GB2212602A

GB2212602A - Heat exchanger plant particularly for generating steam

Info

Publication number: GB2212602A
Application number: GB8726997A
Authority: GB
Inventors: George Edward Preece
Original assignee: National Nuclear Corp Ltd
Current assignee: National Nuclear Corp Ltd
Priority date: 1987-11-18
Filing date: 1987-11-18
Publication date: 1989-07-26
Also published as: GB8726997D0

Abstract

Heat exchanger plant intended, in particular, for a liquid metal cooled fast breeder reactor comprises an integrated pump and steam generating assembly (14) in which the pump unit (30) surmounts the steam generating unit (28). Such an arrangement permits the elimination of considerable lengths of pipework from the plant because the units can be connected together directly without the need for any intervening external pipework. The assembly 14 may be mounted to allow sliding and/or tilting movement to accommodate further expansion of pipework in the plant. <IMAGE>

Description

Heat exchanger plant This invention relates to heat exchanger plant in which hot fluid is caused to flow through a heat exchanger by a pump so as to transfer heat from the pumped fluid to a second fluid. In, for example, a nuclear reactor installation, hot fluid (for instance liquid sodium circulating in a secondary circuit) is pumped through a circuit including a pump and a steam generator in which the hot fluid is used to produce steam for subsequent use in generating electrical power.

In current designs of pool-type fast fission nuclear reactors employing liquid sodium in a secondary circuit, sodium is caused to flow from an intermediate heat exchanger (IHX) installed in the reactor to the steam generating unit (SGU) via pipework (the "hot leg") and returns to the IHX via pipework (the "cold leg") in which a pump is installed, the pipework forming the hot and cold legs incorporating bends which are intended to provide sufficient flexibility to accommodate thermal expansion, there being temperature differentials well in excess of 1000C between the hot and cold legs. Further complexity is introduced into the pipework if the combination of a single SGU and pump is to serve more than one IHX.

The desirability of reducing the length and cost of pipework in the secondary circuit has always been recognised as a design objective but scope for further reductions using conventional layouts is very limited.

According to the present invention there is provided heat exchanger plant comprising a heat exchanger unit connected in circuit with a pump unit which is operable to cause flow of one of the heat exchange media through the heat exchanger unit, characterised in that the heat exchanger unit and the pump unit are arranged with one unit surmounting the other, the upper unit being supported from the ground or other support structure via the lower unit.

Such an arrangement permits the elimination of a considerable length of pipework from the plant because, for instance, the units may be connected together directly without the aid of any intervening external pipework.

In one embodiment of the invention the pump unit surmounts the heat exchanger unit.

The assembly of heat exchanger unit and pump unit is preferably mounted for collective movement, eg sliding and/or tilting movement, to accommodate thermal expansion of pipework in the plant.

The heat exchange unit may be constituted by a steam generating unit and the primary heat exchange medium handled by the pump may comprise a liquid alkali metal, typically sodium.

According to a more specific aspect of the invention there is provided a nuclear reactor installation comprising a nuclear reactor having one or more intermediate heat exchangers (IHX) for effecting heat exchange between a primary coolant circuit and one or more secondary circuits, the or each secondary coolant circuit including at least one secondary pump unit and at least one steam generating unit (SGU), characterised in that the steam generating unit and the pump unit are arranged with one unit surmounting the other, the upper unit being supported from the ground or other support structure via the lower unit.

In a preferred embodiment of the invention, the assembly of SGU and pump unit is mounted adjacent, and in laterally offset relation to, the reactor and the assembly is movable collectively, in sliding and/or tilting manner, towards and away from the reactor to accommodate thermal expansion of the pipework of the secondary circuit.

The pump unit may form part of the hot leg of the secondary circuit and may be mounted above the SGU.

To promote further understanding of the invention, reference is now made, by way of example only, to the accompanying drawings in which: Figure 1 is a schematic front elevation of steam generating plant coupled to a liquid sodium cooled fast breeder reactor; Figure 2 is a fragmentary view on an enlarged scale showing the secondary sodium pump (SSP); Figure 3 is a plan view of the plant; Figure 4 is a plan view of a sliding skate support for the combined SGU and SSP; Figures 5 and 6, 7 and 8, and 9 are views of alternative forms of mounting arrangements for the combined SSP and SGU; Figures 10, 11 and 12 are respectively front, plan and side views of hydraulic jack assemblies for facilitating maintenance and/or replacement of the sliding skate bearings, Figures 10 and 12 being sections in the directions 10-10, 12-12 in Figure 11; and Figure 13 shows the layout, in plan, of the hydraulic jack assemblies in relation to the SGU.

Referring now to Figures 1 to 4, a liquid sodium cooled fast fission reactor is depicted by reference 10 and has a number of secondary sodium circuits each comprising a pair of intermediate heat exchangers (IHX's) 12 coupled by pipework to a combined SGU/SSP 14, the pipework comprising "hot"legs 16 and "cold" legs 18 connected respectively to sodium inlets 19 and sodium outlets 21 of the SGU. The SGU is also supplied with water at inlet region 20 and steam is extracted at outlet region 22 following passage through a bank of tubes (not shown) which extend through a shell along which the secondary sodium flows in passing from inlets 19 to outlets 21. The combined SGU/SSP 14 is mounted immediately alongside the reactor 10 on a support 24 and adjacent the top end of the SGU 28, the combined SGU/SSP is coupled to a seismic restraint arrangement 26.

