JPH08304127A - Apparatus for measuring flow speed and flow rate in pipe - Google Patents

Abstract

PURPOSE: To measure flow rates and flow speeds readily without destruction by a simple external equipment without assembling the equipment such as a flowmeter requiring the maintenance and without decreasing the strength of a piping system. CONSTITUTION: Radioactive isotope is injected into a piping to be measured 1. The radiation of the specified energy of the radioactive isotope is detected by a first detector 11 and a second detector 12. The pulse-height analysis of the detected signal is performed, and only the specified radiation energy is taken out respectively. These signals are counted, and the flow speed and the flow rate are operated with an operating device 15 by the statistic method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe flow velocity flow measuring device for nondestructively measuring a flow velocity of a fluid in a pipe by using a radioactive isotope.

[0002]

2. Description of the Related Art Conventionally, in order to measure the flow velocity of a fluid in a pipe, various measuring instruments such as a current meter and a flow meter are attached to the pipe. If such a measuring instrument cannot be installed, as a non-destructive method, use ultrasonic waves, or install a container at the end of the pipe or in the middle, and measure the rate at which fluid accumulates in this container or the rate at which it decreases. Then, there is a method of calculating the flow rate.

There is also a method of using a short half-life nuclide as one of the methods for measuring the flow velocity by radiation. This method is
^{This is a method in which 16} (nitrogen 16: half-life 3 seconds) is flown into the pipe, and the difference in the intensity of radiation and the half-life are compared at two points at a fixed distance to calculate the flow velocity.

[0004]

However, the conventional method described above may not be adopted depending on the plant or system. For example, when the flow meter is mounted with a pipe having a very high pressure, the flow meter may be very expensive, or leakage from the flow meter may be absolutely unacceptable. In addition, there are cases where the flowmeter cannot be installed because the installation location is narrow. Furthermore, it is not necessary to constantly monitor the flow rate, but the flow rate may be checked only during plant or system maintenance, or a combination of these. Since the method of flowing N ¹⁶ into the pipe measures the radiation dose itself in an analog manner, there is a high possibility that a measurement error will occur depending on the detector installation method.
Measurement accuracy is low.

The present invention has been made in consideration of the above-mentioned circumstances, and it is possible to use a simple external facility without incorporating a facility such as a flow meter which requires maintenance, without lowering the strength of the piping system. It is an object of the present invention to provide a non-destructive in-pipe flow velocity / flow rate measuring device capable of easily measuring a flow rate and a flow velocity.

[0006]

In order to solve the above-mentioned problems, the first aspect of the present invention is to measure the radiation of a specific energy of the radioactive isotope injected into the pipe to be measured, and at a fixed interval from each other. And a first detector and a second detector arranged near the pipe to be measured,
A first wave height analyzer and a second wave height analyzer which perform wave height analysis of these detection signals to extract only specific radiation energy, and signals from these first and second wave height analyzers are respectively counted and statistically calculated. And a calculation processing device that calculates the flow velocity and flow rate by a dynamic method.

A second aspect of the present invention is characterized in that the radioactive isotope of the first aspect is sodium 24. In a third aspect, the compound containing sodium 24 as the radioactive isotope according to the second aspect is NaHCO ₃ , Na.
It is characterized by being one of ₂ CO ₃ and NaOH.

[0008]

According to the first aspect of the present invention having the above-mentioned structure, the radioactive isotope is injected into the pipe to be measured, and the radiation having a specific energy of the radioactive isotope is first emitted.
Of the detector and the second detector, wave height analysis of these detection signals is performed, and only specific radiation energies are taken out, respectively, and then these signals are counted respectively to calculate the flow velocity and flow rate by a statistical method. By calculating with the device, you can easily measure the flow rate and flow velocity non-destructively by simple external equipment without reducing the strength of the piping system without incorporating equipment such as a flow meter that requires maintenance. can do.

According to the second aspect, since the radioactive isotope according to the first aspect is sodium 24, the energy is high with gamma rays and the half-life is neither too short nor too long.

In claim 3, since the compound containing sodium 24 as a radioactive isotope according to claim 2 is any one of NaHCO ₃ , Na ₂ CO ₃ and NaOH, the chemical property is stable, Does not corrode metal. It dissolves easily in the fluid of the piping system, does not deteriorate due to heat, pressure, or radiation, and does not absorb neutrons if it remains.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of a pipe flow velocity / flow rate measuring device according to the present invention. In this embodiment, as shown in FIG. 1, for example, a device cooling pipe in a boiling water reactor is used as the pipe to be measured 1, and the pipe to be measured 1 cools many heat loads 2 in the power plant. It forms a multi-branched pipe system like a blood vessel. A flow rate adjusting valve 3 is attached to each heat load 2 in order to obtain an appropriate amount of cooling water. Further, the whole of a large number of pipes to be measured 1 are connected at both ends, a measurement solution injection port 4 is connected to one end thereof, and an injection port stop valve 5 is attached to the measurement solution injection port 4.

