JPH1073575A - Bubble inspector in structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the presence or absence of the generation of the bubbles in the liquid in the inside of a complicated structure and the position and the scale of the generating position by estimating the presence or absence of the generation of the bubbles in liquid and the state of the bubbles from the frequency spectrum of the Doppler shift when the transmitting sound wave by a transmission sensor is reflected from the bubble. SOLUTION: A detecting part 20 is constituted of a transmitting circuit 3, which generates sound waves, a high-frequency amplifier circuit 4, which amplifies the recessed sound wave, a sound-speed Fourier transformer (FFT) 6 and the like. When a transmission sensor 16 is operated by the transmission circuit 3 and the continuous sine wave is generated in a vapor generating drum 14, the signal is received with a receiving sensor 18. The received sound wave is processed in the sequence of the high-frequency amplifier circuit 4, a synchronous detecting circuit 8, a band-pass filter 9, a low-frequency amplifier circuit 5 and the FFT 6. When bubbles are generated in the liquid, the Doppler shift in correspondence with the amount of the bubbles is generated. The Doppler signal is inputted into a signal processing part 1. The bubbles are generated in the vapor generating drum 14, and it is judged that the generation of the bubbles is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bubble detecting device for detecting whether or not bubbles are generated in a fluid inside a structure. More specifically, the present invention relates to an air bubble detection device inside a structure suitable for a water leak detection system such as a steam generator of a fast breeder reactor.

[0002]

2. Description of the Related Art In a steam generator of a fast breeder reactor, sodium is used as a heat transfer medium. Since sodium is chemically very active, if water leaks from the heat transfer tube, a sodium-water reaction phenomenon occurs, and hydrogen gas is generated. As the water leak progresses, the high-temperature reaction jet may cause damage to propagate to the adjacent heat transfer tube.
Therefore, in order to prevent the propagation of the sodium-water reaction, it is important to detect the water leak from the heat transfer tube early and reliably.

Conventionally, a water leak is detected by a method of detecting hydrogen in sodium or a cover gas with a hydrogen meter, or a method of detecting a pressure rise caused by generated hydrogen gas with a pressure gauge. However, these detection methods require a relatively long time to detect a water leak. For this reason, it is necessary to develop a detection method capable of detecting a small amount of water leak with a short detection time.

On the other hand, as a method for detecting a water leak early and surely, a method utilizing sound has been developed. This acoustic method includes the following two methods.

One is a passive method in which a sound wave generated by a water leak is directly detected by a sensor attached to the outside of the steam generator body. In this method, it is difficult to remove the influence of ambient noise, and therefore, it is necessary to develop a signal processing method, and practical use is difficult.

Another method is an active method, in which a sound wave transmitted into the steam generator is attenuated by hydrogen bubbles generated by a sodium-water reaction, and a water leak is detected. Since the active method receives a transmitted sound wave, it is less affected by ambient noise, and can perform water leak detection with higher precision than the conventional passive method. This is particularly effective when the internal structure in the structure is simple.

[0007]

However, in order to perform water leak detection by the above-described active method, it is necessary to generate a bubble from a received sound wave transmitted through a complicated internal structure of a steam generator including a heat transfer tube and a shroud. It is necessary to detect only the sound wave attenuated by the influence of. Due to the reflection and scattering of the sound wave due to the complicated internal structure, the received sound wave is a sound wave having a long attenuation time via propagation paths of various lengths. When a bubble is generated in such a complicated structure, it is difficult to identify a sound wave attenuated under the influence of the bubble. Further, depending on the bubble generation position and the bubble generation scale, the number of received sound waves may increase due to the reflection of the sound waves by the bubbles, which may be further complicated.

That is, due to a complicated internal structure or a change in bubble generation position or bubble generation scale, a sound wave having a long decay time and a complicated waveform is generated, and the accuracy of bubble generation detection is reduced. There is a risk that it will. For this reason,
Improvements in detection sensitivity and signal processing methods are desired.

