JP2023120990A - Fuel assembly loading method and fuel assembly coupling jig - Google Patents

Abstract

To provide a fuel assembly loading method and fuel assembly coupling jig, which reduce warping of fuel assemblies during an earthquake compared with the conventional method and improve insertability of a control rod.SOLUTION: A fuel assembly 10 loading method is provided, comprising loading multiple fuel assemblies 10 into a reactor core 3, and installing a fuel assembly coupling jig 18 for restricting horizontal movement of top structures of at least adjacent fuel assemblies 10 of the fuel assemblies 10 relative to each other from the top of the reactor core 3.SELECTED DRAWING: Figure 3

Description

The present invention relates to a fuel assembly loading method and a fuel assembly connecting jig.

For the purpose of significantly reducing the relative displacement of the fuel assemblies, preventing short-term application of reactivity, and achieving a C-lattice core that does not apply reactivity even if displaced, Patent Document 1 describes: a fuel assembly having a horizontal lattice-shaped upper lattice plate, a plurality of square tubular channel boxes each standing in a plurality of lattices of the upper lattice plate, and having an upper portion supported in the horizontal direction by the upper lattice plate; Control rods inserted between the plurality of fuel assemblies from below the upper grid plate, means for detecting neutron flux near the fuel assemblies, and inserting the control rods when the neutron flux exceeds a predetermined value. In a boiling water reactor comprising means for performing It is described to have means for constraining displacement.

JP-A-07-209461

A core of a boiling water reactor is loaded with a plurality of fuel assemblies.

The fuel assembly is filled with a plurality of fuel pellets containing nuclear fuel material, e.g., uranium oxide, sealed with a plurality of fuel rods, an upper tie plate supporting the upper ends of the fuel rods, and supporting the lower ends of the fuel rods. It has a lower tie plate, a plurality of fuel spacers for maintaining the spacing between the fuel rods, water rods, and a rectangular tubular channel box with a square cross section.

The channel box has an upper end attached to the upper tie plate and extends toward the lower tie plate and surrounds a plurality of fuel rods bounded by a plurality of axially disposed fuel spacers.

A water rod is arranged in the central portion of the cross section of the fuel assembly, and a plurality of fuel rods are arranged around the water rod. The lower ends of the water rods are supported by the lower tie plate and the upper ends of the water rods are supported by the upper tie plate.

Each fuel rod has a cladding. The lower end of the cladding tube is closed with a lower end plug, and the upper end of the cladding tube is closed with an upper end plug. The cladding tube is filled with a plurality of fuel pellets containing nuclear fuel material.

A plurality of control rod drive mechanism housings are attached to the bottom of the reactor pressure vessel. A control rod guide tube is arranged in the upper part of the control rod drive mechanism housing, and the upper part of the control rod guide tube is fitted into the core support plate. A control rod drive mechanism is disposed within the control rod drive mechanism housing and is connected to a cross-section control rod disposed in a control rod guide tube.

The control rods are inserted into the water gaps between the four fuel assemblies through cross-section through holes formed in the fuel support fittings.

Reaction control of a boiling water reactor during normal operation controls the amount of neutrons in the core by vertically driving control rods with a control rod drive mechanism. Also, in an emergency such as when a large earthquake occurs, all control rods are inserted into the core to bring about an emergency shutdown (hereinafter referred to as "scram") of the boiling water reactor.

Here, when an earthquake occurs, the fuel assembly bends in a bow shape due to the shaking of the earthquake. Therefore, when the control rods are inserted into the core, the fuel assemblies and the control rods come into contact with each other, and frictional drag acts on the control rods. Therefore, it is known that the control rod insertion time during an earthquake is longer than the control rod insertion time during normal operation. Therefore, it is required to shorten the control rod insertion time during a scram by reducing the deflection of the fuel assembly when an earthquake occurs.

Japanese Patent Laid-Open Publication No. 2002-300000 discloses a technique for reducing the deflection of a fuel assembly caused by an earthquake. In this patent document 1, in a fuel assembly in which a plurality of fuel rods are arranged in a lattice in a channel box having a rectangular cross section and an upper tie plate and a lower tie plate are fixed to the upper part and the lower part of the channel box, respectively, the channel It is said to have anti-rolling means securing the tops of the box together.

