JPH0572383A - Nuclear fuel assembly disassembling method - Google Patents

Abstract

PURPOSE:To disassemble a nuclear fuel assembly easily and take out fuel rods smoothly in a sound state. CONSTITUTION:Prior to taking out fuel rods from the grid space of each support grid G1, G2, G3 to G9, a control rod guide tube 13 and an instrumentation tube 14 are cut circumferentially in the vicinity of a key insertion window 16 formed at each support grid G1 to G9. By expanding the diameters of the control rod guide tube 13 and the instrumentation tube 14 and reducing the length of the control rod guide tube 13 and the instrumentation tube 14, a space for inserting a key is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for disassembling a nuclear fuel assembly in which fuel rods are smoothly taken out from a support grid of the nuclear fuel assembly.

[0002]

2. Description of the Related Art Generally, as a nuclear fuel assembly of this type, an upper nozzle and a lower nozzle which are arranged at a predetermined interval, a predetermined interval between these nozzles, and a strap are formed. A plurality of support grids each having a defined grid space, and a control rod guide tube and an instrumentation tube that are inserted into the grid spaces of these support grids and that are coupled to each support grid and that are connected to each nozzle. It is known that a plurality of fuel rods are inserted into the lattice space of each of the support lattices and elastically supported by springs formed in each of the support lattices.

In the case of assembling the above-mentioned conventional nuclear fuel assembly, when the fuel rod is inserted into the lattice space of the support lattice as it is, the springs and dimples formed on the support lattice and the fuel rod exert a restraining force. Since they come into contact with each other, the outer peripheral surface of the fuel rod may be scratched, and various countermeasures have been proposed. For example, Japanese Patent Application No. 64-9
In No. 57, as one of the countermeasures, a key insertion window is formed in the support grid, a key is inserted from the outside by using this key insertion window, and the spring is bent by this key to bend the fuel rod. The present invention proposes a nuclear fuel assembly which is configured to be smoothly inserted into the lattice space of the support lattice. In the event that the fuel rods need to be disassembled after being manufactured, this nuclear fuel assembly holds the fuel rods in a sound state.For example, the key insertion window is used to restrain the fuel rods from the support grid by key operation. If they can be removed smoothly by releasing them, there is a potential advantage that they can be used again for a new nuclear fuel assembly.

[0004]

However, once the nuclear fuel assembly is assembled, the control rod guide tube and the instrumentation tube block the key insertion window and the key cannot be inserted. Therefore, before the key is inserted. Therefore, it has been desired to secure a space for inserting a key.

The present invention solves the above problems and provides a method for disassembling a nuclear fuel assembly, which enables the nuclear fuel assembly to be easily disassembled and the fuel rods to be taken out smoothly and in a sound condition. With the goal.

[0006]

In order to achieve the above object, the present invention provides an upper nozzle and a lower nozzle which are arranged with a predetermined space, and a predetermined space between these nozzles. And a plurality of support grids having a grid space,
The control rod guide pipe and the instrumentation pipe, which are inserted into the lattice space of these support lattices and are coupled to the respective support lattices, and which are connected to the respective nozzles, are also inserted into the lattice space of the respective support lattices. And a nuclear fuel assembly is composed of a large number of fuel rods elastically supported by springs formed in each supporting grid, and by inserting a key into a key insertion window formed in each supporting grid, In the disassembling method of the nuclear fuel assembly, in which the fuel rod is taken out from the lattice space of each of the supporting lattices in a state where the restraining force of the spring and the dimple is eliminated by bending the spring, the fuel rod is supported by each of the supporting members. Prior to taking out from the lattice space of the lattice, the control rod guide pipe and the instrumentation pipe were cut in the circumferential direction in the vicinity of the key insertion window formed in each of the supporting lattices. Performs tube expanding operation in these control rod guide tubes and instrumentation tube, it is to ensure the insertion space of the key shrinks the control rod guide tubes and instrumentation tube in its longitudinal direction.

[0007]

In the disassembling method of the nuclear fuel assembly of the present invention,
After cutting the control rod guide pipe and instrumentation pipe inserted in the lattice space of each support lattice in the vicinity of the key insertion window formed in each support lattice in the circumferential direction, these control rod guide pipe and instrumentation pipe By expanding the pipe and shrinking the control rod guide tube and instrumentation pipe protruding in the key insertion window in the longitudinal direction, and removing the control rod guide pipe and instrumentation pipe from the key insertion window, It is possible to insert a key into the insertion window.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.

