GB2100913A - Nuclear reactor fuel elements - Google Patents

Abstract

A nuclear reactor fuel element having a sheath (21) and fuel pellets (20) has a tubular pellet retainer (10) which is inserted in the sheath with zero-insertion load by virtue of being fluted at a flute (11) and is held in the sheath by reforming into an approximately circular shape (12). <IMAGE>

Description

SPECIFICATION Nuclear reactor fuel elements This invention relates to nuclear reactor fuel elements.

The invention is concerned with the problem, already referred to in our copending application no 8102352, of providing a fuel stack retainer for a nuclearfuel element having a fuel content of pellets.

The retainer of the present invention is characterised in that it is oftubularform with one or more flutes so that it can be undersize when inserted in a circular-section fuel element sheath and thereby require zero insertion load but can be expanded by a former acting on the flutes to set it into an approximately circular section with an interference fit in the sheath whilst providing passage for fission product gases.

Apart from the merit of providing, in a simple manner, a retainer needing zero insertion load and passage for fission gases, the invention also has the merit of providing a retainer which exposes a large open cross section through which dissolution medium can pass freely to attack the fuel during subsequent fuel reprocessing.

One form of retainer according to the present invention will now be described with reference to the accompanying drawing in which Figure lisa plan view of the retainer (enlarged relative to the scale of Figure 2) and Figure 2 shows, in elevation, the retainer in use.

In Figure 1 there is shown a tubular retainer 10 of stainless steel 0.15mm in thickness. The retainer 10 is of nominal circular section over a major part of its periphery but has a flute 11 on a minor part. The periphery has a length which is slightly greater than the material circumference of a fuel element sheath in which it is to fit, typically a length of 1.320 cms to fit a circumference of 1.31scums. The shape of the retainer 10 when expanded to be approximately circular is shown by the line 12, the flutes being worked hardened, do not take up atrue circular form.

In Figure 2, a stack of fuel pellets 20 is shown retained in a nuclear fuel element sheath 21 by the retainer 10. The retainer 10 has been formed to remove the flute and have an approximately circular section and is an interference fit in the sheath 21.

The retainer 10, whilst fluted is a free fit in the sheath 21. When formed to be circular it fits with a push out load of approximately 20 Kg. There is a very clear passage for any fission product gases escaping from the fuel pellets 20. There is no requirement to orientate the retainer in the sheath 21. There is no significant enlargement of the sheath 21 at the position occupied by the retainer 10. A large open cross-section through the retainer 10 is pro vided to assist speedy dissolution of the fuel when the fuel element comes to reprocessing.

The retainer has been shown in use with pelleted fuel but the retainer could also be used with vibro compacted granular fuel interposed between upper and lower stacks of breeder pellets.

1. A nuclear reactor fuel element having a circular-section sheath and a fuel content of pellets in which the pellets are retained in position in the sheath by a retainer of tubular form having, when initially inserted with the sheath, one or more flutes so that it is undersize and is expanded to set it in an approximately circular section with an interference fit in the sheath.

2. A nuclear reactor fuel element as claimed in claim 1 in which the fuel content of pellets define upper and lower breeder stacks with vibrocompacted granular fuel interposed therebetween.

3. A nuclear reactor fuel element substantially as described and shown in the drawings.

4. A method of forming a fuel element having a circular-section sheath and a retained fuel content of pellets comprising inserting into the sheath with zero insertion load a pellet retainer of tubular form with one or more flutes and expanding the retainer with a former acting on the flutes to set the retainer into an approximately circular-section with an interference fit in the sheath.

The drawing(s) originally filed was/were informal and the print here reproduced is taken from a laterfiledformalcopy.

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

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Nuclear reactor fuel elements This invention relates to nuclear reactor fuel elements. The invention is concerned with the problem, already referred to in our copending application no 8102352, of providing a fuel stack retainer for a nuclearfuel element having a fuel content of pellets. The retainer of the present invention is characterised in that it is oftubularform with one or more flutes so that it can be undersize when inserted in a circular-section fuel element sheath and thereby require zero insertion load but can be expanded by a former acting on the flutes to set it into an approximately circular section with an interference fit in the sheath whilst providing passage for fission product gases. Apart from the merit of providing, in a simple manner, a retainer needing zero insertion load and passage for fission gases, the invention also has the merit of providing a retainer which exposes a large open cross section through which dissolution medium can pass freely to attack the fuel during subsequent fuel reprocessing. One form of retainer according to the present invention will now be described with reference to the accompanying drawing in which Figure lisa plan view of the retainer (enlarged relative to the scale of Figure 2) and Figure 2 shows, in elevation, the retainer in use. In Figure 1 there is shown a tubular retainer 10 of stainless steel 0.15mm in thickness. The retainer 10 is of nominal circular section over a major part of its periphery but has a flute 11 on a minor part. The periphery has a length which is slightly greater than the material circumference of a fuel element sheath in which it is to fit, typically a length of 1.320 cms to fit a circumference of 1.31scums. The shape of the retainer 10 when expanded to be approximately circular is shown by the line 12, the flutes being worked hardened, do not take up atrue circular form. In Figure 2, a stack of fuel pellets 20 is shown retained in a nuclear fuel element sheath 21 by the retainer 10. The retainer 10 has been formed to remove the flute and have an approximately circular section and is an interference fit in the sheath 21. The retainer 10, whilst fluted is a free fit in the sheath 21. When formed to be circular it fits with a push out load of approximately 20 Kg. There is a very clear passage for any fission product gases escaping from the fuel pellets 20. There is no requirement to orientate the retainer in the sheath 21. There is no significant enlargement of the sheath 21 at the position occupied by the retainer 10. A large open cross-section through the retainer 10 is pro vided to assist speedy dissolution of the fuel when the fuel element comes to reprocessing. The retainer has been shown in use with pelleted fuel but the retainer could also be used with vibro compacted granular fuel interposed between upper and lower stacks of breeder pellets. CLAIMS

1. A nuclear reactor fuel element having a circular-section sheath and a fuel content of pellets in which the pellets are retained in position in the sheath by a retainer of tubular form having, when initially inserted with the sheath, one or more flutes so that it is undersize and is expanded to set it in an approximately circular section with an interference fit in the sheath.

2. A nuclear reactor fuel element as claimed in claim 1 in which the fuel content of pellets define upper and lower breeder stacks with vibrocompacted granular fuel interposed therebetween.

3. A nuclear reactor fuel element substantially as described and shown in the drawings.

4. A method of forming a fuel element having a circular-section sheath and a retained fuel content of pellets comprising inserting into the sheath with zero insertion load a pellet retainer of tubular form with one or more flutes and expanding the retainer with a former acting on the flutes to set the retainer into an approximately circular-section with an interference fit in the sheath.

The drawing(s) originally filed was/were informal and the print here reproduced is taken from a laterfiledformalcopy.