GB2195044A

GB2195044A - Suspension device

Info

Publication number: GB2195044A
Application number: GB08622081A
Authority: GB
Inventors: Garth James Aspden; Roy Stanley Howard
Original assignee: National Nuclear Corp Ltd
Current assignee: National Nuclear Corp Ltd
Priority date: 1986-09-12
Filing date: 1986-09-12
Publication date: 1988-03-23
Also published as: GB8622081D0

Abstract

A suspension device comprises a split sleeve 18 assembled from a pair of thin-walled semi-cylinders 20 each formed with a radial flange 24 for seating on a support ledge provided eg by a groove 26. The split sleeve may be used for the suspension of thermal insulation from the roof structure 12 of a liquid metal cooled fast neutron reactor. Alternatively, the suspension device may constitute a baffle against convective flow in the cover gas in a liquid metal cooled fast reactor (Fig. 2. not shown). <IMAGE>

Description

SPECIFICATION Suspension devices This invention relates to a suspension device.

The invention has particular applications in nuclear reactor constructions but may find application in other situations.

According to one aspect of the invention there is provided a suspension device for suspension from a support structure, said device comprising at least two part-annular sections which can be assembled together to define a complete annulus, each part-annular section having at or adjacent one end a radially-directed projection for engagement with said structure and means being provided to maintain the sections in the assembled condition.

As will become apparent from the following description (which is by way of example only) referring to the accompanying drawings the suspension device of the inention may be used for the suspension of thermal insulation from the underside of the roof structure above a vessel such as the primary vessel of a nuclear reactor. In an alternative arrangement, the suspension device may constitute a skirt suspended from the roof structure of anuclear reactor to act as a barrier to convective flow of cover gas occupying the space between the roof structure and a pool of coolant within the primary vessel of the reactor.

In the drawings: Figure 1 is a diagrammatic vertical sectional view showing use of the suspension device for support of thermal insulation at the underside of a roof structure; and Figure 2 is a fragmentary diagrammatic view illustrating the use of the suspension device as a convective flow restricting skirt or barrier in a nuclear reactor.

Referring to Figure 1, in a liquid metal cooled fast neutron reactor it is necessary to provide access, via what are known as penetrations, through the: roof structure of the reactor for insertion of plant items, such as coolant pumps and intermediate heat exchangers, instrumentation and such like. It is also necessary to thermally insulate the roof structure and the penetrations provided therefore have to extend through the roof structure proper and the thermal insulation provided at its underside.

Figure 1 illustrates a typical penetration in accordance with the invention. The penetration is formed by a sleeve 10 extending between the top and bottom plates of the roof structure (of which only the bottom plate 12 is shown), an aperture 14 in the bottom plate 12, a tubular spigot 16 projecting downwardly at the underside of the bottom plate and a sleeve 18 which, in addition to providing a continuation of the penetration, also assists in the suspension of multiple-plate thermal insulation packs at the underside of the roof structure.

The sleeve 18 comprises a pair of thinwalled semi-cylinders 20 assembled together to define a substantially complete annulus (apart from the interruptions where the axial edges of the semi-cylinders meet-see reference numeral 22). Each semi-cylinder 20 at its top end is formed with an integral inwardly directed flange 24 which seats on a support ledge afforded by an annular groove 26 in the outer periphery of the support spigot 16. The two halves of the sleeve 18 are maintained in the assembled annular condition by a circumferential band 28 and the reduced diameter lower end 29 of a concentric sleeve 30 which is secured to the sleeve 18, as by welding in the vicinity of the lower end 29. The sleeve 30 is provided with a series of vertically spaced ledges 32 for supporting an assembly of stainless steel plates 34 constituting the multiple plate thermal insulation.

It will be noted that the split sleeve 18 avoids the need for a welded joint with the spigot 16 and hence the junction between the sleeve 18 and spigot 16 effectively acts as a thermal break which prevents the roof structure from being subjected to high thermal stress at this point.

