GB2124953A

GB2124953A - Nuclear reactor fuel elements

Info

Publication number: GB2124953A
Application number: GB08223282A
Authority: GB
Inventors: George Kelly
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1982-08-12
Filing date: 1982-08-12
Publication date: 1984-02-29
Also published as: GB2124953B

Abstract

A casing 1 for a nuclear reactor fuel element is hexagonal in section and a central region as viewed axially of each side is, using isostatic pressure, formed with an outward projection 3 integral with the material of the casing to provide a wear surface. Removable formers 4 having recesses 5 are urged sealingly against the casing sides. The wear surfaces may be provided with a hard facing. <IMAGE>

Description

SPECIFICATION Nuclear reactor fuel elements This invention relates to nuclear reactor fuel element and has particular relevance to that kind of fuel element which in associatiQn with other similar elements in mutually close juxta position form the core of the nuclear reactor. Typical types of nuclear reactor which have this kind of core are fast reactors, pressurised water reactors, and boiling water reactors.

With the said type of core, core restraint is in many cases performed by applying externally a radially inward force at at least two core levels, the force being transmitted throughout the core by the contact of adjacent fuel elements in engagement at least at the levels referred to. Because of relative movement between the fuel elements, it has been deemed expedient to provide bearing surfaces at these engagement positions.

Hitherto, such bearing surfaces have been provided by pads attached to the fuel elements in any convenient manner, such pads having in appropriate cases hardened surfaces whose properties are such that undue wear will not occur during the design life of the fuel elements concerned. In an alternative, it has been proposed to provide the wear surfaces by plasma spraying of appropriate material on ta the bodies of the fuel elements at the appropriate positions. Whilst these forms of wear surfaces are satisfactory in operation, they both involve steps during the manufacture of the fuel elements which have to be carefully controlled in order to avoid adversely affecting the properties of the fuel element material to which the wear surfaces are applied.

It is the object of the present invention to provide a nuclear reactor fuel element with wear surfaces in the appropriate positions which are effective in operation whilst simplifying the effort of production compared with that empioyed hitherto.

According to the invention, a nuclear reactor fuel element has wear surfaces for engagement with the corresponding wear surfaces of adjacent fuel elements in which the wear surfaces project from the outer casing of the fuel element and are integral with the material of the said casing and are produced by isostatic pressing of the material of the said casing employing formers temporarily and sealingly attached to the outer surface of the said casing.

Preferably each wear surface has a hard facing produced thereon by conventional hardening means.

A constructional example embodying the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 is a side view of a typical fast reactor fuel eiement, Figure 2 is an enlarged fragmentary side view of that portion of the fuel element within the circle on Figure 1, Figure 3 is a plan view of Figure 2 with the addition of equipment for providing the wear surfaces shown in Figure 2, and Figures 4, 5and 6are respectively an elevation, side view and end view of one of the expedients shown in Figure 3.

Referring to the drawings, firstly to Figure 1, this illustrates fragmentarilly typical fast reactor fuel element 1 which, together with a multiplicity of similar fuel elements disposed in mutual juxta position form the core of the fast reactor. The fuel element 1 broadly comprises a casing or wrapper 2 within which are disposed a large number of vertically orientated fuel pins carried in appropriate support and spacer grids neither shown but well understood in the art, and providing the usual driver and breeder regions of the core. The core is restrained by radial restraint rings (not shown) applied at two levels, one of which is shown at Figure 1 designated A. At these levels, the fuel element is provided with wear surfaces for engagement with the wear surfaces of the adjacent fuel elements constituting the core and provided for the reasons referred to earlier.It is a feature of this invention that the wear surfaces, designated 3 in the drawings, are produced by outward bulging of the actual material of the wrapper 2. In addition, the outer surface of each bulge is hardened by application of any conventional hardening process appropriate to the material of the wrapper 2, which is in an example a stainless steel known by the designation M31 6. The bulges 3 constituting the wear surfaces can advantageously be produced by isostatic pressing in a manner which will be subsequently described with reference to Figures 3 to 6. In Figure 3, which is a plan view of the upper part of a fuel element wrapper 2, it will be observed that forming plates 4 have been applied to the six surfaces of the hexagonal wrapper 2.Each forming plate 4 has a depression 5 shown particularly in Figures 4, 5 and 6, into which the material of the wrapper 2 is deformed by isostatic pressing from fluid pressure to which the whole assembly is subjected but which effectively acts from within the wrapper 2. Each forming plate 4 is forced into sealing engagement with the surface of wrapper 2 by bolts 6 bearing on each forming plate 4 and in screwed engagement with a massive support ring 7. The ring 7 has apertures 8 for access to screws 9 in screwed engagement with each forming plate 4 and serving for raising each forming plate into a jacked position after the formation of the appropriate bulge. Each forming plate also has a vent plug 10 in communication with the depression 5 from which the bulge is formed.

It will be appreciated that the production of the bulges involves a simple forming step by a technique well known in the art and which does not need to employ high temperatures with the likelihood of adversely affecting the properties of the materials of the wrapper 2.

Instead of hardening the surface of the bulges to assist in providing the necessary wear properties, a hard wearing surface can be produced by plasma spraying of a suitable hard material such as stellite.

