 19 at this passage.

Typically the coolant for the reactor is liquid sodium which is radioactive. The sodium flows through pipes in the pipeway 16 and sampling pipeway 17 and a break in the pipes would produce a spill of the radioactive sodium which must be contained. In addition a controlled atmosphere of nitrogen is maintained in the pipeway 16 and in the sampling pipeway 17. The pipeway 16 and sampling pipeway 17 must be leak-tight against outflow or inflow of fluids such as the nitrogen possibly containing radioactive matter, in the pipeway and sampling pipeway and the outside air. To achieve this purpose the walls of the sampling pipeway and pipeway are provided throughout with liners 23 and 25 (Figs. 2, 7) of, typically, carbon steel sheet. The gap liner 21 is sealed leak-tight to the boundary of the passage 22 and the leak-tightness must be preserved regardless of changes in the gap width.

The gap liner 21 includes angle plates 31 and 33 (Fig. 3) extending along the sides of the boundary of the passage 22. These angle plates are seal-welded to the liner 25 of the pipeway 1 6 and to the liner 23 of the sampling pipeway 17. At each corner of the boundary, the angle plates 31 and 33 are con nected to a flexible corner assembly 35 (Figs.

2, 3, 4, 7). Each corner assembly 35 includes a straight transition section 37 colinear with plates 31 and a straight transition section 39 colinear with plate 33. The straight sections 37 and 39 are joined by what may be described as a curved section. This curved section is formed of smaller subsections 41, 43 and 45 at an angle to each other. Typically there are three such sections, the first 41 at 1 65' to the straight section 37, the second 43 at 150 to the first 41 and the third 45 at 150 to the second 43 and at 165 to the straight section 39. Within the scope of this invention there may be more than three sections. The envelope of the intersections 37 41, 41-43, 43-45 and 45-39 is an arc of a circle parallel to the arc tangent to the walls defining each corner of the boundary. The contour of the sides 31, 41, 43, 45, 39 is generally such an arc.

Each flexible corner assembly 35 is of generally W transverse section (Figs. 7, 9) throughout from the outer end of straight section 37 to the outer end of section 39. It includes a central angle portion 51 which is integral at its ends with members 53 and 55 (Fig. 4) of generally U-transverse section. The members 53 and 55 may be described as box-like open at the bottom. Each member has an outer leg 57 and an inner leg 59 (Figs.

4, 7, 9). Laterally the corner assembly 21 spans the seismic gap 1 9 between the buildings 15 and 17. The outer leg 57 is welded leak-tight to the liner 25 of the pipeway and to the liner 23 of the sampling pipeway. The inner legs 59 are disconnected from the liners 23 or 25 on each side (Figs. 4, 7, 9). The plates 31 and 33 are joined to the angle portion 51 by butt welds 61 and 63 (Fig. 3).

The subsection 41 is joined to the section 37 by butt weld 65, the subsection 43 to subsection 41 by butt weld 67, 43 to 45 by butt weld 69 and 45 to 33 by butt weld 71.

Typically the overall width of a flexible corner assembly may be 38 cm and the width of the members 53 and 55 may be 2.5 cm.

The assembly is centered over the gap 19 with the inner leg 59 of each member 17 cm and the outer leg 57, 19 cm from the center line through the apex of angle plate 51. The end of transition section 39 is typically 63.5 cm from the remote site of transition section 37 and the end of transition section 37 is 63.5 cm from the remote side of transition section 39.

Fig. 8 shows the changes which take place in a gap-liner plate in accordance with the teachings of the prior art when the seismic gap 19 is widened. The ends of angle plate 81 are seal welded to liners 23 and 25 at b and e. Widening of the gap 19 from cd to c'd' displaces the seal welds from b to b' and e to e' and drops the apex a to a'. The strain produced causes cracks to develop in the liner plate 81 at the corners of the passage 22.

Corresponding changes take place where the gap 19 is shortened.

Fig. 9 shows the changes which take place in the gap liner 21 when the gap 19 is widened from gh to g'h'. In this the seal weld at f is moved to f' and the seal weld k to k' but the position of the angle plate 51 remains substantially unchanged. The movement is taken up by the deformation of members 55 and 57 to 55' and 57'. A corresponding change occurs when the gap 19 is shortened.

Claims

1. A seal structure between walls (16, 17) separated by a gap (19) whose width changes responsive to thermal conditions, seismic events, or the like, there being openings in said walls defining a passage across said gap (19), said structure comprising gap liners (23, 25), composed of a material substantially impervious to fluids, spanning said gap (19) and sealed to the boundaries of said passage (16, 17)to form, across said gap (19), a joint substantially leak-tight to fluids, said gap liners (23, 25) having flexible assembly means (35) in regions of said gap (19), characterized in that said assembly means (35) has at each of said regions, at least one member having an outer leg (57) connected to said boundary (25) of said passage (16, 17) and an inner leg (59) spaced from said boundary, whereby, on displacement of the walls at said gap, said member is deformed but said inner and outer legs (57, 59) remain sealed to said boundaries (23, 25) thereby maintaining said joint leak-tight while relieving the strain on said liner.

2. A structure according to claim 1, characterized in that each of said members (53, 55) is of generally U-shaped transverse cross section with the outer leg of the U sealed to the adjacent wall (23, 25) and the inner leg of the U spaced from the adjacent wall.

3. A structure according to claim 1 or 2, wherein the walls of the structure are lined with material which is leak-tight to fluids, characterized in that the gap liners (23, 25) are sealed to the material lining the walls.

4. A structure according to any of claims 1 to 3, wherein the boundary of the passage is generally rectangular, characterized in that the flexible assembly means includes straight flexible corner sections (43, 45) arranged at angles to one another.