First, the nuclear fuel assembly 10 is placed horizontally on the assembly table (or an equivalent product) used during assembly. As shown in FIG. 1, this nuclear fuel assembly 10 is provided with an upper nozzle 11 and a lower nozzle 12 which are arranged with a predetermined gap, and a predetermined gap between these nozzles 11 and 12, and A plurality of (in this embodiment, nine) support grids G1, G2, G3 to G9 having a grid space formed by an inner strap and an outer strap, and a grid space of these support grids G1, G2, G3 to G9. While being inserted into the inside and fixing one end to the upper nozzle 11,
A large number of control rod guide tubes 13 connected to the supporting grids G2 to G9 via sleeves S1 and S2 by expansion and fixing the other end to the lower nozzle 12 while being connected to the supporting grid G1 via an insert I. , The support grids G1 to G
9 is inserted into the central lattice space of each of the supporting grids G and
2 to G9 through the sleeves S1 and S2 by expansion pipes, one instrumentation pipe 14, and the above-mentioned support grids G1 to G1.
It is inserted in the lattice space of G9, and each supporting lattice G1 to G
It is mainly composed of a large number of fuel rods (not shown) elastically supported by springs formed in 9. A key insertion window 16 is formed in each of the support grids G1 to G9. Further, in each of the control rod guide tubes 13, a large-diameter portion 13a is provided from the upper nozzle 11 to the lower nozzle 12 side by a predetermined distance from the support grid G3, and the upper and lower portions (left and right portions in FIG. 1) of the support grid G2. Was
In addition, the other portion is the small diameter portion 13b.

A nuclear fuel assembly 10 constructed as described above.
After installing on the assembly table in the horizontal position, the upper nozzle 11
Is removed from the control rod guide tube 13 and the instrumentation tube 14.
Next, the cutter 20 is mounted on a pedestal (not shown) arranged on the side of the upper nozzle 11 placed on the assembly table.

As shown in FIG. 2, at the tip of the cutter 20, a push rod 20b is slidably provided inside an outer cylinder 20a, and a spring-mounted cylinder 20c screwed to the tip of the outer cylinder 20a. A spring mounting tool 20d is slidably mounted inside the spring mounting cylinder 20 and
A spring 20e that pushes the spring mounting tool 20d and urges the spring mounting tool 20d toward the rod 20b is mounted between the spring mounting tool 20d and the spring mounting tube 20.
While the guide portion 20f is screwed to the tip of c, the pressing tool 20g screwed to the tip of the spring mounting tool 20d is provided inside the guide portion 20f, and the projection 20h screwed to the pressing tool 20g. Is provided movably within a predetermined range in a state of being engaged with the long hole 20i formed in the guide portion 20f, and the cutter body 20j is provided with a shaft 20k in the guide portion 20f at the tip of the pressing tool 20g.
The sloping surface 20l formed at the tip of the pressing tool 20g by the forward movement of the pushing rod 20b presses the cutter body 20j to guide the tip end of the cutter body 20j to the control rod guide. While pressing against the inner surface of the pipe 13 or the instrumentation pipe 14, the outer cylinder 20a (spring mounting cylinder 20c, guide portion 20f) is rotated to move the cutter body 20j along the inner surface of the control rod guide tube 13 or the instrumentation pipe 14. The control rod guide tube 13 or the instrumentation tube 14 is cut by rotating around the circumference.

In cutting the control rod guide tube 13 or the instrumentation tube 14 by the cutter 20, first, the cutter 20 is cut from the upper end (the left end in FIG. 1) of the control rod guide tube 13 or the instrumentation tube 14. It is inserted and cut at a position slightly closer to the lower nozzle 12 side than the key insertion window 16 of the supporting grid G1, and then sequentially cut at a position slightly closer to the upper nozzle 11 side than the key insertion window 16 of the supporting grids G2 to G9. In the cutting operation of the small diameter portion 13b of the control rod guide tube 13, the guide portion 20f for the small diameter portion is used, and the large diameter portion 13a of the control rod guide tube 13 and the instrumentation pipe 14 are used.
In the cutting operation of, the large diameter guide portion 20f is used.

In this way, each control rod guide tube 13 or instrumentation tube 14 has a plurality of cutting tubes A1 to A8 and B1 to B.
After being divided into eight, the inner surface of the tube is inspected with an endoscope to confirm that the cutting has been performed well, and the cutter 20 is removed from the mount. Then, a pipe expanding device (not shown) is mounted on the pedestal, and the pipes are expanded in the order of the cutting pipes A1 to A8 (B1 to B8) to shrink each cutting pipe in the longitudinal direction, and as a result, each key insertion window 16 From cutting tubes A1 to A8, B1
B8 is eliminated.