CLAIMS (filed 26/7/83) 1. A method of forming a nuclear reactor fuel element casing comprising applying isostatic press

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Nuclear reactor fuel elements This invention relates to nuclear reactor fuel element and has particular relevance to that kind of fuel element which in associatiQn with other similar elements in mutually close juxta position form the core of the nuclear reactor. Typical types of nuclear reactor which have this kind of core are fast reactors, pressurised water reactors, and boiling water reactors. With the said type of core, core restraint is in many cases performed by applying externally a radially inward force at at least two core levels, the force being transmitted throughout the core by the contact of adjacent fuel elements in engagement at least at the levels referred to. Because of relative movement between the fuel elements, it has been deemed expedient to provide bearing surfaces at these engagement positions. Hitherto, such bearing surfaces have been provided by pads attached to the fuel elements in any convenient manner, such pads having in appropriate cases hardened surfaces whose properties are such that undue wear will not occur during the design life of the fuel elements concerned. In an alternative, it has been proposed to provide the wear surfaces by plasma spraying of appropriate material on ta the bodies of the fuel elements at the appropriate positions. Whilst these forms of wear surfaces are satisfactory in operation, they both involve steps during the manufacture of the fuel elements which have to be carefully controlled in order to avoid adversely affecting the properties of the fuel element material to which the wear surfaces are applied. It is the object of the present invention to provide a nuclear reactor fuel element with wear surfaces in the appropriate positions which are effective in operation whilst simplifying the effort of production compared with that empioyed hitherto. According to the invention, a nuclear reactor fuel element has wear surfaces for engagement with the corresponding wear surfaces of adjacent fuel elements in which the wear surfaces project from the outer casing of the fuel element and are integral with the material of the said casing and are produced by isostatic pressing of the material of the said casing employing formers temporarily and sealingly attached to the outer surface of the said casing. Preferably each wear surface has a hard facing produced thereon by conventional hardening means. A constructional example embodying the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 is a side view of a typical fast reactor fuel eiement, Figure 2 is an enlarged fragmentary side view of that portion of the fuel element within the circle on Figure 1, Figure 3 is a plan view of Figure 2 with the addition of equipment for providing the wear surfaces shown in Figure 2, and Figures 4, 5and 6are respectively an elevation, side view and end view of one of the expedients shown in Figure 3. Referring to the drawings, firstly to Figure 1, this illustrates fragmentarilly typical fast reactor fuel element 1 which, together with a multiplicity of similar fuel elements disposed in mutual juxta position form the core of the fast reactor. The fuel element 1 broadly comprises a casing or wrapper 2 within which are disposed a large number of vertically orientated fuel pins carried in appropriate support and spacer grids neither shown but well understood in the art, and providing the usual driver and breeder regions of the core. The core is restrained by radial restraint rings (not shown) applied at two levels, one of which is shown at Figure 1 designated A. At these levels, the fuel element is provided with wear surfaces for engagement with the wear surfaces of the adjacent fuel elements constituting the core and provided for the reasons referred to earlier.It is a feature of this invention that the wear surfaces, designated 3 in the drawings, are produced by outward bulging of the actual material of the wrapper 2. In addition, the outer surface of each bulge is hardened by application of any conventional hardening process appropriate to the material of the wrapper 2, which is in an example a stainless steel known by the designation M31 6. The bulges 3 constituting the wear surfaces can advantageously be produced by isostatic pressing in a manner which will be subsequently described with reference to Figures 3 to 6. In Figure 3, which is a plan view of the upper part of a fuel element wrapper 2, it will be observed that forming plates 4 have been applied to the six surfaces of the hexagonal wrapper 2.Each forming plate 4 has a depression 5 shown particularly in Figures 4, 5 and 6, into which the material of the wrapper 2 is deformed by isostatic pressing from fluid pressure to which the whole assembly is subjected but which effectively acts from within the wrapper 2. Each forming plate 4 is forced into sealing engagement with the surface of wrapper 2 by bolts 6 bearing on each forming plate 4 and in screwed engagement with a massive support ring 7. The ring 7 has apertures 8 for access to screws 9 in screwed engagement with each forming plate 4 and serving for raising each forming plate into a jacked position after the formation of the appropriate bulge. Each forming plate also has a vent plug 10 in communication with the depression 5 from which the bulge is formed. It will be appreciated that the production of the bulges involves a simple forming step by a technique well known in the art and which does not need to employ high temperatures with the likelihood of adversely affecting the properties of the materials of the wrapper 2. Instead of hardening the surface of the bulges to assist in providing the necessary wear properties, a hard wearing surface can be produced by plasma spraying of a suitable hard material such as stellite. CLAIMS (filed 26/7/83)

1. A method of forming a nuclear reactor fuel element casing comprising applying isostatic press ure to the casing to form wear surfaces projecting outwardly from the casing and integral with the material of the casing.

2. A method as claimed in claim 1, employing formers temporarily and sealingly attached to the outer surface of the casing.

3. A method as claimed in claim 1 or claim 2, including producing a hard surface on each wear surface.

4. A method as claimed in any preceding claim, in which the casing is hexagonal in section and the wear surfaces are respectively in central regions of the sides as viewed axially.

5. A method of forming a nuclear reactor fuel element casing as claimed in claim 1 and substantially as hereinbefore described.

6. A nuclear reactor fuel element casing made by a method as claimed in any one of the accompanying drawings.

7. A nuclear reactor fuel element having wear surfaces for engagement with the corresponding wear surfaces of adjacent fuel elements in which the wear surfaces project from the outer casing of the fuel element and are integral with the material of the said casing and are produced by isostatic pressing of the material of the material of the said casing employing formers temporarily and sealingly attached to the outer surface of the said casing.

8. A nuclear reactor fuel element as claimed in claim 7, in which each wear surface has a hard facing.

9. A nuclear reactor fuel element as claimed in claim 7 or claim 8 which is hexagonal in section and the wear surfaces are respectively in central regions of the sides as viewed axiaily.

10. A nuclear reactor fuel element substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.