[0009] On the other hand, since it is not known when bubbles are generated, the bubble detecting device must always operate normally. However, since the steam generator has a high temperature and is installed close to the reactor, maintenance of the transmission / reception sensor and the connection cable is difficult. Therefore, it is particularly desirable to monitor whether the transmission / reception sensor is operating normally.

Accordingly, the present invention provides an air bubble detection apparatus which uses a signal processing method capable of detecting the presence or absence of air bubbles in a liquid inside a complicated structure, and detecting the generation position and scale of the air bubbles when they are generated. It is intended to provide. Another object of the present invention is to provide a bubble detecting device capable of monitoring whether or not a transmission / reception sensor is operating normally.

[0011]

In order to achieve the above object, a first aspect of the present invention is a structure in which a transmission sensor for transmitting a sound wave and a reception sensor for receiving a sound wave from the transmission sensor contain a liquid. In the bubble detection device inside the structure installed on the outer wall of the detector, the detection unit that detects the Doppler shift when the sound wave transmitted by the transmission sensor is reflected by the bubble from the sound wave received by the reception sensor, and detects the liquid from the frequency spectrum of the Doppler shift. A signal processing unit is provided for detecting the presence / absence of bubbles inside and for estimating the bubble form when bubbles occur.

[0012] In the present specification, "sound wave" particularly means an ultrasonic wave.

In general, sound waves are reflected at boundaries having different acoustic impedances (ie, the product of the speed of sound and the density of the medium). Therefore, the transmitted sound wave is reflected by the bubbles in the liquid. Since the bubbles in the flowing liquid are moved together with the liquid, the frequency of the sound wave before and after the reflection is changed by the Doppler effect. This change is called a Doppler shift. Further, the bubbles rise even in the stationary liquid, so that the Doppler effect occurs.

Here, since the acoustic impedance of a liquid such as water or sodium and a bubble is remarkably different, the bubble is a good reflection source. For this reason, a Doppler shift occurs when the transmitted sound wave is reflected. Then, this Doppler shift can be calculated by Equation 1.

[0015]

FD = (2 · V · f0 · cos θ) / C where fD: Doppler shift V: velocity of moving object (bubble) f0: frequency of transmitted sound wave θ: angle between moving object and transmitted sound wave C: Sound velocity For example, when the liquid is water, the flow velocity is 1 m / s, and the sound velocity is 1500 m /
In the case of s and the angle of 60 °, when a 200 kHz sound wave is transmitted, the Doppler shift becomes 133 Hz. When the water temperature is 300 ° C. under this condition, the sound speed becomes 980 m / s, and the Doppler shift becomes 204 Hz.

The present invention utilizes the above-described principle. According to the bubble detecting apparatus of the first aspect, it is determined that no bubble is generated unless the detector detects a Doppler shift. If a Doppler shift is detected, it is determined that bubbles have occurred. At this time, the bubble shape is estimated from the envelope shape and intensity of the frequency spectrum of the Doppler shift as shown in FIG.

Further, in the bubble detecting device inside the structure according to the second aspect, a plurality of pairs of the transmission sensor and the reception sensor are arranged along the flow direction of the liquid. Therefore, the bubble generation position in the flow direction of the liquid is specified based on which of the pair of the transmission sensor and the reception sensor detects the bubble.

Further, in the bubble detecting device inside the structure according to the third aspect, the transmission sound wave transmitted by the transmission sensor can be switched to the burst wave. Therefore, as shown in FIG. 6, a delay time t from the transmission of the burst wave to the reception of the received sound wave including the Doppler component is measured by a time gate, and the distance of the bubble from the transmission sensor is calculated based on the delay time t. I do. Thereby, the position where the bubble is generated in the plane on which the set of the transmission sensor and the reception sensor is arranged is specified. The “burst wave” means a sound wave obtained by dividing a continuous sine wave at regular intervals, for example, as shown in FIG.

