JPS62245910A - Method and device for measuring length of radioactive member - Google Patents

Abstract

PURPOSE:To measure the length of a radioactive member with high efficiency and high accuracy by supporting the radioactive member vertically in water, irradiating its upper and lower end parts with ultrasonic waves slantingly from above and below, and detecting their reflected waves. CONSTITUTION:A used fuel assembly 1 is conveyed underwater to a fuel storage pool 11 by the crane, etc., of a nuclear fuel replacing device. This assembly 1 is suspended by a supporting device 13 and held vertically. Then, a couple of upper and lower ultrasonic sensors 20 and 21 fitted to a frame 15 slantingly upward and downward emit ultrasonic output waves to the nuclear fuel channel 5 of the assembly 1. End part echoes are received from the upper and lower end parts of the channel 5, their positions are detected by sensors 20 and 21, and an arithmetic processor 19 finds the length of the channel 5 based on the result.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method and apparatus for measuring the length of a radioactive member, for example, for measuring the total length of a fuel channel of a boiling water reactor in water or the like. In particular, the present invention relates to a method and apparatus for measuring the length of a radioactive member suitable for precision measurement by remote control.

(Prior Art) FIG. 8 shows the configuration of a fuel assembly loaded into the core of a boiling water reactor as an example of a radioactive member.

A fuel assembly 1 has a large number of fuel rods 2 connected to an upper tie plate 3.
It is fixed by a lower tie plate 4, and a fuel channel 5 is attached to the outer circumferential side thereof. The fuel channels 5 of the fuel assembly 1 and the fuel wave iI tubes 2a of the fuel rods 2 are made of zirconium alloy, etc., and these grow in the axial direction due to irradiation with fast neutrons during the operation of the reactor. It is known.

Generally, the upper end of the fuel channel 5 is fixed to the upper tie plate 3 by a channel fastener 6, and the lower end is fitted into the lower tie plate 4. The depth of engagement between the fuel channel 5 and the lower tie plate 4 is set to an appropriate value that allows automatic disassembly by mechanical operation during cleaning after use.

In the fuel assembly 1 having such a configuration, when initially loaded, even if the fuel channel 5 expands due to irradiation growth, the total length of the fuel cladding tube 2a also increases at the same time. The fitting margin Z with the tie plate 4 does not change significantly.

However, in the case where the fuel channel 5 is once used and then used again in combination with a new fuel rod 2 in order to improve usage efficiency, the elongation of the fuel cladding tube 2a due to the irradiation growth of the new fuel rod 2 is Therefore, the fuel channel 5 may be greatly elongated due to the second irradiation growth. In such a case, the fitting margin 2 with the lower tie plate 4 becomes smaller,
The two may interfere and become stuck, which may limit the lifespan of the fuel channel 5.

Therefore, in such a case, before reattaching the fuel channel 5 to the new fuel rod 2, it is recommended to measure the total length of the fuel channel 5 and confirm that it is long enough to prevent interference. It is thought that this problem can be easily avoided. In addition, even if excessive irradiation growth occurs in the fuel cladding tube 2a and the total length of the fuel assembly 1 changes significantly, other Ia
Measuring the length of the fuel assembly 1 itself can also be an important technical issue since problems arise in connection with the fuel assembly 1. Also,
When measuring the total length of the irradiated fuel channel 5 or fuel cladding tube 2a, it is generally recommended to measure the irradiated components in a radiation-shielded area, such as within a fuel storage pool, from the standpoint of radiation exposure protection. It is true.

Conventionally, when performing such length measurements, it has been considered to apply a scale to the object to be measured underwater and read the dimensions directly with a television camera.

(Problems to be Solved by the Invention) Various types of equipment are installed in, for example, a fuel storage pool, and it is difficult to specifically provide a large space for length measurement. For this reason, methods that use television cameras and the like are complicated to operate and cannot be measured efficiently.
It is relatively difficult to perform high-precision measurements quickly.

