JPH11281462A - Liquid level gage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid level gage which reduces the possibility of leakage of liquid metal stored in a container, reduces the waste and the cost, and improves the liquid level measuring accuracy. SOLUTION: This liquid level gage is provided with wave guide elements 13 which are installed in a container 11 storing liquid metal and transmit an ultrasonic wave, an ultrasonic transmitter 15 which sends the ultrasonic wave to the wave guide elements 13, an ultrasonic receiver 16 which receives the ultrasonic wave according to resonance characteristics of the wave guide elements 13, a signal processor 17 which analyses the resonance characteristics, and a level calculating device 18 which calculates the liquid level in the container 11 based on the analysis of the signal processor 17. The plurality of wave guide elements 13 used for measuring the liquid level measures the level using different frequency bands respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level measuring device in which the possibility of leakage of liquid stored in a container is reduced.

[0002]

2. Description of the Related Art Conventionally, the liquid level of a liquid stored in a container has been measured by various methods and devices, and the same applies when the liquid is a metal. As a system for storing a large amount of liquid metal, there is a fast breeder reactor (hereinafter referred to as a fast reactor) using liquid sodium as a coolant.

Conventionally, an inductance probe type liquid level meter utilizing the fact that a coolant is liquid metal has been used for measuring the liquid level of a reactor of a fast reactor. Hereinafter, a liquid level meter used in a fast reactor will be described as a conventional example of a liquid level measuring device with reference to FIG.

FIG. 10 shows an inductance probe type liquid level meter.
As shown in (a), the guide tube 102 is installed in the reactor vessel 11 and a coil is disposed therein. The apparent inductance of the coil inserted into the liquid sodium 106 is the sodium level. Take advantage of things that change with. For example, as shown in FIG. 10A, a primary coil 103 and a secondary coil 104 are used, and the primary coil 1 is used.
03, a constant alternating current is passed, and an induced voltage proportional to the sodium level is taken out from the secondary side.
As the sodium level increases, the eddy current generated in the liquid sodium 106 also increases, canceling out the magnetic flux generated by the primary coil 103, so that the output voltage decreases and the output characteristics as shown in FIG. 10B are obtained. Conventionally, the liquid level in the reactor vessel 11 is calculated from the relationship between the output voltage and the liquid level.

As a liquid level measuring apparatus using the principle of the present invention, for example, an invention disclosed in Japanese Patent Application Laid-Open No. 7-98240 is known. This apparatus, as shown in FIG. 11, measures the level of water 113 stored in a water tank 114, and applies a sine wave ultrasonic wave to the waveguide 13 to oscillate the ultrasonic wave. It comprises an ultrasonic receiver 16 for receiving ultrasonic waves according to the resonance state of the wave body, and a water level calculator 112 for calculating a water level based on a change in the resonance state. The waveguide 13 has, for example, an ultrasonic transducer 115 joined to an upper end thereof, and upper and lower ends held by supports 116.

[0006]

The coil of the inductance probe type liquid level meter is generally made of a ceramic-insulated stainless steel single-core cable.
As shown in (a), the stainless sheath 105 and the liquid sodium 106 are separated by the guide tube 102 so as not to touch.

This guide tube 102 is made of liquid sodium 106
If a crack occurs in the guide tube 102 for some reason, the radioactive liquid sodium 106 enters the guide tube 102 and leaks out of the reactor vessel 11. Has the potential. This guide tube 1
02 extends over the entire length of the liquid level measurement range, and is about 5 m for the safety protection liquid level meter and 10 m for the continuous monitoring liquid level meter.
And has a problem that a boundary area having a possibility of cracking is large. In developing a fast reactor,
It is required to improve safety and reliability, and one of them is to reduce the possibility of sodium leakage.

In addition, the conventional reactor liquid level gauge has been replaced in about 5 years, and radioactive waste is generated. Therefore, reduction of the waste is desired. Further, in order to reduce the power generation cost, it is desired to simplify the apparatus and reduce the cost.

