GB2196098A - Thermal insulation - Google Patents

Abstract

Thermal insulation modules for assembly of thermally insulating structures for vessels such as the primary vessel of a liquid metal cooled fast neutrol reactor comprise packs of stainless steel foils (30, 32) located between front and rear plates (28, 26) and arranged to be interleaved along the side edges. Overlapping foils are pressed into sealing contact by spring elements (48) to restrict radial flow of fluid through the modules. <IMAGE>

Description

SPECIFICATION Jointed thermal insulation structures This invention relates to high temperature thermal insulation and is particularly, but not necessarily exclusively, concerned with thermal insulation for large vessels such as the primary vessel of a nuclear reactor.

It is already known to thermally insulate the upper region of a liquid metal cooled fast neutron reactor by means of a modular thermal insulation structure in which each module comprises a laminate of metal sheets with spaces between the sheets for accommodating a fluid which may have insulating properties but which must be suppressed from leaking through the thickness of the module otherwise undesirable transport of heat from the hot face to the cold face of the insulation can occur.

According to one aspect of the present invention there is provided a thermal insulation module comprising a number of metal sheets located in superposed relation with spaces between adjacent sheets, characterised in that at least some of the sheets have resiliently deformable elements extending along an edge thereof within the space between adjacent sheets, each element being configured so as to substantially bridge the space while permitting insertion of the edge of a sheet of another module in interleaved fashion between the element and one of said adjacent sheets.

Each element may be affixed to one sheet inwardly of one edge of the sheet and extend towards the sheet edge while substantially bridging the space between adjacent sheets, the outermost edge of the element conveniently being obliquely Inclined relative to the sheet to which the element is affixed so as to afford a lead in entry for a sheet of another module.

Each element may present towards each sheet bounding the space in which it is located at least one crest extending lengthwise of the sheet edge, each such crest conveniently being capable of making substantially line contact with the respective sheet. In one embodiment, each element presents a single crest towards the one sheet and a pair of laterally spaced crests towards the opposite sheet, the single crest being disposed intermediate the pair of crests.

According to a second aspect of the invention there is provided a thermal insulation structure comprising a plurality of modules each comprising a number of metal sheets located in superposed relation with spaces between adjacent sheets, characterised in that the modules are jointed in edge to edge relation with sheets of one module interleaved with those of an adjacent module, the overlapping sheet edges of adjacent modules being pressed together by resiliently deformable elements which are located in the spaces between adjacent sheets and extend lengthwise of the sheet edges.

The arrangement may be such that overlapping sheet edges are engaged pairwise between one element on one side of the overlap and a second element on the opposite side of the overlap. The elements on each side of the overlap may each engage the overlapping sheet edges along at least one line of contact extending lengthwise of the sheet edges.

The resiliently deformable elements associated with the joint between adjacent modules may all be carried by the sheets of one module or, alternatively, some elements may be carried by the sheets of one module and the remainder may be carried by the sheets of the adjacent module.

The modules may all be substantially identical to each other; in a presently preferred embodiment, each module is provided with said elements along one edge thereof and the opposite edge of the module is free of said elements, the modules being jointed together with the element-carrying edge of one module interleaved with the element-free edge of the adjacent module.

The invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a diametrally sectioned schematic view of the primary vessel, guard vessel and concrete vault of a liquid metal cooled fast neutron reactor, all of the reactor internals such as fuel assembly, coolant pumps and heat exchangers being omitted since these are not of relevance to the understanding of the present invention; Figure 2 is a fragmentary front view of part of a lightweight modular thermal insulation assembly for insulation of the top part of the reactor primary vessel; Figure 3 is a radial sectional view in the direction 3-3 in Figure 2; Figure 4 is a fragmentary horizontal sectional view in the direction 4-4 in Figure 2; Figure 5 is a fragmentary sectional view in the direction 5-5 in Figure 4; and Figure 6 is a fragmentary sectional view in the direction 6-6 in Figure 2.

