JPH07260976A - Control rod guide tube - Google Patents

Abstract

PURPOSE:To reduce the radiation exposure of a worker and to shorten the process of a periodical inspection, by preventing the floating of a control rod guide tube, and carrying out the process from the upper side in a nuclear reactor. CONSTITUTION:This control rod guide tube is composed of a sleeve 21 to guide the vertical movement of a control rod 6 held by a reactor core holding plate 11 in a reactor pressure vessel 10; a base 22 installed at the lower end of the sleeve 21, and set on a reactor core bottom 7 in the nuclear reactor pressure container 10; and a locking mechanism 30 installed on the side surface of the sleeve 21, and to prevent the floating of the sleeve 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control rod guide tube for guiding the vertical movement of a control rod in a boiling water reactor (hereinafter referred to as BWR).

[0002]

2. Description of the Related Art Generally, as work in a BWR, a fuel, a core instrumentation in a reactor, a control rod replacement work, a reactor confirmation work, and the like, which are scheduled for a periodic inspection, are performed.

On the other hand, in recent years, as work outside the regular inspection,
Remodeling and repair work and inspection work of the bottom of the hearth have been implemented. As a preparation for this furnace bottom inspection work, work for removing the control rod guide tube is performed.

The conventional work of removing the control rod guide tube will be described with reference to FIGS. First, the reactor pressure vessel 10
Remove the four fuel rods 1 from above the upper lattice plate 41 installed inside, and then control rod drive mechanism (hereinafter referred to as CRD)
2 is removed from the reactor bottom 7. Further, the thermal sleeve 3 is removed from below, and the flange closing plate 4 shown in FIG. 9B is attached to the lower end of the control rod drive mechanism housing (hereinafter referred to as CRD housing) 42. After that, as shown in FIG. 9A, from the upper part of the core, the fuel support fitting 5, the control rod 6
The control rod guide tube 20 is removed after the removal. After removing the control rod guide tube 20, the opening 11 of the core support plate 11 is removed.
The underwater television camera (not shown) is inserted from a to inspect the reactor bottom 7. This work is carried out by the operation of the fuel exchanger 9 running on the operating floor 8 shown in FIG. 8, and the fuel 1, the fuel support fitting 5, the control rod 6, and the control rod guide pipe 20 are removed. Also,
Among these operations, the removal work of the CRD 2 and the thermal sleeve 3 and the installation work of the flange closing plate 4 are carried out in the petestal 12 below the reactor pressure vessel 10.

In this way, the control rod guide tube 20 for inspecting the reactor bottom 7 is removed from the lower portion of the reactor pressure vessel 10 in addition to the operation from the fuel exchanger 9 running on the operating floor 8. Work inside the pedestal 12 becomes necessary.

The reason for this is shown in FIGS. 9 and 10. The control rod guide tube 20 is mounted on the CRD housing 42. That is, the base 22 at the lower end of the control rod guide tube 20 is placed on the top of the CRD housing 42. Further, in order to prevent the control rod guide tube 20 from rising, the thermal sleeve 3 is inserted from below the inside of the CRD housing 42. Ie base 22
The convex portions 22b, 22b provided on the side surface of the lower end portion 22a of the
b, 3b, then the thermal sleeve 3 90 °
By turning, the convex portions 22b, 22b and the concave portions 3b, 3b
Are connected. This connection is released by removing a key (not shown) under the thermal sleeve 3 and turning the thermal sleeve 3 by 90 ° with respect to the axis.

[0007]

In the method of fixing the control rod guide tube 20 by the thermal sleeve 3 as described above, when the control rod guide tube 20 is removed, the pedestal 12 is
It must be carried out after removing the CRD 2 and the thermal sleeve 3 and attaching the flange closing plate 4. Since the inside of the pedestal 12 is under high radiation, the worker may be exposed to radiation. Moreover, since the work inside the pedestal 12 is a critical path of the regular inspection process, the above-mentioned work also causes the extension of the regular inspection process. Further, since the work inside the pedestal is urgent from the viewpoint of reducing radiation exposure, there is a limitation that a skilled person must do the same as the above-mentioned work inside the reactor.

