GB1575950A

GB1575950A - Spacers

Info

Publication number: GB1575950A
Application number: GB36413/77A
Authority: GB
Original assignee: Kraftwerk Union AG
Current assignee: Kraftwerk Union AG
Priority date: 1976-09-03
Filing date: 1977-08-31
Publication date: 1980-10-01
Also published as: CH617286A5; BE858280A; FR2363861A1; FR2363861B1; DE2639817A1; ES462079A1; SE7709557L

Abstract

The spacer consists of a web grid (31, 32) which is made from a material that is favourable from the point of view of neutronics, and of resilient bearing elements (6, 7) made from Inconel. Said bearing elements are inserted into the spaces formed by the rigid bearing knobs (41-44), and are latched tight there. The rigid bearing knobs prevent excessive deformation of the resilient bearing elements and serve, at the same time, to ensure the minimum distances between the fuel rods in the event of strong lateral forces such as, e.g. earthquakes. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO SPACERS (71) We, KRAFTWERK UNION AKTIENGESELLSCHAFT, a Germany Company, of Mlheim, (Ruhr), Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a spacer and, more particularly but not exclusively, is concerned with a spacer for the fuel rods of a nuclear reactor fuel element.

According to the present invention there is provided a spacer in the form of a grid which comprises a plurality of sheet-form members arranged perpendicular to a plane so as to intersect and engage with one another to define apertures, each of which apertures is bounded by portions of at least three of said members and has an axis perpendicular to said plane; said portions having projections formed, on each side of each member, from the member, there being disposed between the projections of at least one of said portions of each aperture a resilient member comprising two resilient parts which bear against each other and against the projections of said portion in a manner securely holding said resilient member in said grid.

Preferably the sheet-form members comprise: first sheet-form members which are in parallel, spaced-apart relationship and which are equally spaced; and second sheet-form members which are in parallel, spaced-apart relationship, which are equally spaced, and which are orthogonal to said first sheet-form members; wherein each said portion of each of said first members adjoins the two nearest second members, and each said portion of each of said second members adjoins the two nearest first members; and wherein resilient members are held in at least two adjoining portions of each aperture.

Spacers in accordance with the present invention can be used with advantage for the fuel rods of a nuclear reactor, and the present invention also provides a fuel element comprising at least one spacer according to the invention, a frame which comprises top and bottom plates secured together by control rod guide tubes which pass through the or each spacer, and a plurality of fuel rods, each of which passes through an aperture in the or each spacer, and extends from the top plate to the bottom plate.

In some embodiments of spacers according to the invention there is provided a rigid projection below each resilient part which projections do not normally abut the fuel rod of a fuel element incorporating such spacers. When considerable forces occur whithin the fuel element a fuel rod pushes back the resilient part so that the rigid projections come to bear on the fuel rod and thus prevent a further deformation of the resilient part, and ensure the spacing from neighbouring fuel rods which is necessary for adequate cooling of the fuel rods.

For a better understanding of the present invention and to show more clearly how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows a diagrammatic section through a pressurised water cooled reactor; Figure 2 shows a perspective view of a possible form of a fuel element for the reactor of Figure 1; Figure 3 shows a vertical section through one of the members of a spacer grid with a pair of resilient parts along line III-III of Figure 3a; Figure 3a shows a vertical view of part of the member and the resilient parts of Figure 3; Figure 4 shows a side view of part of the member of Figure 3; Figure 4a shows a vertical view of the part of the member of Figure 4; Figure 5 shows a vertical section through a member of a spacer grid and a pair of resilient parts according to an alternative embodiment of the invention; Figure 6 shows a side view of part of the member of Figure 5; Figure 6a shows a vertical view of the part of the member shown in Figure 6; and Figure 7 shows a vertical view of part of a spacer according to the present invention.

As shown in Figure 1 fuel elements 2 form the core of the pressurized water reactor which is located within a pressure vessel 1. Cooling water flows through the fuel elements 2 from bottom to top, as shown by the arrows. The fuel element 2 (shown in Figure 2) includes a frame which comprises a top and bottom plate 4 linked by control rod guide tubes 5.

The control rod guide tubes 5 extend through a number of superposed spacers 3 and support the spacers 3. The apertures for the fuel rods are shown in Figure 2 but, for the sake of clarity, the nuclear reactor fuel rods 8 extend ing through these (see Figure 7) are not shown.

The fuel rods 8 are supported and centred in the individual apertures, which also provide oscillation-damping. Each of the fuel rods 8 is held by resilient parts and rigid emplacement members in each spacer. The resilient parts normally contact the fuel rod in the centre of that portion of the rod which is in an aperture of the spacer but the rigid emplacement mem bers or projections contact the rod above and below this point. This system of holding a fuel rod in a plane is therefore termed three point support. A support of this type is obtained with the spacer constructions illustrated in the subsequent Figures, as well as the previously described safeguard against excessive laterally occuring forces being pro vided.