Referring to Figure 1, this shows the primary vessel 10, guard vessel 12 and concrete vault 14 of a fast reactor mounted one within the other. The primary vessel 10 forms part of the primary containment boundary of the reactor and, in use, contains a pool of molten sodium which serves as the coolant for the fuel assembly of the reactor.The lower region of the primary vessel contains a pool of relatively cool sodium, eg 3700C while the upper region houses an inner tank 16 containing a pool of hot sodium following circulation of the coolant through the reactor fuel assembly or core, the hot sodium temperature typically being of the order of 540 C. The inner tank 16 is separated from the upper part of the primary vessel by an annular space 18 which opens at its upper end within a region of the primary vessel occupied by a blanket of inert gas, such as argon, above the hot pool of sodium. The space 20 accommodates an annular thermal insulation assembly 22 which constitutes the primary vessel insulation and serves to protect the primary vessel 10 against the direct affect of changes in the sodium conditions, eg rapid temperature fluctuations.The space between the guard vessel 12 and the concrete vault also accommodates a thermal insulation layer 24 but this is not of relevance to the invention and will not therefore be described further.

Referring now to Figures 2 to 5, the thermal insulation assembly 22 is of modular construction and comprises thirty two generally rectangular modules connected long edge-to-long edge around the entire circumference of the primary vessel 10 within the annular space 20. Two complete modules 24 are shown in Figure 2, the modules being viewed from the hot face of the thermal insulation 22, ie the face presented inwardly of the primary vessel 20.

Each module 24 may typically be of the order of 1.8 metres wide and 9 metres long and comprises a back plate 26 (cold face) and front plate 28 (hot face) sandwiching between them a number of layers 30 of dimpled metallic foil spaced by layers 32 of corrugated metallic foil. By way of illustration only, the back and front plates 26, 28 may be of the order of 1.6mm thick, the dimpled foils 30 may be 0.15mm thick, the corrugated foils 32 may be 0.25mm thick and the spacing between adjacent dimpled foils 30 may be 510mm. For a nuclear reactor application, the plates 26, 28 and foils 30, 32 will be of stainless steel and typically each module 24 will comprise for example ten or eleven layers each of dimpled and corrugated foil, ie a total of twenty or twenty two layers sandwiched between the back and front plates.Each module 24 is suspended from a structural part 34 of the reactor roof by a single centrallylocated hanger 36 with clearance gaps 38, 40 (see Figure 3) between the module hot and cold faces and the adjacent surfaces of the inner tank 16 and primary vessel 10. Convective flow of gas along the clearance gap 40 is restricted by resiliently deflectable inclined baffles 42 which are attached to the back plates 26 of the modules, and bear against the primary vessel. The baffles 42 extend around the full circumference of the insulation assembly 22. The hot face of each module may be maintained at a fixed spacing from the inner tank 16 by some form of spring device or devices (not shown). The top edges 44 of each module are closed by suitable capping which forms no part of the invention and will not therefore be described further.

As shown in detail in Figures 4 and 5, along the length of one edge thereof, each module 24 is provided with spring formations 48, eg of stainless steel, for effecting edge joints between adjacent modules. At the long edges of each module, the corrugated foils 32 are folded back on themselves so as to be of double thickness and the spring formations 48 have one edge thereof secured at 50 to the double thickness region. Each spring formation 48 ie generally coextensive with the long edges of the foils 32 and extends obliquely across the gap between successive foils in a zig-zag fashion to form a number of crests of which one provides a line of contact 54 with the overlapping foils and the other two 52 are clear of the adjacent foil, ie only the crests 54 contact the overlapping foils.The free edge 56 of each spring formation, being obliquely inclined, provides a lead-in entry for the folded-back edge of a foil of the adjacent module to enable two modules to be linked together by offsetting them slightly in a radial direction so that the edges of the plates 26 and foils 32 of one module can be brought into interleaved relation with those of the other module and then displacing the modules relative to one another in a circumferential drection to trap the foils 32 of one module between the spring formations 48 and foils 32 of the other module in the manner illustrated in Eigure 4. (It will be appreciated that some of the spring formations in Figure 4 have been omitted for the sake of clarity).

