JPH0249995A - Built-in type recirculation pump for nuclear reactor - Google Patents

Abstract

PURPOSE:To relieve the discharge amount of a recirculation pump for recirculating coolant through a core section of a boiling water type nuclear reactor, during a pump trip, by using a material having a density higher than that of the material of a rotary shaft of a motor for rotating the pump, for a rotary part of the motor so as to increase the inertia moment thereof. CONSTITUTION:An internal pump 8 is composed of a pump section 9 consisting of an impeller 4 and a diffuser 5 which are disposed in a pressure vessel 1, and a motor section 10 disposed in a motor casing 3 welded to a pump nozzle 2 in the pressure vessel 1. The motor section 10 composed of a stator 6 and a rotor 7, and an upper end ring 11 and a lower slide disc 12 of the motor section 10 is made of tungsten alloy having a density higher than that of carbon steel or stainless steel used for a shaft 14 of the motor section 10. Accordingly, the inertia moment of the motor increases so as to relieve an abrupt decrease in discharge amount during a pump trip, thereby it is possible to enhance the soundness of fuel and the reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a recirculation pump built into a nuclear reactor that forcibly circulates cooling water in a nuclear reactor.

(Prior art) Generally, in a boiling water nuclear power plant, a coolant circulation system is installed in the reactor, and the reactor coolant is forced to circulate to the reactor core, thereby removing heat and generating steam in the reactor core. There is. In addition, by changing the flow rate of the reactor coolant, the nuclear reactivity of the reactor core is adjusted and the plant output is controlled. The circulation systems include a so-called external recirculation system that has a coolant circulation loop outside the reactor pressure vessel, and an internal pump system that has a reactor built-in recirculation pump (hereinafter referred to as an internal pump) installed in the reactor pressure vessel. is known.

Hereinafter, a boiling water nuclear power plant using an internal pump will be explained with reference to FIG. In FIG. 3, the internal pumps 20 are arranged on the circumference of the lower mirror part of the reactor pressure vessel 28 on the order of 1O, and the coolant in the upper part of the reactor core is pumped by the rotation of the pump 29 inside the reactor pressure vessel 28. The reactor core 27 is forced to circulate.

The internal pump 20 has its shaft extending below the pressure vessel 28 and passing through the pressure vessel 28, and is connected to a motor 23 driven by a static power supply device including a rectifier 21, an inverter 22, etc., and is operated at a variable speed. There is. Furthermore, the third
In the figure, 18 is the reactor containment vessel. When the on-site source is lost, many of the electric on-site auxiliary machines are shut down, so the reactor emergency shutdown system is activated and all control rods (not shown) are rapidly inserted into the reactor core 27.

On the other hand, the internal pump 20 is connected to the reactor pressure vessel 28.
Since it is housed in a motor casing that is welded to the bottom nozzle of the motor, the design is compact due to layout constraints. Therefore, the moment of inertia of the rotating parts of the pump 29 and the motor 23 is small, and the discharge flow rate decreases in a relatively short time when the pump trips.

In order to increase the moment of inertia without affecting the pump characteristics or critical speed, a method has been proposed to increase the size of the motor rotor and thrust disk. However, this has the problem of increasing the size of the motor and increasing motor loss, which affects the layout design, and may also lead to an increase in the size of the building.

(Problems to be Solved by the Invention) As described above, the conventional internal pump has a small moment of inertia, and the discharge flow rate decreases in a relatively short time when the pump trips.

Furthermore, increasing the size of the motor rotor and thrust disk in order to increase the moment of inertia causes the motor to become larger and motor loss to increase, which also affects layout design and the like.

The present invention has been made in view of the above points, and an object of the present invention is to provide an internal pump that can increase the moment of inertia while minimizing increases in motor size and motor loss.

[Structure of the invention]

(Means for solving problems) ”-2 In order to achieve the objective, in the present invention.

An internal pump consisting of a pump section that is immersed in the coolant of a pressure vessel of a boiling water reactor and forcibly circulates the coolant to the reactor core, and a motor section that drives the pump section, the rotating section of the motor section. To provide an internal pump characterized in that the internal pump is made of a material having a higher density than the material of the rotating shaft.

(Function) In the internal pump configured in this way,
By arranging the rotating portion of the motor section with a material having a higher density than the material of the rotating shaft, the moment of inertia of the motor section can be increased and the rate of decrease in the discharge flow rate due to pump trips etc. can be alleviated. Therefore, the time required for the pump rotational speed to halve during a pump trip can be extended several times.

In addition, since high-density metal is used, the increase in motor dimensions is kept to a minimum, and the increase in motor size and motor loss is also suppressed, which improves the impact on layout design, etc. .

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2.

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

The internal pump 8 is composed of a pump part 9 which is installed in the reactor pressure vessel 1 and includes an impeller 4 and a diffuser 5, and a motor part 10 which is installed in a motor casing 3 that is welded to the reactor pressure vessel pump nozzle 2. ing.

The motor part 10 consists of a stator (stationary part) 6 and a rotor (rotating part) 7, and an end ring 11 disposed on the upper part of the rotor 7 and a thrust disk 12 disposed on the lower part are made of a motor part made of tungsten alloy. A metal having a higher density than the carbon steel or stainless steel used for the shaft 14 of 10 is used.

Therefore, the internal pump of this embodiment can increase the moment of inertia while suppressing the increase in motor size and motor loss. This makes it possible to reduce the rate of decrease in the discharge flow rate when the pump trips.

FIG. 2 is a longitudinal sectional view showing another embodiment of the internal pump according to the present invention. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals, and the explanation of the structure of the parts will be omitted. In FIG. 2, the internal pump 15
A flywheel 13 made of high-density metal such as tungsten alloy is installed above the rotor 7 and stator 6 of the motor section 16. Therefore, the motor section 16
The moment of inertia can be increased. The flywheel 13 can also be installed below the rotor 7 and stator 6 of the motor section 6.

In addition, the end ring 11 and the thrust disk 1 mentioned above
2. Although tungsten alloy is shown as the material for the flywheel 13, the functions and effects of the present application can also be achieved even if depleted uranium, tantalum, or the like is used as a metal with a higher density than the carbon steel or stainless steel used for the shaft 14. be able to.

〔Effect of the invention〕

According to the present invention, it is possible to increase the moment of inertia while minimizing the increase in motor size and motor loss, that is, without significantly affecting layout design. Therefore, the rate of decrease in the discharge flow 1lIi at the time of a pump trip is moderated, so that the decrease in the flow rate of the reactor during a core transient event caused by a pump trip is slowed down, so that the health and reliability of the fuel can be improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a recirculation pump built into a nuclear reactor showing one embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of a recirculation pump built into a nuclear reactor showing another embodiment of the invention. FIG. 3 is a schematic system diagram showing a conventional example of a boiling water nuclear power plant using a recirculation pump built into the reactor. 1... Reactor pressure vessel 8.15... Reactor built-in recirculation pump (internal pump) 9... Pump section 10.16...
・Motor part 11... End ring 12... Thrust disk 13... Flywheel 14...
・Axis agent Patent attorney Nori Chika Ken Yudo Daishimaru Ken Figure 2 Figure 1

Claims (1)

[Claims] A reactor built-in recirculation pump comprising a pump part that is immersed in the coolant of a pressure vessel of a boiling water reactor and forcibly circulates the coolant to the reactor core, and a motor part that drives the pump part, wherein the motor A recirculation pump built into a nuclear reactor, characterized in that a material having a higher density than the material of the rotating shaft is arranged in the rotating part of the reactor.