JPH0411839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for assembling a fuel assembly, and more particularly to a method for assembling a fuel assembly suitable for continuous use with a channel box being rotated in any direction.

FIG. 1 shows a conventional fuel assembly. The fuel assembly 1 includes an upper tie plate 2, a lower tie plate 3, a fuel spacer 4, and a fuel spacer 4.
A plurality of fuel rods 5 with mutual gaps maintained at
and a channel box 6 containing the fuel bundle 12, a channel spacer spacing member 7 made of an elastic member, and a channel spacer spacing made of an inelastic member that backs up the spacing member 7. It has a member 11. Both ends of the fuel rod 5 are held by an upper tie plate 2 and a lower tie plate 3. The spacing member 7 maintains a gap between the fuel assembly 1 attached to the upper tie plate 2 and the adjacent fuel assembly 1 when the channel box 6 is loaded into the reactor core. 8
is an expansion spring provided between the fuel rod 5 and the upper tie plate 2. The channel box 6 also has a clip 13 at its corner at the upper end of the channel box 6, as shown in FIG. The clip 13 is an engagement means for holding the channel box 6, which is placed over the fuel bundle 12, on the upper tie plate 2. in fact,
The channel box 6 is detachably attached to the upper tie plate 2 with a set screw 15 provided on the channel fastener. The set screw 15 is
It engages with the upper tie plate 2 through a hole 14 provided in a clip 13 of the channel box 6.

As shown in FIG. 2, about 400 to 800 fuel assemblies 1 are regularly loaded in a nuclear reactor to form its core, depending on its output. In FIG. 2, reference numeral 9 indicates a cross-shaped control rod, and each fuel assembly 1 is loaded adjacent to one of the control rods 9. FIG. 3 is an enlarged view of a portion of the reactor core shown in FIG. 2. Four fuel assemblies 1 and a cross-shaped control rod 9
A box-shaped upper grid plate 10 constitutes a unit cell, and this unit cell is provided in the reactor vessel.
It is loaded so that it fits inside the box. The spacing L between the fuel assemblies 1 within a unit cell is maintained by spacing members 7 made of elastic members of the four fuel assemblies 1, and serves as a passage for the control rods 9. Even if the spacing member 7 is damaged,
The spacing members 11, which are adjacent inelastic members, ensure a passage for the control rods 9 for stopping the nuclear reactor. On the other hand, the distance M between the unit cells is maintained by the upper grid plate 10.

By the way, the distance L between the fuel assemblies 1 inside the unit cell must always be maintained at a certain distance or more so as not to interfere with the smooth operation of the control rods 9. However, it has become clear from experience that the channel box 6 deforms when used at high temperatures for long periods of time. Even if the fuel assembly 1 is exchanged in position within the core as combustion progresses, in the conventional fuel assembly 1, the spacing member 7 can only be attached to one specific corner of the channel box 6. It is designed so that it cannot be attached to other corners. Therefore, since the surface of the control rod 9 that is close to the central axis is always the same portion, the deformation of the channel box 6 always tends to expand in the same direction (toward the passage of the control rod).

Furthermore, the fuel assembly 1 at the outermost periphery of the core, shown in section P in FIG. 2, is usually left at the outermost periphery position for a long period of time, in some cases until the end of its life. Moreover, the slope of the neutron flux is large at the outermost circumferential position, and if the fuel assembly 1 is used as it is for a long time, it is conceivable that the channel box 6 will bend. If the channel box 6 is deformed so as to narrow the interval L, the operation of the control rods will be obstructed, which may impede the operation control of the nuclear reactor.

The present invention has been made in view of the above,
It is an object of the present invention to provide a method for assembling a fuel assembly that allows effective use of channel boxes and allows for easy reassembly of the fuel assembly.

