WO1998026427A1

WO1998026427A1 - Apparatus for loading nuclear fuel pellets

Info

Publication number: WO1998026427A1
Application number: PCT/GB1997/003335
Authority: WO
Inventors: Graeme Michael Wigg; Michael Kevin Bridges
Original assignee: British Nuclear Fuels Plc
Priority date: 1996-12-09
Filing date: 1997-12-03
Publication date: 1998-06-18
Also published as: GB9625516D0; AU5232198A

Abstract

There is provided an apparatus for loading nuclear fuel pellets into a carrier tube, the apparatus comprising a first support body for holding in parallel relationship about a common axis a plurality of pellet column holders and for rotating said holders about said axis and a second support body for holding in parallel relationship about a common axis a plurality of fuel tube holders, and for rotating said fuel tube holders about said axis, said support bodies being dimensioned such that they may be brought together in an end-to-end staggered relationship to align one of said pellet column holders with a fuel tube holder to allow transfer of pellets therebetween, each of said bodies being mounted for rotation about its common axis in order to align another of said pellet column holders with one of the fuel tube holders.

Description

APPARATUS FOR LOADING NUCLEAR FUEL PELLETS

FIELD OF THE INVENTION

This invention relates to apparatus for loading nuclear fuel pellets into carrier tubes to form loaded rods which are then inserted into a skeleton of grids to form the assembled nuclear fuel element.

BACKGROUND OF THE INVENTION

In a typical process for assembling nuclear fuel elements, nuclear fuel pellets of required enrichments are loaded into carrier tubes to form loaded fuel rods. The tube may be required to be filled with a stack of pellets all of the same enrichment or with a plurality of substacks of different enrichments. The tube itself may be located in an area free of radioactivity whereas the pellets are assembled for loading into the tube in an active area (uranic contaminated), there being a barrier between the two areas.

When a tube is to be loaded with, for instance, a plurality of substacks, trays of pellets are selected in the active area, from which trays pellets are removed to build the substacks of the required length. The substacks are supported on stack weigh tracks for weighing purposes and for loading the pellets into the tube. The stack weigh track supports a row of pellets in an end-to-end arrangement and the entire row of pellets may be pushed through a fuel load head, which acts as an aligning device, into the tube. This procedure is repeated until all the required substacks have been loaded into the fuel tube.

This process is a relatively inflexible operation. For instance, it is necessary to load completely a fuel tube with all the required substacks before it can be removed and a further tube brought into position to be loaded. There is a need for a more flexible arrangement which allows substacks to be directed to any one of a plurality of tubes all available to be filled at the loading station. In this way, best use can be made of the trays of pellets which are in the assembly area. STATEMENTS OF INVENTION

According to the present invention there is provided apparatus for loading nuclear fuel pellets into a carrier tube, the apparatus comprising a first support body for holding in parallel relationship about a common axis a plurality of pellet column holders and for rotating said holders about said axis, and a second support body for holding in parallel relationship about a common axis a plurality of fuel tube holders, and for rotating said fuel tube holders about said axis, said support bodies being dimensioned such that they may be brought together in an end-to-end staggered relationship to align one of said pellet column holders with a fuel tube holder to allow transfer of pellets therebetween, each of said bodies being mounted for rotation about its common axis in order to align another of said pellet column holders with one of the fuel tube holders.

Preferably, each support body includes a plurality of holders which are radially spaced from the common axis and are peripherally spaced apart. More preferably, they are equally spaced radially from the common axis and each is spaced from its neighbours by the same circumferential distances.

Preferably, means are provided for rotating each body about its common axis. More preferably, said means include means for indexing the rotation to allow a particular holder to take up a position formerly occupied by an adjacent holder.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:-

Figure 1 is a plan view of apparatus in accordance with the present invention;

Figure 2 is a side elevation of the apparatus of Figure 1;

Figure 3 is an end view of the fuel rod rotary cassette of the apparatus of Figure 1; and Figure 4 is an end view of the substack rotary cassette of the apparatus of Figure 1 and showing its alignment with the fuel rod rotary cassette.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION Referring to Figures 1 and 2 of the accompanying drawings, apparatus for loading nuclear fuel pellets into fuel tubes may be operated automatically under the control of a computer control system (not shown). The apparatus includes a tray retrieval unit (not shown) for delivering trays 3 from a tray storage location (not shown) to an index table 4. On the trays 3, the pellets are arranged in parallel grooves. The index table 4 is operated to present a tray 3 to a position such that a column of pellets, located in one of the grooves in the tray is below a pellet pusher actuator system 5. This system 5 causes an entire column of pellets, or a part thereof, to be transferred from the tray 3 to a stack weigh track 7. The length of pellets on the stack weigh track 7 may be weighed before the pellets are pushed from the weigh track 7 into channels or tubes of a rotary substack cassette 9 located adjacent to the position of the weighing station.

Substack rotary cassette 9 is a support body for holding in parallel relationship about a common axis a plurality of pellet column holders in the form of channels or tubes 11. Rotary cassette 9 includes a number of annular grids 13 which are held in spaced apart relationship by the channels 11. As best seen in Figure 4, channels 11 are each equally radially spaced from a common axis 15 and are equally circumferentially spaced about the grids 13. There are typically eight such channels 11 within the rotary cassette 9. The skeleton of channels 11 and grid 13 is mounted on rollers 17 which in turn are mounted on a support table 19. A central drive roller 21 also engages grids 13 and may be driven to cause rotation of the entire skeleton.

