FR2730339A1 - DEVICE AND METHOD FOR REPLACING NUCLEAR FUEL PENCILS - Google Patents

Abstract

Device for replacing nuclear fuel rods in a fuel assembly (1), comprising a device comprising a tool (6) for replacing a fuel rod intended respectively for extracting a fuel rod (10) from the fuel assembly ( 1) and when inserting a fuel rod (10) into the fuel assembly (1) and guide means (11) intended to guide the fuel rod replacement tool (6) in a position (12 ) fuel rod chosen from the fuel assembly (1). The guide means (11) comprise a guide device (13) which is guided into a fuel rod position (12) chosen by means of a table (14) with coordinate system.

Description

l Device and method for replacing nuclear fuel rods

TECHNICAL AREA

  The present invention relates to a device and a method for replacing nuclear fuel rods. In irradiated fuel assemblies, the predicted life of which has not been completed, certain defective fuel rods may appear. A fuel assembly of this kind is repaired by replacing the defective fuel rods, the fuel assembly can then be reinserted into the reactor for continued operation. In some cases, one or more rods are removed from the fuel assembly for the sole purpose of inspecting them. PRIOR ART, PROBLEMS A fuel assembly comprises a number of oblong fuel rods which are fixed at a distance

  to each other by means of what are called spacers. The fuel rods are approximately 4 meters long and approximately 1 cm in diameter.

  During repair or inspection, the rods are respectively removed from the fuel assembly and reinserted into the fuel assembly. The relationship between the length of the fuel rods and their diameter is a problem in particular during insertion. There is a danger that the pencil will break during insertion due to bending. Another problem consists in guiding the tool used to replace the fuel rod to a selected fuel rod position in order to extract or insert a chosen fuel rod. When extracting or inserting fuel rods, a remote-controlled installation is generally used and it includes a lifting device which transmits a vertical movement which extracts the rod from the fuel assembly and inserts it into the fuel assembly. Guide means are also used

  which ensure that the correct pencil is handled by the lifting device.

  In the description of the Swedish patent, the publication number of which is 429 071, an installation is described.

  for replacing fuel rods. This installation includes a fuel rod replacement tool intended to extract a fuel rod from a fuel assembly under water or to insert it there. The fuel rod replacement tool comprises an oblong support body provided with a gripping element intended to take the end of a fuel rod. The installation further comprises a centering plate which can be fixed to the fuel assembly and which has centering holes intended to guide the gripping element towards the correct rod in the fuel assembly. Breakage of fuel rods during the extraction of a fuel assembly or insertion into a fuel assembly is avoided by the arrangement of a support tube which is designed to surround the gripping element and a fuel rod extract which is arranged therein so that the fuel rod is guided in the support tube. When you insert the fuel rod, which is pulled into

  the support tube, in the fuel assembly, the support tube prevents the gripping member from moving laterally and therefore from causing deformation loads on the thin fuel rods.

  An important part of the fuel rod replacement device is the centering plate. The role of the centering plate is to guide the fuel rod replacement tool into a position above a fuel rod position to extract or insert a fuel rod. As the fuel rods are very close to each other, a centering hole of conical shape for each position of fuel rod cannot be provided in the centering plate. This difficulty has been eliminated by arranging the centering holes only for certain selected fuel rod positions and in such a way that, when the centering plate is turned four times, all the positions of

  fuel rods can be reached.

  The disadvantage of the centering plate is that it must be turned in steps of 90 so that all the positions of the fuel rods can be obtained. To be able to turn the centering plate, a device provided above the plate must be moved to the side 20 to make it accessible. In addition, the dimension of the conical-shaped centering holes is limited by adjacent holes, that is to say that the amplitude of the guide movement is limited. It is advantageous to have as large a hole as possible because the gripping member is remotely controlled and must be moved into the correct centering hole with only visual inspection. Another disadvantage is that the guidance is monitored only by visual inspection and by operation

  manual which provides the possibility of discovering disturbances.

  As the handling takes place 7 to 10 meters below the surface of the water, it is difficult to monitor the work there, which means that the device must have a design which ensures correct handling without much

visual inspection.