When the modules are interleaved in the manner of Figure 4, the foil edges along the left hand side of the right hand module will be seen to be pressed firmly with an extended area sealing action against respective ones of the foll edges at the right hand side of the left hand module, the foil edges so sealed being pressed together along the lines of contact 54. After the modules have been interconnected in this manner, the partly overlapping back plates of adjacent modules are secured together along their long edges so that when all of the modules are assembled, the back plates 26 are linked together around the entire circumference of the primary vessel to provide continuity between adjacent modules and also prevent independent vertical displacement of one module relative to the others. The front plates 28 of the modules are also linked together to provide continuity between adjacent modules and also link the modules together to prevent independent vertical displacement of one module relative to the others. Thus, as shown, adjacent the tops of the modules, the link is effected by a sliding hasp 62 and keeper 64 type coupling and, adjacent the bottoms of the modules, the link is effected by a bolt 66 coupling together brackets 68.

The modules in the illustrated embodiment may be all identical with each other since each module has spring formations 48 along one long edge only for co-operation with the spring formation-free edge of an adjacent module. In an alternative arrangement however, there may be two types of module: a first with spring formations along both long edges thereof and a second without spring formations along either long edge. The insulation assembly in this instance may be constructed with joints formed in the manner illustrated in Figure 4 but in such a way that each second module-type is located beween a pair of the first module-type.

In both cases, ie identical module-type and two module-type constructions, it will be seen that the spaces, such as those depicted by reference numeral 60 in Figure 4, are substantially isolated from one another with respect to radial fluid flow because of seals effected by the spring formations 48, thereby suppressing radial flow of fluid and hence radial heat transport from the hot face to the cold face. In addition to the sealing function, the interleaved arrangement of the modules and the spring formations serve to accommodate thermal expansion effects and manufacturing tolerances while reducing the risk of undesirable bulging at the edges of the modules.

At spaced locations in the vertical direction, each module 24 incorporates means for controlling the pack thickness without relying on any expedients, such as studs, which penetrate the foil layers collectively with consequent risk of radial fluid leakage through the thickness of the pack and also thermal conduction via the studs. Referring to Figure 5, each of the corrugated foils 32, including the foil 32 attached to the backplate 26, has a generally horizontal strap 70 secured (as by welding for example) to its front face, ie to the bases of those corrugations which project towards the front plate 28 so that the straps 70 bridge the troughs formed by the corrugations which project towards the back plate 26.

Clips 72 are secured to the backface of the front plate 28 and also the foils 32 at one or more horizontally spaced positions with the aid of straps 72, again by welding for example. The clips 72 are dimensioned and positioned to fit within and register with the troughs provided by the rearwardly projecting corrugations of the adjacent foil 32. As seen in Figure 5, each clip 72 includes a vertical leg 74 which when the layers of foils 30, 32 are assembled engages behind the strap 70 of the adjacent foil layer, the free edge 76 of each clip being angled to facilitate assembly by sliding one foil layer relative to the other.

The straps 71 together with the clip legs 74 provide slots 78 which overlie the straps 70 for reasons that will be referred to later. The extent to which the clip legs 74 overlap with the straps 70 is normally determined by the hanger arrangement. From the backplate 26 to the front plate 28, each corrugated/dimpled foil layer 30, 32 is located by engagement of its clip 72 with the strap 70 to the rear of that layer, the front plate 28 being similarly located by engagement of its clip with the strap 70 attached to the foil layer 30, 32 closest to the hot face. The clip/strap arrangement will be seen to limit the overall thickness of each module without the need for studs or the like penetrating through the full thickness of the module.In addition, the arrangement will accommodate thermal movements and as described later it affords the possibility of secondary support of the module in the event of certain failure modes of the hanger 36.

The hanger arrangement is shown in detail in Figure 6 to which reference is now made.