Further, the air bubble detecting device in the structure according to the fourth aspect is provided with a monitoring unit which constantly monitors whether or not the level of the sound wave received by the receiving sensor is within a predetermined range. . Therefore, when the level of the received sound wave is within the predetermined range, it is determined that the operations of the transmission sensor and the reception sensor are normal. When the level of the received sound wave is not within the predetermined range, it is detected that an abnormality has occurred in the transmission sensor or the reception sensor.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail based on an embodiment shown in the drawings. In this embodiment, a case is described in which the air bubble detection device inside the structure is applied to a steam generator of a fast breeder reactor.

FIGS. 1 to 4 show an embodiment of the bubble detecting apparatus according to the present invention. The air bubble detection device 10 of this embodiment includes:
Transmission sensor 1 installed on the outer wall of a structure containing liquid
6, a reception sensor 18, a detection unit 20 for detecting the Doppler shift when the sound wave transmitted by the transmission sensor 16 is reflected by the bubble from the sound wave received by the reception sensor 18, and the generation of the bubble in the liquid from the frequency spectrum of the Doppler shift. A signal processing unit 1 for detecting presence / absence and estimating a bubble form when a bubble is generated.

As shown in FIG. 3A, one transmission sensor 16 and two reception sensors 18 are provided outside the steam generator body 14 as an outer wall of the steam generator 12 as a structure.
18 are arranged at intervals of about 120 °. For this reason, the blind spot of the reception by the reception sensor 18 can be minimized. In addition, by installing a plurality of transmission sensors 16, the blind spot of reception can be further reduced.

A vibrator is used as the transmission sensor 16 and the reception sensor 18. As the vibrator, a piezoelectric ceramic or a crystal capable of withstanding high temperatures is preferable.
Further, a magnetostrictive vibrator can be used as the vibrator. Further, different vibrators may be employed for the transmission sensor 16 and the reception sensor 18.

In this embodiment, one transmission sensor 1
6 and the two receiving sensors 18 are arranged at an interval of about 120 °, but the present invention is not limited to such an arrangement. They may be arranged, or one transmission / reception sensor 2 may be used as both a transmission sensor and a reception sensor as shown in FIG. In this case, a bridge circuit is used to separate transmission and reception signals.

As shown in FIG. 2, inside the substantially cylindrical steam generator body 14, a cylindrical outer shroud 22 slightly separated from the inner surface of the steam generator body 14, and the outer shroud 22 A cylindrical inner shroud 24 is provided, which is appropriately separated from the inner surface. And
Between the outer shroud 22 and the inner shroud 24, radial heat transfer tube support structures 26 are provided at about every 45 degrees. In a space surrounded by the outer shroud 22 and the inner shroud 24, heat transfer tubes 28 having a circumferential direction as a longitudinal direction are provided at regular intervals in a radial direction.

Then, water flows through the inside of each heat transfer tube 28, and high-temperature sodium flows through a space surrounded by the outer shroud 22 and the inner shroud 24, and heat exchange is performed between the water and the sodium. Will be Note that the space between the steam generator barrel 14 and the outer shroud 22 and the inside of the inner shroud 24 are stationary only because they are filled with sodium.

Further, as shown in FIG.
Along the flow direction N of sodium in 4, a plurality of transmission sensors 16-1, 16-2, 16-3, 16-4, 16-5 and reception sensors 18-1, 18-2, 18-3, 18-4 and 18-5 are attached. Here, the direction of the sensors 16 and 18 is 45 ° with respect to the flow direction N.
It is installed to be. In addition, each sensor 16, 1
Reference numeral 8 is attached to the steam generator body 14 by an angle holding holder. Therefore, the angle between each of the sensors 16 and 18 and the flow direction N can be kept constant. It should be noted that the angle between the directing directions of the sensors 16 and 18 and the flow direction N is not limited to 45 °.

