JPH0572382A - 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, a slot 15a is formed in the length direction in the pipe diffuser part formed by a control rod guide tube 13 and an instrumentation tube 14. By this, when the control rod guide tube 13 and the instrumentation tube 14 are withdrawn out of the grid space in the support grids, the pipe diffuser part 15 is constricted and reduced in diameter. Thus, they can be easily taken out and a space for inserting a key is assured.

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 this nuclear fuel assembly, if it is necessary to dismantle the fuel rods after manufacturing, the fuel rods are held in a healthy state. Releasing the restraint has the potential advantage that it can be used again on a fresh nuclear fuel assembly if they can be removed smoothly.

[0004]

However, once this 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. It was desired to secure an insertion space for the.

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 rods are taken out from the lattice space of each of the supporting lattices in a state where the restraining force of the springs and the dimples is eliminated by bending the springs, Prior to taking out from the lattice space of the lattice, by forming slots in the expanded direction on the control rod guide pipe and the instrumentation pipe in the longitudinal direction, The control rod guide tubes and instrumentation tube the expanded portion when pulled out of the lattice space of each support grid is squeezed, in which as easily retrievable.

[0007]

In the nuclear fuel assembly disassembling method of the present invention, the control rod guide pipe and the instrumentation pipe are formed by forming slots (slits) in the longitudinal direction in the expanded portions formed in the control rod guide pipe and the instrumentation pipe. When the pipe is pulled out from the lattice space of the support lattice, the expanded portion is squeezed to reduce the diameter and can be easily taken out, so that the key insertion space can be secured.

[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, the tip of the cutter 20 has a push rod 20b slidably provided inside an outer cylinder 20a, and a spring mounting cylinder 20c screwed to the tip of the outer cylinder 20a. The tool 20d is slidably mounted inside, and the spring 20 for pushing the spring fitting 20d between the spring fitting cylinder 20c and the spring fitting 20d and urging it toward the rod 20b.
While the e is mounted and the guide portion 20f is screwed to the tip of the spring mounting cylinder 20c, the pressing tool 20g screwed to the tip of the spring mounting tool 20d is provided inside the guide portion 20f. The protrusion 20h screwed to the pressing tool 20g is movably provided within a predetermined range in a state of being engaged with the elongated hole 20i formed in the guide portion 20f, and the guide portion is provided at the tip of the pressing tool 20g. In 20f, a pair of cutter bodies 20j is attached to the shaft 20.
The pair of inclined surfaces 20l formed in a taper shape at the tip of the pressing tool 20g by the forward movement of the pushing rod 20b is provided with the tapered surfaces 20m of the pair of cutter bodies 20j. By pressing the tip end of the cutter body 20j against the inner surface of the control rod guide tube 13 or the instrumentation tube 14 and retracting the outer cylinder 20a (spring mounting cylinder 20c, guide portion 20f). A slot (slit) having a predetermined width in the longitudinal direction of the pipe 13 or the expanded pipe portion 15 of the instrumentation pipe 14
15a is formed.

In the operation of forming the slot 15a in the expanded pipe portion 15 of the control rod guide pipe 13 or the instrumentation pipe 14 by the cutter 20, as shown in FIG.
Perform the slot 15a formation operation twice, and perform 4 at 90 ° intervals.
Slots 15a are formed at the places. In addition, as shown in FIG. 5, when the expansion part 15 is squeezed, the slot 15a is formed so that the inside diameter of the sleeves S1 and S2 is equal to or smaller than that of the slots 15a.
Set the width of.

In this way, after forming the slot 15a in the expanded tube portion 15 of each control rod guide tube 13 or the instrumentation tube 14, the inside surface of the tube is inspected by the endoscope and the slot 15a is inspected.
After confirming that the formation of No. 2 was performed well, the cutter 20 is removed from the mount. Then, the control rod guide tube 13 and the instrumentation tube 14 are separated from the lower nozzle 12 and pulled out from the lattice space of each of the supporting lattices G1 to G9.

Subsequently, an outer key (of the same type as that 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. 6 and 7, the inner key 30 has convex portions 31 and 32 formed alternately at appropriate intervals, and as shown in FIGS.
6 from the inner key 30 inserted into each opening 17
By rotating and then pulling, 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 fuel rods are pulled in a machine (Fig. (Not shown) pulling out (or extruding) from the supporting grids G1 to G9,
Next, the taken out fuel rod is inspected.

[0015]

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 taking out the control rod guide tube and the instrumentation tube, slots are formed in the expanded portion formed in the control rod guide tube and the instrumentation tube in the longitudinal direction, so that the control rod guide tube and the instrumentation tube are connected to the support grids. When the tube is pulled out from the inside of the lattice space, the expanded part is squeezed and can be taken out easily, the key can be easily inserted into the key insertion window, the nuclear fuel assembly can be easily disassembled, 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 an explanatory diagram of a pipe expanding portion before slot processing.

FIG. 4 is an explanatory diagram of a pipe expanding portion after slot processing.

FIG. 5 is an explanatory view showing a pulled-out state of a control rod guide tube or an instrumentation tube.

FIG. 6 is a front view showing an example of an inner key.

7 is a partially enlarged view of FIG.

FIG. 8 is an explanatory diagram showing a state where an inner key is inserted.

FIG. 9 is an explanatory diagram showing a state where the inner key is rotated by 90 °.

FIG. 10 is an explanatory view showing a state where the inner key is pulled.

FIG. 11 is an explanatory diagram of a state in which an inner key is finally set.

FIG. 12 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 15 Expanded Portion 15a Slot (Slit) 16 Key Insertion Window 18 Fuel Rod 19a Spring 30 Inner Key G1 Support Grid G2 Support Grid G3 Support Grid G9 Support lattice

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 rods are taken out from the lattice space of each of the supporting lattices in a state where the restraining force of the springs and the dimples is eliminated by bending the springs, Prior to taking it out from the lattice space of the lattice, by forming slots in the expanded portion formed in the control rod guide pipe and the instrumentation pipe in the longitudinal direction, Expanded pipe portion is throttled control rod guide tubes and instrumentation tube when pulled out of the lattice space of the respective support grid,
A method for disassembling a nuclear fuel assembly, characterized by being easily taken out.