GB1593579A

GB1593579A - Nuclear reactor fuel element

Info

Publication number: GB1593579A
Application number: GB19386/78A
Authority: GB
Original assignee: Interatom Internationale Atomreaktorbau GmbH
Current assignee: Interatom Internationale Atomreaktorbau GmbH
Priority date: 1977-05-14
Filing date: 1978-05-12
Publication date: 1981-07-22
Also published as: DE2721869A1; BE866951A; IT7823266A0; FR2390805B1; IT1095143B; IT7823267A0; FR2390805A1; IT1095142B; BE866950A; GB1593578A; FR2390806A1; FR2390806B1

Description

PATENT SPECIFICATION

Application No 19386/78 ( 11) ( 22) Filed 12 May 1978 Convention Application No.

2 721 869 ( 32) Filed 14 May 1977 in Fed Rep of Germany (DE) Complete Specification published 22 July 1981

INT CL 3 G 21 C 3/32 Index at acceptance G 6 C UW ( 54) A NUCLEAR REACTOR FUEL ELEMENT ( 71) We, INTERATOM, INTERNATIONALE ATOMREAKT Ok BAU GMBH, of 5060 Bergisch Gladbach 1, Germany (Fed.

Rep), a German company 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 nuclear reactor fuel element of the type comprising a plurality of fuels rods disposed parallel to one another within a casing and fixedly held in relation thereto More particularly this invention relates to fuel elements of such type in which the fuel rods are secured in a so-called rod-holding plate at the lower end of the casing, and are allowed to freely expand upwards whilst being laterally guided by spacers The necessary mechanical strength of the element is provided by the casing, and coolant flowing around and along the fuel rods is guided by the casing It is desirable for the means used to secure the fuel rods in relation to the casing to be as simple as possible, not only with regard to the manufacture and assembly of the element, but also with regard to the subsequent dismantling of the spent element, which as is known, can be carried out only by means of remote-controlled tools because of intense radiation Since a large number of fuel elements are required for loading an individual nuclear reactor and since requirements with regard to the quality thereof are most stringent, even a small saving in the manufacture and assembly of individual parts has an appreciable effect on total costs.

Various methods have already been proposed for securing the fuel rods in the rod-holding plate For example, each rod end extending through the plate may be secured thereto by means of a nut secured on to the rod end The nut must, however, be secured against loosening during operation, for example by spot welding The rod end may alternatively be made in resilient form so that parts pressed together for passage through the bore in the rod-holding plate spread apart again thereafter and thus secure the fuel rod, it being possible for the locking action of the springing parts to be overcome during withdrawal by a sharp tug on the opposite end of the rod, just as it is overcome by pressure during their insertion 55 (see German Offenlegungsschrift 25 20 233 or U S Patent Specification 3 945 885).

However, owing to the fact that the fuel rods are very thin and have small wall thickness, application of appreciable pulling and 60 pushing forces which are necessary for the assembly and dismantling of such fuel rods is not desirable.

Securing means are also known in which one end of the fuel rod is shaped in the form 65 of a simple key barrel and is pushed into a corresponding keyhole-shaped aperture in the rod-holding plate and is locked by rotation about its longitudinal axis (see German Offenlegungsschrift 25 20 234) This form 70 of construction tends to lead to jamming in some cases, and hence it may be necessary to apply undue force whereby the strength of the rods is endangered A further proposal is to form the ends of the fuel rods with 75 keyhole-like openings which extend transversely in relation to the longitudinal axis of the rod, and through which correspondingly shaped holding members are passed These members also engage with corresponding 80 apertures in the casing, there being mounted on each of the holding members a row of fuel rods (see German Offenlegungsschrift 31 641 or U S Patent Specification 3

890 197) Apart from the fact that the man 85 ufacture of the fuel rods with ends of a complex shape involves considerable cost, these constructions have the disadvantage that even when the rod-holding plate has, in addition to the bores receiving the fuel rods, 90 further openings for the passage of coolant, the cross-sectional area of flow available within the casing is reduced to a greater extent than by the fuel rods themselves in the further course of the flow In other 95 words the rod-holding plate causes a pressure loss which necessitates the installation of more powerful and costly pumps in the coolant circuit.

According to the present invention, there 100 ( 21) ( 31) ( 33) ( 44) ( 51) ( 52) 1 593 579 1 593 579 is provided a nuclear reactor fuel element comprising a plurality of fuel rods disposed substantially parallel to one another within a casing, a plurality of rod-holding plates each having a pair of opposed faces and being disposed between the fuel rods transversely thereto, thereby dividing them into a plurality of rows, and one or more elongate members extending through the rod-holding plates and releasably connected to mounting means fixedly disposed in the casing, wherein each fuel rod has, at one end, projections engaged in corresponding recesses of arcuate cross-section formed alternately on the two faces of each rod-holding plate.

Each fuel rod is desirably formed at said one end with two parallel flat faces such that the maximum thickness of fuel rod removed to form each face is at least equal to the depth of the recesses, and such that the length of each face is at least equal to the width of the adjacent rod-holding plates between the recesses and adjacent margins thereof These parallel faces should be formed at a distance from said end of the rod which is, at most, equal to the width of the corresponding recess.