  The present invention relates to a device and a method for facilitating the guiding of the gripping element towards the correct fuel rod position and for ensuring correct handling without requiring a great deal of

visual inspection.

  In particular, the invention relates to a device for replacing nuclear fuel rods in a fuel assembly, which comprises a tool for replacing a nuclear fuel rod intended respectively for extracting a fuel rod from the fuel assembly and for l insertion of a fuel rod into the fuel assembly, and guide means intended to guide the fuel rod replacement tool towards a selected fuel rod position of the fuel assembly, characterized in that the

  guide means include a guide device for receiving the fuel rod replacement tool and a coordinate system table for transporting the guide device to a position above the selected fuel rod position.

  An improvement of the invention consists in that the coordinate system table is in Cartesian coordinates and includes a first carriage which can be moved in the X direction of the coordinate system table and a second carriage which can be moved according to direction Y of the table with coordinate system, and in that the guide device is mounted on the second carriage. 30 An improvement of the invention consists in that the first carriage can be moved along first rails arranged in parallel to each other and on each side of the coordinate system table, and in that the first carriage in itself comprises second parallel rails35 along which the second carriage is arranged

  so that it can be moved.

  An improvement of the invention consists in that the first carriage is connected to a motor which, by means of a drive screw parallel to the first rail, is designed to transport the first carriage to a position in the direction of the X of the coordinate system table above a chosen fuel rod position, and in that the second carriage can be moved in an equivalent manner to the first in a position in the Y direction of the system table coordinates. An improvement of the invention consists in that the table with coordinate system is in polar coordinates and comprises an arm, the length of which is variable and the end of which is mounted in rotation, and in that the guide device is arranged at the other end of the arm. An improvement of the invention consists in that the arm which can vary longitudinally in rotation is connected to a motor intended to transport the guide device to the position located above the chosen fuel rod position. An improvement of the invention consists in that the guide device is in the form of a funnel for

  facilitate receipt of the fuel rod replacement tool.

  An improvement of the invention consists in that an eddy current coil is arranged in the

  Guidance device for detecting faults in the fuel rod which has passed through the eddy current coil.

  An improvement of the invention consists in that the device comprises an element intended to ensure that the central axis of the fuel rod replacement tool is in correspondence with the central axis of the

fuel rod handled.

  An improvement of the invention consists in that the element comprises a vertical plumb pendulum and a table with an upper coordinate system arranged at the upper part of the fuel rod replacement tool. The invention further relates to a method for replacing nuclear fuel rods in a fuel assembly, comprising the use of a device comprising a tool for replacing a nuclear fuel rod intended respectively for the extraction of a fuel rod from the fuel assembly and the insertion of a fuel rod into the fuel assembly and guide means intended to guide the fuel rod replacement tool in a selected fuel rod position of the fuel assembly,

  characterized in that the guiding means are provided with a guiding device which is guided towards the fuel rod position chosen by means of a table with coordinate system.

  An improvement of the process consists in moving the fuel rod replacement tool towards

  new fuel rod positions of the same fuel assembly while the fuel rod replacement tool is inserted into the guide device.

  SUMMARY OF THE INVENTION, ADVANTAGES The guiding movement is facilitated by having, at the upper part of the fuel assembly, automatic guiding means intended to guide the fuel rod replacement tool towards a selected fuel rod position. The guide means comprise a funnel-shaped guide device arranged on a table with a coordinate system. The coordinate system table, the coordinates can be polar or Cartesian, makes it possible to move the guide device to a position above each fuel rod position

of the fuel assembly.

  The funnel of the guide device has a dimension and a width such that the fuel rod replacement tool can be guided there without difficulty. Once the fuel rod replacement tool has been guided into the guide device, this device is moved using the coordinate system table to a desired new fuel rod position without having to move the tool fuel rod replacement to move the guide device to a new position and then again guide the tool 15 into the guide device. Thus, the fuel rod replacement tool does not need to be

  lifted out of the guide device and moved separately to find a new fuel rod position, and the tool only accompanies the guide device 20 during its movement.