From the measurement solution injection port 4, a short half-life radioactive isotope is injected into the cooling water, so that a measurement solution containing a trace amount of the radioactive isotope is injected. This measurement solution passes through the inlet stop valve 5 and flows into each pipe to be measured 1 along the pipe flow direction shown by the arrow.

Of the many pipes 1 to be measured, in the vicinity of one pipe 1 to be measured and on the upstream side in the flow direction, a first detector composed of a germanium detector or the like having a high energy resolution is provided. While the upstream side detector 11 is arranged, the downstream side detector 12 as a second detector composed of the same is also arranged on the downstream side thereof. In this case, the distance between the upstream detector 11 and the downstream detector 12 is
It is necessary to accurately measure the distance L between the measurement points in advance. The upstream-side measuring device 11 and the downstream-side detector 12 detect the radiation of the specific energy of the radioactive isotope when the measurement solution in the pipe 1 to be measured flows near the upstream-side detector 11 and the downstream-side detector 12. .

Upstream detector 11 and downstream detector 12
The detection signals from are input to the upstream wave height analyzer 13 as the first wave height analyzer and the downstream side wave height analyzer 14 as the second wave height analyzer, respectively, and these wave height analyzers 13 and 14 detect The wave height of the signal is analyzed, and only specific energy is extracted and output to the arithmetic processing unit 15.
The arithmetic processing unit 15 counts the signals from the wave height analyzers 13 and 14 to obtain the count-time relationship shown in FIG. The flow velocity and flow rate values thus obtained are displayed on the flow velocity / flow rate output device 16.

Next, the operation of this embodiment will be described.
FIG. 2 shows changes with time in the signal obtained from the upstream side detector 11 and the signal obtained from the downstream side detector 12, with the vertical axis representing the count and the horizontal axis representing the time. From the upstream wave height analyzer 13 and the downstream wave height analyzer 14 to the processing unit 1
The signal sent to No. 5 has a normal distribution shape as shown in FIG. Then, in FIG. 2, tu is the upstream measurement center time, and td is the downstream measurement center time. Here, in order to calculate the measurement center from the input signal shown in FIG.
As shown in FIG. 3, the leading time t1 and the trailing time t2 for the peak value kp and the half peak value kh of the count are obtained, and the measurement center t0 is calculated from these values. However, actually, the data as shown in FIG. 4 is obtained. The formula of the above normal distribution is as follows. That is,

[0016]

[Equation 1]

In this equation, C (t) is the count value at time t, Co is the peak count value, t is any time, and t0
Is the time at the time of the peak count value, and σ is the variance (> 0). As shown in FIG. 4, assuming that the actual number of data is n, the count value C1 when the time t1 is 31 is 51 and the time t2 is t2.
, The count value C2 is 52, the count value Ci is the time ti, and the count value Cn is 69 when the time tn is 49.

Optimal values of Co, t0 and σ in the above equation are calculated from this raw data by the method of least squares. If you draw a curve of normal distribution based on this constant, it will be the theoretical curve that uses the most raw data. The value t0 on this curve is the value required in this embodiment. These arithmetic processes are performed by the arithmetic processing unit 15. Flow velocity is upstream t0 value (tu above)
(Td-tu) from the downstream side t0 value (td above)
And the distance L is divided by this time (td-tu). Here, the flow rate can be calculated by inputting the diameter of the pipe. The flow rate and flow rate are displayed on the flow rate / flow rate output device 16.

The radioactive isotope used in this embodiment must have the following properties. That is, the half-life should be 6 to 24 hours. If the half-life is too short, the attenuation will be large and it will be difficult to handle. If it is too long, the nuclide injected into the pipe will remain, and the radiation background will rise during re-measurement, increasing the measurement error.

Radiation is a gamma ray and has high energy, and it is preferably 500 keV or more. Higher energy is preferable for permeation even when the pipe is thick.