However, in the method disclosed in Patent Document 1, since the fuel assembly is fixed by inserting the fixing metal fittings into the channel box, the excitation force during an earthquake is applied to the contact surface between the fixing metal fittings and the channel box. Become.

Here, the main purpose of the channel box is to secure the cooling water flow path, guide the control rods, and fix and protect the fuel rods. It was possible.

SUMMARY OF THE INVENTION The present invention provides a fuel assembly loading method and a fuel assembly connecting jig capable of reducing deflection of a fuel assembly in the event of an earthquake compared with conventional methods and improving insertability of control rods.

The present invention includes a plurality of means for solving the above problems, and one example thereof is a method of loading fuel assemblies, comprising the steps of loading a plurality of fuel assemblies into a nuclear reactor core; and a step of installing, from above the reactor core, jigs for constraining mutual horizontal movement of upper end structures of at least adjacent fuel assemblies among the fuel assemblies. and

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to reduce the deflection of the fuel assembly when an earthquake occurs, compared with the conventional art, and improve the insertability of the control rods. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

1 is a partially cut perspective view showing the internal structure of a boiling water reactor; FIG. 1 is a perspective view showing a support structure for fuel assemblies arranged in a boiling water reactor; FIG. 1 is a perspective view of a fuel assembly connecting jig according to a first embodiment; FIG. FIG. 4 is a plan view showing a state in which the fuel assembly connecting jig according to the first embodiment is loaded in the core; FIG. 5 is a top view of a fuel assembly connecting jig according to a second embodiment; FIG. 11 is a perspective view of a fuel assembly connecting jig according to a third embodiment; FIG. 11 is a perspective view of a fuel assembly connecting jig according to a third embodiment;

Embodiments of a fuel assembly loading method and a fuel assembly connecting jig according to the present invention will be described below with reference to the drawings. In the drawings used in this specification, the same or corresponding components are denoted by the same or similar reference numerals, and repeated descriptions of these components may be omitted.

<First embodiment>
A fuel assembly loading method and a fuel assembly connecting jig according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG.

First, the schematic configuration of a boiling water reactor to which the fuel assembly loading method and the fuel assembly connecting jig of the present embodiment are suitably applied will be described with reference to FIG. FIG. 1 is a partially cut perspective view showing the internal structure of a boiling water reactor 1 according to the first embodiment.

As shown in FIG. 1, a boiling water reactor 1 includes a reactor pressure vessel 2, a core 3, a core shroud 4, a control rod guide tube 5, a control rod drive mechanism housing 6, and an upper grid plate 7. , and a core support plate 8 , and a plurality of fuel assemblies 10 are loaded in the core 3 .

Inside the reactor pressure vessel 2 are a core 3 loaded with a plurality of fuel assemblies 10, a core shroud 4 surrounding the fuel assemblies 10 constituting the core 3, and control rods 17 (see FIG. 2 described later). , a lattice-shaped upper lattice plate 7 arranged above the core shroud 4 and serving to support the fuel assemblies 10 in the lateral direction, and arranged below the core shroud 4 A core support plate 8 that supports the fuel assemblies 10 is arranged.

A plurality of control rod drive mechanism housings 6 are provided at the bottom of the reactor pressure vessel 2 . The upper portion of the control rod drive mechanism housing 6 penetrates through the bottom of the reactor pressure vessel 2 and is connected to the lower portion of the control rod guide tube 5 . The upper portion of the control rod guide tube 5 is fitted into a fuel support fitting 9 (see FIG. 2 described later) of the core support plate 8 .

A control rod drive mechanism (not shown for convenience of illustration) is provided inside the control rod drive mechanism housing 6 so that the control rods 17 stored in the control rod guide tubes 5 can be inserted into the core 3 . It has become.

FIG. 2 is a perspective view showing a support structure for fuel assemblies 10 arranged in the boiling water reactor 1 according to the first embodiment. In FIG. 2, the fuel assembly 10 on the front side and a part of the upper grid plate 7 are shown cut away.

