JPH06118194A - Method for detecting vapor phase, which appears in liquid phase in room, with ultrasonic wave - Google Patents

Abstract

PURPOSE: To detect a gaseous phase which appears in a liquid phase in a chamber by detecting whole outlet signals of a liquid phase/chamber system and detecting the possible attenuation of the amplitude characteristic of the gaseous phase in the liquid phase by separating an effective part from the signals. CONSTITUTION: A synchronous pulse generator 28 generates pulses 2 and 4. The pulses control a sine wave generator 30 at an ultrasonic frequency and generate wave trains 6 and 8. The wave trains are amplified by means of an amplifier 32 and excite a radiation transducer 34. The ultrasonic wave trains carried to the wall 22 of a steam generator 20 are collected by means of a waveguide 38 and a reception transducer 40. The received wave train IC is amplified 44 after pre-amplification 42. Received composite signals are filtrated to reduce background noise and shaped by means of a shaper 46. Synchronous detection which is delayed by time (t) by a window having a width Δt is synchronized to a synchronization generator 28 and a signal 1f is obtained at the outlet of a synchronous detector 48 and compared with an alarming threshold 18 at a comparator 50. When the peak of a signal 14 received by the comparator 50 is smaller than the threshold 18, the presence of a gaseous phase which attenuates the energy of the ultrasonic wave trains on an ultrasonic route can be inferred.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to monitoring such liquid phases for the purpose of identifying the appearance of bubbles which may be inside the liquid entering or entering the chamber.

[0002]

BACKGROUND OF THE INVENTION The problem of monitoring is, in some industries, more precisely and characteristically, that water in a steam generator cooled by liquid sodium causes water or steam to leak from the tubes of the steam generator. It is generated in the case of a steam generator of a fast neutron reactor, which is designed to indicate contact with sodium as soon as possible.

In fact, the reaction of sodium with water is a violent chemical reaction that results in the formation of hydrogen bubbles, the appearance of which in association with other phenomena causes very serious damage to the interior of the steam generator. Cheap. It is therefore essential to be able to detect the leak once it appears, ie as soon as hydrogen bubbles begin to appear in the steam generator, before this event causes serious damage.

Heretofore, in the prior art, the presence of the gas phase in the liquid was placed in direct contact with the liquid so that it was not affected by unwanted signals that would inevitably occur on the wall of the chamber containing the liquid. Detected with the help of a sound wave transmitter / receiver system. These systems are described in French patent FR-A-7337233.

[0005]

The method described above, however, presents a serious drawback in that the wall of the chamber containing the liquid phase must be perforated in order to be able to install the transducer. For this reason, the structure is easily broken, and it is also necessary to perform pre-positioning to accurately determine the measurement point.

It is an object of the present invention to provide a method for ultrasonically detecting the appearance of a gas phase in a liquid phase that is in or flowing into a room without invading the room itself.

[0007]

SUMMARY OF THE INVENTION This method provides a very short time of 1 second, even in the presence of large amounts of background noise, such as the broadband background noise of steam generators at nominal power. It is simply implemented by disclosing the installed dual phase.

The method comprises: using at least one ultrasonic transmitter, through a system composed of a chamber and a liquid, frequencies above 20 kHz and short durations of about 10 ^-3 s and sufficient time intervals; Passing a wave train having preferably about 10 ^-1 s to 10 ^-2 s such that the received signals collected at their outlets in the chamber do not overlap, -using at least one ultrasonic receiver, Detecting the entire exit signal transmitted through the liquid / chamber system, -separating the effective part corresponding to the passage of the liquid phase from the whole received signal, -for this effective part of the signal in the liquid phase Detecting possible attenuation of the amplitude characteristic of the existing gas phase.

As will be seen, the method of the present invention comprises a chamber traversed by a beam of ultrasonic waves and a liquid contained in the chamber to control the transparency of the liquid phase to ultrasonic radiation periodically at several times per second. It is configured with a system.

