JPH0245145B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a void ratio meter for measuring the ratio of gas to liquid in piping of nuclear reactors, boilers, etc. through which high-temperature, high-pressure steam and water flow.

[Technical background of the invention]

Generally, a mixed fluid of gas and liquid phases, such as steam and water, is called a two-phase flow, and the ratio of steam in the two-phase flow within a pipe cross section is called the void ratio. This void ratio is one of the important measurement items in nuclear reactors and boilers that handle two-phase flow.
It's becoming one.

This type of void rate meter uses radiation. Figure 1 shows a conventional void ratio meter, in which a radiation source 2 that emits an X-ray beam 4 and an X-ray detector 3 are installed, sandwiching a cylindrical measuring section 1 through which a two-phase flow, which is the object to be measured, flows. It is located. This X-ray beam 4 is focused by a collimator 5 into a narrow parallel beam, passes through the measuring section 1, and enters the X-ray detector 3 through the slit 6. The output signal from this X-ray detector 3 is transmitted to the signal cable 7
to a signal processing circuit (not shown).
In the figure, reference numeral 8 indicates vapor bubbles mixed in the liquid flowing inside the measuring section 1.

In the conventional void ratio meter configured as described above, the void ratio α is determined by the following equation (1).

α=ρ _w /ρ′ _w −ρ′ _v・_lo (V _x /V _w )/ _lo (V _A /V _w )
−ρ _w −ρ′ _w /ρ′ _w −ρ′ _v ...(1) Here, V _A : Output voltage of the X-ray detector when the inside of the measuring section 1 is empty V _w : When the inside of the measuring section 1 is empty Output voltage of the X-ray detector when it is filled with water V _x : Output voltage of the X-ray detector when the two-phase flow to be measured is flowing in the measuring section 1 ρ _w : Density of water ρ' _w : Density of high temperature water ρ′ _v : Density of steam.

This void ratio α is determined by assuming that the lengths of the X-ray beam 4 crossing the large number of vapor bubbles 8 existing in the measuring section 1 are l ₁ , l ₂ , ... l _i , ... _lo respectively, and the length of the X-ray beam 4 crossing the measuring section 1 is If the length of the line beam 4 is l _D , it is equivalent to α in the following equation (2).

α=[ _o 〓 ⁱ⁼¹ l _i ]/l _D ……(2) In other words, the void fraction measured by a void fraction meter using X-rays is the length l of the two-phase fluid traversed by the X-ray beam. is the ratio of the total length across the vapor bubble to _D. Such a void ratio is especially called a local void ratio.

Now, for example, as shown in FIG. 2, if the radiation source 2, X-ray detector 3, collimator 5, and slit 6 are moved up and down in a plane perpendicular to the central axis of the measuring section 1, then Line beam 4 height x
The void ratio α(x) in is obtained in the same manner.

The inner diameter of this measurement part 1 is 2r ₀ , and α(x) is
From the line beam height x=-r ₀ to x=r ₀ , the following equation (3) is used.
Integrate with a weight of l _D = 2√ ₀ ² − ² , and measure the
By dividing by the internal cross-sectional area A=πr ₀ ² , the average void fraction within the cross-section is obtained.

= [∫ ^r0 _-r0 2√ ₀ ² − ²・α(x)dx]/πr ₀ ² …
...(3) [Problems with the background art] As described above, theoretically accurate average void fraction within the cross section can be obtained.

However, conventional void rate meters measure with one fixedly installed X-ray beam 4 as shown in Figure 3, or with three fixedly installed X-ray beams 4 as shown in Figure 4. Many of them are formed by measuring with an X-ray beam 4, and the radiation source is also inconvenient to handle, and many use gamma ray sources with low ray flux. However, in measurements using about three X-ray beams 4, there was a practical disadvantage in that the average void fraction within the cross section could exceed 25% when the measurement error was large depending on the flow pattern of the two-phase flow. .

[Purpose of the invention]

The present invention has been made in view of these points, and it is an object of the present invention to provide a void ratio meter that can determine the local void ratio distribution and accurately determine the average void ratio within a cross section even during high-speed transient phenomena. purpose.

[Summary of the invention]

The void ratio meter of the present invention is provided with a radiation source that irradiates X-rays over the entire cross section of the measuring section on one side of a measuring section through which a two-phase flow flows, which is the object to be measured, and a radiation source opposite to the radiation source of the measuring section. The side receives the entire range of X-rays that have passed through the measuring section and emits a number of radiation intensity signals.
A CCD image element, a CCD image element for intensity comparison and correction that directly receives the X-rays emitted from the radiation source through a slit without any obstacles in the way, and a visible light rays on the front surface of these CCD image elements on the measuring section side. It is characterized in that it is equipped with a metal beryllium light-shielding plate that blocks the light, determines the local void fraction distribution over the entire cross section of the measurement part, and determines the average void fraction within the cross section.