Next, in the case of a conventional liquid level measuring device using a waveguide, when measuring the liquid level of a liquid metal or the like,
Unless the temperature and density are corrected, there are problems such as a large error. In particular, when considering application as a liquid level measuring device for fast reactors, temperature / density correction methods according to operating conditions such as when the reactor is started and stopped, and further reduction of errors caused by swelling of the resonance frequency, or In the case where the above-mentioned waveguides are arranged, there are problems such as prevention of mutual resonance between the waveguides.

[0010] The present invention has been made in view of such a conventional situation, and it is possible to reduce the possibility of leakage of liquid metal stored in a container, reduce waste, and reduce costs. An object of the present invention is to provide a liquid level measuring device with improved position measuring accuracy.

[0011]

In order to achieve the above object, according to the present invention, there is provided a waveguide which is installed in a container storing liquid metal and propagates ultrasonic waves, and a waveguide for transmitting ultrasonic waves. An ultrasonic transmitter for transmitting ultrasonic waves to the ultrasonic wave, an ultrasonic receiver for receiving ultrasonic waves according to the resonance characteristics of the waveguide, a signal processing device for analyzing the resonance characteristics, and an analysis result of the signal processing device A liquid level calculating device that calculates a liquid level in the container based on the liquid level, wherein the waveguide used for liquid level measurement is composed of a plurality of liquid waveguides, each of which uses a different frequency band. It is characterized by performing a position measurement. As described above, since a plurality of waveguides are used for the liquid level measurement, and the liquid level is measured using different frequency bands, resonance between the waveguides can be eliminated.

According to the second aspect of the present invention, there is provided the first aspect.
Is characterized in that it has a function of limiting the frequency transmitted from the ultrasonic transmitter to only the frequency band used for liquid level measurement.

Further, according to a third aspect of the present invention, the signal processing apparatus according to the first aspect has a function of calculating a liquid level by using a plurality of resonance orders of the waveguide. . According to such a configuration, it is possible to improve the measurement accuracy in a region where the change in the resonance frequency due to the change in the liquid level is small.

On the other hand, a fourth aspect of the present invention is characterized in that the waveguide according to the first to third aspects is provided with a temperature sensor. The invention is characterized in that it is a thermocouple built in the wave body, and the invention according to claim 6 is an ultrasonic transducer installed at an end of the waveguide. According to the sixth aspect of the present invention, the temperature sensor can measure the temperature based on the propagation time of the ultrasonic wave transmitted from the ultrasonic transducer attached to one end of the waveguide.

According to a seventh aspect of the present invention, the liquid level calculating device according to the fourth to sixth aspects has a function of correcting the temperature dependence of the physical constant of the liquid metal or the waveguide. It is characterized by having. According to such a configuration,
It is possible to improve the liquid level calculation accuracy obtained from the resonance frequency based on the temperature measured by the temperature sensor.

Further, the invention described in claim 8 is the first invention.
The waveguide for propagating ultrasonic waves according to any one of claims to 7 has an ultrasonic transducer unit for bending and vibrating the waveguide and a transmission unit for transmitting ultrasonic waves, and the ultrasonic transducer unit is provided from the propagation unit. It has a removable structure. According to such a configuration, when the ultrasonic transducer part has deteriorated, only the part needs to be replaced, and the propagation part of the waveguide, whose deterioration does not matter much, does not need to be replaced (maintenance-free).

Finally, the invention according to claim 9 is based on claim 1.
The surface of the waveguide for transmitting the ultrasonic wave according to claim 8 is plated with gold, and the ultrasonic wave is reliably transmitted from the waveguide to the sodium even at a relatively low temperature of about 200 ° C. And accurate liquid level measurement can be performed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 9, the same or corresponding parts are denoted by the same reference numerals. (First Embodiment) (Claim 1, Claim 2, Claim 8)
FIG. 1 is a diagram showing an apparatus configuration of a liquid level measuring apparatus according to the present invention applied to a fast reactor. The liquid level measuring device includes a waveguide 13 with a piezoelectric element that penetrates a roof deck 12 that closes a reactor vessel 11 that stores liquid sodium 106 at an upper end, an ultrasonic transmitter 15 that transmits ultrasonic waves, and a piezoelectric element. An ultrasonic receiver 16 for receiving ultrasonic waves emitted from 14,
The signal output from the ultrasonic transmitter 15 and the ultrasonic receiver 16
Signal processing device 17 for obtaining the resonance or anti-resonance frequency of waveguide 13 based on the signal received by
The liquid level calculating device 18 obtains a liquid level from the resonance or anti-resonance frequency obtained in step 7. Although only one waveguide 13 is shown in FIG. 1 for simplicity, a plurality of waveguides 13 actually exist.