As shown in FIG. 2, a fuel assembly 10 constituting the core 3 has a plurality of fuel rods 11 arranged in a square lattice and surrounded by channel boxes 12 on the sides. Channel fasteners 13 and channel spacers 14 are attached to the upper portions of the fuel assembly 10 and the channel box 12 .

An upper tie plate 15 and a fuel assembly handle portion 16 are arranged above the fuel rods 11 . At the time of refueling, a gripping mechanism (not shown) for fuel replacement is used to grip the fuel assembly handle portion 16 to install the fuel assembly 10 in the core 3 or remove it from the core 3 .

A plurality of fuel support fittings 9 are arranged on the core support plate 8 . A set of four fuel assemblies 10 is supported by fuel support fittings 9 . As a result, gaps are formed between the fuel assemblies 10 supported as a set of four. The upper portion of the control rod guide tube 5 is fitted to the lower side of the fuel support fitting 9 .

The control rods 17 are driven by a control rod drive mechanism (not shown) provided inside the control rod drive mechanism housing 6 (see FIG. 1). By operating a control rod drive mechanism (not shown), the cross-section control rods 17 pass from the control rod guide tube 5 through the cross-section through holes 9a formed in the fuel support fittings 9, and the four bodies are assembled into one. It is inserted in the gap between the fuel assemblies 10 supported as a set.

FIG. 3 shows an outline of the fuel assembly connection jig 18 of this embodiment, and FIG. 4 shows how the fuel assembly connection jig 18 of this embodiment is installed above the fuel assembly 10, viewed from above the core. shows a plan view of the time.

A fuel assembly connecting jig 18 shown in FIG. A jig for restricting movement in the horizontal direction, and has a fuel assembly handle insertion portion 18a, a connecting jig handle portion 18b, a retainer leaf spring 18c, and a flat plate 18d.

The fuel assembly handle portion inserting portion 18a is formed by inserting at least a portion of each of the fuel assembly handle portions 16 of two adjacent fuel assemblies 10 in the same cell of the upper grid plate 7 from below so that the fuel assembly handle portion insertion portion 18a is horizontal. It is a portion that fixes the relative positional relationship of the directions, and has at least one retaining plate spring 18c that presses and holds the fuel assembly handle portion 16. As shown in FIG.

The connecting jig handle portion 18b is provided for lifting the fuel assembly connecting jig 18 by a gripping mechanism for fuel replacement when the fuel assembly connecting jig 18 is installed from above the core 3. It plays substantially the same role as the body handle portion 16 .

The flat plate 18d is a member for fixing the relative positional relationship of the plurality of fuel assembly handle portion insertion portions 18a.

Such a fuel assembly connecting jig 18 is used after a plurality of fuel assemblies 10 are loaded into the core 3 using a gripping mechanism for fuel replacement (a step of loading a plurality of fuel assemblies 10 into the core 3). Using the same gripping mechanism for fuel replacement, the connecting jig handle portion 18b is gripped, and from above the fuel assembly 10, each adjacent fuel assembly handle portion 16 is inserted into the fuel assembly handle portion insertion portion 18a. It is loaded so as to be inserted (a step of installing the fuel assembly connecting jig 18 from above the core 3).

Next, the effects of this embodiment will be described.

The method of loading the fuel assemblies 10 according to the first embodiment of the present invention described above comprises a step of loading a plurality of fuel assemblies 10 into the core 3, and installing from above the core 3 a fuel assembly connecting jig 18 for constraining mutual horizontal movement of the side structures.

In recent years, seismic evaluation standards have become stricter, and the possibility of fuel displacement exceeding the allowable value has increased, and there is a demand to avoid resonance of the fuel assembly 10 with the building of the boiling water reactor 1. . The inventors of the present invention have found that the fuel assembly 10 vibrates in the event of an earthquake, similar to the support by the upper end pin, so that it is effective to change the support to a higher-rigidity support.

Here, the channel box 12 used in Patent Document 1 is not a structural member designed on the assumption that it will bear the load, and if it receives a large seismic load, it may be damaged by the reaction force generated in the restraint part. have a nature. Moreover, since there is only one restraining portion, there is a risk of concentration of reaction force, which increases the risk of damage.

