WO1998026428A1

WO1998026428A1 - Apparatus for loading nuclear fuel pellets

Info

Publication number: WO1998026428A1
Application number: PCT/GB1997/003339
Authority: WO
Inventors: Graeme Michael Wigg; Michael Allen
Original assignee: British Nuclear Fuels Plc
Priority date: 1996-12-09
Filing date: 1997-12-03
Publication date: 1998-06-18
Also published as: AU5232598A; GB9625513D0

Abstract

There is provided apparatus for loading nuclear fuel pellets into a carrier tube. The nuclear fuel pellets being located, prior to loading, in a first zone and the carrier tube being located, prior to and after loading, in a second zone, the two zones being separated from each other by a barrier to prevent radioactive material (other than the pellets) passing from said first zone to said second zone, the apparatus comprising tube handling means, located in said second zone for supporting a carrier tube and for moving it longitudinally into engagement with a pellet load head, said pellet load head being positioned so that pellets may be loaded into it via an entrance located in said first zone, means for isolating the end of the tube from the second zone within a third zone located between the first and second zone and means for opening the first zone to said third zone to allow the handling means to move the tube into engagement with the load head while the tube head remains isolated from the second zone.

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 nuclear fuel element assembly, the required nuclear fuel pellets to be loaded into a carrier tube are assembled in end-to-end relationship for insertion into an open end of a carrier tube. Typically, the fuel pellets are assembled by appropriate apparatus as, for instance, described in our co-pending patent application filed on the same date as the present application. As the result of the use of such apparatus, a length of the nuclear fuel pellets is loaded onto a stack weigh track on which the length of pellets may be weighed. The stack weigh track is then brought to a position where one end is aligned with an open end of the carrier tube with a pellet load head located in between. The stack weigh track and the tube are brought into engagement with the pellet load head which facilitates transfer of the pellets into the tube.

One such arrangement is described in US4,748,798. This document describes a process in which the carrier tube is pushed towards a pellet load head which is termed a centre aligning device and is illustrated in Figure 10 of the document. The device includes a through bore having a convergent conical section at each opposed bore opening. The fuel tube end is inserted into one bore opening and the device for carrying the pellets into the other bore opening. Pushing the row of pellets in a direction towards the fuel tube results in the easy passage of the pellets into the fuel tube due to the accurate alignment within the centre aligning device. Assembly of the pellets ready to be passed through the pellet load head into the fuel tube can all be arranged to take place within an "active" region or zone of the facility for manufacturing the fuel elements. Once the pellets are located within tubes to form the fuel rods, there is no exposed uranic contamination. If the fuel pellet assembly zone can be radioactively separated from the remainder of the fuel element assembly area, it is possible to allow personnel to operate safely outside the active zone. However, it is difficult to provide a sufficiently sealed barrier between the active and inactive zones because of the need for the passage of fuel pellets across this barrier.

STATEMENTS OF INVENTION

According to the present invention there is provided apparatus for loading nuclear fuel pellets into a carrier tube, the nuclear fuel pellets being located, prior to loading, in a first zone and the carrier tube being located, prior to and after loading, in a second zone, the two zones being separated from each other by a barrier to prevent radioactive material (other than the pellets) passing from said first zone to said second zone, the apparatus comprising tube handling means, located in said second zone for supporting a carrier tube and for moving it longitudinally into engagement with a pellet load head, said pellet load head being positioned so that pellets may be loaded into it via an entrance located in said first zone, means for isolating the end of the tube from the second zone within a third zone located between the first and second zones, and means for opening the first zone to said third zone to allow the handling means to move the tube into engagement with the load head while said tube end remains isolated from said second zone.

In this way it is possible to ensure that radioactive materials do not enter the second, inactive zone and that the radioactive material remains confined to the first and third zones.

Preferably, said isolating means includes an opening allowing said tube end to enter said third zone and sealing means to effect a seal between said isolating means and said tube.

Preferably, said sealing means includes an annular member defining said opening, said annular member being deformable and said sealing means including means of causing said annular member to deform to engage the outer surface of the tube to effect said seal. More preferably, the annular member deforming means includes means for applying gas pressure to said annular member.

