JPH04283694A - Upper plug of internal pump - Google Patents

Abstract

PURPOSE:To prevent mistaken removal of an upper plug by a construction wherein a float is provided in the lower half part of the main body of the upper plug, a valve seat is provided on the top side thereof and the head part of a shaft having a valving element to be put on the seat is shaped same as the head part of a pump. CONSTITUTION:A float 33 being movable vertically is inserted into and fitted to the main body 32 of a plug and they are sealed mutually with a sealing material 34. In the upper half part 32a of the main body, a guide part 37 supporting slidably a shaft 36 piercing the part vertically is provided, and a head part 39 is provided in the upper end of the shaft 36, while a valving element 40 is provided in the lower end thereof. The lower end part of the valving element 40 corresponds to a valve seat 42 in an opening of a communicating passage 41 formed through the center of the float 33. The head part 39 is formed in the same shape with that of the head part of an internal pump. According to this constitution, the head part 39 is located at a normal grip position and can be handle only when buoyancy acts on the float 33. When no buoyancy acts thereon, the head part 39 is positioned below and there is no possibility of the upper plug being removed by mistake on the occasion of disassembly and reassembly of the pump.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] The present invention relates to an upper plug of an internal pump incorporated in a boiling water nuclear reactor, and in particular is constructed to prevent accidental removal during disassembly and reassembly of the internal pump. Regarding the upper plug of the internal pump.

0003

[Prior Art] Generally, during periodic inspections of boiling water reactors, the top cover of the reactor pressure vessel is removed and the inside of the reactor pressure vessel and the reactor well above the core of the reactor pressure vessel are filled with water. Provide radiation shielding. Additionally, fuel changes and other operations are done underwater.

[0004] Incidentally, a nuclear reactor pressure vessel is provided with a nozzle for connecting piping and attaching equipment. When removing equipment or piping attached to these nozzles, the nozzles must be blocked to prevent reactor water from flowing out.

[0005] The clogging of the nozzle will be explained below. FIG. 5 is a schematic vertical cross-sectional view showing the schematic configuration of a boiling water reactor incorporating a conventional internal pump, FIG. 6 is a vertical cross-sectional view of a conventional internal pump, and FIG. 7 is a main part of the internal pump. FIG. In FIG. 5, a reactor core 2 is housed in a reactor pressure vessel 1, and a downcomer 3 with an annular cross section formed between the reactor core 2 and the inner peripheral surface of the reactor pressure vessel 1 has a reactor pressure A plurality of internal pumps 4 are installed so as to penetrate the lower mirror 1A of the container 1 at a penetrating portion 1B and are equally spaced in the circumferential direction. Note that the coolant 5 is forcibly circulated by the internal pump 4.

In FIG. 6, the internal pump 4 is composed of a pump section 10 and a motor section 11. The pump section 10 is connected to the pump shaft 1 by the motor section 11.
5, and a diffuser 13 that concentrically surrounds the impeller 12. Diffuser 1
3 is provided protruding from the bottom of the reactor pressure vessel 1 and is fixed via a stretch tube 17 to the upper part of a nozzle 16 that concentrically surrounds the pump shaft 15 . The stretch tube 17 is fixed by a stretch tube nut 18. Further, a secondary seal 19 is installed below the stretch tube nut 18.

The motor unit 11 has a rotor 20 and a stator 21, and the tip of a motor casing 22 housing these is inserted into the nozzle 16, and the reactor pressure vessel 1 is inserted into the nozzle 16.
It is fixed to the lower mirror 1A by welding. In addition, in the figure, 23 is a cooling water circulation pipe that communicates with the motor casing 22, and 24 is a cooling water circulation pipe that communicates with the motor casing 22.
25 is a coupling stud nut that connects the pump shaft 15 and the motor part 11, and 26 is a main stud nut that fixes the bottom plate 22a of the motor casing 22. There is.

[0008] In the conventional internal pump 4 having the above structure, maintenance and inspection work is carried out as follows. That is, first, the motor casing 2 is sealed by the secondary seal 19.
2 and the pump shaft 15, the reactor water in the reactor pressure vessel 1 is shut off, and then the water in the motor casing 22 is discharged. Next, the auxiliary cover 24 is removed from the bottom plate 22a of the motor casing 22, the coupling stud nut 25 is removed, and the pump shaft 15 and the motor section 11 are separated. In this state, loosen the main stud nut 26 and remove the motor part 11 and pump shaft 15.
are lowered approximately 10 mm by their own weight. This lowering causes the protrusion 15 provided inside the furnace of the pump shaft 15 to
a is in contact with the upper surface of the nozzle 16 to seal the reactor water (hereinafter referred to as a primary seal). In this state, the secondary seal 19 is working, and the water inside the motor casing 22 is drained again.
Drain the inside completely. Here, main stud nut 2
6 and remove the motor section 11.