The present invention has been made in consideration of the above points, and the work inside the pedestal of rotating the thermal sleeve to prevent the control rod guide tube from being lifted is abolished, and the control rod guide pipe is installed from above the reactor. Accordingly, it is an object of the present invention to provide a control rod guide tube that can reduce the radiation exposure of the worker and shorten the regular inspection process.

[0009]

In order to achieve the above-mentioned object, in the invention according to the first, second or third aspect, by inserting it into the opening of the core support plate installed in the reactor pressure vessel. A sleeve that is supported and guides the vertical movement of the control rod, a base that is attached to the lower end of this sleeve and is installed at the bottom of the reactor in the reactor pressure vessel, and a lock that is attached to the side of the sleeve and prevents the sleeve from rising. And a mechanism for providing a control rod guide tube.

According to a fourth aspect of the present invention, there is provided a control rod guide tube characterized in that a lock mechanism is operated by inserting a fuel support fitting for supporting a lower end of a fuel rod into an upper opening of a sleeve. .

[0011]

With the above-mentioned structure, the first and second aspects can be obtained.
Alternatively, according to the invention described in 3, the sleeve having the lock mechanism can be inserted into the opening of the core support plate to prevent the control rod guide tube from rising. In this way, by eliminating the work inside the pedestal for preventing the control rod guide tube from rising, it is possible to reduce the radiation exposure of the worker and to shorten the periodic inspection process.

According to the fourth aspect of the present invention, the lock mechanism can be operated by inserting the fuel support fitting for supporting the lower end of the fuel rod into the upper opening of the sleeve. In this way, the radiation exposure of the worker can be reduced and the regular inspection process can be shortened.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In FIG. 6, the control rod guide tube 20
Will be described. The control rod guide tube 20 is a reactor pressure vessel.
It is supported by being inserted into the opening 11a of the core support plate 11 installed in the inside 10. In the control rod guide tube 20, the control rod 6 moves up and down by the CRD 2. On the other hand, the fuel support fitting 5 is inserted into the upper opening 20a of the control rod guide tube 20. Four fuels 1 are loaded on the upper portion of the fuel support fitting 5, and the upper portion of the fuel 1 is supported by the upper lattice plate 41 shown in FIG. The aforementioned control rod 6 is inserted between the fuel 1 through the inside of the fuel support fitting 5.

As shown in FIG. 1, the control rod guide tube 20 is composed of a sleeve 21 which is inserted into and supported by the opening 11a of the core support plate 11 and which guides the vertical movement of the control rod 6. Lugs 23, 23 are attached to the upper portion of the sleeve 21 and are used for orienting or lifting the control rod guide tube 20. The fuel support fitting 5 is inserted into the upper opening 20a of the sleeve 21. Further, a cooling hole 21a through which a coolant passes is provided on the upper side surface of the sleeve 21. A base 22 is fixed to the lower portion of the sleeve 21, and the base 22 is loaded on the top of the CRD housing 42. Also sleeve
A lock mechanism 30 is provided on the upper side surface of 21. As shown in FIGS. 4 and 5, one or a plurality of lock mechanisms 30 are provided in the notch 21b provided on the upper side surface of the sleeve 21. That is, the lock plate 31 is rotatably attached to the side surface of the notch 21b via the pin 35. A roller 32 is rotatably attached to one end of the lock plate 31, and a balance plate 34 is fixed to the other end.

Next, the operation of this embodiment having such a structure will be described with reference to FIGS. 6 and 7. When the fuel support fitting 5 is inserted into the upper opening 20a of the control rod guide tube 20, the lower end of the fuel support fitting 5 contacts the roller 32. When the roller 32 is pushed down, the lock plate 31 rotates and enters the lower surface of the core support plate 11, so that the lock plate 31 is locked by the core support plate 11.

