JPH01318792A - Internal pump - Google Patents

Abstract

PURPOSE:To prevent the invasion of a clad in a nuclear reactor to an internal pump by providing a projection at the top of a diffuser surrounding the outer periphery of an impeller, to be inserted to an inverse U-shape groove provided at the boss of the impeller. CONSTITUTION:In a water boiler type reactor, an impeller 3 is installed to the upper end of a pump shaft 1 which penetrates a pressure container 11 through a connecting rod 2. And a diffuser 7 provided at the lower stream side of the impeller 3 is fixed to a pump nozzle through a stretch tube 8. In this case, at the upper end of a boss 4 in the diffuser 7, a conical surface 4a is formed, while at the lower side of a boss 10 in the impeller 3, an inverse U-shape groove 10b having a conical surface 10a is formed. At the top of the boss 4, a projection 6 to be inserted to the groove 10b is formed. As a result, at the entrance of the pressure container 11, a flow passage facing upward is formed, and the area of the flow passage is restricted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Object of the Invention) (Industrial Application Field) The present invention relates to an internal pump used in a boiling water nuclear reactor.

(Prior Art) An internal pump A is installed in a boiling water reactor pressure vessel as shown in FIG. An impeller 3 is attached to the connecting rod 2 by means of a connecting rod 2. A diffuser 7 for rectification installed outside the impeller 3 and on the downstream side of the flow is pulled downward via a stretch tube 8 and fixed to an internal pump nozzle 9 which is a nozzle of the pressure vessel 11.

Below the pump shaft 1, there is a rotor 17 connected to the pump shaft 1 and a stator 18 installed outside the rotor 17.
A motor section 19 consisting of the following is incorporated.

The motor casing 1 is used to cool the motor section 19.
Motor cooling system piping 1 is installed at the upper and lower ends of 5, respectively.
4.16 is open, and a heat exchanger (not shown) is connected between it and the motor cooling system piping 14.16.

A secondary seal 20 is arranged above the motor cooling system piping 14 to seal the gap between the motor casing 15 and the pump shaft 1, and the secondary seal water piping 13 opens into the secondary seal 20.

This secondary seal 20 performs a sealing function by introducing pressurized water into the secondary seal during maintenance of the motor section 19, etc., and is not used during normal operation.

No sealing mechanism is installed between the stretch tube 8 and the pump shaft 1, and the pressure inside the pressure vessel 11 and the pressure in the motor section 19 are equal. In order to suppress the inflow of fine rads, a purge system piping 12 is installed at the lower end of the stretch tube 8 to supply cold water at a constant flow rate.

Further, FIG. 5 shows details of the joint between the impeller 3 and the diffuser 7, which is the part where the purge water flows out into the furnace. The purge water is distributed between the lower end of the impeller boss 10 and the diffuser boss through the annular flow path A between the stretch tube 8 and the pump shaft 1 and the annular flow path opening between the diffuser boss 4 and the pump shaft 1. It flows out into the reactor from the flow path C with the upper end of the section 4.

(Problems to be Solved by the Invention) In the conventional internal pump, the distance between the flow path C between the lower end of the impeller boss section 10 and the upper end of the diffuser boss section 4 is as follows.
In the current design, it takes about 10 seconds and the flow path area is relatively large, so there is a possibility that the crud inside the reactor will enter the internal pump body due to the vortices and turbulent flow caused by the blade surface 3a when the impeller 3 rotates. be. If the purge water flow pulsates or stops flowing for some reason, the possibility of crud entering the internal pump increases.

If the cladding falls into the inside of the motor section 19, the amount of radiation exposure of workers during maintenance and inspection of the motor section 19 increases. Further, there is a problem in that the crud that has entered the motor section 19 flows between the pump shaft 1 and the shaft bearing, causing the bearing, which is made of carbon material, to wear out.

The present invention has been made in consideration of these problems, and it is possible to more reliably prevent the crud in the furnace from flowing into the pump even when the operating conditions of the purge water are disturbed, even under normal purge water conditions. It is an object of the present invention to provide an internal pump that can prevent this as much as possible, and can also reduce the amount of radiation exposure during maintenance and inspection of the motor section, etc.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a motor casing installed vertically at the bottom of a reactor pressure vessel, a pump shaft installed on the central axis of the motor casing, and a lower end attached to the pump shaft. an impeller having an inverted U-shaped groove in the boss portion of the impeller, a diffuser provided to surround the outer periphery of the impeller, a stretch tube for fixing the diffuser to the reactor vessel, and a motor built in the motor casing. In the internal pump, a smooth protrusion is provided on the top of the diffuser so as to be partially or completely fitted into the inverted U-shaped groove of the impeller, and to face each other with a gap. It is characterized by

(Function) The engagement (fitting part) between the lower part of the impeller and the upper part of the diffuser forms an upward contracting flow path in the flow path communicating from the reactor pressure vessel to the motor. This passage prevents crud in the furnace from entering the motor. Further, by providing a plurality of protrusions on the insertion portion of the impeller, the intrusion of crud can be suppressed due to the pump effect.