As shown in greater detail in Figure 2, the SSP 30 surmounts the SGU 28 and, in effect, forms part of the hot leg supply to the SGU, the pump 30 being arranged to draw sodium from the inlets 19 and feed it into the main shell of the SGU 28 via the path indicated by arrows 32 in Figure 2. In operation, secondary sodium is passed through the IHX's 12 in heat exchange relation with primary circuit sodium heated by passage through the reactor core and the secondary sodium is pumped around the secondary circuit by the SSP to generate steam which can be used to drive electricity-generating turbines. -As is usual, the secondary circuit has a dump tank 36 associated with it into which the secondary sodium can be dumped via line 38 if the need arises, eg in the event of a sodium-water interaction.

A feature of the invention lies in the mounting of the SSP and SGU one above the other so that any external pipework between the SSP 30 and the SGU 28 is eliminated.

To cater for thermal expansion and contraction effects, the combined SGU/SSP 14 is mounted on the support 24 via an arrangement which allows movement of the combined unit in directions which accommodate thermal expansion and contraction of the pipework. As shown in the embodiment of Figures 1-4, the mounting arrangement comprises a skate 38 comprising generally horizontal side members 40 which extend generally parallel to a plane which is radial with respect to the vertical axis 42 of the reactor and also parallel to the pipework legs 18. Each side member 40 seats on the support 24 via dry bearings 44 so that the skate 38 can slide towards and away from the reactor. In addition to providing sliding support for the SGU/SSP 14, the skate 38 also permits tilting of the SGU/SSP 14 by acting as a fulcrum via pivotal connections 46 with the SGU/SSP 14. It will be seen that these connections 46 (whose axes extend generally horizontally and transversely of the pipework legs 18) permit the SGU/SSP 14 to tilt in a vertical plane generally radially of the reactor.

Figures 5 and 6 illustrate an alternative mounting arrangement in which the SGU/SSP 14 is afforded freedom of movement in the same directions as the embodiment of Figures 1-4 by means of a skate 38 which provides a knife edge-type fulcrums 50. Again the skate 38 is mounted on the support 24 via dry bearings 44.

Figures 7 and 8 illustrate another alternative mounting arrangement in which the previously-mentioned degrees of freedom, sliding and tilting, are afforded by elastomer bearings 52 on pedestals 54, the SGU/SSP 14 engaging the bearings 52 via a friction plate 56. In a further modification shown in Figure 9, the SGU/SSP 14 is mounted on the elastomer bearings 52 via a pair of plates 58, 60 affixed respectively to the bearings 52 and the SGU 28 respectively with dry bearings interposed therebetween to allow the SGU/SSP 14 to slide towards and away from the reactor independently of the elastomer bearings.

Figures 10-13 illustrate yet another form of mounting arrangement in which the skate 38 seats on four hydraulic jack assemblies 62 located in the manner shown in Figure 13, each jack assembly extending generally in the direction towards the reactor 10. Each assembly comprises a concrete plinth 64 on the support 24 and a base plate 66 affixed to the plinth via a layer of grout 68 and a cruciform-shaped shear stub 70 embedded into the concrete of the plinth 64. A platen 72 is mounted above the base plate 64 and is displaceable vertically by hydraulic piston and cylinder units 74 from a retracted position as shown in Figure 10 to an extended position (not shown) in which dry bearings 76 carried at the upper surface of the platon 74 contact the underside of the skate 38 to support the SGU/SSP 14 for sliding movement in the directions 78. In normal use all four assemblies will be extended to support the SGU/SSP 14. When maintenance/replacement of the dry bearings is to be carried out, each jack assembly can be retracted, in turn, to provide access while the remaining jacks are maintained extended. If desired, the arrangement may be such that the jacks are in their retracted positions when they support the SGU/SSP 14. In this event, access to each jack assembly can be obtained by extending the other three to lift the skate 38 away from the jack assembly which is to receive attention.

Claims

1. Heat exchanger plant comprising a heat exchanger unit connected in circuit with a pump unit which is operable to cause flow of one of the heat exchange media through the heat exchanger unit, characterised in that the heat exchanger unit and the pump unit are arranged with one unit surmounting the other, the upper unit being supported from the ground or other support structure via the lower unit.

2. Heat exchanger plant as claimed in Claim 2 in which the pump unit surmounts the heat exchanger unit.

3. Heat exchanger plant as claimed in Claims 1 or 2 in which the assembly of heat exchanger unit and pump unit is mounted for collective movement to accommodate thermal expansion of pipework in the plant.

4. heat exchanger plant as claimed in Claim 3 in which said movement comprises sliding and/or tilting movement.

5. Heat exchanger plant as claimed in any one of Claims 1-4 in which the heat exchange unit is constituted by a steam generating unit and the primary heat exchange medium handled by the pump comprises a liquid alkali metal.

6. A nuclear reactor installation comprising a nuclear reactor having one or more intermediate heat exchangers (IHX) for effecting heat exchange between a primary coolant circuit and one or more secondary circuits, the or each secondary coolant circuit including at least one secondary pump unit and at least one steam generating unit (SGU), characterised in that the steam generating unit and the pump unit are arranged with one unit surmounting the other, the upper unit being supported from the ground or other support structure via the lower unit.

7. An installation as claimed in Claim 6 in which the assembly of SGU and pump unit is mounted adjacent, and in laterally offset relation to, the reactor and the assembly is movable collectively towards and away from the reactor to accommodate thermal expansion of the pipework of the secondary circuit.

8. An installation as claimed in Claim 7 in which said movement comprises tilting and/or sliding movement.

9. An installation as claimed in Claim 6, 7 or 8 in which the pump unit forms part of the hot leg of the secondary circuit and is mounted above the SGU.

10. An installation as claimed in Claim 6, 7 or 8 in which the pump unit surmounts the SGU.

11. Heat exchanger plant substantially as hereinbefore described with reference to, and as shown in, any one of the embodiments illustrated in the accompanying drawings.