Preferably, said isolating means includes means allowing the tube to be moved longitudinally relative to the barrier while said tube end is isolated from said second zone. More preferably, said movement allowing means is in the form of a flexible enclosure surrounding said tube. For instance, the flexible enclosure may have a bellows-like construction allowing the enclosure to extend and contract longitudinally.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate an embodiment of the present invention, by way of example only, the Figures of the drawings being as follows:

Figure 1 is a plan view of apparatus for loading nuclear fuel pellets into tubes; and Figure 2 is a side elevation showing in more detail that part of the apparatus in Figure 1 concerned with the entry of the pellets into the tubes.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Referring to Figure 1 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 1 for delivering tray 3 from a tray storage location (not shown) to an index table 5. On the trays 3 the pellets are arranged in parallel grooves and a robot 7 is operated to remove pellet retaining bars from the opposite ends of each tray. The index table 5 is then 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 9. This system 9 causes an entire column of pellets, or a part thereof, to be transferred from the tray 3 to a stack weigh track 11. The length of pellets on the stack weigh track 11 may be weighed while the stack weigh track is in the position indicated by solid lines in Figure 1 before it is moved laterally to the position indicated by broken lines in Figure 1. In this latter position the left hand end (as viewed in Figure 1) of the stack weigh track is aligned with the pellet load head 13.

On the opposite side of pellet load head 13 an empty fuel tube 15 is located on a handling device 17 which both supports the tube and allow it to be moved longitudinally. Handling arrangement 17 is operated to cause tube 15 to be moved in a direction towards pellet load head 13, during which movement the right hand end of the tube (as seen in Figure 1) passes through a sealing device 19 to be described in detail below.

The dotted line 21 in Figure 1 indicates a barrier located between the active area located to the right of the barrier in which the pellets are assembled and delivered to the load head 13 and an inactive area to the left in which the pellets are encased within a fuel tube 15. Accordingly, the area to the right of barrier 21 is a first, active zone and the area to the left is a second, inactive zone.

Referring now to Figure 2 of the accompanying drawings, the barrier 21 (not shown in Figure 2) includes a mechanical closure plate 23 which, as shown in Figure 2, is positioned with the lower part of its left hand surface abutting a fixed plate 25 carrying a circular sealing ring 27 and having a circular hole 29 extending therethrough. Plate 25 is fixed to wall member 31 which also has a hole through it which is aligned with hole 29.

To the left of wall member 31 is a further wall member 33 also having a hole therethrough which is aligned with the holes located in plate 25 and wall member 31.

To the right of mechanical closure plate 23 is located the pellet load head 13.

Extending through load head 13 is a bore 35 which is aligned with the above mentioned holes 29, 32 and 34. Bore 35 includes convergent cone sections 37 and 39 which extend inwardly from opposite entrances of the bore. Figure 2 shows an end of the stack weigh track 11 in a position such that a length of fuel pellets 41 may be pushed to the left so that the fuel pellets enter the wide entrance to bore 35, cone section 37 ensuring that the pellets are accurately guided towards the opposite entrance 39 of bore 35.

The fuel tube 15 to be loaded with pellets is positioned with its right hand end up against closure plate 23. In this position it is clamped by means of radial clamp 43 mounted on a carriage 51. Carriage 51 is moveable along a track by means of a double ended cylinder 45. This movement is such that a tube 15, clamped in radial clamp 43, is caused to move towards and away from the aligned holes 29, 32 and 34. Between radial clamp 43 and wall member 33 there is located a device, indicated generally by 47, which enables the right hand end of the tube to be isolated from the second inactive zone while the fuel pellets are being loaded into the tube. Isolating device 47 includes a pneumatic seal arrangement 49 which is mounted on the carriage 51 and is therefore moveable under the operation of cylinder 45. Pneumatic seal 49 includes a cylindrical rubber tube 53 having integral end flanges 55 and 57. Tube 53 is sealingly mounted within a housing 59 providing a central annular space 61 around seal 49 to which compressed air may be delivered. Typically, an external pneumatic pressure of approximately 15 psig is effective to cause the rubber tube to be squeezed down onto the outside diameter of the fuel tube 15.

