GB2553090A

GB2553090A - Method of manufacture

Info

Publication number: GB2553090A
Application number: GB1613971.9A
Authority: GB
Inventors: Turner Joel
Original assignee: Rolls Royce Power Engineering PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 2016-08-16
Filing date: 2016-08-16
Publication date: 2018-02-28
Also published as: GB201613971D0

Abstract

A method of manufacturing a silicon carbide (SiC) member for a nuclear fuel rod may comprise providing a silicon carbide tube 32 and a silicon carbide sealing arrangement for one or both ends of the silicon carbide tube. The sealing arrangement may provide a gas tight seal which comprises a cover member 36 over an end plug 34, with a joint intermediary material such as titanium foil or silicon carbide slurry. The sealing method may comprise applying electrical current and pressure, such as that performed in spark plasma sintering (SPS) or field assisted sintering techniques (FAST). The end plug 34 may be tapered or frustroconical in shape and the cover member 36 may be provided in two hemi-cylindrical parts. The tube 32 may be rotated during the joining process.

Description

(54) Title of the Invention: Method of manufacture

Abstract Title: A method of manufacturing a silicon carbide member for a nuclear fuel rod (57) A method of manufacturing a silicon carbide (SiC) member for a nuclear fuel rod may comprise providing a silicon carbide tube 32 and a silicon carbide sealing arrangement for one or both ends of the silicon carbide tube. The sealing arrangement may provide a gas tight seal which comprises a cover member 36 over an end plug 34, with a joint intermediary material such as titanium foil or silicon carbide slurry. The sealing method may comprise applying electrical current and pressure, such as that performed in spark plasma sintering (SPS) or field assisted sintering techniques (FAST). The end plug 34 may be tapered or frustroconical in shape and the cover member 36 may be provided in two hemi-cylindrical parts. The tube 32 may be rotated during the joining process.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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Method of Manufacture

Technical Field

The present disclosure concerns a fuel rod, a nuclear power plant, a component, a method of manufacturing a component and/or a method of manufacturing a fuel rod.

Background

A nuclear power plant generally includes a nuclear reactor, a primary circuit, a heat exchanger, a secondary circuit, and a turbine. The primary fluid in the primary circuit is heated by the nuclear reactor. The primary fluid flows to the heat exchanger, where it heats secondary fluid in the secondary circuit. The heated secondary fluid is then used to drive the turbine to generate electricity.

The nuclear reactor generally includes a plurality of fuel rods. Fuel rods are rods that contain nuclear fuel. Typically, a fuel rod is a tubular member containing uranium dioxide pellets. The fuel rod is clad in a zirconium alloy, commonly referred to a zircaloy. The zirconium alloy typically has at least 95% by weight zirconium, and the remainder is made up of other metallic elements.

Zirconium has a very low absorption of thermal neutrons, and is hard, ductile and corrosion resistant, which are the properties needed for the cladding of a nuclear fuel rod. However, zircaloy reacts with steam to produce hydrogen in an exothermic reaction. As such, a power plant needs to include many active control measures to handle hydrogen in an accident scenario. Accordingly, there is a move in the industry to improve the accident resistance of nuclear fuel rods.

Silicon carbide has been considered for use as a cladding material. Silicon carbide has a higher melting point than zircaloy and does not form large amounts of hydrogen when it contacts steam, but it is notoriously difficult to join. Any joints of the cladding of the fuel rod need to be gas tight, and to the best of the applicant’s knowledge, at the time of filing the present application, it has not been possible to manufacture a fuel rod with silicon carbide cladding, the fuel rod having gas tight seals at both ends.

Summary

According to an aspect there is provided a method of manufacturing a nuclear fuel rod, the method comprising providing a silicon carbide tube and providing a sealing arrangement for sealing an end of the silicon carbide tube. The sealing arrangement comprises a silicon carbide member and an end plug. The method comprises applying electrical current and pressure to the sealing arrangement and an end portion of the tube so as to join the silicon carbide member of the sealing arrangement to the tube.

That is, the sealing arrangement is joined to an end portion of the tube using a method that may be generally referred to as sintering using the direct application of electrical current, for example spark plasma sintering or field assisted sintering techniques. The end plug provides support to the tube during the joining process.