In the following description, among the resonance characteristics of the waveguide 13, the description regarding the anti-resonance frequency is omitted, but the same can be said for the case where the resonance frequency is used. The waveguide 13 has a structure in which one end of a solid stainless steel rod having an outer diameter of, for example, 20 mm is cut into a rectangular shape, and the rectangular portion is used as a center electrode, and piezoelectric elements 14 are bonded to both surfaces. A structure in which two thin plates of a piezoelectric element are bonded to each other with a metal elastic plate, that is, a center electrode set at 0 minute obtained by shaving a stainless steel bar into a rectangular shape (referred to as a bimorph type),
If one of the piezoelectric elements is connected so that one expands by voltage and the other contracts, it bends and vibrates according to the waveform of the applied voltage,
It can be used as an actuator. The liquid level measuring apparatus is used to forcibly vibrate the waveguide 13 using this.

An ultrasonic transducer 110 comprising a piezoelectric element 14 and a metal elastic plate (center electrode) is electrically connected to an ultrasonic transmitter 15 and an ultrasonic receiver 16, respectively. The ultrasonic transmitter 15 forcibly vibrates the waveguide 13 by applying a sine wave signal whose frequency changes with time to the ultrasonic transducer 110. The waveguide 13 has a unique resonance frequency determined by its material, length, and rate of inertia (radius of gyration), and its characteristic is that when the ultrasonic wave is propagated to the propagation portion 112 of the waveguide 13, Be demonstrated.

The signal processing device 17 calculates the waveguide 13 from the impedance of the received signal with respect to the frequency-swept sine wave signal.
Is determined. Although the resonance frequency of the waveguide 13 decreases in proportion to the length of the liquid in which the waveguide 13 is immersed, that is, the liquid level, from the resonance frequency of the waveguide 13 obtained by the signal processing device 17, The liquid level calculator 18 calculates the liquid level using the relationship between the liquid level and the resonance frequency that has been acquired in advance. Further, the liquid level can be displayed on the liquid level display device 19 to notify the operator of the nuclear reactor or the like.

As described above, the liquid level measuring apparatus according to the present invention measures the liquid level by directly contacting the liquid sodium 106 and the waveguide 13, but the waveguide 13 is made of solid stainless steel. The boundary for considering the leakage of liquid sodium 106 out of the reactor vessel 11 is as follows.
Only the attachment point 111 of the waveguide 1 and the waveguide 13 is sufficient, and the possibility of leakage can be reduced. In addition, since the waveguide 13 at the portion to be inserted into the reactor is a simple stainless steel rod, there is no particular need for replacement, and waste can be reduced.

Further, if the ultrasonic transducer 110 outside the reactor vessel is connected to the propagation portion 112 of the waveguide 13 by screwing and has a detachable structure, the piezoelectric element 1
If only the transducer 4 has deteriorated or failed, only the transducer section needs to be replaced, so that waste can be further reduced.

Next, the contents of the invention relating to applicability as a liquid level measuring device will be described. For example, in a system that requires a high degree of safety, such as a fast reactor,
It is necessary to consider multiplexing in the measuring system of the liquid level measuring device.
For example, a measurement system applied for a safety protection system needs to be divided into four sections. Further, conventionally, these four-section measurement systems are arranged at three positions in the circumferential direction of the reactor vessel, which are substantially equally divided into three.

Since the resonance frequency of the waveguide is determined by the size of the waveguide as described above,
If the same size waveguide is used for the segmented measurement system, the resonance characteristics will be the same, and resonance will occur between the waveguides, and the change in the resonance frequency due to the liquid level change of each waveguide can be obtained accurately. There is a possibility that there is no.