Further, a detecting unit 20 is connected to each of a pair of the transmission sensor 16 and the reception sensor 18 facing each other. This connection is made with a heat-resistant coaxial cable. And the detection part 20 is installed in the position sufficiently distant from the steam generator 12. Each detection unit 20-1, 20-2, 20-
3, 20-4 and 20-5 are connected to the signal processing unit 1. The detection unit 20 and the signal processing unit 1 are actually configured by a computer, a sequence circuit, and the like.

As shown in FIG. 1, the detecting section 20 includes a transmitting circuit 3 for generating a sound wave, a circuit 4 for amplifying a received sound wave,
5 and a fast Fourier transformer (FFT) 6.

The transmission circuit 3 is connected to the transmission sensor 16 and generates a continuous sine wave. Further, a pulse generation circuit 7 is connected to the transmission circuit 3. The pulse generation circuit 7
When a trigger signal is input from the signal processing unit 1, a burst wave is generated in the transmission circuit 3.

The high frequency amplifier circuit 4 is connected to the reception sensor 18 and amplifies a weak reflected signal from the reception sensor 18 to a level that can be detected. The amplified received sound wave
It has a transmitted sound wave component and a Doppler signal component. A synchronous detection circuit 8 is connected to the high-frequency amplification circuit 4. This synchronous detection circuit 8 is also connected to the transmission circuit 3. Then, a beat is generated by the transmission signal and the reception signal, and the Doppler signal is detected.

The synchronous detection circuit 8 includes a band-pass filter 9
Is connected to remove noise other than the Doppler signal of the received signal. Furthermore, the low-frequency amplifier circuit 5 is connected to the band-pass filter 9 to adjust the received signal to an appropriate level. Then, the FFT 6 is connected to the low-frequency amplifier circuit 5, and performs fast Fourier transform on the received signal and outputs the result to the signal processing unit 1 as a Doppler signal.

Further, a level detection circuit 11 as a monitoring unit is connected to the high-frequency amplification circuit 4 and the synchronous detection circuit 8. The level detection circuit 11 includes an envelope detection circuit, an averaging filter, and a comparator. The level detection circuit 11 detects the sound level of the received signal and outputs the result to the signal processing unit 1 as a level signal.

As shown in FIG. 4, the signal processing section 1 is connected to a display section 13 such as a display. The signal processing unit 1 receives the Doppler signal and the level signal from each detection unit 20 and performs a predetermined process.

The bubble detecting device 10 constructed as described above
The procedure for detecting bubbles will now be described.

The transmission circuit 16 activates the transmission sensor 16 to generate a continuous sine wave inside the steam generator body 14. The transmitted sine wave is transmitted in the sodium of the steam generator 12 and the structure of the outer shroud 22 and the inner shroud 24, and is received by the reception sensor 18. And
The received sound wave is sequentially processed by the high-frequency amplification circuit 4, the synchronous detection circuit 8, the band-pass filter 9, the low-frequency amplification circuit 5, and the FFT 6.

When no bubbles are generated in the liquid, the Doppler shift is 0, and no Doppler signal is generated. For this reason, no Doppler signal is generated,
The signal processing unit 1 determines that no bubbles are generated inside the steam generator body 14.

On the other hand, when bubbles are generated in the liquid, a Doppler shift occurs according to the amount of the bubbles and is detected as a Doppler signal. Therefore, when this Doppler signal is input to the signal processing unit 1, it is determined that air bubbles have been generated inside the steam generator body 14.

The relationship between the frequency and the intensity of the Doppler signal at this time is as shown in FIG. 5, for example. In the figure, hatched portions indicate background noise due to vibration of the heat transfer tube 28 or the like. As can be seen from the figure, the background noise and the Doppler signal can be separated in the frequency domain. Here, the maximum amplitude of the Doppler signal is
Obtained as the same average flow rate as the flow rate of sodium. Further, the spread of the frequency spectrum of the Doppler signal and the change over time indicate a shape and a pattern reflecting the number and size of the bubbles. Therefore, the amount of generated bubbles can be estimated from the shape of the Doppler signal.