In the present application, reference to silicon carbide refers to monolithic silicon carbide or silicon carbide composites. For example silicon carbide composites including a fibre weave, e.g. a silicon carbide fibre weave. In particular, the silicon carbide tube, silicon carbide member, and/or later discussed silicon carbide end plug and/or silicon carbide cover member may be made from a monolithic silicon carbide, or silicon carbide composites for example silicon carbide composites including a fibre weave, e.g. a silicon carbide fibre weave.

The silicon carbide member may be the end plug.

The method may comprise applying electrical current and pressure to the end plug and an end portion of the tube so as to join the end plug to the tube.

According to an aspect there is provided a method of manufacturing a nuclear fuel rod, the method comprising providing a silicon carbide tube. A silicon carbide end plug is provided and positioned in the silicon carbide tube. The method comprises applying electrical current and pressure to the end plug and an end portion of the tube so as to join the end plug to the tube.

The end plug may be considered to be solid. That is, the end plug may be considered not be hollow, e.g. not contain a cavity.

The sealing arrangement may comprise a cover member.

The method may comprise providing a cover member over the end plug and an end portion of the tube, and joining the cover member to the tube and/or the end plug.

The cover member may be provided over the end plug and end portion of the tube prior to the end plug being joined to the tube. The cover member may be joined to the end plug and/or the tube by applying current and pressure to the cover member and the end plug and tube at the same time as the end plug is joined to the tube.

The cover member may be made from a plurality of parts, e.g. two or more parts. When the cover member is provided in two parts, a join between the two parts may be perpendicular to the direction of pressure applied during the spark plasma sintering.

The cover member may be a cylindrical cap. For example, the cover member may have a circular end face and an annular wall connected to the circular end face. When the cover member is provided in two parts, each part of the cover member may be a hemi-cylindrical cap, e.g. having a semi-circular end face and a semi-annular end wall.

The cover member may be made from silicon carbide. Alternatively, the cover member may be made from a metallic material.

A joint intermediary (e.g. titanium foil or silicon carbide slurry) may be provided between the cover member and the tube and/or between the cover member and the end plug, before the cover member is joined to the tube and/or the end plug.

The method may comprise providing a joint intermediary (e.g. titanium foil or silicon carbide slurry) between the end plug and the tube prior to joining the end plug to the tube. The joint intermediary, e.g. the titanium foil, may be for example 20 to 40 pm thick, e.g. 30 pm thick.

The plug may be tapered. The taper may provide a lead in for positioning the plug in the tube. That is, when the end plug is positioned in the tube, the narrower end of the plug may be innermost the tube.

The tube and sealing arrangement may be rotated circumferentially (e.g. about the longitudinal axis of the tube) and electrical current and pressure is applied, such that the direction of the pressure applied is in a different direction to the applied pressure when the sealing arrangement is first joined to the tube.

This process may be repeated.

During the or a further joining process, pressure may be applied in a direction substantially parallel to a longitudinal axis of the tube. In this way, if desired, a joint between the cover member and an end face of the end plug can be reinforced.

Nuclear fuel may be provided in the tube prior to joining the sealing arrangement to the tube. For example, one end of the tube may be sealed using the method described above. Fuel may then be provided in the tube and the other end of the tube may be sealed using the method described above. Alternatively, the fuel may be provided in the tube and both ends of the tube may then be sealed using the method described above.

The nuclear fuel may comprise fissile isotopes of uranium or plutonium. The fuel may be provided in pellet form.

A plenum of inert gas, for example helium, may be provided in the tube.

The method may comprise providing two end plugs and simultaneously joining both end plugs to the tube using the method described herein.

Two spark plasma sintering or field assisted sintering chambers or machines may be provided, one for joining each end of the tube to a respective end plug.

According to an aspect there is provided a nuclear fuel rod comprising a silicon carbide tube in which nuclear fuel is housed. The tube is sealed at each end, and the seal comprises an end plug.

The seal may comprise a cover member that extends over the end plug and along an end portion of the tube.

The end plug and/or the cover member may be made from silicon carbide.

The nuclear fuel rod may be a nuclear fuel rod manufactured using the method according to any one of the previous aspects.

According to an aspect there is provided a nuclear power plant comprising a plurality of nuclear fuel rods according to the previous aspect, and/or nuclear fuel rods manufactured using the method according to one or more of the previous aspects.

