GB2070998A

GB2070998A - Welding by laser beam

Info

Publication number: GB2070998A
Application number: GB8105892A
Authority: GB
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1980-03-03
Filing date: 1981-02-25
Publication date: 1981-09-16

Abstract

A laser (10) which does not require a vacuum and the beam (11) from which can be projected over a distance without loss of power is sited outside a welding zone (4) and the beam (11) projected through a replaceable laser transparent window (8). The window is designed and shaped to facilitate access of the beam of workpiece items (2, 3) to be welded in containment. Either the workpiece or the laser beam may be moved during welding. <IMAGE>

Description

SPECIFICATION I Nuclear fuel pin manufacture This invention relates to nuclear fuel pin manufacture.

One method of manufacturing nuclear fuel pins employs a non-consumable electric arc fusion process. A disadvantage of this method in the manufacture of fuel pins containing plutonium or other toxic material is that it requires access for operations such as changing electrodes and adjustment of associated equipment. Since irradiation levels on operators and maintenance staff is stringently controlled, it is desirable to provide a method of and apparatus for pin manufacture which requires as little exposure time for operators as is possible.

An object of the present invention is to tend to provide a method and apparatus which entails less operator exposure than hitherto.

According to one aspect of the present invention, a method of manufacturing nuclear fuel pins comprises; arranging a laser externally of a containing vessel for the fuel pin, welding components of the fuel pin together with a beam from the laser and providing access for the beam to the inside of the container by means of a laser transparent window.

According to another aspect of the invention, apparatus for manufacturing nuclear fuel pins comprises a container for containing contaminants associated with the nuclear fuel pin, a laser for welding together parts of the nuclear fuel pin, which laser is locatable externally of the container and a laser transparent aperture for allowing access of the laser beam into the container.

Preferably the aperture is contained within a frame. Conveniently, the frame provides a cylindrical cross-section within which part of a fuel element to be welded is received. Preferably, the frame is detachably mounted on the containers. Advantageously, means is provided in the container for moving the fuel element relative to the laser beam. Means may be provided for moving the laser beam relative to the frame. Control means for the laser beam may be provided within the container.

Two embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is an incomplete diagrammatic section of a nuclear fuel pin manufacturing facility, and Figure 2 shows a detail of the manufacturing facility for a different type of fuel pin.

Reference is made firstly to Fig. 1, in which a nuclear fuel pin is indicated by 1. The fuel pin comprises a cladding 2 and end cap 3. In manufacture of the fuel pin, it is necessary to weld the end cap 3 to the cladding 2. The fuel pin is contained within a contained area 4 of which part of the walls are indicated by 5a, 5b. A gap is situated between the walls 5a, 5b and this gap is closed by a frame 6 secured to the walls. The frame 6, which is of cylindrical cross-section, contains an aperture 7. The aperture is closed by a laser transparent window 8 which prevents egress of materials from the contained area 4. A laser 10 projects its beam 11 to the joint between cladding 2 and end cap 3 via a mirror 12 and window 8.A focusing lens 9 is provided in the frame 6 inside containment for use with the laser 10, but if suitable focal lengths are determined, the lens may be situated outside containment or may be redundant. It is also possible to locate a focusing mirror within the containment. The heat from the laser beam is sufficient to weld the end cap to the cladding.

The fuel pin can be rotated about its axis by a motor 14 and its control unit. Such rotation enables the laser beam to be moved around the joint. Alternatively, the beam may be rotated by moving the mirror with a motor and control unit 15. From the above description, it can be seen that a simple manufacturing facility is provided, in which the only part that needs maintenance within containment is the window 8 and possibly the frame 6. The frame 6 is shaped so as to receive the fuel pin to be handled.

In the Fig. 2, to which reference is now directed and wherein like reference numerals are used for like parts, there is shown a different type of fuel pin wherein the end cap 3 is of a different shape. In order to have access to the joint between cladding 2 and end cap 3, it is necessary for the incident angle of the laser beam to be at 90 to that shown in Fig. 1. This is because the end cap obscures the upper surface of the cladding.

Therefore, the frame 6 has an aperture in its side wall instead of its upper surface.

Consequently, the laser beam can impinge on the wrapper from the side so that the end cap can be welded on.

In other embodiments of the invention, the laser itself can be moved around the frame 6, an annular window 8 being necessary for this purpose in connection with fuel pins as described in the second embodiment above.

It will be appreciated that laser welding need not require a vacuum and that the beam can be projected over a long distance where necessary, without significant loss of power.