Shown in Figure 3 are two resilient parts 6 and 7 which form a resilient member. Metal sheet-form members 31, 32 are provided with slots 33 by means of which they are inserted into, and engage with one another so as to form a spacer 3. Stamped-out rigid projections 41 and 42 on the upper edge and 43 and 44 on the lower edge of the sheet-form members 31 and 32 form intermediate spaces. These spaces are used, as shown in Figure 3, to support and retain the resilient parts 6 and 7. The resilient member comprises the two parts 6 and 7 which are partially bent back at their ends in the manner illustrated and thus mutually engage to securely hold one another in the spaces formed by the projections 41 - 44. The assembly of this apparatus is very simple. First the resilient part 7 is pushed in until its central section 7a engages in the space between the projections 42 and 43, and then the resilient part 6 is pushed in from below until its central section 6a in turn engages in the space between the projec tions 41 and 44. The bent upper section 6b of the resilient part 6 then lies within the bent upper section 7b of the resilient part 7 and the lower bent section 6c of the resilient part 6 presses on the flat section 7c of the resilient part 7, which abuts the projection 43. Figure 3a shows this arrangement from above. The parts 6 and 7 of the resilient member are narrower than the flat part of the stamped-out projections 41 to 44 so that a full abutment of the resilient parts 6 and 7 with the rigid pro jections of the sheet-form members 31, 32 is provided. The resilient parts 7a, 6a, can only be deformed until the fuel rod abuts the rigid projections 41, 42, 43 and 44, and thus an over stressing or permanent deformation of the resilient parts is prevented.

In the alternative embodiment shown in Figures 5 to 7 the structural form and support principle is similar to the resilient members and the rigid projections of Figures 3 and 4. The difference is that the sheet-form metal mem bers 31 and 32 have a rectangular cut-out 34 between the projections, which means that the insertion of the resilient parts 6 and 7 is facilitated and that there is a saving in material for the members 31 and 32. Furthermore, a connection is thus provided between the cool ant streams within the spacer which improves the cooling action in the region of the spacer.

With reference to Figure 7 it can be seen that in the two coordinate directions every second member 31 and 32 is provided with resilient parts 6 and 7, whilst those lying in between are provided only with the projections as shown in Figure 4 or Figure 6. This means that initially all the metal members 31 and 32 can be manufactured alike. The differences only appear as a result of the insertion of the resilient parts 6 and 7. Thus, of the two portions of each sheet-form members 31 and 32, defining an aperture, one is provided with a resilient member and the other is provided only with rigid projections, so that the afore mentioned three point support in a plane is obtained. To achieve this type of support, an arrangement of projections and resilient part could be selected, wherein portions with resilient parts and portions with projections only alternate with one another on each sheet-form member.

WHAT WE CLAIM IS: 1. A spacer in the form of a grid which comprises a plurality of sheet-form members arranged perpendicular to a plane so as to intersect and engage with one another to define apertures, each of which apertures is bounded by portions of at least three of said members and has an axis perpendicular to said

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Claims

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one of the members of a spacer grid with a pair of resilient parts along line III-III of Figure 3a; Figure 3a shows a vertical view of part of the member and the resilient parts of Figure 3; Figure 4 shows a side view of part of the member of Figure 3; Figure 4a shows a vertical view of the part of the member of Figure 4; Figure 5 shows a vertical section through a member of a spacer grid and a pair of resilient parts according to an alternative embodiment of the invention; Figure 6 shows a side view of part of the member of Figure 5; Figure 6a shows a vertical view of the part of the member shown in Figure 6; and Figure 7 shows a vertical view of part of a spacer according to the present invention.

As shown in Figure 1 fuel elements 2 form the core of the pressurized water reactor which is located within a pressure vessel 1. Cooling water flows through the fuel elements 2 from bottom to top, as shown by the arrows. The fuel element 2 (shown in Figure 2) includes a frame which comprises a top and bottom plate 4 linked by control rod guide tubes 5.

The control rod guide tubes 5 extend through a number of superposed spacers 3 and support the spacers 3. The apertures for the fuel rods are shown in Figure 2 but, for the sake of clarity, the nuclear reactor fuel rods 8 extend ing through these (see Figure 7) are not shown.

The fuel rods 8 are supported and centred in the individual apertures, which also provide oscillation-damping. Each of the fuel rods 8 is held by resilient parts and rigid emplacement members in each spacer. The resilient parts normally contact the fuel rod in the centre of that portion of the rod which is in an aperture of the spacer but the rigid emplacement mem bers or projections contact the rod above and below this point. This system of holding a fuel rod in a plane is therefore termed three point support. A support of this type is obtained with the spacer constructions illustrated in the subsequent Figures, as well as the previously described safeguard against excessive laterally occuring forces being pro vided.