[Embodiments of the invention]

The present invention will be described below with reference to embodiments shown in FIGS. 5 to 7.

FIG. 5 shows an embodiment of the present invention, in which a radiation source 2 and a CCD image element 9 are provided facing each other with a measuring section 1 in between. The X-ray beam 4 irradiated from this radiation source 2 is formed into a fan shape by a collimator 5, and is irradiated across the entire cross section of the measuring section 1, in which the two-phase flow that is the object to be measured flows, from the upper end to the lower end. Ru. In addition to emitting X-rays as in this embodiment, this radiation source 2 can also transmit other radiation such as gamma rays through the measuring section, and attenuate according to changes in the void ratio of the two-phase flow. Any device that emits radiation with energy that can cause a significant difference in amount may be used. Furthermore, although the X-ray beam 4 is fan-shaped, by setting the distance L between the radiation source 2 and the axis of the measuring section 1 at least 10 times the inner diameter _2r0 of the measuring section 1, the X-ray beam 4 can be made almost parallel. It can be regarded as a beam and measured. Further, the CCD image element 9 is formed by arranging a large number of fine unit semiconductor elements 11 in a straight line on the side surface facing the measuring section 1 of the vertically long main body 9a. Each unit semiconductor element 11 is sensitive to electromagnetic waves ranging from visible light to ultraviolet rays, X-rays, gamma rays, etc., and accumulates charges corresponding to the intensity of the electromagnetic waves received. In this embodiment, the vertical length of the unit semiconductor element 11 is set to be such that it can receive the entire range of the X-ray beam 4 that has passed through the measuring section 1. A light shielding plate 17 is provided on the front surface of this unit semiconductor element 11 to block visible light. This light shielding plate 1
As 7, a metal beryllium plate is used which reduces the amount of attenuation of the X-ray beam 4. Furthermore, in addition to the CCD image element 9, an X-ray beam 4 emitted from the radiation source 2 is also provided.
A CCD image element 10 for intensity comparison and correction is provided which receives the image directly through the slit 6 without any obstacles in the way. This CCD image element 1 for intensity comparison correction
Similar to the CCD image element 9, the unit semiconductor element 11 is provided in the main body 10a, and a light shielding plate 17 is provided on the front surface of the unit semiconductor element 11.
It is formed by providing

FIG. 6 shows a block diagram of a device for extracting radiation intensity signals from the CCD image element 9 in the void rate meter of the present invention formed as shown in FIG. In the figure, reference numeral 12 is a clock pulse oscillator that sends a clock pulse 13 to the CCD image element 9 and preamplifier 15.

Next, the operation of this embodiment will be explained with reference to FIGS. 5 and 6.

At the time of measurement, the radiation source 2 is first activated. Then, an X-ray beam 4 is emitted from this radiation source 2, and this X-ray beam 4 is converged by a collimator 5 so as to be directed toward the entire range of the measuring section 1 and the CCD image element 10 for intensity comparison and correction. Then, the X-ray beam 4 that has passed through the measuring section 1 has its intensity changed depending on the state of the two-phase flow, and passes through the light shielding plate 17 of the CCD image element 9 to each unit semiconductor element 1.
1 and 11. Then, charges corresponding to the intensity of the incident X-ray beam 4 are accumulated in each unit semiconductor element 11. Thereafter, each unit semiconductor element 11 is connected to a clock pulse oscillator 1 in order from top to bottom.
A clock pulse 13 is sent from 2. When each unit semiconductor element 11 receives the clock pulse 13, it emits an output current 14 to the preamplifier 15 in accordance with the magnitude of the accumulated charge.

On the other hand, the intensity comparison and correction CCD image element 10 directly receives the X-ray beam 4 from the radiation source 2 without being attenuated, and outputs an output current 18 according to the intensity.
is emitted toward the preamplifier 15.

Now, a case will be described in which one X-ray beam 4 at a distance x from the center is incident on the CCD image element 9.

An output current 14 is emitted from this CCD image element 9 to a preamplifier 15, and at the same time a clock pulse 1
3 is issued to the preamplifier 15. This results in
The preamplifier 15 identifies the position of the unit semiconductor element 11 at which the output current 14 is emitted, and
Next, the output current 14 is divided by the output current 18 received from the CCD image element 10 for intensity comparison and correction to prevent measurement errors caused by noise caused by temporal intensity changes of the X-ray beam 4 emitted from the radiation source 2. do. Next, the preamplifier 15 operates according to the magnitude of the output current 14 divided by the output current 18.
A radiation intensity signal 16 is generated consisting of an output voltage corresponding to the intensity of the radiation V _x volts. Therefore, by substituting this radiation intensity signal 16 into the above equation (1), the void ratio α can be determined.