Further, when a Doppler signal is detected, a trigger signal is transmitted from the signal processing unit 1. This allows
The transmission sensor 16 via the pulse generation circuit 7 and the transmission circuit 3
Is activated, and a burst wave is generated inside the steam generator body 14. Then, as shown in FIG. 6, a delay time t from the transmission of the burst wave to the reception of the received sound wave including the Doppler component is measured by a time gate, and this delay time t is measured.
To calculate the distance from the transmission sensor 16 to the bubble.
Thereby, it is possible to specify the position where the bubble is generated in the plane where the pair of the transmission sensor 16 and the reception sensor 18 are arranged.

Further, by detecting the Doppler signal by each set of the transmission sensor 16 and the reception sensor 18, the position where the Doppler signal is detected and the position where the Doppler signal is not detected are determined, and the bubble generation in the liquid flow direction N is performed. The position can be detected.

For example, as shown in FIG.
-2 and the pair of the receiving sensors 18-2 and the pair of the transmitting sensors 16-3 and the receiving sensors 18-3, when air bubbles are generated, only the receiving sensors 18-3, 18-4, and 18-5 are used. The Doppler signal is received, and is not received by the receiving sensors 18-1 and 18-2. Thereby, the receiving sensor 18-2 and the receiving sensor 18-3
It is detected that a bubble is generated between. Then, by analyzing the Doppler signals of the receiving sensors 18-3, 18-4, and 18-5, the amount of generated bubbles can be estimated. Further, the transmission sensor 16-3 closest to the bubble generation position
, A burst wave is generated, and the distance from the tube wall to the bubble is calculated. Then, these detection results are displayed on the display unit 13.
Is displayed as a graphic.

Therefore, according to the present embodiment, the bubble generation position in the flow direction N of sodium and one set of the transmission sensor 1
6 and the bubble generation position in the arrangement plane of the receiving sensor 18 can be detected, so that the steam generator 1 having a complicated shape can be detected.
The position where the bubbles are generated inside 2 can be grasped with high accuracy.

Further, since the level signal is transmitted from the level detection circuit 11 to the signal processing section 1 during the operation of the detection section 20, the operation states of the transmission circuit 3, the sensors 16, 18 and the high frequency amplification circuit 4 are determined. Can be monitored. That is, if the magnitude of the level signal is within a predetermined range,
It is determined that the receiving operation state is normal. On the other hand, if the magnitude of the level signal is out of the predetermined range, it is determined that the transmission / reception operation state is abnormal. Accordingly, it is possible to immediately grasp the failure of the transmission / reception sensors 16 and 18 and the connection cable under a high temperature, which are particularly difficult to maintain, and to promptly deal with the failure.

The above embodiment is an example of a preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, the bubble detection device 10 is applied to the steam generator 12 of the fast breeder reactor, but is not limited to this, and may be applied to other structures. For example, in a heat exchanger or the like in which two kinds of liquids are in contact with each other across a partition, the present invention can be applied to a case where a liquid that generates bubbles when used is used.

In the present embodiment, the case of detecting bubbles in a flowing liquid is described. However, the present invention is not limited to this, and the detection of bubbles in a stationary liquid may be performed. Even if the liquid is stationary, the bubbles rise and the Doppler effect occurs, so that by detecting this, bubbles can be detected.

