JPS63149593A - Control rod assembly - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in control rods for nuclear reactors, and particularly to control rod assemblies inserted from below into nuclear reactors.

[Conventional technology]

Control rods are used to control nuclear fission reactions in nuclear reactors and to safely shut down the reactor. Control rods used in light water reactors are broadly divided into cluster-type control rods used in pressurized wood reactors and cross-type control rods used in boiling water reactors.

A cruciform control rod is a control rod in which neutron absorption rods are arranged in a plate shape to form wings, and these wings are combined in a cruciform shape, and requires a relatively large space to be inserted into the reactor core. On the other hand, a cluster type control rod is composed of a spider having a plurality of spider arms and a neutron absorption rod attached to the spider arm. In this control rod, the neutron absorption rods are inserted into the reactor core while being guided by a control rod guide tube installed within the fuel assembly, and the neutron absorption rods can be inserted and arranged relatively uniformly within the fuel assembly. For this reason, the nucleus
Technology 59 (November 1982) pp. 212-227 (Nuel, Technol, 59(1)
982, 11) p. 212-227), it is not appropriate to provide a large space for control rod insertion in terms of core configuration and core characteristics. It is considered reasonable to use cluster control rods. Therefore, even when configuring the core as described above in a boiling water reactor, it is natural to consider using raster type control rods like those used in pressurized water reactors. By the way, in a pressurized wooden reactor, the control rods are inserted from the top of the core, but in a boiling water reactor, a steam separator, etc. is installed at the top of the core, so it is better to insert the control rods from the bottom of the core. This is convenient because it does not involve major changes in the core structure.

The configuration of cluster control rods is described in the Nuclear Reactor Handbook (Ohmsha) as a control rod for pressurized wooden reactors.

[Problem that the invention seeks to solve]

When the cluster type control rods used in the pressurized water reactors are inserted from the bottom of the reactor core, several problems arise. In other words, with the method of inserting from the top of the core, the control rod drive device and spider can be separated and the control rods can be taken out of the reactor together with the fuel assemblies, but with the method of inserting from the bottom of the core, the control rods can be taken out together with the fuel assemblies. is difficult. For this reason, when replacing fuel, (1) the control rods are pulled out below the reactor core and then the fuel is taken out of the reactor (
2) There is an option to remove the fuel from the furnace while leaving the III control rod in the furnace. In the former case, since the control rods are withdrawn while leaving fuel in the reactor, it is necessary to provide a sufficient margin for so-called reactor shutdown so that the reactor core does not become critical due to the withdrawal of the control rods.

Therefore, considering safety and the like, the latter method is considered to be more preferable. However, in the latter case, the control rod guide tube is removed together with the fuel, so in the conventional cluster control rod, there is nothing to maintain the spacing between the neutron absorption rods, especially at the tip, and each neutron absorption rod is 1 i
It will be in a defeated state.

This state is undesirable because stress occurs at the joint between the neutron absorber and the spider arm, and it is difficult to maintain the independence of the neutron absorber. therefore.

An object of the present invention is to solve these problems regarding cluster-type control rods inserted from the lower part of the reactor core.

[Means for solving problems]

The above objectives are achieved by maintaining the spacing of the neutron absorbing rods even when the fuel is removed and by suppressing movement of each neutron absorbing rod. However, providing a fixed spacer for this purpose makes it impossible to insert the control rods into the fuel assembly. Therefore, in the present invention, the above object is achieved by using a movable spacer.

[Effect]

FIG. 1 shows a schematic diagram of a control rod assembly according to the present invention.

Hereinafter, the present invention will be explained in detail using this figure. The control rod assembly of the present invention consists of a spider 1 having a plurality of spider arms 3, a neutron absorber 2, and a movable spacer 4 that moves longitudinally along the neutron absorber rod.