Also, if the weight is set so that it will not come off due to the impact of an earthquake, creep damage may occur at high temperatures due to its own weight during operation, and the channel box 12 and the upper grid plate 7 may be damaged. .

Therefore, it is proposed that the structure of the upper end of the fuel assembly 10 having a strong structure is connected, and the behavior of the upper ends of the fuel assembly 10 is mutually restrained by utilizing the mismatch of the behavior of the respective upper ends of the fuel assembly 10, so that high-rigidity support can be achieved. conceived. Further, by setting the fuel assembly connecting jig 18 from the upper part of the core 3, it is possible to eliminate the need for retaining the fuel assembly by its own weight and prevent the weight from becoming excessively large. Therefore, damage to the members of the fuel assembly 10 can be reduced, the bending of the fuel assembly 10 can be reduced compared to the conventional art, and the insertability of the control rods 17 can be improved. Further, since the positions of the fuel assemblies 10 are constrained to each other, the gap between the adjacent fuel assemblies 10 can be kept constant, and the insertability of the control rods 17 can be efficiently improved.

Also, the upper end structure is the fuel assembly handle portion 16 of the fuel assembly 10 . The fuel assembly handle portion 16 of the fuel assembly 10 and the upper tie plate 15 to which it is connected are the basic structural members of the fuel assembly 10. It is very suitable as a target for installing the fuel assembly connection jig 18 when restraining the horizontal movement of the fuel assembly. In addition, since it can be restrained at a plurality of points, the reaction force is not concentrated and the possibility of damage can be further reduced.

Furthermore, in the step of installing the fuel assembly connection jig 18, by installing the fuel assembly connection jig 18 with respect to the fuel assembly 10 in the same cell of the upper grid plate 7, the fuel assembly connection jig The fuel assembly connecting jig 18 can have a lightweight structure because the fuel assembly connecting jig 18 does not need to be structured to straddle the upper grid plate 7 .

Further, the fuel assembly handle portion inserting portion 18a has a retainer plate spring 18c for pressing and holding the fuel assembly handle portion 16, thereby fixing the fuel assembly connecting jig 18 and the fuel assembly handle portion 16. can be made stronger, and the mutual horizontal movement of the upper end side structures of the fuel assembly 10 can be more effectively restrained.

Furthermore, the fuel assembly connection jig 18 constrains two adjacent fuel assemblies 10 in the same cell of the upper grid plate 7, so that the structure of the fuel assembly connection jig 18 can be minimized. and a lightweight structure.

Further, by providing the flat plate 18d for fixing the relative positional relationship of the plurality of fuel assembly handle portion insertion portions 18a, it is possible to suppress the horizontal movement of the fuel assembly 10 relative to each other.

<Second embodiment>
A fuel assembly loading method and a fuel assembly connecting jig according to a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a top view of a fuel assembly connecting jig according to the second embodiment.

As shown in FIG. 5, the fuel assembly connecting jig 18A of the present embodiment has four fuel assembly handle insertion portions of the fuel assembly connecting jig 18 of the first embodiment shown in FIG. 18a are connected by a flat plate 18d1, and four fuel assemblies 10 in the same cell of the upper grid plate 7 are restrained. Moreover, the connecting jig handle portion 18b is arranged in the center of the flat plate 18d1. Further, the flat plate 18d1 is provided with an opening 18e1 to reduce its weight.

Other configurations and operations are substantially the same as those of the fuel assembly loading method and the fuel assembly connecting jig of the first embodiment, and the details thereof are omitted.

In the fuel assembly loading method and the fuel assembly connecting jig of the second embodiment of the present invention, substantially the same effects as those of the fuel assembly loading method and the fuel assembly connecting jig of the first embodiment are obtained. can get.

Moreover, the fuel assembly connection jig 18A loads the fuel assembly connection jig 18A in the same cell of the upper grid plate 7 by constraining the four fuel assemblies 10 in the same cell of the upper grid plate 7. The number of times of loading becomes one, which is one-fourth of the number of times (four times) of loading the fuel assembly connecting jig 18 of the first embodiment, and the work time can be shortened.

<Third Embodiment>
A fuel assembly loading method and a fuel assembly connecting jig according to a third embodiment of the present invention will be described with reference to FIGS. 6 and 7. FIG. 6 and 7 are perspective views of a fuel assembly connecting jig according to the third embodiment.