When there is no leakage and therefore sodium reaction to water, this is the case with sodium cooled reactor steam generators, but the transparency mentioned above is maximal. On the other hand, as soon as a dual phase appears at any point in the liquid medium, ie, in effect bubbles in the ultrasonic path, these bubbles immediately lose energy and the aforementioned transparency decreases fairly quickly.

According to the method of the present invention, it is not necessary to penetrate the wall of the chamber before the measurement is carried out, and the ultrasonic transmitter, like the ultrasonic receiver, is of the type of chamber that constitutes the liquid phase case. Since it is installed outside, it relates to non-intrusive active acoustic detection. Furthermore, each ultrasonic transmitter and receiver can be directly coupled to the chamber by fixing it directly to the outer surface of the chamber wall, or, on the other hand, installed at a certain distance from the chamber, ie welded to the chamber. A waveguide can connect to the wall of the chamber.

The Applicant has found that the frequency is above 20 kHz and has a duration of about 10 ^-3 s and a sufficient time interval (preferably 1
It has been demonstrated that it is possible to avoid overlapping received signals collected at the exit of the chamber by using a wave train as an ultrasonic source having 0 ^{-1 to} 10 ^-2 s). Furthermore, if the wave trains radiated at the inlet of the system have constant amplitude and are sufficiently temporally separated from each other, signals are received at the outlet of the chamber and these signals are received in different environments (chamber, liquid, First because of various propagation speeds of ultrasonic waves in possible obstacles in the room, etc.)
Second, it exhibits several different amplitude peaks, each corresponding to a particular ultrasonic path in the system. It is then sufficient to separate from these successive amplitude peaks the ones corresponding to the useful part of the signal, ie the ones corresponding to the transitions of the ultrasonic waves through the liquid phase.

In the particular case of sodium / water exchange steam generators in nuclear reactors, the separation of the active ingredients is facilitated by the fact that the velocities of the ultrasonic waves in the three media making up the system are different: It can be carried out. 6000 m / s for steel, 2200 m / s in sodium and 15 in water
00 m / s.

According to the invention, the detection of the active component of the signal is synchronized with the emission start time of each wave train, but with a delay corresponding to the time of appearance of a particular amplitude peak of the ultrasonic transition in the liquid. Have and be done.

By preliminarily empirically calibrating the device, the time of appearance of the useful part of the signal after the start of injection of each wave train, and secondly, by experimentally injecting gas into the liquid to be monitored, A critical amplitude threshold is also determined, i.e. below which a useful signal collected exhibits a sufficiently wide range of amplitude attenuation so that it is possible to confirm the presence of the gas phase in the ultrasound path. It becomes possible to do.

[0016]

In any case, the invention should be understood more easily by reading the embodiments of the invention, which are illustrated by way of illustration with reference to FIGS. 1 and 2. By way of illustration and not limitation, this example relates to the case of monitoring a sodium / steam generator of a sodium cooled fast neutron reactor.

FIG. 1 shows square pulses 2 and 4 which synchronize the course of the method as a function of time on the abscissa. In other words, the pulses 2 and 4 pass through the time axis and the system through which the wave trains 6 and 8 consist of the chamber of the steam generator, the sodium contained in the chamber and the water pipe traversing the chamber. It defines the strobe to be transmitted and injected.

As can be seen in FIG. 1b, the wave trains 6 and 8
Have a constant amplitude and are the same for both. According to the invention, the wave trains 6 and 8 are at least 20 kHz.
With frequencies of about 10 ^-3 s and separated by about 10 ^-1 s.

FIG. 1c shows the signal collected at the outlet of the steam generator chamber as it exits the steam generator. This figure also shows some phenomena.

First, first, the time shift of the received wave train 6a corresponds to the wave train 6, and 8a corresponds to the wave train 8. Of course, this time shift corresponds to the transit time of the ultrasonic signal through the transverse structure. Another phenomenon that can be seen in this FIG. 1c is that the received wave trains 6a and 8a are time-extended with respect to the radiated wave trains 6 and 8. This stretching results from the different propagation speeds of the ultrasonic waves in the various transverse media (steel, sodium ...) And from the multiple reflections that the ultrasonic beam receives from the various elements along its path. Finally 10
In addition to the background noise seen at 2 above, the overall raw signal received should be as shown in the phase shown in FIG. 1c.