  To ensure a correct position, in the vertical direction, of the fuel rod when it is extracted or inserted, an element intended to ensure that the central axis of the fuel rod coincides with the central axis of the 'fuel rod replacement tool is arranged according to a special embodiment of the invention. This element consists, for example, of a vertical pendulum and an upper table with coordinate system arranged in the upper part of the lifting device. A suitable upper coordinate system table corresponds to the coordinate system table described above. The design of the upper coordinate system table may however be considerably simpler than the coordinate system table which is arranged on the fuel assembly and

  can be manually controlled as appropriate.

  The advantage of the invention is that the need for visual inspection, which is somewhat unreliable, is reduced by guiding the fuel rod replacement tool in a simple and reliable manner towards the position of fuel rod chosen using the funnel-shaped guide device and the coordinate system table. In addition, the fuel rod replacement tool can be moved to new fuel rod positions within a single fuel assembly, while being inserted into the guide device. The fuel rod replacement tool should only be guided back into the guide device in cases where fuel rods are completely removed from the fuel assembly and moved to another position at

  the exterior of the fuel assembly.

  The need for visual inspection is further reduced by the arrangement of a device which ensures that the central axis of the fuel rod coincides with the central axis of the fuel rod replacement tool,

  the correct guiding of the fuel rods in the total fuel assembly being carried out both during the extraction and the insertion of the fuel rod. 25 SHORT DESCRIPTION OF THE DRAWINGS

  The invention can be understood more easily by referring to the accompanying drawings.

  FIG. 1 represents a fuel assembly and a fuel rod replacement tool placed above

  above the latter, in the upper part of the fuel assembly, guide means intended to guide the fuel rod replacement tool towards a chosen fuel rod position. Figure 2a shows guide means in a side view, comprising a funnel-shaped guide device arranged on a table with coordinate system. Figure 2b shows the guide means of Figure 2a in a plan view, comprising a table with Cartesian coordinate system. Figure 2c shows the guide means of Figure 2a in a plan view, comprising a table

polar coordinate system.

  Figure 3a shows a system top table

Cartesian coordinates.

  FIG. 3b represents a top table with a polar coordinate system.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 represents a fuel assembly 1

  disposed in water 2 of a pool 3 for storing spent fuel for fuel maintenance.

  The fuel assembly 1 is of the pressurized water type and is placed in a fuel rack (shown only partially in FIG. 2a by the reference numeral 4), which is disposed at the bottom 5 of the swimming pool. As a variant, the fuel assembly 1 can be arranged in

  a fuel hoist (not shown). A fuel rod replacement tool 6 comprising a lifting device 7 and a gripping element 8 is disposed at the

  above the fuel assembly 1 and is for the most part immersed in water 2. The fuel rod replacement tool 6 comprises a tube 9 for fixed support and an arm (which is not shown precisely in the figures) which can move there in the vertical direction by means of the lifting device 7 and which is connected to the gripping element 8. The function of the support tube 9 is to guide the arm with the gripping element 8 and to prevent any bending of the fuel rod 10, when it is drawn in the support tube 9, in the lateral direction in order to avoid thus the breaking of this pencil. When a fuel rod 10 is extracted from a fuel assembly 1, the fuel rod 10 is pulled into the support tube 9 when the arm, with the gripping element 8, moves upward in the tube. In the upper part of the fuel assembly 1, automatic guide means 11 are arranged to guide the fuel rod replacement tool 6 towards a selected fuel rod position; we will refer to the reference

numeric 12 of Figure 2b.

  FIG. 2a shows that the guide means 11 comprise a funnel-shaped guide device 13 on a table 14 with a coordinate system. The coordinate system table 14 makes it possible to transport the guide device 13 to a position located above each pencil position 12

  fuel of the fuel assembly 1.

