JPS6021487A - Preventive device for leakage of water in reactor - 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 Application of the Invention] The present invention relates to an in-reactor paper-type recirculation pump (hereinafter abbreviated as internal pump) installed in a new type of boiling water nuclear reactor.
The present invention relates to a reactor water leakage prevention device using a shape memory alloy for the purpose of preventing leakage of primary coolant from a pump and protecting a portion of a motor.

[Background of the invention]

In the new boiling water reactor, the primary coolant is not circulated using the conventional external loop of recirculation pumps and jet pumps, but instead uses an internal pump that is welded to the nozzle of the reactor pressure vessel by induction welding. A method has been adopted in which the cooling water is sent into the reactor core without being taken out of the reactor pressure vessel.

The wet motor type internal pump used in the new boiling water reactor has a structure in which a vertical shaft single stage mixed flow pump is driven by a submersible wet motor.

That is, the hydraulic parts such as the impeller, diffuser, and wear ring are housed at the bottom of the reactor pressure vessel, and part of the motor, which includes the motor rotor, motor stator, bearing, etc., is housed in the motor casing.
It is 4tt when I looked at C1 clean water.

In addition, some motors have a dedicated cooling heat exchanger, one for each internal pump, and the inside of the motor is cooled to below 60°C (motor winding temperature is 45°C). It is built in 119 buildings. Furthermore, high-pressure purge water
As shown in the figure 1-, the pump is injected from the pump neck and serves as a mechanism to prevent high-temperature reactor water from the reactor side and accompanying corrosion products from entering a part of the motor.

Pure purge water is supplied from the control rod drive system and injected into the pump shaft and stretch tube IMIII. Purge water also has the role of preventing heat from the pressure vessel from being transferred by thermal conduction, and maintains an inlet temperature that does not cause excessive thermal stress to the shaft, L/tube, pressure vessel nozzle, diffuser, impeller, etc. (approximately 70°C).

Purge water injected from the motor casing neck rises along the gap between the shaft and stretch tube, reaches the top of the pump diffuser center body, and exits to the reactor water side.

However, if leakage occurs due to breakage from the speedometer wiring cable penetration part installed in a part of the pump motor, the dynamic power cable joint at the bottom of the motor cover, or the entrance/exit piping to the motor cooling heat exchanger, the inside of the casing The pressure of the reactor decreases, and high-temperature reactor water enters a part of the motor along with purge water.

As a result of this leakage of reactor water, it is expected that a portion of the motor of the internal pump itself will become abnormally hot due to the intrusion of high-temperature, radioactive water, resulting in damage to a portion of the motor.

In conventional internal pumps, there is no special mining equipment or protection system installed to prevent leakage from a part of the motor and motor cooling water piping. The output temperature is transmitted by the output temperature. That is, during normal operation, the motor part cooling water outlet temperature is approximately 50°C, and the pump is designed to trip when the outlet water temperature reaches 70°C.

[Purpose of the invention]

The present invention ensures that even if leakage occurs from the wiring cable penetration part for pump speed ignition, the dynamic power cable attachment part, and the inlet/outlet piping on the next side of the heat exchanger for motor cooling, the reactor water in the reactor pressure vessel is maintained. The purpose is to minimize the intrusion into a part of the motor and to protect internal equipment of the motor from damage due to an excessive temperature rise in a part of the motor.

[Summary of the invention]

In plants that use internal pumps to circulate coolant in the reactor pressure vessel, the nozzle part is sealed by direct welding to the pump casing, and the conventional external loop is used to prevent leakage of reactor water. Safety is improved compared to nuclear reactors with recirculation systems. However, if there is a leak from a part of a wet well type motor, high temperature reactor water will enter the motor due to the drop in internal pressure, causing damage to the motor's internal equipment. In addition, reactor water will flow out from the leakage point into the reactor containment vessel together with the clean water inside the motor.

[Embodiments of the Invention] What is shown in Figure 21, 31zl is the reactor water leakage shutoff device 4 of the present invention. This device focuses on the fact that nuclear reactor water is a high-temperature fluid with a temperature of 279°C.
If reactor water enters a part of the motor, the temperature of that part will rise rapidly. The leakage cutter is made of a shape memory alloy whose shape changes depending on the set temperature.

The seal is manufactured in a ring shape and is installed in a groove cut into the motor casing during normal operation as shown in Figure 2. However, when the temperature of this seal device rises due to the intrusion of reactor water, the third As shown in the figure, the seal is deformed into a shape that firmly adheres to the shaft portion.

It is conceivable that the installation location of this seal would be directly under the secondary seal part, which is installed for the purpose of cutting off leakage of reactor water during maintenance. This may be caused by part of the reactor water entering the motor (r) The upper part of the pump should be placed in the upper part of the pump, which has quick contact with the reactor water, so that it can be detected immediately and the intruding reactor water can be cut off using the sealing device of the present invention. And, depending on the seal structure, it is appropriate to install it on the opening part.

The present invention is characterized in that since it is an annular seal made of a shape memory alloy, no activation signal is required for the activation VC of shutoff. During the disturbances, measuring points for temperature, pressure, differential pressure, etc. to detect leakage of reactor water is a serious battle, but the present invention Q, C/L.