Furthermore, the chemistry of the measurement solution is a stable compound, which does not corrode metals and easily dissolves in the fluid of the piping system. If it remains without being altered by heat, pressure, or radiation, do not absorb neutrons. Therefore, the thermal neutron absorption cross section is sufficiently small, does not affect the operation of the nuclear power plant, and does not increase the radiation exposure during periodic inspections due to induced radioactivity.

Explaining an example of use, Na ²⁴ (sodium 24) has a half-life of 15 hours, a typical gamma ray energy of 1.37 MeV, and the stable isotope of sodium is only Na ^23. Na ²³ is 1
It is 00%.

The compounds include NaHCO ₃ (sodium hydrogen carbonate), Na ₂ CO ₃ (sodium carbonate),
Examples include NaOH (sodium hydroxide). NaHC
O ₃ is weakly basic, almost harmless to metal systems, and soluble in water (8.8 g / 100 g (15 ° C.) with respect to water). 300
Pyrolysis ℃ or higher (chemically stable), with Na ²³ is a carrier, H, C, O are both extremely low thermal neutron absorption cross section. Na ₂ CO ₃ has a slightly strong basicity, and if it is a dilute solution, it is almost harmless to metal systems like NaHCO ₃ , has a large solubility in water, and is chemically stable. Na
OH has a very strong basicity, so if it is a dilute solution, NaHC
Similar to O _3, it is almost harmless to metallic materials, has a high solubility in water, and is chemically stable.

In this embodiment, remeasurement can be performed without removing the measurement solution injected into the pipe. Also,
When the measurement continues and the radiation background becomes high, re-measurement can be performed with high accuracy by replacing the nuclide with exactly the same principle.

Furthermore, in the above-mentioned embodiment, an example of application to equipment cooling pipes in a boiling water reactor has been described, but the present invention is not limited to this and can be applied to other plants and systems.

[0026]

As described above, according to the first aspect of the present invention.
According to the method, the radiation of specific energy of the radioactive isotope injected into the pipe to be measured is measured, and the first detector and the second detector are arranged in the vicinity of the pipe to be measured with a constant interval therebetween. And a first wave height analyzer and a second wave height analyzer which perform wave height analysis of these detection signals and take out only specific radiation energy, respectively.
By installing a processing unit that counts the signals from these first and second wave height analyzers and calculates the flow velocity and flow rate by a statistical method, a facility that requires maintenance such as a flow meter is incorporated. The flow rate and flow velocity can be measured non-destructively and easily by simple external equipment without lowering the strength of the piping system.

According to the second aspect, since the radioactive isotope according to the first aspect is sodium 24, the energy is high with gamma rays and the half-life is neither too short nor too long.

According to claim ₃ , since the compound containing sodium 24 as a radioactive isotope according to claim 2 is any one of NaHCO ₃ , Na ₂ CO ₃ and NaOH, the chemical property is stable. , Does not corrode metal. It dissolves easily in the fluid of the piping system, does not deteriorate due to heat, pressure, or radiation, and does not absorb neutrons if it remains.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an in-pipe flow velocity / flow rate measuring device according to the present invention.

FIG. 2 is a timing chart showing an input signal to the arithmetic processing device of FIG.

FIG. 3 is an explanatory diagram for calculating a measurement center.

FIG. 4 is a diagram showing a signal actually obtained from the upstream side wave height analyzer or the downstream side wave height analyzer of FIG. 1;

[Explanation of symbols]

 1 Pipe to be measured 2 Heat load 3 Flow rate adjusting valve 4 Measurement solution inlet 5 Injection stop valve 11 Upstream detector (first detector) 12 Downstream detector (second detector) 13 Upstream wave height analysis Device (first wave height analyzer) 14 downstream wave height analyzer (second wave height analyzer) 15 arithmetic processing device 16 flow velocity flow rate output device

Claims (3)

[Claims] 1. A method for measuring radiation of a specific energy of a radioactive isotope injected into a pipe to be measured,
A first detector and a second detector, which are arranged in the vicinity of the pipe to be measured with a constant interval from each other, and a first wave height analysis which performs wave height analysis of these detection signals and extracts only specific radiation energy, respectively. And a second wave height analyzer, and an arithmetic processing unit that counts signals from the first and second wave height analyzers and calculates the flow velocity and flow rate by a statistical method. Flow velocity and flow measurement device. 2. The radioactive isotope is sodium 24
The pipe flow velocity / flow rate measuring device according to claim 1, wherein 3. A compound containing sodium 24 as a radioactive isotope is NaHCO ₃ , Na ₂ CO.
_3. The pipe flow velocity and flow rate measuring device according to claim 2, wherein the device is either ₃ or NaOH.