Another important observation underlying the practice of the invention results from the particular shape of the exit wave train 6a and 8a shown in FIG. 1c. In fact, each of these effectively consists of an amplitude variation divided into three peaks, one inlet peak 12, one intermediate peak 14 and one outlet peak 16. These interpretations are straightforward. The inlet peak 12 corresponds to the transition of the wave train in the steel structure of the steam generator, whose propagation speed of 6000 m / s is virtually the highest. The central amplitude peak 14 corresponds to the signal transmitted by the liquid, sodium in this example, at a speed of about 2200 m / s. With respect to the third amplitude peak 16, this is due to the multiple reflections within the liquid sodium of the first wave train due to traversing or encountered structures.
As explained above, it is this particular form consisting of three amplitude peaks that results from the choice of various frequencies and the absence of overlapping parameters of the continuous wave train, which allows the appearance of a series of bubbles to It becomes possible to implement the detection method by selecting the part of the signal corresponding to the transmission of ultrasonic waves by the liquid, which can be detected very quickly.

To achieve this, the procedure is as follows. First of all, as shown in FIG. 1d, the background noise is removed and a profile of the maximum amplitude of the received signal is constructed, thus giving three amplitudes 12, 14, and 16 in the profile representing the actual value of the signal. Only explicitly.

Next, it is necessary to select one characteristic of liquid phase transfer from these three peaks. Generally speaking and in the examples represented in Figures 1e and 1f, the central peak is selected. Synchronous detection is performed by opening a selection strobe at the end of time with a period Δγ that allows the selection of the calibrated pulse with the maximum amplitude of the central peak 14. However, in some cases-for example, if the chamber is large and has a large number of internal structures-it may be advantageous to select a peak 16 due to multiple reflections in the liquid sodium of the wave train by the internal structure. .

On the basis of the known situation and with a device which has been calibrated beforehand by pouring into the liquid with careful and good regulation of the gas flow, below which the attenuation of the amplitude 14 is necessarily gas phase. The alarm threshold value 18 meaning the occurrence is experimentally determined.

FIG. 2 diagrammatically shows a sodium-cooled reactor sodium / water steam generator which is passed by a metallic steel chamber 22, a liquid sodium phase 24 and water. A heat exchange tube 26 is provided.

The device is used as shown in FIG. 2 in order to monitor what is occurring inside this steam generator 20, in particular the appearance of hydrogen bubbles in the sodium 24.

The sync pulse generator 28 generates pulses such as the pulses (2 and 4) of FIG. 1a. These pulses then control the sine wave generator 30 at the ultrasonic frequency, which produces the wave trains 6 and 8 of FIG. 1b. These wave trains at the outlet of the generator 30 are amplified by the amplifier 32 and then guided by the waveguide 36 to the outer wall 22 of the steam generator 20.
To excite a radiation transducer 34 coupled to the. Thus generated, the wall 22 of the steam generator 20
The wave train of ultrasonic waves carried up by the tube spreads through the system described above and is then collected by the waveguide 38 and the receiving transducer 40. The received wave train, which is in the form of that shown in FIG. 1c, is then pre-amplified at 42, 44
Is amplified by.

The received composite signal is thus the first corresponding to the structure, ie the transmission of the wall 22 of the chamber of the generator 20.
, A central part corresponding to the transmission through the liquid, and broadband background noise obtained from the steam generator. This composite signal corresponds to that of FIG. 1c, but
A narrow band centered at the emission frequency of the wave train is then filtered to minimize background noise, and then a device 46 consisting of a narrow band filter and an actual value shaper 46, as shown in FIG. 1d. Is formed according to the actual value of.