In order to load a column of pellets from weigh track 7 onto rotary cassette 9, a carrier 11 is aligned with the weigh track and the pellet pusher actuator system is operated to push the pellets into the channel. If desired, further channels may be loaded with pellets by the appropriate indexing of the skeleton to bring other channels into alignment with the weigh track. In order to transfer a column of pellets from one of the channels 11 of rotary cassette 9, a second rotary cassette 21 is used.

This cassette 21 includes a table 23 mounted on wheels 25. Supported on table 23 by means of uprights 27, 29 is a fuel tube holder 31. Holder 31 includes a central axle 33, at the opposite ends of which bearing members 35, 37 are located in bearings mounted on uprights 27, 29, through which the tube holder 31 may be rotated about its longitudinal axis.

Mounted on axle 33 at each end thereof adjacent to bearing members 35, 37 are wheels 39, 41 each of which is in the form of a plurality of radial spokes 43, each extending from axle 33 to a tube holder 45. Extending between each pair of adjacent tube holders 45 is a further spoke 47. Accordingly, as viewed in Figure 3, the arrangement resembles a Ferris wheel.

Between substack rotary cassette 9 and fuel rod rotary cassette 21, there is located a barrier 51 which separates an active zone, located to the right of barrier 51 , where the pellets are assembled and loaded into rotary cassette 9, and an inactive zone, to the left of barrier 51, where the active fuel pellets are situated within fuel tubes. Associated with barrier 51 is a pellet load head, which facilitates transfer of pellets between the rotary cassette and a sealing arrangement which prevents radioactive material escaping from the active zone to the inactive zone while pellet loading is taking place. In operation, fuel rod rotary cassette 21 is loaded with fuel tubes and brought to the position shown in Figures 1 and 2 adjacent to barrier 51. As illustrated in Figure 4, the fuel rod rotary cassette 21 is positioned so that the two rotary cassettes lie on staggered axes such that one peripheral channel of each coincides at position 53. The pellet load head is located between the aligned channels. As will be appreciated, rotation of the cassettes relative to one another allows any substack cassette channel to be aligned with any fuel tube cassette channel for substack loading. The method gives flexibility in that any substack can be loaded into any fuel tube. Other fuel rod finishing stations may be located on the interface plane at the position of other channels of the fuel rod rotary cassette. Such stations may include those for spring/getter insertion, tube end cleaning, tube plugging, end plug welding, helium fill and drogue hole welding.

The rod finishing processes can be carried out while (in parallel with) loading of subsequent fuel tubes with pellet substacks is in progress, thereby improving the cycle time of the process.

In another embodiment of the present invention, the arrangement is such that the two channels of one cassette may be caused to coincide (be aligned with) two respective channels of the other cassette. With such an embodiment, the process throughput may be increased by loading two substacks simultaneously.

The fuel tube rotary cassette can be arranged to engage its multiplicity of fuel tube ends with a seal plate carrying a pneumatic seal at each tube location, the seal plate being capable of rotating with, and on the same axis as, the fuel tube rotary cassette.

Furthermore, the rotary cassettes can be designed as substack and fuel tube storage modules, and a considerable number of the cassettes will then be located in both the manufacturing facility and its associated storage facilities. The particular cassettes will be called upon to interface with the seal plate/pellet load head only when fuel rod loading of the particular pellet substacks/fuel tubes are required in a production schedule. As a result, there is considerable flexibility of manufacturing capability.

Claims

1. Apparatus for loading nuclear fuel pellets into a carrier tube, the apparatus comprising a first support body for holding in parallel relationship about a common axis a plurality of pellet column holders and for rotating said holders about said axis, and a second support body for holding in parallel relationship about a common axis a plurality of fuel tube holders, and for rotating said fuel tube holders about said axis, said support bodies being dimensioned such that they may be brought together in an end-to-end staggered relationship to align one of said pellet column holders with a fuel pellet holder to allow transfer of pellets therebetween, each of said bodies being mounted for rotation about its common axis in order to align another of said pellet column holders with one of the fuel tube holders.

2. Apparatus as in Claim 1 in which each of said bodies includes a plurality of holders which are radially spaced from the common axis and are peripherally spaced apart.

3. Apparatus as in Claim 1 or claim 2 in which said plurality of holders are equally spaced radially from the common axis and each is spaced from its neighbours by the same circumferential distances.

4. Apparatus as in any of the preceding claims in which at least one pellet column holder contains fuel pellets of enrichment value different from at least one other of said pellet column holders.

5. Apparatus as in any of the preceding claims in which said support bodies are such that a plurality of pellet column holders may be caused to be aligned with a plurality of fuel tube holders.

6. Apparatus as in any of the preceding claims in which the apparatus includes means for indexing the rotation of the holders to allow a particular holder to take up a position formerly occupied by an adjacent holder.

7. Apparatus as in any of the preceding claims in which rotation of the holders is affected by roller means operatively connected to each of said support bodies.

8. Apparatus as in any of the preceding claims in which rotation of the holders of one support body relative to holders of the other support body allows any pellet column holder to be aligned with any fuel tube holder for the purpose of substack loading.

9. Apparatus as in any of the preceding claims in which radiation barrier means are used to separate the first and second support barriers.

10. Apparatus as in Claim 9 in which the nuclear fuel pellets are transferred from a pellet column holder to a fuel tube holder through an interface in the radiation barrier.