1. A method of manufacturin nuclear fuel pins comprising; arranging a laser externally of a containing vessel for the fuel pin, welding components of the fuel pin together with a beam from the laser and providing access for the beam to the inside of the container by means of a laser transparent window.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION I Nuclear fuel pin manufacture This invention relates to nuclear fuel pin manufacture. One method of manufacturing nuclear fuel pins employs a non-consumable electric arc fusion process. A disadvantage of this method in the manufacture of fuel pins containing plutonium or other toxic material is that it requires access for operations such as changing electrodes and adjustment of associated equipment. Since irradiation levels on operators and maintenance staff is stringently controlled, it is desirable to provide a method of and apparatus for pin manufacture which requires as little exposure time for operators as is possible. An object of the present invention is to tend to provide a method and apparatus which entails less operator exposure than hitherto. According to one aspect of the present invention, a method of manufacturing nuclear fuel pins comprises; arranging a laser externally of a containing vessel for the fuel pin, welding components of the fuel pin together with a beam from the laser and providing access for the beam to the inside of the container by means of a laser transparent window. According to another aspect of the invention, apparatus for manufacturing nuclear fuel pins comprises a container for containing contaminants associated with the nuclear fuel pin, a laser for welding together parts of the nuclear fuel pin, which laser is locatable externally of the container and a laser transparent aperture for allowing access of the laser beam into the container. Preferably the aperture is contained within a frame. Conveniently, the frame provides a cylindrical cross-section within which part of a fuel element to be welded is received. Preferably, the frame is detachably mounted on the containers. Advantageously, means is provided in the container for moving the fuel element relative to the laser beam. Means may be provided for moving the laser beam relative to the frame. Control means for the laser beam may be provided within the container. Two embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is an incomplete diagrammatic section of a nuclear fuel pin manufacturing facility, and Figure 2 shows a detail of the manufacturing facility for a different type of fuel pin. Reference is made firstly to Fig. 1, in which a nuclear fuel pin is indicated by 1. The fuel pin comprises a cladding 2 and end cap 3. In manufacture of the fuel pin, it is necessary to weld the end cap 3 to the cladding 2. The fuel pin is contained within a contained area 4 of which part of the walls are indicated by 5a, 5b. A gap is situated between the walls 5a, 5b and this gap is closed by a frame 6 secured to the walls. The frame 6, which is of cylindrical cross-section, contains an aperture 7. The aperture is closed by a laser transparent window 8 which prevents egress of materials from the contained area 4. A laser 10 projects its beam 11 to the joint between cladding 2 and end cap 3 via a mirror 12 and window 8.A focusing lens 9 is provided in the frame 6 inside containment for use with the laser 10, but if suitable focal lengths are determined, the lens may be situated outside containment or may be redundant. It is also possible to locate a focusing mirror within the containment. The heat from the laser beam is sufficient to weld the end cap to the cladding. The fuel pin can be rotated about its axis by a motor 14 and its control unit. Such rotation enables the laser beam to be moved around the joint. Alternatively, the beam may be rotated by moving the mirror with a motor and control unit 15. From the above description, it can be seen that a simple manufacturing facility is provided, in which the only part that needs maintenance within containment is the window 8 and possibly the frame 6. The frame 6 is shaped so as to receive the fuel pin to be handled. In the Fig. 2, to which reference is now directed and wherein like reference numerals are used for like parts, there is shown a different type of fuel pin wherein the end cap 3 is of a different shape. In order to have access to the joint between cladding 2 and end cap 3, it is necessary for the incident angle of the laser beam to be at 90 to that shown in Fig. 1. This is because the end cap obscures the upper surface of the cladding. Therefore, the frame 6 has an aperture in its side wall instead of its upper surface. Consequently, the laser beam can impinge on the wrapper from the side so that the end cap can be welded on. In other embodiments of the invention, the laser itself can be moved around the frame 6, an annular window 8 being necessary for this purpose in connection with fuel pins as described in the second embodiment above. It will be appreciated that laser welding need not require a vacuum and that the beam can be projected over a long distance where necessary, without significant loss of power. CLAIMS

2. Apparatus for manufacturing nuclear fuel pins comprising a container for containing contaminants associated with the nuclear fuel pin, a laser for welding together parts of the nuclear fuel pin, which laser is locatable externally of the container and a laser transparent aperture for allowing access of the laser beam into the container.

3. Apparatus as claimed in Claim 2, in which the aperture is contained within a frame.

4. Apparatus as claimed in Claim 3, in which the frame provides a cylindrical crosssection within which part of a fuel element to be welded is received.

5. Apparatus as claimed in Claim 3, in which the frame is detachably mounted on the container.

6. Apparatus as claimed in Claim 2, in which means is provided in the container for moving the fuel element relative to the laser beam.

7. Apparatus as claimed in Claim 2, in which means is provided for moving the laser beam relative to the frame.

8. Apparatus as claimed in Claim 2, in which control means for the laser beam is provided within the container.

9. A method for manufacturing nuclear fuel pins substantially as herein before described and as shown in the accompanying drawings.

10. Apparatus for manufacturing nuclear fuel pins substantially as herein before described and as shown in the accompanying drawings.