  The weight of the coordinate system table 14 is balanced in the vertical direction by the parts where it is placed, that is to say on the fuel rack 4 shown in FIG. 2a. In the horizontal direction, the coordinate system table 14 is arranged so as to be supported by the upper spacer 15 of the fuel assembly 1. As the spacers 15 contained in the fuel assembly 125 grow when irradiated, the coordinate system table 14 is not arranged in horizontal contact at all of its corners. The corners of the coordinate system table 14, which are not arranged in fixed contact, are suitably arranged in elastic contact. A corner of the coordinate system table 14 having fixed contact with the fuel assembly 1 constitutes a reference point for the coordinates on the coordinate system table 14. FIG. 2b represents in a plan view a table 14 with Cartesian coordinate system, which is provided 1! with a first and a second carriage 16, 17. The first carriage 16 can move in the direction of the Xs of the table 14 with coordinate system by the installation of a first rail 18 on each side of the table 14 to coordinate system, the first carriage 16 being able to be moved on these first rails 18. The first carriage 16 is moved along the rails 18 by means of a screw 19 which is driven by an electric motor 20. The first carriage 16 comprises second rails 21 on which the second carriage 17 is arranged so that it can be moved in the Y direction of the table 14 with coordinate system. The guide device 13 is associated with the second carriage 17 and is thus movable in the direction of the X and Y in such a way that all the positions 12 of fuel rods can be reached. The second carriage 17 can also be moved using a screw 22 which is also controlled by an electric motor 23. The position of the guide device 13 relative to the table 14 with coordinate system 20 is known, as well as the position table 14 with coordinate system with respect to the fuel assembly thanks to

  the existence of the benchmark described above.

  FIG. 2c represents a plan view of a table 14 with a polar coordinate system which is provided with an arm 27, the length of which is variable and the end of which is mounted in rotation at the point designated by the reference numeral 28. The guide device 13 is disposed at the other end of this arm 27. The arm may be telescopic as shown in FIG. 2c, or may, for example, have the shape of a drawer. By means of the telescopic and rotatable arm 27, the guide device 13 can be moved to a position above each of the positions 12 of fuel rods. In one embodiment of the invention, the movement of the arm 35 is driven by an electric motor 29. The funnel of the guide device 13 has a dimension and a width such that the fuel rod replacement tool 6 can be guided in the funnel without difficulties. When the fuel rod replacement tool 6 has been guided in the guide device 13, this is moved using the coordinate system table 14 to a new pencil position 12 without having to guide the fuel rod replacement tool back into the guide device 13. Thus, the fuel rod replacement tool 6 does not need to be removed by lifting the guiding device 13 and moved separately to find a new fuel rod position 12, but only accompanies the device 13

guide in its movement.

  The arrangement of the coordinate system table 14 above the fuel assembly 1 is produced using a tool which is remotely controlled from above, while the fuel rod replacement tool 6 has been moved to the side. After the fuel rod replacement tool 6 has been placed in the guide device 13, no further mechanical manipulation is necessary until the work with the fuel assembly 1 being processed is completed. The drawbacks linked to the fact that the dimensions of the spacers 15, and therefore also the spacing distances of the rods 10 change during irradiation, are resolved by determining the coordinates for the positions 12 of the fuel rods 30 assuming growth averaged over a number of cycles, making them as general as possible. To ensure correct guidance of the fuel rod 10 throughout the fuel assembly 1, when it is extracted or inserted, an element 14 is arranged to ensure that the central axis of the pencil 10 fuel coincides with the central axis of the fuel rod replacement tool 6. This element 24 consists, for example, of a pendulum 24a of vertical lead and of a table 26 with an upper coordinate system arranged in the upper part of the fuel rod replacement tool 6. A coordinate system table suitable for this purpose is shown in the figures.

3a and 3b.

  FIG. 3a represents a table 26 with an upper Cartesian coordinate system comprising a first carriage 30 which, by means of an element 31, can be moved manually in the direction of the Y, this element possibly being, for example, a rack 31a. A second carriage 32 is disposed at the level of the first carriage 30. The second carriage 32 can be moved manually, by means of an element 33, in the direction of the X, for example along a screw 34. A device 35 for guidance is associated with the second carriage 32. The guidance device 35 is connected

  at the upper part of the fuel rod replacement tool 6.