In the present embodiment, as shown in FIG. 2, the resonance characteristics are made different by changing the length of each waveguide 13, so that resonance between the waveguides does not occur. The resonance frequency of the waveguide 13 can be calculated by equation (1) when the waveguide 13 is not immersed in the liquid. In the case of the safety protection system of the fast reactor, the length of the waveguide 13 is about 5 m. However, a stainless steel rod having a diameter of 20 mm is used as the waveguide 13 and the liquid level measurement is performed by using, for example, the 30th resonance. If you do, 10cm
When the length of the waveguide is changed, the resonance frequency shifts by several tens of Hz, so that resonance between the waveguides can be eliminated.

[0027]

F (L) = (2m + 1) ² × {πR / (8L ² )} × (E / ρ) ^0.5 (1) where f [Hz] is a resonance or anti-resonance frequency, and R [m]
Is the radius of gyration of the waveguide, L [m] is the length of the waveguide, and E [N
/ M2] is the Young's modulus of the waveguide, and ρ [kg / m3] is the density of the waveguide.

As another method for eliminating the resonance between the waveguides, the lengths of the waveguides are kept the same, but the liquid level measurement uses different resonance frequency bands, ie, resonances of different orders. There is. When a waveguide similar to the above is used, the resonance frequencies of the 30th and 31st orders differ by about 100 Hz, and it is possible to eliminate resonance between the waveguides.

In this case, for example, as shown in FIG. 3, different ultrasonic transmitters 15 and ultrasonic receivers 16 are provided for the respective waveguides.
5 has a function of transmitting ultrasonic waves in different frequency bands (f1, f2, f3, f4).
To prevent transmission outside the frequency band used for liquid level measurement. In this way, the four waveguides 13 vibrate in different frequency bands, and the resonance between the waveguides can be eliminated. In FIG. 3, the ultrasonic transmitter 1
5. Although it is described that each of the waveguides 13 has the ultrasonic receiver 16 and the signal processing device 17, one set of ultrasonic transmissions is performed by transmitting and receiving signals with a time lag. It is also possible to use a device, an ultrasonic receiver and a signal processing device.

(Second Embodiment) (Corresponding to claim 3) In a liquid level measuring apparatus using resonance of a waveguide, a swell (ripple) as shown in FIG. 4 is generated between the resonance frequency and the liquid level. Can be seen.

For example, a liquid level measurement for a safety protection system is required to have an accuracy of about ± 30 mm. However, if there is a ripple, a region where the resonance frequency hardly changes even if the liquid level fluctuates occurs. Therefore, reduction of the influence is desired. The relationship between the resonance frequency and the liquid level is as shown in FIG.

As can be seen from FIG. 5, for example, in the case of the n-th order resonance, the change in the resonance frequency is small between the liquid levels h1 and h2, making it difficult to accurately determine the liquid level. In contrast,
When the m-order resonance is used, the liquid level can be accurately measured because the resonance frequency changes smoothly even if the liquid level is between h1 and h2. In this embodiment, the waveguide 1
The resonance characteristics of each order used in the liquid level measurement of No. 3 are previously collected outside the container, and the relationship between the liquid level measurement range and the resonance frequency and the corresponding resonance order to be used are stored in a database and stored in the signal processing device 17. Keep it.

The signal processor 17 selects an order to be applied based on the flow shown in FIG. That is, it is determined whether or not the measured frequency is in the region (f1 <f <f2) where the change in the resonance frequency is small in the resonance frequency band of the nth order. The resonance frequency band is applied, and the frequency band transmitted to the waveguide 13 is limited to the vicinity of the m-th resonance frequency.

The resonance characteristics outside the furnace can be grasped by conducting a test under the same conditions as in the container and collecting them, or by performing a temperature correction at a lower temperature than the inside of the furnace and correcting the temperature. It is also possible.

(Third Embodiment) (corresponding to Claims 4 to 7) FIG. 7 has a plurality of built-in thermocouples so that the temperature of the waveguide can be measured.