According to an aspect there is provided a method of manufacturing a component, the method comprising providing a silicon carbide hollow member and providing a silicon carbide support member. The method comprises positioning the support member in the hollow member. The method further comprises applying electrical current and pressure to the support member and at least a portion of the hollow member so as to join the support member to the tube using spark plasma sintering.

The method may comprise providing a cover member over the end plug and joining the cover member to the end plug and/or to the hollow member.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

Drawings

Embodiments will now be described by way of example only, with reference to the Figures, in which:

Figure 1 is a schematic of a nuclear power plant;

Figure 2 is a schematic cross section of a fuel rod;

Figure 3 is a schematic cross section of an end of the fuel rod of Figure 2; Figures 4A to 4E schematically illustrate steps in forming a fuel rod,

Figure 4A illustrates a tube, Figure 4B illustrates end plug being inserted into one end of the tube of Figure 4A, Figure 4C illustrates a cover member being positioned over the end plug and tube of Figure 4B, Figure 4D illustrates the arrangement of Figure 4C positioned in a spark plasma sintering machine, and Figure 4E illustrates an end view of the arrangement positioned between punches of the spark plasma sintering machine; and

Figure 5 illustrates an arrangement for optionally simultaneously sealing both ends of the fuel rod.

Description

Referring to Figure 1, a nuclear power plant is indicated generally at 10. The plant includes a reactor vessel 11 housing nuclear fuel, a primary circuit 14, a heat exchanger which in this example is a steam generator 16, a secondary circuit 18 and a turbine 20. The primary fluid in the primary circuit is heated by the nuclear reactor. The primary fluid then flows to the steam generator, where it heats secondary fluid, in this example water, in the secondary circuit. The heated secondary fluid is then used to drive the turbine 20. The secondary fluid then flows to a condenser 19 where it is cooled using water from an ultimate heat sink 21. The ultimate heat sink may be a cooling tower, river, lake, or any other suitable supply of cooling water.

Referring to Figure 2, the nuclear reactor includes a plurality of fuel rods. Each fuel rod 22 includes fuel 24 provided optionally between insulating pellets 26. The fuel contains fissile material, for example the fuel may contain isotopes of uranium or plutonium, e.g. uranium-235, plutonium-239, or plutonium 241. The fuel may be provided as pellets, or in any other suitable form. An example fuel that may be used is uranium silicide (U3S12). At one end of the fuel rod a support sleeve 28 is provided, on which one of the insulating pellets is seated. At the opposite end of the fuel rod, a compression spring 27 is provided. The compression spring compresses against the arrangement of insulating pellets, fuel and support sleeve. A fission gas plenum 29 is provided in the region of the compression spring. The entire fuel rod is covered in a cladding 30. In the presently described example, the cladding is a silicon carbide cladding, more particularly the cladding is made from silicon carbide composite, e.g. silicon carbide with a fibre weave. However, in alternative embodiments the silicon carbide cladding may be monolithic silicon carbide.

Referring now to Figure 3, the silicon carbide cladding is defined by a tube 32 made from silicon carbide, and an end plug 34 made from silicon carbide. In the present example, a cover member 36 is also provided, and in this example the cover member is made from silicon carbide. An end plug and cover member are provided at both longitudinal ends of the tube, each cover member extends over the respective end plug and a respective end portion of the tube. The end plug and cover member seal the ends of the tube so as to provide a gas tight volume in which the fuel can be provided.

The tube 32 is cylindrical. The end plug 34 is frustroconical in shape. That is, the end plug is tapered with the narrower end of the end plug being innermost the tube 32. The taper of the end plug is shallow and varies from a maximum inner diameter of the tube to a minimum (or just below minimum) diameter of the tube, to account for manufacturing tolerances. The end plug is solid. That is, the end plug is free from any significant internal cavity. The cover member 36 defines a cylindrical cap, having a circular end face 38 and an annular wall 40 connected to the circular end face.

A method of manufacturing the fuel rod will now be described with reference to Figures 4A to 4E.