The rod-holding plates are formed with apertures through which the elongate members can be passed These apertures are so distributed along the length of the rodholding plates that when a plate is disposed within the casing the apertures are aligned with those in the rod-holding plates When the elongate members are passed through these apertures the individual rod-holding plates, and with them the fuel rods, are combined to form an assembly.

Rows of fuel rods and rod-holding plates are alternately assembled in the correct orientation in relation to one another, the rod-holding plates are secured against slipping in relation to one another by means of the mounting means, and the whole bundle of fuel rods thus produced is pushed into the casing which prevents the elongate members from falling out and thus ensures that the bundle is held together The spent fuel element is taken apart in the inverse sequence, in which process as in the assembly, no fixed connections, or connection which may have become fixed in the course of the use in the reactor, such as weld seams, screw connections and the like have to be broken No special forces have to be applied to dismantle the assembly into individual parts because the bundle breaks up into its individual parts after having been withdrawn from the casing No single rod-holding plate as such is employed, it being replaced by a plurality of rod-holding plates and elongate members which have only a small cross-section in the direction of flow of coolant, so that the available cross-sectional area of flow is less restricted in the region in which most heat is emitted by the rods.

For a better understanding of the present invention and to show how the same may be carried into effect reference will now be made, by way of example, to the accom 70 panying drawings in which:Figures 1 and 2 show vertical and horizontal sections respectively through part of a nuclear reactor fuel element according to the invention, the section of Figure 1 being 75 taken along the line AB of Figure 2, and the section of Figure 2 being taken along the line CD of Figure 1; Figure 3 shows in more detail the end of a fuel rod and associated rod-holding plate in 80 section along the line X of Figure 2; and Figure 4 shows a horizontal section through part of a nuclear reactor fuel element according to the invention taken along the line EF of Figure 1 85 The illustrated part of the fuel element shown in the accompanying drawings comprses a plurality of fuel rods 1 in the form of long cylindrical pins disposed in a hexagonal pattern within a casing 2 These rods engage 90 at the lower ends as shown in closure or rod-holding plates 3 which in turn are held together by elongate members 5 passed therethrough The members 5 are fixed in corresponding slots in mounting means 95 which takes the form of a retaining ring 6.

The assembly is put together outside the casing 2 by pushing together the parts 1, 3 and 5 The finished bundle is pushed into the casing 2 and prevented from falling out by a 100 sleeve 8 which is connected to the retaining ring 6 by means of screws 7 and which is secured to the casing 2 by further screws (not shown here) or by welding.

The structure of the ends of the fuel rods 105 will be described in more detail with reference to Figure 3 The rods 1 have on their solid end piece 11 flat faces 111 cut into the cylindrical form of the rods and produced by milling for example, whereby an effective 110 projection 112 is formed at the lower end of the rod by the retention of the full circular cross-section At its upper end, the end portion 11 is adjoined by a hollow can 12 which is for the greater part filled by fuel pellets 115 13 The associated rod-holding plate 3 has alternately on both sides (see also Figure 2) recesses 31 of arcuate cross-section into each of which there fits the projection 112 of one fuel rod Above and below the line of 120 the recesses 31, the rod-holding plate comprises strips 32 and 33 respectively of full cross-section The overlap of the contour of the rod-holding plate 3 with that of the end piece 11 of the fuel rod is made possible in 125 the region of the strip 32 by the faces 111.

In the region of the strip 33, the rodholding plates 3 are formed with apertures 331 through which the elongate members 5 are pushed during assembly As is apparent 130 1 593 579 from Figure 4, different rod-holding plates 3 have different lengths The apertures 331 in individual rod-holding plates are each offset from the centre of the plate to the same extent so that the apertures are aligned with one another when the fuel rod assembly is put together.

Claims

WHAT WE CLAIM IS:-

1 A nuclear reactor fuel element comprising a plurality of fuel rods disposed substantially parallel to one another within a casing, a plurality of rod-holding plates each having a pair of opposed faces and being disposed between the fuel rods transversely thereto, thereby dividing them into a plurality of rows, and one or more elongate members extending through the rod-holding plates and releasably connected to mounting means fixedly disposed in the casing, wherein each fuel rod has, at one end, projections engaged in corresponding recesses of arcuate cross-section formed alternately on the two faces of each rod-holding plate.

2 A nuclear reactor fuel element as claimed in claim 1, wherein each fuel rod is formed at said one end with two parallel flat faces such that the maximum thickness of fuel rod removed to form each face is at least equal to the depth of said recesses, and such that the length of each face is at least 30 equal to the width of the adjacent rodholding plates between the recesses and adjacent margins thereof, the parallel faces being formed at a distance from said end of the rod which is, at most, equal to the width 35 of the corresponding recess.

3 A nuclear reactor fuel element, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings 40 HASELTINE, LAKE & CO, Chartered Patent Agents, Hazlitt House, 28, Southampton Buildings, Chancery Lane, London WC 2 A l AT also Temple Gate House, Temple Gate, Bristol B 51 6 PT and 9, Park Square, Leeds L 51 2 LH, Yorks.

Agents for the Applicants Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd, Berwick-upon-Tweed, 1981 Published at the Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.