As shown in FIG. 6, the fuel assembly connecting jig 18B of this embodiment has a plurality of circular holes 18e2 through which cooling water flows in a flat plate 18d2 arranged between two fuel assembly handle insertion portions 18a. , to reduce the pressure loss in the cooling channel.

The structure for flowing cooling water is not limited to the circular hole 18e2, and a flat plate 18d3 disposed between the two fuel assembly handle insertion portions 18a, like the fuel assembly connection jig 18C shown in FIG. can be provided with a grid of holes 18e3.

Other configurations and operations are substantially the same as those of the fuel assembly loading method and the fuel assembly connecting jig of the first embodiment, and the details thereof are omitted.

In the fuel assembly loading method and the fuel assembly connecting jig of the third embodiment of the present invention, substantially the same effects as those of the fuel assembly loading method and the fuel assembly connecting jig of the first embodiment are obtained. can get.

Further, the flat plates 18d2 and 18d3 have holes 18e2 and 18e3 for passage of the coolant, thereby reducing the pressure loss in the cooling flow path.

<Others>
In addition, the present invention is not limited to the above-described embodiments, and includes various modifications. The above embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the described configurations.

It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

Reference Signs List 1 Boiling water reactor 2 Reactor pressure vessel 3 Core 4 Core shroud 5 Control rod guide tube 6 Control rod drive mechanism housing 7 Upper grid plate 8 Core support plate 9 Fuel support fitting 9a Through hole 10 Fuel assembly 11 Fuel rod 12 Channel box 13 Channel fastener 14 Channel spacer 15 Upper tie plate 16 Fuel assembly handle 17 Control rods 18, 18A, 18B, 18C Fuel assembly Connection jig 18a -- Fuel assembly handle portion insertion portion (fixed portion)
18b... Connecting jig handle portion 18c... Retaining plate springs 18d, 18d1, 18d2, 18d3... Flat plate (connecting portion)
18e1... Openings 18e2, 18e3... Holes

Claims (11)

A method of loading a fuel assembly, comprising:
a step of loading a plurality of said fuel assemblies into a nuclear reactor core;
and installing a jig from above the reactor core for constraining mutual horizontal movement of at least upper end structures of adjacent fuel assemblies among the fuel assemblies. loading method of the fuel assembly. The fuel assembly loading method according to claim 1,
A fuel assembly loading method, wherein the upper end structure is a handle portion of the fuel assembly. The fuel assembly loading method according to claim 1,
A method of loading a fuel assembly, wherein in the step of installing the jig, the jig is installed with respect to the fuel assembly in the same cell of the upper grid plate. A connecting jig for constraining mutual horizontal movement of upper end structures of at least adjacent fuel assemblies among a plurality of fuel assemblies constituting a nuclear reactor core,
A fuel assembly connecting jig, comprising a fixing portion fixed to each of the upper end structures. In the fuel assembly connection jig according to claim 4,
The upper end structure is a handle portion of the fuel assembly,
A fuel assembly connection jig, wherein the fixing portion is inserted into at least a portion of the handle portion. In the fuel assembly connecting jig according to claim 5,
The fuel assembly connecting jig, wherein the fixing portion has a leaf spring that presses and holds the handle portion. In the fuel assembly connection jig according to claim 4,
A fuel assembly connection jig, wherein the fuel assembly connection jig constrains the fuel assemblies in the same cell of the upper grid plate. In the fuel assembly connecting jig according to claim 5,
A fuel assembly connection jig, wherein the fuel assembly connection jig constrains two adjacent fuel assemblies in the same cell of the upper grid plate. In the fuel assembly connecting jig according to claim 5,
A fuel assembly connection jig, wherein the fuel assembly connection jig constrains the four fuel assemblies in the same cell of the upper grid plate. In the fuel assembly connecting jig according to claim 5,
A fuel assembly connecting jig, comprising a connecting portion that fixes the relative positional relationship of the plurality of fixing portions. In the fuel assembly connecting jig according to claim 10,
A fuel assembly connecting jig, wherein the connecting portion has a hole for passing a coolant.

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