Extending between housing 59 and wall member 33 is a bellows-like flexible tube 63 having integral end flanges 65, 67 by which it is sealingly attached to wall member 33 and housing 59 respectively. Accordingly, the bellows-like tube 63, the housing 59, including seal 49, and wall member 33 define a third zone which lies between the second inactive zone and the first active zone.

In operation, fuel tube 15 is, as mentioned above, brought to a position shown in

Figure 2. Clamp 43 is then engaged and pneumatic seal 49 operated to effect a seal around the tube. Double ended cylinder 45 is now actuated to cause it to move the carriage 51 a short distance, typically about 12 mm, to the left. As a result, the end of the fuel tube 15 is separated from the closure plate 23, thereby avoiding the scuffing of the end of tube 15 during the next step. Closure plate 23 then opens by lateral movement to bring hole 69 in this plate into alignment with hole 29. It will be appreciated that the above mentioned third zone, which has already been isolated from the second inactive zone, is now open to the first active zone.

Cylinder 45 is then actuated to cause carriage 51 to move to the right to bring the fuel tube end through the closure plate and into the pellet load head 13. Once this engagement has been effected, the pellets on the stack weigh track 11 are pushed through the load head and into the fuel tube. This process is repeated until the fuel tube is loaded with its full requirement of pellets. The fuel tube 15 may then be further treated, including the insertion of other necessary internal components such as a spring and getter as well as an end plug.

Once the fuel tube treatment has been completed, a reversal of the above described procedure leads to the breaking of the seal, putting the third zone into contact with the second inactive zone, but with the latter isolated from the first active zone. The fuel tube is then removed for further processing prior to loading into a fuel skeleton to form a fuel element.

Claims

1. Apparatus for loading nuclear fuel pellets into a carrier tube, the nuclear fuel pellets being located, prior to loading, in a first zone and the carrier tube being located, prior to loading, in a second zone, the two zones being separated from each other by a barrier to prevent radioactive material (other than the pellets) passing from said first zone to said second zone, the apparatus comprising tube handling means located in said second zone for supporting a carrier tube and for moving it longitudinally into engagement with a pellet load head, said pellet load head being positioned so that pellets may be loaded into it via an entrance located in said first zone, means for isolating the end of the tube from the second zone within a third zone located between the first and second zones, and means for opening the first zone to said third zone to allow the handling means to move the tube into engagement with the load head while said tube end remains isolated from said second zone.

2. Apparatus as in Claim 1 in which said isolating means includes an opening allowing said tube end to enter said third zone and sealing means to effect a seal between said isolating means and said tube.

3. Apparatus as in Claim 1 and Claim 2 in which said sealing means includes an annular member defining said opening, said annular member being deformable and said sealing means including means for causing said annular member to deform so as to engage the outer surface of the tube to effect said seal.

4. Apparatus as in Claim 3 in which the annular member deforming means includes means for applying gas pressure to said annular member.

5. Apparatus as in any of the preceding claims in which said isolating means includes means for allowing the carrier tube to be moved longitudinally relative to the barrier while said tube end is isolated from said second zone.

6. Apparatus as in Claim 5 in which said movement allowing means is in the form of a flexible enclosure surrounding said tube, said flexible enclosure having a bellows-like construction allowing the enclosure to extend and contract longitudinally.

7. Apparatus as in any of the preceding claims in which the tube handling means includes carriage means mounted on a track and operatively connected to actuator means.

8. Apparatus as in any of the preceding claims in which the tube handling means further includes clamping means to secure the carrier tube in the desired position.

9. Apparatus as in any of the preceding claims in which the pellet load head includes means for ensuring pellets are accurately guided through said pellet load head.

10. Apparatus as in Claim 9 in which said pellet guiding means comprises a bore having convergent cone shaped sections.

11. Apparatus as in any of the preceding claims in which the barrier includes a mechanical closure plate with a hole, said plate being, in use, moveable laterally with respect to said carrier tube, such that said hole in said closure plate can be moved in and out of alignment with the longitudinal axis of said carrier tube.