[0047]

As is apparent from the above description, in the bubble detecting device inside the structure according to the first aspect of the present invention, the Doppler shift when the sound wave transmitted by the transmitting sensor is reflected by the bubble is detected by the receiving sensor. Since it has a detection unit that detects from the received sound wave and a signal processing unit that detects the presence or absence of bubbles in the liquid from the frequency spectrum of the Doppler shift and estimates the bubble form when bubbles are generated, the detection of Doppler shift The presence / absence of bubbles can be determined based on the presence / absence, and when a Doppler shift is detected, the bubble shape, that is, the number and size of bubbles, is determined from the envelope shape and intensity of the frequency spectrum of the Doppler shift as shown in FIG. Can be estimated. For this reason, the generation of air bubbles inside a complicated structure can be detected early and with high accuracy, and the scale of generation can be detected, so that quick and accurate measures can be taken.

Further, in the bubble detecting device inside the structure according to the second aspect, a plurality of pairs of the transmission sensor and the reception sensor are arranged along the flow direction of the liquid. The position where the bubble is generated in the flow direction of the liquid can be specified depending on whether the bubble is detected. Therefore, it is possible to quickly and accurately cope with the generation of bubbles inside a complicated structure.

Further, in the bubble detecting device inside the structure according to the third aspect, since the transmission sound wave transmitted by the transmission sensor can be switched to the burst wave, the bubble from the transmission sensor can be changed by the delay time t shown in FIG. By calculating the distance, the generation position of the bubble in the plane on which the set of the transmission sensor and the reception sensor is arranged can be specified. Therefore, it is possible to quickly and accurately cope with the generation of bubbles inside a complicated structure.

Further, the bubble detecting device in the structure according to the fourth aspect is provided with a monitoring unit for constantly monitoring whether or not the level of the sound wave received by the receiving sensor is within a predetermined range. Therefore, the operating states of the transmission sensor and the reception sensor can be constantly monitored. For this reason, it is possible to quickly grasp a failure of the transmission / reception sensor or the connection cable in a place where maintenance is particularly difficult such as under a high temperature, and it is possible to take prompt measures.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a bubble detection device according to the present invention.

FIG. 2 is a cross-sectional view of a steam generator showing a state in which the bubble detection device of the present invention is attached to a steam generator of a fast breeder reactor.

FIGS. 3A and 3B are cross-sectional views illustrating a positional relationship between a transmission sensor and a reception sensor. FIG. 3A illustrates a case where one transmission sensor and two reception sensors are arranged, and FIG. 3B illustrates a case where one transmission and reception sensor is arranged. Is the case.

FIG. 4 is a longitudinal sectional view showing a state in which a plurality of transmission sensors and reception sensors are attached along the flow direction of the steam generator.

FIG. 5 is a graph showing a Doppler signal.

FIG. 6 is a time chart illustrating timings of a transmission burst wave and a reception signal.

[Explanation of symbols]

 Reference Signs List 1 signal processing unit 2 transmission / reception sensor (transmission sensor, reception sensor) 10 bubble detection device 11 level detection circuit (monitoring unit) 12 steam generator (structure) 14 steam generator body (outer wall) 16 transmission sensor 18 reception sensor 20 detection Department

Claims (4)

[Claims] 1. A bubble detection device inside a structure, wherein a transmission sensor for transmitting a sound wave and a reception sensor for receiving a sound wave from the transmission sensor are installed on an outer wall of a structure containing a liquid. A detection unit that detects a Doppler shift when the transmission sound wave is reflected by the bubble from the reception sound wave by the reception sensor, and detects the presence or absence of bubble generation in the liquid from the frequency spectrum of the Doppler shift, and generates a bubble. And a signal processing unit for estimating the form of the bubble. 2. The apparatus according to claim 1, wherein a plurality of pairs of the transmission sensor and the reception sensor are arranged along a flow direction of the liquid. 3. The transmission sound wave transmitted by the transmission sensor can be switched to a burst wave.
Or an air bubble detection device inside a structure according to 2. 4. The apparatus according to claim 1, further comprising a monitoring unit that constantly monitors whether a level of a received sound wave received by the reception sensor is within a predetermined range. An air bubble detection device inside the structure as described.