When the temperature of the pump exceeds a certain set temperature due to its own temperature rise, the pressure Mk is applied to the pump shaft as shown in FIG.

However, the pump trip signal required before the shutoff device of the present invention crimps the pump shaft and cuts off the intrusion of reactor water into a part of the motor is generated by the motor cooling installed in the pump from the beginning. Utilizes high water outlet temperature.

The internal pump is equipped with a heat exchanger for cooling part of the motor, one for each pump, but during normal operation of the reactor, the temperature at the motor cooling water inlet remains constant. 44°C, outlet temperature 50°C. The internal pump has an interlock structure that trips when the hot air at the cooling water outlet reaches 70°C. Therefore, the temperature at which the seal made of the shape memory alloy of the present invention deforms into the seal shape shown in FIG.
It is necessary to set the temperature to a higher temperature lW.

Also, during normal operation, the temperature inside the motor is 58℃ or less at the upper radial bearing, the motor winding temperature is 45℃, the upper thrust bearing temperature is 50℃ or less, and the lower thrust bearing temperature is 500℃ or less. .

Among the internal components of the motor, the motor windings are the most susceptible to heat, so it is undesirable to expose them to high temperatures of 70°C or higher, and even at temperatures of 90°C, they can be seriously damaged by heat. .

Therefore, with respect to the shape deformation temperature e of the shape memory alloy and the pump trip temperature (2) of 70°C, there is a large margin temperature Wt.
It was found that the seal shape deformation temperature of the present invention is set to 75°C, taking a margin temperature of 5°C from 70°C.

FIG. 4 shows a diagram of this temperature relationship. The actual temperature shown in P is the motor winding temperature and the motor cooling water outlet temperature, and the broken line is the motor temperature and the pump trigger temperature due to the motor cooling water outlet temperature. Furthermore, the most important feature is the leakage cutoff device using the shape memory base Knoll Q of the present invention. The dashed line 1 indicates the temperature at which the motor windings can be severely damaged by high heat.

With the above temperature settings, when reactor water starts to enter the motor side due to leakage from the motor side, the internal temperature of the motor increases, and the outlet temperature of the motor cooling water increases accordingly, and when it reaches 70℃, Trip the internal pump. Even after a pump trip, reactor water continues to enter and the internal temperature of the motor continues to rise, but when the temperature of the shutoff device using the shape memory alloy of the present invention reaches the set temperature of 75°C, the shape changes and the pump Crimp onto the shaft. During this time, it is expected to be extremely short, and the time during which the internal components of the motor, such as the temperature of the motor windings, are exposed to the high-temperature water is very short.

The following method can also be considered as a blocking device using a shape memory alloy. In other words, when reactor water leaks from a part of the motor and enters the motor side together with purge water, the high temperature fluid locally contacts the shape memory alloy, changes the shape of the sealing device, and seals the seal onto the pump shaft. There is a possibility that a mechanism will work. In this case, since the pump is not stopped, the seal will press against the rotating pump shaft, which is inconvenient for the seal mechanism. Therefore,
By making the shape of the shape memory alloy so that the temperature exceeds the set temperature and the inner diameter of the annular seal is slightly larger than the outer diameter of the pump shaft, the amount of reactor water leaking to the motor side can be kept to a minimum. Even if the sealing device according to the invention were to be implemented earlier than the pump trip, it would not affect the rotating pump shaft.

With this method, the amount of reactor water that enters the motor from the reactor side is kept to a very small amount, so the internal temperature of the motor does not suddenly rise to a high temperature, and the motor cooling water outlet temperature remains at 70°C.
Once the temperature is reached, the pump will be tripped. Therefore, the temperature inside the motor does not reach a high temperature of 70° C. or higher, and damage can be prevented. In this case, the deformation temperature of the sealing device using the shape memory alloy of the present invention does not need to be given priority to the pump trip, so it can be set independently of the pump IJ knob No. 1. However, the motor winding temperature W [capacity temperature is approximately 9
Considering that the temperature is 0°C, a temperature of about 80°C is appropriate.

The present invention can be easily implemented since the only device used is a seal made of a shape memory alloy.

〔Effect of the invention〕

According to the present invention, it is possible to minimize the total intrusion of reactor water due to leakage of only a portion of the motor.

This 71 not only prevents radioactive reactor water from entering a part of the motor, but also prevents damage to a part of the motor due to abnormally high temperatures.

[Brief explanation of the drawing]

Figure 1 is an internal structure diagram of the internal pump, Figure 2 (a)
and (b) are cross-sectional views and plan views of the seal structure made of shape memory alloy during normal operation, and Figures 3 (a) and (b) are cross-sectional views of the seal structure made of shape memory alloy during shutoff of reactor water leakage. and a plan view, and FIG. 4 is an explanatory diagram of the leakage detection device temperature and allowable temperature.

Claims (1)

[Claims] 1. Features a reactor water cut-off system using a shape memory alloy to prevent leakage of reactor water from internal pumps and damage to parts of the motor due to high-temperature reactor water entering the motor. Reactor water leak prevention device.