Shown in Figure 3 are two resilient parts

6 and 7 which form a resilient member. Metal sheet-form members 31, 32 are provided with slots 33 by means of which they are inserted into, and engage with one another so as to form a spacer 3. Stamped-out rigid projections

41 and 42 on the upper edge and 43 and 44 on the lower edge of the sheet-form members 31 and 32 form intermediate spaces. These spaces are used, as shown in Figure 3, to support and retain the resilient parts 6 and 7. The resilient member comprises the two parts 6 and 7 which are partially bent back at their ends in the manner illustrated and thus mutually engage to securely hold one another in the spaces formed by the projections 41 - 44. The assembly of this apparatus is very simple. First the resilient part

7 is pushed in until its central section 7a engages in the space between the projections 42 and 43, and then the resilient part 6 is pushed in from below until its central section 6a in turn engages in the space between the projec tions 41 and 44. The bent upper section 6b of the resilient part 6 then lies within the bent upper section 7b of the resilient part 7 and the lower bent section 6c of the resilient part 6 presses on the flat section 7c of the resilient part 7, which abuts the projection 43. Figure 3a shows this arrangement from above. The parts 6 and 7 of the resilient member are narrower than the flat part of the stamped-out projections 41 to 44 so that a full abutment of the resilient parts 6 and 7 with the rigid pro jections of the sheet-form members 31, 32 is provided. The resilient parts 7a, 6a, can only be deformed until the fuel rod abuts the rigid projections 41, 42, 43 and 44, and thus an over stressing or permanent deformation of the resilient parts is prevented.

In the alternative embodiment shown in Figures 5 to 7 the structural form and support principle is similar to the resilient members and the rigid projections of Figures 3 and 4. The difference is that the sheet-form metal mem bers 31 and 32 have a rectangular cut-out 34 between the projections, which means that the insertion of the resilient parts 6 and 7 is facilitated and that there is a saving in material for the members 31 and 32. Furthermore, a connection is thus provided between the cool ant streams within the spacer which improves the cooling action in the region of the spacer.

With reference to Figure 7 it can be seen that in the two coordinate directions every second member 31 and 32 is provided with resilient parts 6 and 7, whilst those lying in between are provided only with the projections as shown in Figure 4 or Figure 6. This means that initially all the metal members 31 and 32 can be manufactured alike. The differences only appear as a result of the insertion of the resilient parts 6 and 7. Thus, of the two portions of each sheet-form members 31 and 32, defining an aperture, one is provided with a resilient member and the other is provided only with rigid projections, so that the afore mentioned three point support in a plane is obtained. To achieve this type of support, an arrangement of projections and resilient part could be selected, wherein portions with resilient parts and portions with projections only alternate with one another on each sheet-form member.

WHAT WE CLAIM IS: 1. A spacer in the form of a grid which comprises a plurality of sheet-form members arranged perpendicular to a plane so as to intersect and engage with one another to define apertures, each of which apertures is bounded by portions of at least three of said members and has an axis perpendicular to said

plane; said portions having projections formed, on each side of each member, from the member, there being disposed between the projections of at least one of said portions of each aperture a resilient member comprising two resilient parts which bear against each other and against the projections of said portion in a manner securely holding said resilient member in said grid.
2. A spacer as claimed in claim 1, wherein the sheet-form members comprise: first sheetform members which are in parallel, spacedapart relationship and which are equally spaced; and second sheet-form members which are in parallel spaced-apart relationship, which are equally spaced, and which are orthogonal to said first sheet-form members; wherein each said portion of each of said first members adjoins the two nearest second members, and each said portion of each of said second members adjoins the two nearest first members; and wherein resilient members are held in at least two adjoining portions of each aperture.
3. A spacer as claimed in claim 1 or 2, wherein said sheet-form members are formed from metal.
4. A spacer as claimed in claim 1 or 2, wherein there is provided first and second projections which are on opposite sides of said sheet and which are near one edge of said sheet, and third and fourth projections which are on opposite sides of said sheet and which are near an edge of said sheet which is opposite to said one edge.
5. A spacer as claimed in claim 4, wherein each resilient member is held between projections on one side of its respective portion and projections on the other side of its respective portion.
6. A spacer as claimed in any preceding claim, wherein the region in the middle of each portion of each sheet-form member is cutaway.
7. A spacer as claimed in any preceding claim, wherein each pair of resilient parts project on opposite sides of their respective sheetform member, and are secured by their bent form.
8. A spacer substantially as hereinbefore described with reference to or as shown in Figures 3, 3a, 4 and 4a or Figures 5,6, 6a and 7 of the accompanying drawings.
9. A fuel element comprising at least one spacer as claimed in any one of the preceding claims, a frame which comprises top and bottom plates secured together by control rod guide tubes which pass through the or each spacer, and a plurality of fuel rods, each of which passes through an aperture in the or each spacer, and extends from the top plate to the bottom plate.
10. A fuel element substantially as hereinbefore described with reference to or as shown in Figure 2 and Figures 3, 3a, 4 and 4a, or Figures 5,6, 6a and 7 of the accompanying drawings.