Next, a bottom plate 22a is attached to the motor casing 22.
, After attaching the auxiliary cover 24, auxiliary water is filled into the motor casing 22, and the seal by the secondary seal 19 is released here. In this state, the impeller 12 and the pump shaft 15 are removed by remote control from above the reactor pressure vessel 1. Then, from above the reactor pressure vessel 1, the diffuser 13 is
The opening of the motor casing 22 is closed by an upper plug 31 as shown in FIG. 7, and the inside of the motor casing 22 is drained.

Here, the bottom plate 22 of the motor casing 22
a and remove the secondary seal 19 from inside the motor casing 22.
, remove the stretch tube nut 18. Next, after reattaching the bottom plate 22a to the motor casing 22, pure water from the make-up water system (MUW) is injected into the motor casing 22, and the internal pump is attached in the reverse order to the above.

[0011]

[Problems to be Solved by the Invention] When an internal pump is attached to the lower mirror portion 1A of the reactor pressure vessel 1 and removed, if the upper plug 31 of the internal pump is attached and the bottom plate 22a is removed, Bottom plate 22a again
work is being carried out in the lower part of the motor casing 22 until it is installed. The procedure is such that the upper plug 31 must never be removed; however, there is a problem in that the upper plug 31 may be removed in the unlikely event that an operator at the upper part of the reactor pressure vessel makes an incorrect operation.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an upper plug of an internal pump that cannot be removed until the bottom plate 22a is properly attached and there is no danger of reactor water leakage. be. [Structure of the invention]

[0013]

[Means for Solving the Problems] The present invention provides a motor casing for an internal pump that is vertically installed through a lower mirror of a nuclear reactor pressure vessel and has an opening on the inner surface of the lower mirror of the reactor pressure vessel. The upper plug of the internal pump to be closed includes a hollow cylindrical upper half that forms the main part of the upper plug body, and a hollow cylindrical upper half that extends from the upper half and has a smaller diameter than the upper half and hangs down from the lower end of the upper half. A hollow cylindrical lower half having an inverted cone, a vertically movable float provided in the lower half to maintain watertightness, a valve seat provided on the upper surface of the float, and the valve seat. a shaft having a valve body placed on the float and moving up and down in a movable range larger than the movable range of the float; a head formed at the upper end of the shaft in the same shape as the head of the internal pump; The present invention is characterized by comprising a communication path that communicates with the valve seat provided on the float.

[0014]

[Operation] The upper plug of the conventional internal pump,
If the surrounding environment is the same, gripping with a gripper is possible. However, in the present invention, when the upper plug is attached to the internal pump opening and the water inside the motor casing is drained, the head is lowered and cannot be gripped. Then, when the motor casing is filled with water again, the head rises and becomes available for gripping.

Furthermore, when lifting is started, a valve connected to the head opens and the pressure in the reactor pressure vessel and the pressure in the motor casing can be matched, so that the main body of the upper plug is lifted.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the upper plug of an internal pump according to the present invention will be described with reference to FIGS. 1 to 4. In FIG. 1, the upper plug 31a has a hollow cylindrical upper half 32a, which is the main part of the plug body 32, and a hollow cylindrical lower half 32, which has a slightly smaller diameter than the upper half 32a.
The plug body 32 includes a plug body 32 having Lower half 32
A float 33 is inserted into the cylinder b, using the cylinder inner wall surface as a sliding surface, and is movable up and down with respect to the plug body 32. A sealing material 34 is inserted into a gap 43 between the float 33 and the lower half portion 32b to maintain watertightness. A main seal portion 35 that constitutes a seating surface and a sealing surface is provided at the lower end of the upper half portion 32a. A guide portion 37 is provided within the upper half portion 32a and slidably supports a shaft 36 that vertically passes through the upper half portion 32a. This guide part 37 is attached to a disc 38 having a plurality of openings 38a, and this disc 38 has a plurality of openings 38a.
8 is fixed to the inner surface of the upper half portion 32a. shaft 36
A head 39 is provided at the upper end, and a valve body 40 is provided at the lower end. The lower end of the valve body 40 is connected to the tapered valve seat portion 4 of the opening of the communication passage 41 provided through the center of the float 33.
It is formed on a tapered surface corresponding to 2. The head 39 is formed in the same shape as the head of the impeller 12 of the internal pump 4.