Further, the lock plate 31 of the lock mechanism 30 becomes vertical and is pulled back from the core support plate 11 only by removing the fuel support fitting 5 from the control rod guide tube 20, so that the lock mechanism can be released. The balance plate 34 is the control rod guide tube 20.
When the fuel support bracket 5 is pulled out, the control rod guide tube 20
It is a weight for smoothly pulling back the lock plate 31 inside.

As described above, according to this embodiment, by inserting the fuel support fitting 5 into the upper opening 20a of the control rod guide tube 20, the lock plate 31 of the lock mechanism 30 is moved to the core support plate 11.
The control rod guide tube 20 can be prevented from being lifted by projecting it to the lower surface of the. Further, simply by removing the fuel support fitting 5 from the control rod guide tube 20, the lock plate 31 of the lock mechanism 30 is brought into a vertical state and is pulled back from the core support plate 11 to release the lock mechanism 30.

[0018]

According to the present invention, the sleeve is provided with the lock mechanism to prevent the control rod guide tube from being lifted, so that the work inside the pedestal is abolished, and the worker It is possible to reduce the radiation exposure to and to shorten the regular inspection process.

According to the fourth aspect of the present invention, the control rod guide tube is prevented from rising and the work inside the pedestal is abolished simply by inserting the fuel support fitting into the upper opening of the control rod guide tube. As a result, the radiation exposure of the worker can be reduced and the regular inspection process can be shortened.

[Brief description of drawings]

FIG. 1 is a bird's-eye view showing a schematic structure of a control rod guide tube according to an embodiment of the present invention.

FIG. 2 is an enlarged front view of the lock mechanism displayed in the A section of FIG.

FIG. 3 is an enlarged cross-sectional view taken along the line BB of FIG.

FIG. 4 is an enlarged vertical sectional view showing a lock mechanism applied to FIG.

FIG. 5 is a top view showing the lock mechanism applied to FIG. 1 by cutting it.

6 is a schematic vertical cross-sectional view of an internal structure of a reactor to which the control rod guide tube shown in FIG. 1 is applied.

7 is a longitudinal sectional view showing a locked state of the lock mechanism applied to FIG. 1. FIG.

FIG. 8 is an overall view showing a state of removing a conventional control rod guide tube.

FIG. 9A is a vertical cross-sectional view showing a conventional lifting prevention mechanism for a control rod guide tube, and FIG. 9B is a front view in which a flange closing plate is attached to a CRD housing.

10A is a vertical cross-sectional view showing a locked state of a conventional control rod guide tube, FIG. 10B is a bottom view showing the control rod guide tube applied to FIG. 10A, and FIG. The top view which shows the thermal sleeve applied to 10 (A).

[Explanation of symbols]

 5 ... Fuel support bracket 7 ... Reactor bottom 10 ... Reactor pressure vessel 11 ... Core support plate 20 ... Control rod guide tube 21 ... Sleeve 21b ... Notch 22 ... Base 30 ... Lock mechanism 31 ... Lock plate

Claims (4)

[Claims] 1. A sleeve for supporting up and down movement of a control rod, which is supported by being inserted into an opening of a core support plate installed in a reactor pressure vessel, and a reactor pressure vessel attached to the lower end of the sleeve. A control rod guide tube, comprising: a base installed at the bottom of the reactor inside; and a lock mechanism attached to a side surface of the sleeve to prevent the sleeve from rising. 2. The control rod guide tube according to claim 1, wherein a lock plate of the lock mechanism is projected to a lower surface of the core support plate to prevent the sleeve from rising. 3. The lock mechanism is installed in a notch formed in a side surface of the sleeve.
The described control rod guide tube. 4. The control rod guide tube according to claim 1, wherein the lock mechanism is operated by inserting a fuel support metal fitting supporting a lower end of the fuel rod into an upper opening portion of the sleeve.