The present invention is characterized in that a plurality of fuel rods, an upper tie plate that holds the upper end of the fuel rod, and an engagement member having a hole that engages with the upper tie plate have a plurality of corner portions at the upper end. a channel box that surrounds the bundle of fuel rods; a plurality of first spacing members that are located on two adjacent sides of the channel box and are made of inelastic members; One of the channel boxes facing the control rods in the core
a second spacing member made of an elastic member that is located at one corner of the fuel assembly and maintains a distance between the fuel assembly and another adjacent fuel assembly when the fuel assembly is loaded in the core; and a spacing-keeping structure in which the first and second spacing-keeping members are integrated, and the spacing-keeping structure is detachably attached to the upper tie plate through the hole of the engagement member. The attached fuel assembly is removed from the core of the nuclear reactor, the spacing structure is removed from the upper tie plate, and the channel box is removed from the upper tie plate holding the upper ends of the fuel rods. the channel box is mounted on the upper tie plate so that the curved surface of the channel box is moved away from the central axis of the control rod, and the spacing structure is attached to the one corner facing the control rod. The fuel assembly is attached to the upper tie plate through the hole of the other engaging member located in the upper tie plate.

A method of assembling a fuel assembly, which is a preferred embodiment of the present invention, will be described below. Figures 5 and 6 are
The structure of the fuel assembly used in this example is shown.
Components that are the same as those of the conventional example are indicated by the same reference numerals.

Similar to the conventional fuel assembly 1, the fuel assembly 20 of this embodiment includes a fuel bundle 12 composed of an upper tie plate 2, a lower tie plate 3, a fuel spacer 4, and a plurality of fuel rods 5. There is. Further, the fuel assembly 20 includes a channel box 21 that is detachably attached to the fuel bundle 12 and an integral structure 24 for maintaining a distance that is detachably attached to the fuel bundle 12. In this embodiment, the structure of the channel box 21 is different from that of the conventional channel box 6, and in addition, a space maintaining integral structure 24 is newly provided.

As shown in FIG. 5, the channel box 21 has clips 22 provided at the upper end of the channel box 21 and at each corner thereof. The clip 22 has a hole 23 extending therethrough. As shown in FIG. 6, the distance maintaining integral structure 24 is constructed by attaching a distance maintaining member 26 made of an elastic member and a distance maintaining member 27 made of an inelastic member to an L-shaped member 25. Part 2
6 and a spacing member 27 are integrated.
Two spacing members 27 are provided on both sides of the L-shaped member 25, and two spacing members 26 are provided on both sides of the L-shaped member 25.
The L-shaped member 2 is located between the spacing members 27.
It is attached to the corner of 5.

The channel box 21 has a clip 22 that engages with the upper tie plate 2.
The fuel bundle 12 is attached to the fuel bundle 12 while being held in place. The integral spacing structure 24 is attached to one corner of the channel box 21 attached to the fuel bundle 12, as shown in FIG. That is, the integral spacing member 24 is secured to the upper tie plate 2 by tightening the set screw 15 provided on the integral spacing member 24 to the upper tie plate 2 through the hole 23 in one clip 22 of the channel box 21. It is detachably attached to the tie plate 2. Naturally, the channel box 21 is also detachably attached to the upper tie plate 2 by means of a set screw 15. In this state, the spacing member 27 is located on two adjacent side surfaces of the channel box 21, and the spacing member 26 is located on one corner of the channel box 21 between the two side surfaces of the channel box 21. It is located in The spacing member 26 has the same function as the spacing member 7,
The spacing member 27 has the same function as the spacing member 11.

At the time of periodic inspection after the fuel bundle 12 of the fuel assembly 20 has been burned for a certain period of time, the set screw 15 is loosened and the spacing maintenance integral structure 24 is removed, and then only the channel box 21 is pulled upward and removed from the fuel bundle 12. .