Following this, delayed synchronous detection of time t by a window of width Δt is performed by the synchronous generator 28 which operates in synchronization with the synchronous generator 28. The signals of FIG. 1f are obtained at the exit of this synchronous detector 48, and these signals are then compared in a comparator 50 with the alarm threshold 18 of FIG. 1f, which threshold was explained previously. As such, it is experimentally predetermined. When the signal amplitude reduction or attenuation is received by the comparator 50, the peak of the signal 14 is the alarm threshold 1.
If it is smaller than 8, it can be deduced from this that there is a gas phase on the ultrasound path that has caused this considerable attenuation of the energy of the ultrasound wave train.

The apparatus of FIG. 2 performs detection in a period of about 1 s, and for equivalent water flows of less than 1 g / s, the length 18
It made it possible to carry out the method according to the invention which reveals a water leak from a straight tube of m, 0.4 m diameter in less than 1 second.

For certain applications, for example in the case of large chambers with a large number of internal structures, it may be advantageous to fix several radiating transducers 34, in particular several receiving transducers, to the chamber.

[0032]

The main advantages of the detection method of the present invention are as follows. It is possible to draw out its extremely fast response time of less than 1 second, and Generally speaking, the crossing system, which is related to the quality of the measurement, is less affected by background noise, and the sensitivity of leak detection is excellent, even at very small leaks, and it enters the chamber through which the monitored liquid phase passes. Never. Moreover, because the transducers are outside the chamber, they are always accessible and can operate without unacceptable overheating when the liquid phase is hot.

[Brief description of drawings]

1a to 1f show the operating stages of the method from the various signals transmitted, received and analyzed.

2 shows a simplified diagram of an apparatus for detecting the appearance of hydrogen gas in the sodium of a steam generator with the aid of the invention by means of ultrasound.

[Explanation of symbols]

 2,4 Square pulse 6,8 Wave train 10 Background noise 12 Inlet peak 14 Intermediate peak 16 Outlet peak 20 Steam generator 22 Chamber 24 Liquid sodium 26 Heat exchange tube 28 Pulse generator 30 Sine wave generator 32, 42, 44 Amplifier 34 Radiation Transducer 36, 38 Waveguide 40 Receiving Transducer 46 Narrow Band Filter and Actual Value Shaper 48 Synchronous Detector 50 Comparator

Claims (6)

[Claims] 1. A method for ultrasonically detecting a gas phase appearing in a liquid phase in a room, wherein at least one ultrasonic oscillator is used and has a frequency of more than 2 kHz and continues for about 10 ^-3 s. Passing the chamber and the liquid through a wave train sufficiently separated, preferably between about 10 ^-1 s and 10 ^-2 s, so that the received signals collected at the outlet of the chamber do not overlap. Detecting at least one exit signal transmitted through the liquid / chamber system using at least one ultrasonic receiver; separating the effective part corresponding to the passage of the liquid phase from the whole received signal; Detecting the possible attenuation of the amplitude characteristic of the gas phase present in the gas phase within the liquid phase for the effective part of the signal. 2. The wave train in the system has a constant amplitude, the wave train at the exit of the system is time calibrated and has several amplitude peaks each corresponding to a particular ultrasonic path in the system. Therefore, its detection is synchronized with the period of occurrence of the onset of each wave train, but with the delay corresponding to the appearance of a particular amplitude peak of the ultrasonic transition through the liquid phase, and thus the useful part of the signal. The detection method according to claim 1, wherein the detection method is selected. 3. The presence of a gas phase in the liquid phase is detected by the fact that the amplitude of the effective part of the signal is below the experimentally predetermined threshold by injecting gas into the liquid during calibration. The method according to claim 1 or 2, characterized in that. 4. Method according to claim 1, characterized in that the ultrasonic transmitters and / or receivers at the inlet and outlet of the system are fixed directly to the outer surface of the wall of the chamber. 5. The method according to claim 1, wherein the ultrasonic transmitters and / or receivers at the inlet and outlet of the system are connected to the outer surface of the wall of the chamber by a waveguide welded to the chamber. 6. When monitoring a leak in a steam generator of a reactor cooled by a liquid metal, the appearance of hydrogen gas in the metal causes the metal of the generator to be accompanied by a leak in one of the water tubes of the generator. Application of the method according to any one of claims 1 to 5, characterized in that it is monitored by acting on water.