GB2102617A

GB2102617A - Fuel element casing

Info

Publication number: GB2102617A
Application number: GB08216497A
Authority: GB
Inventors: Capellen Heinz Meyer Zur
Original assignee: Interatom Internationale Atomreaktorbau GmbH
Current assignee: Interatom Internationale Atomreaktorbau GmbH
Priority date: 1981-07-20
Filing date: 1982-06-07
Publication date: 1983-02-02
Also published as: FR2509896B1; GB2102617B; DE3128652A1; DE3128652C2; FR2509896A1

Abstract

There is proposed a casing having easy-to-manufacture spacers. Projections (4) are pressed out of a hexagonal casing (t) in the region of the longitudinal edges (3) of the casing in the spacer plane, without the thickness of the wall of the casing being changed to any great extent thereby. The projections (4) extend generally parallel to the sides (2) of the casing (1) and thus form two contact surfaces for adjacent casings on each side of the casing in the spacer plane. The sides (2) of the casing (1) are less expanded in the area of the spacer plane than the edges (3). Particularly if the projections are rounded here, or pass into the remaining parts of the casing tube by means of transitional sections, the proposed device enables, in spite of simple manufacture and great rigidity, the individual casings to be drawn-out without difficulty even if the adjacent casing is slightly distorted. <IMAGE>

Description

SPECIFICATION Casing with spacers for fast breeder nuclear reactors This invention relates to a casing with spacers for use in fast breeder nuclear reactors.

Usually, the casing, which generally have a hexagonal cross-section, are placed adjacently into the nuclear reactor and are kept at a certain distance by spacers. In reactor operation with a fast breeder, the behaviour of the nuclear elements is determined by the behaviour of the material under the effects of neutron irradiation and high operating temperatures. The neutron flux is highest roughly in the centre of the nucleus and reduces towards the foot and head of the element and radially outwards. The materials then exhibit significant enlargements in volume under the effects of irradiation in rapid neutron flux, which enlargements are dependent on the neutron dosage, temperature and the state of the material.Due to these dependent relationships, various flexions occur in combination with the temperature fields present in the nuclear element, which, when restrained, lead to tensions in the structural parts of the element. These tensions can be relaxed or limited by neutron-induced and thermal creeping.

As a result of the difference in pressure between the inner and outer sides of the casing, the originally hexagonal cross-section of the casing buckles due to the neutroninduced creeping in the sides. An increase in size of the cross-section of the casing caused by swelling in volume is superposed on the expansion from creeping. A casing shape which bulges in the longitudinal section of the casing is produced corresponding to the said neutron flux profile with its maximum near the centre of the nucleus. In order to provide sufficient free space between the casings for these expansions of the casing arising from creeping and swelling, and in order to achieve defined contact points for transferring the nuclear fission energy between the casings, the casings are separated and reinforced by spacers. These spacers are arranged in various spacer planes.

Embodiments of these spacers implemented or planned up till now display welded-on, screwed-on or stamped projections on the sides of the casing. These projections come into contact when casings are arranged adjacent and thus effect a constant distance between them. Welded-on hexagonal annuli are also known as spacers. When such annuli are used, stellite plates are occasionally welded to the edges of the casing to increase resistance to wear.

The embodiments known up till now have various disadvantages: In the vicinity of the welded-on annuli or projections, the wall of the casing in the spacer planes is thicker than in the rest of the casing, which is undesirable for reasons of neutron economy and due to complications in calculating the design. Moreover, the welded areas are delicate and can be made only at great expense. A further definite disadvantage consists in the fact that casings with the spacers on the sides are not be removed individually without difficulty, since in the area of the nuclear centre, the spacers can not in certain circumstances be drawn past the expanded adjacent casing, which is enlarged particularly at the sides.

The present invention has been developed primarily (though not exclusively) with a view to provide a casing in the simplest possible manner with spacers which give a high degree of rigidity to the casing, permit the transfer of greater nuclear fission energy, but yet which can still be removed individually without difficulty.

According to the invention there is provided a casing with spacers for use in fact breeder reactors, in which the spacers consist of projections mounted on the casings in the spacer planes, in which: a) the projections are pressed out of the casing in the region of the edges of the casing, b) the thickness of the wall of the casing is approximately the same in the region of the spacer planes and the projections as in the remaining region; c) the outer surfaces of the projections extend approximately parallel to the sides of the casing and thus form on each side of the casing in the spacer plane two contact surfaces for adjacent casings; d) the sides of the casing are less expanded in the region of the spacer plane than the edges of the casing.

In this casing, the projections acting as spacers are pressed out of the casing in the areas of the casing edges. With this process, the thickness of the walls of the casing remains more or less constant even in the area of the projections. The shape of the projections is such that the outer faces run approximately parallel to the sides of the casing, whereby two contact surfaces for similarly constructed adjacent casings are produced on each side of the casing in the spacer plane.

The projections do not then project far into the sides of the casing, with the result that these sides are less expanded than the area of the edges. The advantage of this type of spacer is in the first place simple manufacture and in the second place considerably improved statics, i.e. greater rigidity of the casing in the area of the spacers. The forces between the individual casings are now transferred not on to the sides, but on to the edge area. A casing provided with this type of spacer can also be withdrawn individually without any difficulty, since the projections in the edge area can not collide against the swellings of adjacent casings.