(Embodiment) An embodiment of an internal pump according to the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 is a partial sectional view showing the main parts of the internal pump, and the same parts as in FIG. 5 are designated by the same reference numerals. The internal pump has the same structure as the conventional structure shown in FIG. 5, except for the inlet portion on the reactor pressure vessel side of the flow path leading from the reactor pressure vessel to the motor, so a detailed explanation will be omitted.

In FIG. 1, a conical surface 4a is formed at the upper end of the diffuser boss 4, and an inverted U-shaped groove 10b having a conical surface 10a is formed on the lower surface of the impeller boss 10 corresponding to the conical surface 4a. . Impeller boss portion 10 facing the conical surface 4a provided at the upper end of the diffuser boss portion 4
The horizontal gap between the groove 10b and the conical surface 10a is the gap between the outer peripheral surface of the impeller 3 and the inner peripheral surface of the outer cylinder part of the diffuser 7 (approximately 1 mm in the radial direction). The cylindrical portion 4a and the impeller boss 10 do not come into contact with each other during the maintenance and inspection. Next, a seal is formed to isolate the inside of the furnace and the inside of the motor casing 15, but the lowering amount of the pump shaft 1 (approximately 10 mm> is necessary, but by providing a large inclination of the conical surfaces 4a and 10a, It is possible to reduce the distance and narrow the flow path.

In this way, according to this embodiment, in the flow path communicating from the reactor pressure vessel to the motor, an upward flow path is formed at the inlet on the reactor pressure vessel side, and the area of the flow path is narrowed, so that the cladding inside the reactor is reduced. can be suppressed from flowing into the motor section.

Further, by restricting the flow path area as described above, the flow rate of the purge water injected from the motor is increased in the relevant portion, which helps to prevent intrusion of crud.

Further, other embodiments of the present invention are shown in FIGS. 2 and 3. 2 is an enlarged view of the lower part of the impeller boss portion 10 shown in FIG. 1, and FIG. 3 is a view taken along the line A-A of FIG. 2. Reference numeral 6 denotes a small number of protrusions provided on the conical surface 10a of the lower surface of the impeller boss 10, which have an inclination in the same direction as the inclination of the blade surface 3a of the impeller 3, as shown in FIG. When the impeller rotates during normal operation, the conical surface 10a on the lower surface of the impeller boss 10 and the conical surface 4a on the upper surface of the diffuser boss portion 4
The fluid in the flow path formed by the projection 6 is pressurized toward the atomic reactor pressure vessel side by the pumping effect produced by the projection 6, thereby preventing the crud in the reactor from entering the motor.

In the two embodiments described above, even if the purge water stops or pulsates for some reason, it is possible to prevent crud from entering the reactor.

〔Effect of the invention〕

According to the present invention, it is possible to prevent the crud in the furnace from entering the internal pump body and falling into the motor section, contaminating the motor section with radioactivity, thereby preventing workers from being exposed to radiation during maintenance and inspection work. can do.

Furthermore, it is possible to prevent the crud that has entered the motor section from entering between the impeller shaft and the bearing and abrading the bearing surface, thereby providing a highly reliable internal pump.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing a main part of an embodiment of an internal pump according to the present invention, FIG. 2 is a vertical cross-sectional view showing a main part of another embodiment of an internal pump according to the present invention, and FIG. The figure is a view taken along the line A-A in Figure 2, Figure 4 is a sectional view showing the entire groove bottom of a conventional internal pump, and Figure 5 is an enlarged view of the purge water outlet of a conventional internal pump. FIG. 1... Pump shaft 2... Connecting rod 3... Impeller 4... Diffuser boss portion 4a... Conical surface 5... Diffuser vane 6... Protrusion 7... Diffuser 8... Stretch tube 9... Internal pump nozzle 10... Impeller boss portion 10a... Conical surface 10b... Inverted U-shaped groove Agent Patent attorney Yoshiaki Inomata (and 1 other person) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] A motor casing installed vertically at the bottom of the reactor pressure vessel, a pump shaft installed on the central axis of the motor casing, and an impeller installed on the pump shaft and having an inverted U-shaped groove in the boss section at the lower end. and a diffuser provided to surround the outer periphery of this impeller,
In an internal pump consisting of a stretch tube that fixes the diffuser to the reactor pressure vessel and a motor built in the motor casing, the internal pump is partially or completely fitted into an inverted U-shaped groove of the impeller. An internal pump characterized in that smooth protrusions are provided on the top of the diffuser so as to face each other with a gap therebetween.