Firstly, the silicon carbide tube 32 is provided (see Figure 4A). The end plug 34 (which also may be referred to as a support member) is then provided and wrapped in a titanium foil 42. In the present example, the titanium foil is approximately 30pm thick. The end plug and titanium foil are then inserted into one end of the tube (see Figure 4B), with the narrow end of the end plug being inserted into the tube first. The end plug is inserted into the tube to the extent that the end plug plugs the end of the tube. It is not necessary for an end face of the end plug to be flush against a respective end face of the tube.

The titanium foil is provided around the end plug because it has been found to improve the strength of a joint between the end plug and the tube. However, in alternative examples, the titanium foil may be omitted, or an alternative intermediary may be used, for example silicon carbide slurry.

The cover member 38 is provided in two parts 38A, 38B. Each of the two parts is hemi-cylindrical, such that together they define the cylindrical cap shaped cover member. Each of the two parts of the cover member are positioned over the respective end cap 34 and the respective end of the tube 32 (see Figure 4C). In the present example, titanium foil 44 is provided on an inner surface of the cover member before it is positioned over the end cap and respective end of the tube. However, in alternative embodiments no titanium foil may be provided, or the titanium foil may be provided only around the annular wall of the cover member instead of being provided along the annular wall and on the end face of the cover member, and/or an alternative intermediary may be used, for example silicon carbide slurry.

The respective end assembly of the nuclear fuel rod is then positioned in equipment that is configured to apply an electrical current and a pressure to a component or medium positioned in a chamber of said equipment (see Figure 4D and 4E). Such equipment may be generally referred to as equipment used for sintering by the direct application of electrical current, for example spark plasma sintering or field assisted sintering techniques. In the present example, the equipment is a spark plasma sintering machine. Spark plasma sintering machine Spark plasma sintering (SPS) machines can be purchased and are well-documented so will not be explained in detail here. However, generally the end assembly of the fuel rod is provided between two electrically conductive parts, which may be referred to as punches or rams, in a chamber 48. In the present example, the punches do not contact, but in alternative embodiments the punches may be in contact. That is, the punches when in contact may circumscribe the full circumference of the end assembly of the nuclear fuel rod.

The chamber 48 is then evacuated. A press 50 pushes down on the punches and tube end assembly applying pressure to the assembly, and at the same time an electrical current is passed through the punches via electrodes. Sufficient pressure and current is applied for a sufficient period of time to bond the cover member to the tube and the end plug to the tube. The pressure may be ramped and held in intervals as required. The pressure and time required for forming the joint is similar to that for joining two flat pieces of silicon carbide, the details of which are well documented in the literature so will not be included in more detail here.

Referring to Figure 5, both ends of the tube can be sealed using a similar end assembly as described above. As such, in the present example it is proposed to provide an arrangement of two SPS machines, or an SPS machine having two chambers, presses and sets of punches. In this way, an end plug and cover member can be assembled at both ends of the tube 32, then one end of the tube can be provided in one SPS machine or chamber 48, and the other end of the tube can be provided in the other SPS machine or chamber 48. The end plugs and cover members at each end of the tube can then be simultaneously joined to the tube.

Optionally, during the joining process, the tube may be turned and the SPS joining process repeated, that is the pressure may be applied at an alternative location. The tube may be rotated multiple times so that the pressure is perpendicular to multiple circumferential locations.

A further optional modification to the joining process is to also apply pressure in a direction substantially aligned with the longitudinal axis of the tube during the SPS joining process. This can help to form an improved bond between the end plug and the cover member.

The above described method enables a gas tight fuel rod to be made from silicon carbide. To the applicant’s knowledge, at the time of filing, silicon carbide fuel rods have been discussed in the literature but nobody has yet found a way to form a silicon carbide fuel rod with a gas tight seal at both ends.

Using the described method, it is possible to test that a gas-tight seal has been formed using the chamber of the SPS machine to apply a vacuum to the chamber and then testing to see whether any of the plenum gas escapes, for example test whether any helium is detected, in a similar manner to vacuum helium leak tests conventionally used in the art. In this way the manufacturing and testing processes can be conducted one after the other without the need to move the fuel rod from the SPS machine to a testing machine.

So far, the method of joining has been described with respect to manufacturing a fuel rod. However, the method of joining could be applied to other components having two silicon carbide members requiring joining. In such examples, a support member is required to provide support of the structure during the SPS process, in a similar manner to which the end plug supports the end assembly of the fuel rod in the described example.