Preferably, the regions of the projections providing a transition to the non-expanded wall of the casing are rounded. Thus, the projections should not be pressed out of the casing in such a manner as to have sharp edges, but be provided with chamfered, rounded transitional areas. Mutual hooking, or interengagement, of the casings is thereby also avoided.

In a further preferred development, and for the purpose of accommodating specific requirements, the casing may have transitional sections between the projections and the nonexpanded parts of the sides in the area of the spacer planes. As a result of this, each side of the casing consists, in the area of a spacer plane, of five sections: a central, non-expanded, or else only sightly expanded section, two projecting sections running more or less parallel thereto, and two transfer sections lying between them. Stress analyses and adjustment to various parameters, such as temperature, neutron irradiation, wall thickness, nuclear fission energy, manipulation etc. allow optimal relative sizes and angles of these various sections to be determined.According in each case to the demands made on rigidity and simplicity of manufacture, various possibilities are then produced, which are illustrated in the embodiments.

A further embodiment of the invention provides a casing in which the central section of each side is very short or can even be omitted completely. In this case, the whole side in the area of the spacer plane is expanded to a greater or lesser extent at the same time and continues across into the projection at the edge. This embodiment is easy to manufacture and is very rigid.

According to another preferred arrangement, several groups of axially displaced pressed-out projections are provided in the area of the spacer planes. This results in a further increase in rigidity and is of advantage in the production or manipulation of the casings. In this way, not just two, but more contact surfaces are produced in the area of the spacer planes for each adjacent casing.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings which show embodiments of casings with spacers for use in fast breeder nuclear reactors, and in which: Figure 1 is a perspective view of a casing cut away axially in a spacer plane; Figure 2 is a cross-section of a casing in the spacer plane; Figure 3 is an enlarged cutaway portion from Fig. 2, namely the area of one side of the casing in the spacer plane; Figure 4 is a side view of a casing in the spacer plane, where the spacer is of a specific design; Figure 5 is a cross-section along line V-V in Fig. 4; Figure 6 is a side view of a casing in the area of the spacer plane where the spacer has a different embodiment; and Figure 7 is a cross-section through Fig. 6 along line VII-VII.

The casing is indicated generally by reference 1 in the drawings. It has a hexagonal cross-section, with the result that the casing consists of six sides 2 and six edges 3.

Projections 4 are pressed out of the casing in the spacer plane, without however, the thickness of the wall of the casing being changed thereby to any great extent. The projections are situated in the region of the edges 3 and in each case a small portion of them continues over into the area of the sides 2. The sides 2 themselves are not greatly expanded, at least in their centre, whereby some free space is produced for bulging under the effects of rapid neutron irradiation. The relatively sharp edges of the projections 4 shown in Figs. 1 and 2 can, as shown in Fig. 3, be moderated by transitional sections 22. Fig. 3 shows the cross-section of one side in the area of a spacer plane, divided up into five sections: in the centre, the non-expanded area of the side 23, outside, the sections 21 belonging to the projections, and in between, the transitional sections 22.The relative sizes and angles of these various sections can be selected to be different according in each case to specific requirements and to tolerance limits. Further embodiments of the spacers are shown in the following figures.

One type is shown in Fig. 4, in which the section 23 is not formed completely in the side, so that the sides too are somewhat pressed out at the upper and lower edges 41 of the spacer. The actual spacer projections 40, however, lie once again in the area of the edges 3. Fig. 6, on the other hand, shows an embodiment in which the section 23 has been completely omitted, so that the sides are somewhat pressed out in the spacer plane.

However, as the cross-section shows in Fig. 7, the actual spacer projections 42 are situated in the area of the edges 3. This embodiment is distinguished by particular rigidity, but does not offer so much free play for expansions of the adjacent casing.

Claims

1. A casing with spacers for use in fast breeder reactors, in which the spacers consist of projections mounted on the casings in the spacer planes, in which: a) the projections are pressed out of the casing in the region of the edges of the casing; b) the thickness of the wall of the casing is approximately the same in the region of the spacer planes and the projections as in the remaining region; c) the outer surfaces of the projections extend approximately parallel to the sides of the casing and thus form on each side of the casing in the spacer plane two contact surfaces for adjacent casings; d) the sides of the casing are less expanded in the region of the spacer plane than the edges of the casing.

2. A casing according to claim 1, in which the region of the projections providing a transition to non-expanded wall of the casing are rounded.

3. A casing according to claim 1, in which each side of the casing comprises in the area of one spacer plane, of five sections: a central, non-expanded or slightly expanded section, two projecting portions extending generally parallel thereto, and two transitional portions.

4. A casing according to claim 3, in which the central portion is very short or is completely omitted.

5. A casing according to any one of the preceding claims, in which the casing is provided, in the area of the spacer planes, with a plurality of axially displaced groups of pressed-out projections.

6. A casing according to claim 1 and substantially as hereinbefore described with reference to, and as shown in any one of the embodiments illustrated in the accompanying drawings.

7. A fast breeder reactor including a casing according to ay one of the preceding claims.