The resonance frequency of the waveguide 13 depends on the density and Young's modulus of the waveguide as shown in the equation (1). Further, when the waveguide is immersed in the liquid, it also depends on the density of the liquid. Therefore, when the coolant temperature changes when the reactor is started or stopped, a temperature correction is required. In this embodiment, the temperature-dependent data of the density and Young's modulus of the waveguide 13 and the temperature-dependent data of the liquid (coolant) density are incorporated in the liquid level calculating device 18 in advance, and based on the temperature measured by the thermocouple 71. Make corrections.

As shown in FIG. 8, for the correction of the density and Young's modulus of the waveguide 13, the temperature used for the correction is an average value of the temperatures of the thermocouples 71 of the entire waveguide 13. The temperature used for the density correction of the liquid sodium 106 is lower than the liquid level, that is, the thermocouple 7 in the coolant.
A value obtained by averaging the temperatures of 1 will be used. In this embodiment, the temperature correction is performed as follows. First, the relationship between the resonance frequency and the liquid level is simplified by Expression (2).

[0038]

F (h, t) = A (t) −B (t) × h + g (h) (2) where f (h, t) [Hz] is a liquid level h [m] and a temperature t
A (t) [Hz] is the resonance frequency at [° C.], B (t) is the change rate of the resonance frequency with respect to the liquid level change [Hz / m], g (h) [Hz] is a function of the liquid level h representing the effect of ripple.

A (t) and B (t) are determined in advance based on the results of measurements performed at a plurality of points by a factory test. The temperature not measured in the factory test is obtained by extrapolation and interpolation from the factory test data of the measured temperature. First, solving equation (2) for the liquid level h gives

[0040]

H = (f−g−A) / B (3) where f is a measured resonance frequency, and A and B are values for which temperature dependency has been determined in advance. A is the waveguide 13
The average temperature of the entire waveguide 13 is used as the correction temperature of A in order to represent the resonance frequency when the liquid level is zero. On the other hand, since B is a value related to the change rate of the resonance frequency with respect to the liquid level, the temperature used for the correction is the temperature of the coolant,
In the case of the present embodiment, the average temperature of the thermocouple 71 during cooling is used. In equation (3), g is a function depending on the liquid level, but h may be determined so as to best satisfy equation (3).

As a temperature sensor used for measuring the temperature of the waveguide 13, not a thermocouple 71 but an ultrasonic transducer 91 for transmitting an ultrasonic wave for measuring the temperature of the waveguide 13 as shown in FIG. Alternatively, the temperature may be obtained from the propagation time of the ultrasonic wave. The propagation speed of the ultrasonic wave in the metal depends on the density and the elastic constant, and the temperature is obtained by using the fact that the density and the elastic constant change with the temperature. As shown in FIG.
When a pulse wave is propagated through the projections 93, the propagation time required for reflection and return to the projections 93 changes depending on the temperature up to the projections 93. Therefore, the propagation time from each projection is determined to obtain the temperature distribution. Can be obtained.

(Fourth Embodiment) (Corresponding to claim 9) When ultrasonic waves are propagated in metallic sodium, ultrasonic waves may not propagate in sodium due to the interface state (wetting property) between sodium and the metal. is there. In particular, such a phenomenon occurs when the metal contained in sodium does not go through a high temperature state and the sodium temperature is low (around 200 ° C.).
It is considered that this is caused by an oxide formed on the metal surface becoming an obstacle.

In the present embodiment, in order to solve the above-mentioned problems, the surface of a metal waveguide is plated with gold, and the gold plating prevents the waveguide from being exposed to the atmosphere. In this way, for example, when used as a liquid level gauge for a reactor vessel, the waveguide is not exposed to a high temperature before the reactor is started up, and the reactor has a sodium temperature around 200 ° C. The liquid level can be measured accurately even when receiving sodium. Also, when used as a tank level meter for low temperature sodium (about 200 ° C.) such as a dump tank, the liquid level can be accurately measured.