  FIG. 3b represents a table 26 with an upper polar coordinate system comprising an arm 35, the length of which is variable. One end of the arm 35 is rotatably mounted at the digital reference point 36. A guide element 37 is connected to the other end of the arm 35. The arm 35 can be rotated manually by means of an element 38 which is fixed to the arm 35 at the digital reference point 36 and the length of which can vary manually 30 by means of an element 39, for example connected to a screw 39a. The guide device 37 is connected to the upper part of the fuel rod replacement tool 6. With regard to fuel rod replacement, it is often desired to monitor for defects in the fuel channels which constitute the outer part of the fuel rod which is being handled. This can be achieved using an annular eddy current coil 15 through which the pencil 10 is passed. In a particular embodiment of the invention, such an eddy current coil 25 is disposed in the guiding device 13 so that it accompanies the guiding device at all times and the rods 10, independently of the position 12 of the fuel rod, are drawn through them. The eddy current coil 25 can be arranged so as to be

  divisible so that the gripping element 8 of the fuel rod replacement tool 6 can pass there in the divided state.

Claims (12)

  1. Device for replacing nuclear fuel rods in a fuel assembly (1), which comprises a tool (6) for replacing a nuclear fuel rod intended respectively for the extraction of a fuel rod (10) from the fuel assembly (1) and on insertion of a fuel rod (10) into the fuel assembly (1), and guide means (11) intended to guide the fuel rod replacement tool (6) towards a position (12) of a fuel rod chosen from the fuel assembly (1), characterized in that the guide means (11) comprise a guide device (13) intended to receive the tool (6) for replacing the fuel rod and a coordinate system table (14) for transporting the guide device (13) to a position above the selected fuel rod position (12). 2. Device according to claim 1, characterized in that the table (14) with coordinate system is in Cartesian coordinates and comprises a first carriage (16) which can be moved in the direction of the X of the table (14) with system coordinates and a second carriage (17) which can be moved in the Y direction of the table (14) with coordinate system, and in that the guide device (13) is mounted on the second carriage (17). 3. Device according to claim 2, characterized in that the first carriage (16) can be moved along first rails (18) arranged parallel to each other and on each side of the table (14) with coordinate system, and in that the first carriage (16) comprises in itself second parallel rails (21) along which the second carriage (17) is arranged so as to be able to be moved.   4. Device according to claim 3, characterized in that the first carriage (16) is connected to a motor (20) which, by means of a screw (19) driving parallel to the first rail (18), is designed to transport the first carriage (16) to a position in the X-direction of the coordinate system table 14 above a selected fuel rod position, and in that the second carriage (17) can be moved in a way   equivalent to the first in a position in the Y direction of the coordinate system table (14).   5. Device according to claim 1, characterized in that the table (14) with coordinate system has polar coordinates and comprises an arm (27), the length of which is variable and one end of which is mounted in rotation (28), and in that the guide device (13) is arranged at the other end of the arm (27). 6. Device according to claim 5, characterized in that the arm (27) which can vary longitudinally in   rotation is connected to a motor intended to transport the guide device (13) to the position located above   above the selected fuel rod position (12). 7. Device according to claim 1, characterized in that the device (13) for guiding is shaped   funnel to facilitate the reception of the fuel rod replacement tool (6).   8. Device according to claim 1, characterized in that an eddy current coil (25) is arranged in the guide device (13) to detect faults in the fuel rod (10) which has passed through the eddy current coil.   9. Device according to claim 1, characterized in that it comprises an element (24) intended to ensure that the central axis of the tool (6) for replacing fuel rod is in correspondence with the central axis   fuel rod (10) handled.   10. Device according to claim 7, characterized in that the element (24) comprises a pendulum (24a) with vertical plumb and a table (26) with upper coordinate system arranged at the upper part of the tool (6)   fuel rod replacement.   11. Method for replacing nuclear fuel rods in a fuel assembly (1), comprising the use of a device comprising a tool (6) for replacing nuclear fuel rod intended respectively for the extraction of a fuel rod ( 10) of the fuel assembly (1) and the insertion of a fuel rod (10) into the fuel assembly (1) and of the guide means (11) intended to guide the tool (6) 20 replacement of fuel rod in a selected fuel rod position (12) of the fuel assembly (1), characterized in that the guide means (11) are provided with a guide device (13) which is guided towards   the fuel rod position (12) chosen by means of a coordinate system table (14).   12. Method according to claim 11, characterized in that one moves the tool (6) for replacing   fuel rod to new positions (12) of fuel rods of the same fuel assembly (1) 30 while the fuel rod replacement tool (6) is inserted into the guide device (13).