Typically the spigot 16 can be of carbon steel while the insulation supporting sleeve 18 will be of stainless steel because of the higher temperature conditions to which the sleeve is exposed. In previous design proposals involving the connection of a stainless steel thermal insulation cylinder to the carbon steel roof structure, a transition weld between the two components has been proposed. The split sleeve construction of the invention obviates the need for a transition weld and its attendant drawbacks, eg thermal gradients along the cylinder resulting in high bending stresses at the welded joint and the need to use a thick cylinder whose thickness is dictated by welding rather than duty load requirements.

Figure 2 shows an alternative use of the split sleeve as a convective flow barrier in a liquid metal cooled fast reactor. In Figure 2, only as much as the reactor is illustrated as is needed to gain an understanding of this aspect of the invention. The reactor core 40 is enclosed within an inner cylindrical tank 42 which is itself enclosed within the reactor primary vessel 44 housed within a concrete vault 46. The reactor includes a roof structure 48 incorporating a rotary shield arrangement from which the above-core structure 50 is carried.

The thermal insulation is not illustrated in this embodiment. Various items of plant (eg pump 54) and instrumentation penetrate into the primary vessel, for example coolant pumps and heat exchangers. The primary vessel contains a pool of liquid sodium coolant, the surface of which is depicted by reference numeral 52.

As is well known in the art, the coolant in the primary circuit is continually circulated through the core by the coolant pumps and discharges into a hot zone 56 above the core 40 and within the inner tank 42 from where it is drawn into the intermediate heat exchangers for transfer of heat from the primary circuit to a secondary, liquid sodium, circuit.

A protective cover gas, eg argon, is provided in the space between the surface 52 of the coolant pool and the roof structure 48.

For efficient thermal insulation of the top part of the primary vessel, it is important to restrict convective flow of the cover gas, which may be laden with hot sodium aerosols, into an annular insulating space 60 between the inner tank 42 and the primary vessel 44. In accordance with a feature of the invention, this can be achieved by providing an annular skirt 62 which extends around the inner tank 42 in the vicinity of the side wall of the latter and dips into the coolant pool to form a barrier to convective flow of the cover gas. The skirt 62 is fabricated from at least two partannular sections assembled together to form a substantially complete annulus and held together in the assembled condition. Each section (as in the embodiment of Figure 1) is provided with an inwardly directed flange for seating on an annular support ledge 64 located at the underside of the roof structure.

As in the embodiment of Figure 1, the skirt is suspended from the roof structure in a manner which effectively provides a thermal break between the skirt and the roof structure whilst eliminating the need for a transition weld and avoiding to a significant degree subjecting the roof structure to a high thermal gradient and hence unacceptable bending stresses.

Claims

1. A suspension device for suspension from a support structure, said device comprising at least two part-annular sections which can be assembled together to define a complete an nulus, each part-annular section having at or adjacent one end a radially-directed projection for engagement with said structure and means being provided to maintain the sections in the assembled condition.

2. A vessel having a thermally insulated roof structure at the top of the vessel and penetrations in the roof structure for insertion of components into the vessel, at least one of the penetrations being defined, at least in part, by a suspension device for supporting thermal insulation at the underside of the roof structure, the or each suspension device com prising at least two part-annular sections which can be assembled together to define a complete annulus, each part-annular section having at or adjacent one end a radially-di rected projection for engagement with said structure and means being provided to maintain the sections in the assembled condition.

3. A nuclear reactor having a primary vessel containing a nuclear fuel core immersed in a pool of coolant, pump means for circulating the coolant through the core and a roof structure located above the vessel and enclosing a volume of cover gas in a space above the pool of coolant, characterised by a suspension device which depends from the roof structure and forms an annular skirt whose lower end is immersed in the coolant pool to restrict convective flow of the cover gas, the suspension device comprising at least two part-annular sections which can be assembled together to define a complete annulus, each part-annular section having at or adjacent one end a radially-directed projection for engagement with said structure and means being provided to maintain the sections in the assembled condition.

4. A device as claimed in Claim 1, 2 or 3 in which each section has a radially inwardly directed projection in the form of an integral flange.

5. A device as claimed in Claim 4 in which the flanges of said sections are co-extensive with the annular dimensions of the respective sections.

6. A device as claimed in any one of Claims 1 to 5 in which there are two such sections, each in the form of a semi-cylinder.

7. A suspension device substantially as hereinbefore described with reference to, and as shown in, any one of the embodiments illustrated in the accompanying drawings.