Subsequently, an outer key (of the same type as used for assembling) for flexing the spring of the outer strap and a spring for flexing the spring of the inner strap are fitted to the key insertion windows 16 having no obstacles. Attach the inner key 30. As shown in FIGS. 3 and 4, this inner key 30 has convex portions 31 and 32 formed alternately at appropriate intervals, and as shown in FIGS.
The inner key 30 inserted in each opening 17 from
By pulling after rotating, the spring 19a of the inner strap 19 is bent without damaging the fuel rod 18.

Further, in order to confirm that the fuel rods can be easily taken out from the supporting grids G1 to G9, the fuel rod holding (pulling) force is measured by a push-pull scale, and then the tube expanding device is mounted on the pedestal. Remove, then
Remove the lower nozzle 12. Subsequently, the fuel rod 1 is pulled out (or pushed out) from the supporting grids G1 to G9 by a pull-in machine (not shown), and then taken out.
5 inspection is performed.

[0016]

As described above, according to the present invention, an upper nozzle and a lower nozzle which are arranged with a predetermined space therebetween, and a plurality of nozzles which are arranged with a predetermined space between these nozzles and have a lattice space. Support grids, control rod guide tubes and instrumentation tubes inserted into the grid spaces of these support grids and coupled to the respective support grids, and connected to the respective nozzles, and the grids of the respective support grids. A nuclear fuel assembly is composed of a large number of fuel rods which are inserted into the space and elastically supported by springs formed in each supporting grid, and a key is inserted in a key insertion window formed in each supporting grid. In the disassembling method of the nuclear fuel assembly, the fuel rods are flexibly bent and the fuel rods are smoothly taken out from the lattice spaces of the supporting lattices. Prior to removing the control rod guide pipes and instrumentation pipes in the vicinity of the key insertion windows formed in the support grids, the control rod guide pipes and instrumentation pipes are cut in the circumferential direction before being taken out from the space. By expanding the pipes and shrinking the control rod guide pipes and instrumentation pipes in the longitudinal direction to remove them from the key insertion window, a key insertion space can be secured and the nuclear fuel assembly can be simplified. The fuel rod can be taken out smoothly, and the fuel rod can be taken out smoothly and in a healthy state.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a nuclear fuel assembly to which an embodiment of the present invention is applied.

FIG. 2 is a cross-sectional view showing an example of a cutter.

FIG. 3 is a front view showing an example of an inner key.

FIG. 4 is a partially enlarged view of FIG.

FIG. 5 is an explanatory diagram showing a state where an inner key is inserted.

FIG. 6 is an explanatory diagram showing a state where the inner key is rotated by 90 °.

FIG. 7 is an explanatory diagram showing a state where the inner key is pulled.

FIG. 8 is an explanatory diagram of a state in which an inner key is finally set.

9 is a perspective view showing a main part of FIG.

[Explanation of symbols]

 10 Nuclear Fuel Assembly 11 Upper Nozzle 12 Lower Nozzle 13 Control Rod Guide Tube 14 Instrumentation Tube 16 Key Insertion Window 18 Fuel Rod 19a Spring 30 Inner Key G1 Support Grid G2 Support Grid G3 Support Grid G9 Support Grid

Claims (1)

[Claims] 1. An upper nozzle and a lower nozzle which are arranged at a predetermined interval, and a plurality of support grids which are arranged at a predetermined space between these nozzles and have a grid space,
The control rod guide pipe and the instrumentation pipe, which are inserted into the lattice space of these support lattices and are coupled to the respective support lattices, and which are connected to the respective nozzles, are also inserted into the lattice space of the respective support lattices. And a nuclear fuel assembly is composed of a large number of fuel rods elastically supported by springs formed in each supporting grid, and by inserting a key into a key insertion window formed in each supporting grid, In the disassembling method of the nuclear fuel assembly, in which the fuel rod is taken out from the lattice space of each of the supporting lattices in a state where the restraining force of the spring and the dimple is eliminated by bending the spring, the fuel rod is supported by each of the supporting members. Prior to taking out from the lattice space of the lattice, the control rod guide pipe and the instrumentation pipe were cut in the circumferential direction in the vicinity of the key insertion window formed in each of the supporting lattices. A nuclear fuel assembly characterized by expanding the control rod guide pipe and the instrumentation pipe and contracting the control rod guide pipe and the instrumentation pipe in the longitudinal direction to secure an insertion space for the key. Dismantling method.