Since the spacing members 26 and 27 do not separate from each other when the integral spacing member 24 is removed, the removal work can be done in a short time, and the removed spacing members 26 and 27 are easy to handle. . The amount of deformation of the removed channel box 21 is measured using a channel box dimension measuring device 30 shown in FIG. The channel box measuring device 30 is composed of a straight guide rod 31 that serves as a reference, and a head 32 that slides vertically on the guide rod 31 to detect deformation of the channel box 21. will be installed.

The amount of deformation of the channel box 21 is detected during periodic inspection using the channel box measuring device 30. For channel boxes 21 that are deformed by more than a predetermined amount, the channel boxes 21 are rotated so that the convex deformed portions are located on the side far from the control rods 9, and then placed over the fuel bundles 12. Then, the integral spacing member 24 is positioned at a corner of the channel box 21 located on the control rod 9 side, and is attached to the upper tie plate 2 together with the channel box 21 using a set screw 15. In this way, the channel box 21 is provided for continued use in the next cycle. Therefore, channel boxes 2
1 is deformed and the distance L between adjacent fuel assemblies is narrowed, and there is no risk that the operation of the control rods 9 will be hindered, and safety can be improved. Further, the fuel assembly 20 can be easily reassembled by reattaching the channel box 21 to the fuel bundle 12 after rotation. This is because the spacing member 26 and the spacing member 27 are integrated, making their handling much easier.

According to the present invention, since channel boxes can be used effectively, the number of channel boxes to be discarded can be significantly reduced. There will be no hindrance to control rod operation, improving reactor safety. Furthermore, the fuel assembly can be easily reassembled.

[Brief explanation of drawings]

Figure 1 is a partially broken front view of a conventional fuel assembly, Figure 2 is a cross-sectional view of a boiling water reactor core, and Figure 3 is a fuel assembly consisting of the fuel assembly shown in Figure 1. A plan view of a unit cell, FIG. 4A is a plan view of the channel box of the conventional fuel assembly shown in FIG. 1, FIG. 4B is a front view of FIG. 4A, and FIG. 5 is an embodiment of the present invention. 5A is a plan view of the channel box, FIG. 5B is a front view of FIG. 5A, and FIG. 6 shows the channel box of FIG. The structure of the attached fuel assembly, which is an embodiment of the present invention, is shown, and FIG. 6A is a plan view of the fuel assembly, FIG. 6B is a front view of the upper part of FIG. 6A, and FIG. 7 5 is an explanatory diagram when measuring the dimensions of the channel box shown in FIG. 5. FIG. 2... Upper tie plate, 5... Fuel rod, 9...
... Control rod, 20 ... Fuel assembly, 21 ... Channel box, 22 ... Clip, 23 ... Hole, 24 ... Gap maintaining integral structure, 26, 27
...Space maintaining member.

Claims (1)

[Claims] 1. A plurality of fuel rods, an upper tie plate that holds the upper end portions of the fuel rods, and engagement members having holes that engage with the upper tie plate are provided at a plurality of corner portions at the upper end portions, respectively, a channel box surrounding the bundle of fuel rods; a plurality of first spacing members located on two adjacent sides of the channel box and made of inelastic members;
and a fuel assembly located at one corner of the channel box facing the control rods in the reactor core between the two side surfaces and interfacing with other adjacent fuel assemblies when the fuel assembly is loaded in the reactor core. a second spacing member made of an elastic member to maintain a spacing therebetween, and a spacing maintaining structure in which the first and second spacing members are integrated, and taking out a fuel assembly whose structure is removably attached to the upper tie plate through the hole of the engagement member from the core of the nuclear reactor;
The spacing structure is removed from the upper tie plate, the channel box is removed from the upper tie plate holding the upper end of the fuel rod, and the curved surface of the channel box is aligned with the central axis of the control rod. The channel box is mounted on the upper tie plate so as to be away from the upper tie plate, and the spacing structure is inserted through the hole in the other engaging member located at the one corner facing the control rod. A method for assembling a fuel assembly, comprising attaching it to the upper tie plate.