During reactor operation, that is, when the control rods are moved upwardly within the fuel assembly, the spacer is fixed to the lower end of the fuel assembly (indicated by the broken line) as shown in Figure 1(a), and the neutron absorption rods are It passes through the spacer and is driven up and down. When the fuel assembly is taken out of the reactor, the movable spacer moves upward along the neutron absorber and is fixed to the upper part of the neutron absorbing rod as shown in FIG. 1(b). As a result, the distance between the neutron absorbers is maintained in the upper part of the neutron absorber, and it is possible to prevent the individual neutron absorbing rods from being deflected and separated by their own weight.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an embodiment of a movable spacer used in a control rod assembly according to the present invention. In this spacer, a cylindrical body 17 having an inner diameter slightly larger than the outer diameter of the neutron absorber 2 is provided, and the cylindrical body related to the neutron absorbing rod located at the center and the cylindrical body related to the neutron absorbing rods on the outer periphery are separated. A compressible spring 6 is provided on the support material to be tied. Furthermore, the cylindrical body related to the neutron absorber on the outer periphery is connected to the outer frame 8 via the leaf spring 7. Figure 3 shows the movable spacer A-
It is an A' sectional view. The outer periphery of the neutron absorber is pressed against the central neutron absorber rod by a spring 6 to prevent the movable spacer from slipping off. As will be explained in detail later, the lower part of the fuel assembly and this spacer are connected to each other by a coupling groove 16.
connected via.

At this time, the leaf spring 7 is pressed against the outer frame, and the neutron absorbing rod on the outer periphery is returned to a position where it does not receive any force, so that the spacer can move along the neutron absorbing rod.

FIG. 4 shows the tip of the neutron absorbing rod of the control rod assembly according to the present invention. The tip of the neutron absorbing rod is provided with a groove 10 for fixing a movable spacer, The structure is such that the body is hooked into this groove when the spacer is fixed.

FIG. 5 is a diagram showing a second embodiment of a movable spacer used in a control rod assembly according to the present invention.

In this embodiment, a spring 12 is provided between the leaf spring 7 and the outer frame 8. When the spacer is fixed, the stopper 11 is pressed against the neutron absorption rod as shown in FIG. 6, and the spacer is fixed to the neutron absorption rod.

FIG. 7 shows the relationship between the control rod assembly and fuel assembly according to the present invention. When the fuel assembly 5 is loaded into the reactor core, the movable spacer 4 is fixed to the lower part of the fuel assembly. When the fuel assembly is taken out above the reactor core, the movable spacer is pulled up above the control rod while connected to the fuel assembly, and is separated from the fuel assembly when it reaches the upper end of the control rod. This separation loosens the leaf spring and fixes the movable spacer to the upper end of the neutron absorbing rod.

Hereinafter, a method of coupling the fuel assembly and the movable spacer will be explained.

FIG. 8 shows the lower structure of the fuel assembly. A cylindrical coupling member 14 is provided at the lower part of the fuel assembly. This member further includes a protrusion 15 which is adapted to fit into the coupling groove 16 described above. FIG. 9 shows a part of the outer frame of the movable spacer. After pressing the projection against the coupling groove 16, the fuel assembly is rotated horizontally. In this way, the protrusion moves along the groove provided in the outer frame, and the movable spacer and fuel assembly are coupled together. Furthermore, at this time, the above-mentioned leaf spring is pressed against the outer frame, and the movable spacer is removed from the neutron absorption rod at the same time.

In the above embodiment, the case of seven neutron absorption rods has been described, but the present invention can also be applied to a case of having a larger number of neutron absorption rods.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent the neutron absorption rods of the cluster type control rod from becoming separated when the fuel assembly is removed and the neutron absorption rods are inserted from the lower part of the reactor core. As a result.

It is possible to alleviate the stress generated at the joint between the neutron absorption rod and the spider arm, and furthermore, it is possible to ensure the independence of the neutron absorption rod.

There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a control rod assembly according to an embodiment of the present invention, and FIG.
The figure is a plan view showing a first embodiment of the movable spacer used in the control frame assembly according to the present invention, and FIG.
A' sectional view, FIG. 4 is an explanatory diagram showing the tip structure of the neutron absorption rod, FIGS. 5 and 6 are configuration diagrams showing the second embodiment of the movable spacer, and FIG. FIG. 8 is a plan view showing the lower structure of the fuel assembly, and FIG. 9 is a perspective view showing a part of the outer frame of the movable spacer. be. 1... Spider, 2... Neutron absorption rod, 3...
Spider arm, 4... Movable spacer, 5... Fuel assembly, 8... Outer frame, 9... Support material, 10... Fixing groove, 11... Stopper, 13...・Support material, 1
5...Protrusion, 16...Joining groove
,,4:,'−.

Claims (1)

[Claims] 1. A control rod assembly comprising a spider having a plurality of spider arms and a neutron absorption rod, characterized in that a movable spacer is provided to maintain the spacing between the plurality of neutron absorption rods.