The hanger comprises a stud 80 which is suspended from the roof structural part 34 and is connected to a plate 82 carrying a composite crosspin 84 made of two interfitting tubes 86, 88 closed off at each end by plugs 90. The crosspin 84 passes through the full thickness of the module and is trapped in position- by front and rear retainer plates 92 which also serve to cover the apertures in the plates and foil layers of the module so as to suppress fluid leakage and hence heat transport in this region. To facilitate assembly of the module to the hanger, the front plate and the foil layers 30, 32 are all formed with vertically elongated apertures to provide the clearance 94 which is sufficient to allow the clips 72 to.

clear the straps 70 and then slide behind the straps 70 while the front plate 28 or the respective foil layer 30, 32 is engaged with the crosspin.

The module can thus be assembled by: initially fastening the crosspin 84 to the backplate 26; assembling say one half of the foil layers 30, 32 to the crosspin and effecting sliding of the layers to engage the clips 72 with the straps 70; assembling and welding the plate 82 to the crosspin; assembling the remaining foil layers 30, 32 and the front plate 28 to the crosspin in the manner previously mentioned; and finally welding the front closure plate 92 to the crosspin. The hanger 36 is located centrally of the module and the foil layers 30, 32 immediately adjacent the hanger plate 82 and also the top capping 44 are adapted to allow for some degree of articulation of the hanger within the module so as to facilitate interlinking of the modules edgeto-edge during assembly of the cylindrical thermal insulation structure 22.

The completed insulation structure incorporates a number of safeguards against failure of the hangers 36. For example, if one of the hanger plates 82 should break, the integrity of the respective module remains intact provided the crosspin does not fail at the same time.

The module in question will remain in position by virtue of linking of its back and front plates 26, 28 of the adjacent modules. Failure of the crosspin is less likely because of its doubletube construction but, even in these unlikely circumstances, the integrity of the module will remain substantially intact since, at worst, the foil layers 30, 32 will slide downwardly but only to the extent determined by the straps 70 which will tend to enter the gaps 78 (see Figure 5). The clip/strap arrangements will also be capable of supporting the front plate 28 should its links with the front plates of adjacent modules fail for any reason.

Although the invention has been described above with specific reference to its application to the primary vessel of a nuclear reactor, it will be appreciated that it can be equally applied to other situations in which a substantially vertical wall is to be insulated.

Claims (7)

1. A thermal insulation structure comprising a plurality of modules each comprising a number of metal sheets located in superposed relation with spaces between adjacent sheets, characterised in that the modules are jointed in edge to edge relation with sheets of one module interleaved with those of an adjacent module, the overlapping sheet edges of adjacent modules being pressed together by resiliently deformable elements which are located.

in the spaces between adjacent sheets and extend lengthwise of the sheet edges.

2. A thermal insulation module comprising a number of metal sheets located in superposed relation with spaces between adjacent sheets, characterised in that at least some of the sheets have resiliently deformable elements extending along an edge thereof within the space between adjacent sheets, each element being configured so as to substantially bridge the space while permitting insertion of the edge of a sheet of another module in interleaved fashion between the element and one of said adjacent sheets.

3. A module as claimed in Claim 1 or 2 in which each element is affixed to one sheet inwardly of one edge of the sheet and extends towards the sheet edge while substantially bridging the space between adjacent sheets, the outermost edge of the element being obliquely inclined relative to the sheet to which the element is affixed so as to afford a lead-in entry for a sheet of another module.

4. A module is claimed in Claims 1, 2 or 3 in which each element presents towards each sheet bounding the space in which it is located at least one crest extending lengthwise of the sheet edge, each such crest being capable of making substantially line contact with the respective sheet.

5. A module as claimed in Claim 4 in which each element presents a single crest towards the one sheet and a pair of laterally spaced crests towards the opposite sheet, the single crest being disposed intermediate the pair of crests.

6. A thermal insulation module substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

7. A thermal insulation structure substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.