FIG. 2 is an enlarged view of section A in FIG. That is, in FIG. 2, the sealing material 34 is inserted into an annular groove 32c formed on the inner surface of the lower half portion 32b and an annular groove 33a formed in the float 33, respectively.
The bulges 34a and 34b of No. 4 are inserted, and the bulges 34
A cylindrical portion 34c connected to a and 34b is attached in a watertight manner so as to hang down in a gap 43 between the lower half portion 32b and the float 33. The sealing material 34 is made of an elastic material such as synthetic rubber, and as the float 33 moves up and down, the cylindrical part 34c on the float 33 side moves up and down, and the bottom surface also moves up and down accordingly. Although the cylindrical portion 34c maintains a hanging state, watertightness is maintained.

The upper plug 31a of the above embodiment is used in the same manner as the conventional upper plug 31 shown in FIG. That is, after removing the impeller and pump shaft of the internal pump, the upper plug 31a is attached. Head 3
9 matches the shape of the head of the impeller 12, so
The upper plug 31a is handled by grasping the head 39 using the gripping tool used to remove the impeller 12, and the lower half 32b of the plug body 32 is inserted into the communication port to the nozzle 16. After the upper plug 31a is attached to the communication port as described above, the motor section 11 is pulled out downward and the closing flange 29 is attached to the lower surface of the motor casing 22.

In the upper plug 31a of this embodiment installed as described above, only when the float 33 is buoyant, the head 39 is in the normal gripping position as shown in FIG. It becomes possible. On the other hand, as shown in FIG. 4, when the float 33 is not buoyant, the head 39 is located lower than normal and cannot be handled by the gripper 7.

Further, a valve body 40 is opposed to the opening of the communication passage 41 provided at the center of the float 33 on the reactor pressure vessel 1 side, and the head 39 can be operated with a grip to open and close the opening. Therefore, during lifting, the valve body 40 can be reliably opened, the motor casing and the inside of the reactor pressure vessel 1 can be communicated with each other, and the pressures therebetween can be matched.

[0021]

According to the present invention, there is no danger of accidentally removing the upper plug when disassembling and reassembling the internal pump, especially during the operation of taking in and taking out the motor and the operation of attaching and detaching the bottom plate and closing flange. Therefore, inspection work on the internal pump can be performed safely and reliably, and work time can be significantly shortened. As a result, the radiation exposure of workers will be significantly reduced, and the operating efficiency of the reactor will be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing one embodiment of an upper plug of an internal pump according to the present invention.

FIG. 2 is an enlarged longitudinal cross-sectional view of section A in FIG. 1, showing a sealing state between the float and the main body.

FIG. 3 is a partial sectional view showing the state of the upper plug in FIG. 1 when there is water on the motor casing side.

FIG. 4 is a partial sectional view showing the state of the upper plug in FIG. 1 when there is no water on the motor casing side.

FIG. 5 is a schematic vertical cross-sectional view showing a schematic structure of a boiling water reactor with a built-in internal pump to explain a conventional example.

FIG. 6 is a longitudinal sectional view showing the internal pump in FIG. 5;

7 is a vertical sectional view partially showing in block form the state in which the upper plug of FIG. 6 is attached to the motor casing; FIG.

[Explanation of symbols]

1...Reactor pressure vessel, 2...Reactor core, 3...Downcomer, 4
...internal pump, 5...coolant, 11...motor section,
12... Impeller, 13... Diffuser, 15... Pump shaft, 16... Nozzle, 17... Stretch tube, 1
8...Stretch tube nut, 19...Secondary seal, 2
0...Rotor, 21...Stator, 22...Motor casing, 23...Cooling water circulation piping, 24...Auxiliary cover, 25...Coupling stud nut, 26...Main stud nut, 31/31a...Upper plug, 32...Plug body, 3
2a...upper half, 32b...lower half, 33...float, 34
...Sealing material, 35...Main seal part, 36...Shaft, 37
...Guide portion, 38...Disc, 39...Head, 40...Valve body, 4
1...Communication path, 42...Valve seat.

Claims (1)

[Claims] 1. An upper part of an internal pump that is installed vertically through a lower mirror part of a reactor pressure vessel and that closes a motor casing of the internal pump that has an opening on the inner surface of the lower mirror part of the reactor pressure vessel. The plug includes a hollow cylindrical upper half that forms the main part of the upper plug body, and an inverted conical part that is connected to the upper half and has a smaller diameter than the upper half and hangs down from the lower end of the upper half. A cylindrical lower half, a vertically movable float provided in this lower half to maintain watertightness, a valve seat provided on the upper surface of this float, and a valve body placed on this valve seat. a shaft that moves up and down in a movable range larger than the movable range of the float; a head formed at the upper end of the shaft in the same shape as the head of the internal pump; An upper plug for an internal pump characterized by having a communication passage communicating with a valve seat.