[0044]

According to the present invention, since the method of measuring the liquid level by changing the resonance frequency of the waveguide is used, the possibility of sodium leakage due to the installation of the reactor level gauge is reduced, and waste is reduced. And the cost can be reduced. Further, in the inventions of claims 1 to 3, accuracy is improved by using a plurality of resonance characteristics. Further, in the fourth to seventh aspects, by performing the temperature correction, it becomes possible to improve the reactor level measurement accuracy. According to the eighth aspect, only the deteriorated portion can be replaced, and the waste can be further reduced.
Further, according to the ninth aspect, by plating the waveguide with gold, it is possible to prevent oxides from being generated on the surface of the waveguide, promote the propagation of ultrasonic waves, and enable accurate liquid level measurement. Can be.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a liquid level measuring device according to the present invention.

FIG. 2 is a partially enlarged explanatory view showing a configuration for eliminating resonance between waveguides.

FIG. 3 is a partially enlarged explanatory view showing another configuration for eliminating resonance between waveguides.

FIG. 4 is a characteristic diagram showing a relationship between a resonance frequency and a liquid level.

FIG. 5 is a characteristic diagram showing a relationship between different orders of resonance frequencies and liquid levels.

FIG. 6 is a flowchart for obtaining a liquid level using a plurality of resonance orders in the second embodiment of the present invention.

FIG. 7A is a configuration diagram illustrating a third embodiment of the present invention, and FIG. 7B is a diagram illustrating AA in FIG. 7A.
FIG.

FIG. 8 is a configuration diagram showing a relationship between a thermometer installation position of a waveguide and a liquid level according to a third embodiment.

FIG. 9 is a diagram showing a waveguide including an ultrasonic thermometer according to the third embodiment.

FIG. 10 is a diagram showing an outline of a conventional inductance probe type liquid level meter.

FIG. 11 is a diagram showing a configuration of a conventional ultrasonic water level meter using resonance.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Reactor vessel 12 ... Roof deck 13 ... Waveguide 14 ... Piezoelectric element 15 ... Ultrasonic wave transmitter 16 ... Ultrasonic receiver 17 ... Signal processing device 18 ... Liquid level calculation device 19 ... Liquid level display device 71 ... Thermoelectric Pair 91 Ultrasonic transducer 92 Waveguide 93 Projection 102 Guide tube 103 Primary coil 104 Secondary coil 105 Stainless steel sheath 106 Liquid sodium 110 Ultrasonic transducer 111 Attachment point 112 Water level calculator 113 ... water 114 ... water tank 115 ... ultrasonic transducer 116 ... support

Claims (9)

[Claims] 1. A waveguide installed in a container storing liquid metal for transmitting ultrasonic waves, an ultrasonic transmitter for transmitting ultrasonic waves to the waveguide, and according to resonance characteristics of the waveguide. An ultrasonic receiver for receiving the ultrasonic waves, a signal processing device for analyzing resonance characteristics, and a liquid level calculating device for calculating a liquid level in the container based on an analysis result of the signal processing device A measuring device, wherein the waveguide used for liquid level measurement,
A liquid level measuring device, comprising: a plurality of liquid level measuring units each using a different frequency band. 2. The liquid level measuring device according to claim 1, wherein the signal processing device has a function of limiting a frequency transmitted from the ultrasonic transmitter to only a frequency band used for liquid level measurement. . 3. The liquid level measuring device according to claim 1, wherein the signal processing device has a function of calculating a liquid level by using a plurality of resonance orders of the waveguide. 4. The liquid level measuring device according to claim 1, wherein the waveguide has a temperature sensor. 5. The liquid level measuring device according to claim 4, wherein the temperature sensor is a thermocouple built in the waveguide. 6. The liquid level measuring device according to claim 4, wherein the temperature sensor is an ultrasonic transducer installed at an end of the waveguide. 7. The liquid according to claim 4, wherein the liquid level calculating device has a function of correcting a temperature dependency of a physical constant of the liquid metal or the waveguide. Position measuring device. 8. The ultrasonic wave propagating waveguide has an ultrasonic transducer section for bending and vibrating the waveguide, and a propagating section for transmitting ultrasonic waves, wherein the ultrasonic transducer section is provided from the propagating section. The liquid level measuring device according to claim 1, wherein the liquid level measuring device has a detachable structure. 9. The liquid level measuring device according to claim 1, wherein the surface of the waveguide that propagates the ultrasonic wave is gold-plated.