A fuel rod is generally a cylindrical rod, but it will be appreciated that the described method can be applied to tubes and fuel rods with alternative cross sections. In such embodiments the cross section of the plug and cover member is shaped to be complimentary to the shape of the tube.

One type of fuel rod has been described, but in alternative embodiments the fuel rod may have a different internal arrangement.

In the present example, a cover member is provided to further improve the seal 10 at the end of the fuel rod. However, in alternative embodiments no cover member may be provided.

The cover member has been described as being made from silicon carbide, but in alternative embodiments the cover member may be metallic, e.g. a zirconium alloy. In further alternative examples, the cover member may be made from silicon carbide and the plug may be metallic, e.g. a zirconium alloy.

The SPS machine used in the described method may be modified to include shaped electrodes, and as such punches may not be required.

It will be understood that the invention is not limited to the embodiments abovedescribed and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and subcombinations of one or more features described herein.

Claims

1. A method of manufacturing a nuclear fuel rod, the method comprising: providing a silicon carbide tube;

providing a sealing arrangement for sealing an end of the silicon carbide tube, the sealing arrangement comprising a silicon carbide member and an end plug; and applying electrical current and pressure to the sealing arrangement and an end portion of the tube so as to join the silicon carbide member of the sealing arrangement to the tube.

2. The method according to claim 1, wherein the silicon carbide member is the end plug, and the method comprises applying electrical current and pressure to the end plug and an end portion of the tube so as to join the end plug to the tube.

3. The method according to claim 1 or 2, wherein the sealing arrangement comprises a cover member, and the method comprises providing a cover member over the end plug and an end portion of the tube, and joining the cover member to the tube and/or the end plug.

4. The method according to claim 3, wherein the cover member is made from silicon carbide.

5. The method according to claim 3 or 4 as dependent on claim 2, wherein the cover member is provided over the end plug and end portion of the tube prior to the end plug being joined to the tube, and wherein the cover member is joined to the end plug and/or the tube by applying current and pressure to the cover member and the end plug and tube at the same time as the end plug is joined to the tube.

6. The method according to any one of claims 3 to 5, wherein the cover member is provided in two parts, and wherein a joint between the two parts is perpendicular to the direction of pressure applied during the joining of the cover member to the tube and/or end plug.

7. The method according to any one of claims 3 to 6, wherein a joint intermediary (e.g. titanium foil or silicon carbide slurry) is provided between the cover member and the tube and/or between the cover member and the end plug, before the cover member is joined to the tube and/or the end plug.

8. The method according to any one of the previous claims, comprising providing a joint intermediary (e.g. titanium foil or silicon carbide slurry) between the end plug and the tube prior to joining the end plug to the tube.

9. The method according to any one of the previous claims, wherein the plug is tapered so as to provide a lead in for positioning the plug in the tube.

10. The method according to any one of the previous claims, wherein the tube and sealing arrangement are rotated circumferentially (e.g. about the longitudinal axis of the tube) and electrical current and pressure is applied, such that the direction of the pressure applied is in a different direction to the applied pressure when the sealing arrangement is first joined to the tube.

11. The method according to any one of the previous claims, wherein during the or a further joining process, pressure is applied in a direction substantially parallel to a longitudinal axis of the tube.

12. The method according to any one of the previous claims, wherein nuclear fuel is provided in the tube prior to joining the sealing arrangement to the tube.

13. The method according to any one of the previous claims, comprising providing two sealing arrangements and simultaneously joining both sealing arrangements to the tube using the method according to any one of the previous claims.

14. A nuclear fuel rod comprising a silicon carbide tube in which nuclear fuel is housed and the tube being sealed at each end, the seal comprising an end plug.

15. The nuclear fuel rod according to claim 14, wherein the seal comprises a cover member that extends over the end plug and along an end portion of the tube.

16. A nuclear power plant comprising a plurality of nuclear fuel rods according to claim 14 or 15, and/or nuclear fuel rods manufactured using the method according to any one of claims 1 to 13.

10

17. A method of manufacturing a component, the method comprising providing a silicon carbide hollow member;

providing a silicon carbide support member and positioning the support member in the hollow member;

applying electrical current and pressure to the support member and at 15 least a portion of the hollow member so as to join the support member to the hollow member.

Intellectual

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