By performing such an operation for each unit semiconductor element 11, the void fraction distribution of the measuring section 1 is determined, and furthermore, the average void fraction within the cross section is determined based on the above equation (3).

Generally, the CCD image element 9 has approximately 1000 unit semiconductor elements 11 closely arranged in parallel within a length of approximately 2.5 cm, so that the resolution of the void ratio is extremely high. For example, it is 300 times or more compared to the conventional example shown in FIG.

If this measurement is continued, the void fraction can be measured with sufficient accuracy and resolution even during fast transient phenomena during nuclear reactor operation.

Furthermore, since the light shielding plate 17 is provided, visible light can be blocked and only radiation used for measurement, such as X-rays and gamma rays, can be made to enter the unit semiconductor element 11, thereby improving measurement accuracy. In addition, the light shielding plate 17
Since a metal beryllium plate is used for the sensor, X-rays are not attenuated as much as in a typical glass plate-sealed CCD image element, and measurement accuracy is improved.

In addition, the shape of the measurement part 1 is not only cylindrical, but also
The shape is not limited to a rectangular tube shape, a box shape, etc. However, it is preferable to use metal beryllium, which has a small amount of attenuation of the X-ray beam 4, as its material.

FIG. 7 shows another embodiment of the present invention, in which the void ratio can be measured by rotating the X-ray beam 4 with respect to the fixed measuring section 1.

That is, four support rollers 20, 20 are protruded from the frame 19, and the support rollers 2
A rotary disk 21 is rotatably supported around a horizontal axis by 0 and 20. Actual measurements are performed by reciprocating half a rotation. This rotating disk 21 is rotated by applying rotational force from a drive motor 22 to one support roller 20 via an endless belt 23. In addition, the rotating disk 21
As in the previous embodiment, a radiation source 2, a collimator 5, a slit 6, a CCD image element 9, and a CCD image element 10 for intensity comparison and correction are provided. This is because the CCD image element 9 is extremely small and lightweight and can now be rotated together with the rotating disk 21.

The measurement according to this embodiment is performed while the rotating disk 21 is rotated by the drive motor 22. That is, the CCD image element 9 and the intensity comparison correction
Output currents 14 and 18 obtained from the CCD image element 10 are connected to a signal cable 24 whose length is slackened to allow half a rotation of the rotary plate 21.
The radiation is guided to the interface mechanism 25 and subjected to signal processing to become a radiation intensity signal 16. Receiving this radiation intensity signal 16, the computer 26 specifies the rotational position of the rotating disk 21 and the X-ray beam 4, sends a signal 28 to the cathode ray tube 27, and displays a tomographic image of the two-phase flow in the measuring section 1. .

By forming in this way, it is possible to provide a void ratio meter that can easily obtain a tomographic image of a two-phase flow.

〔Effect of the invention〕

In this way, the void ratio meter of the present invention is small and has high resolution, and can determine the local void ratio distribution and accurately determine the cross-sectional average void ratio, and can also be used reliably even during high-speed transient development where changes are rapid. The cross-sectional average void fraction can be determined in a manner similar to the above, and the accuracy of void fraction measurement is extremely high.
In addition, since the CCD image element directly receives the radiation that has passed through the measurement section, it is possible to convert the radiation into light, for example.
Compared to the case of a CCD image element, the linearity of the number of radiation fats and output voltage is extremely good, and highly accurate data can be obtained. In addition, since there is no need to provide a light conversion device that converts radiation into light, the device can be simplified, and there is no interference of light within the light conversion device, making it possible to achieve very high resolution. .

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing the principle of a conventional void rate meter, FIG. 2 is a schematic configuration diagram showing the principle of measuring the local void rate α(x) at the height x of the X-ray beam,
FIG. 3 is a schematic configuration diagram showing a conventional one-beam void rate meter, FIG. 4 is a schematic configuration diagram showing a conventional three-beam void rate meter, and FIG. 5 is a schematic configuration diagram showing an embodiment of the present invention. FIG. 6 is a block diagram showing a signal processing system according to the present invention, and FIG. 7 is a schematic configuration diagram showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Measuring unit, 2... Radiation source, 4... X-ray beam, 9... CCD image element, 16... Radiation intensity signal, 17... Light shielding plate.

Claims (1)

[Claims] 1. A radiation source that irradiates X-rays over the entire cross section of the measuring section is provided on one side of the measuring section through which the two-phase flow that is the object to be measured flows, and a radiation source that irradiates X-rays over the entire cross section of the measuring section is provided, and A CCD image element that receives the entire range of X-rays and emits a large number of radiation intensity signals, and a CCD image element that receives the entire range of X-rays from the radiation source and receives the X-rays directly through a slit without any obstacles in the way for intensity comparison correction.
This void ratio meter is equipped with a CCD image element and a metallic beryllium shielding plate that blocks visible light on the front side of the measurement section of the CCD image element.