The present invention has been made in view of these circumstances, and provides a method for measuring the length of a radioactive member that can efficiently and accurately measure the length of a radioactive member without requiring a large work space. The purpose is to provide such equipment.

(Structure of the Invention) (Means for Solving the Problems) A method for measuring the length of a radioactive member according to the present invention is to support the radioactive member vertically in water, and to diagonally support the radioactive member in water. By applying ultrasonic waves from above and diagonally downward and detecting the reflected waves, the diagonal distance from each ultrasonic oscillation position to the upper and lower ends of the radioactive member is determined, and each distance is calculated as the vertical distance. It is characterized in that the length of the radioactive member is measured by converting the respective vertical distances into , and subtracting the sum of the vertical distances from the preset vertical relative distance between each ultrasonic oscillation position.

Moreover, the radioactive member length measuring device according to the present invention includes a support device that supports the radioactive member vertically in water, and a support device that faces the upper end and the lower end of the supported radioactive member from diagonally above and diagonally below, respectively. a pair of upper and lower ultrasonic sensors provided at The diagonal distance from each sensor to the upper and lower ends of the radioactive member is determined based on the output signals from the device and the signal processing device, and the multi-values are converted to a vertical distance, and the sum of the vertical distances is calculated. and an arithmetic device that calculates the length of the radioactive member by subtracting it from a preset vertical relative distance between each sensor.

(Function) By detecting the positions of the upper and lower ends of the radioactive member using an ultrasonic sensor and calculating based on the distance between the ultrasonic sensors, the total length of the radioactive member can be determined at a distance wA while attached to the fuel assembly. It can be easily measured by operation and at a high degree of precision.

In addition, the device structure is relatively simple as it does not have any complicated moving parts, and the ultrasonic sensor is installed at an angle, which reduces the width and creates an elongated structure. Therefore, the space within the fuel pool can be used effectively. The operation can be performed efficiently in short bursts using, for example, an existing fuel exchanger, and is also effective for large-scale measurements.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 7.

This embodiment is for measuring the length of a fuel channel in a fuel assembly of a boiling water reactor once subjected to combustion.

The structure of the fuel assembly and its fuel channel is the same as that shown in FIG. 8, so the corresponding parts in the figure are given the same reference numerals as in FIG. 8, and the explanation thereof will be omitted.

First, the configuration of the measuring device will be explained.

FIG. 1 shows a schematic configuration of the entire device, and FIG. 2 shows a detailed arrangement of the main parts of the device.

In FIG. 1, reference numeral 11 denotes a fuel storage boule provided in the upper part of the reactor building, in which a spent fuel storage rack (not shown) and the like are installed, as well as containing boule water 12 for radiation shielding. A support device 13 for supporting the fuel channel 5 is provided at the bottom of one side of the fuel storage boul 11.

The support device 13 includes a lower support stand 14 that supports the lower end of the fuel assembly 1 , a columnar frame 15 erected on the lower support stand 14 , and a columnar frame 15 that projects from the frame 15 and supports the upper end of the fuel assembly 1 . The upper support 16 supports the vicinity of the upper part. The lower support stand 14 is placed on the bottom of the fuel storage boule 11, and has a spherical recess 17 on its upper surface into which the lower tie plate 4 of the fuel assembly 1 is fitted, as shown in FIG. This recess 17 determines the horizontal position of the fuel assembly 1. Further, the upper nabot 16 has a frame shape that opens in the vertical direction, and the fuel channel 5 portion of the fuel assembly 1 can be inserted into and removed from above from above. The center line of the opening of the upper support 16 and the center line of the recess 17 of the lower support base 14 are aligned on a vertical line.

Thereby, the fuel channel 5 is held vertically by the upper support 16 and the lower support 14. Further, the upper support 16 has a height that supports a portion lower than the upper end of the fuel channel 5, so that the upper end edge of the fuel channel 5 is exposed in the water.

On the other hand, an ultrasonic position detector 18 and an arithmetic processing unit 19 are provided as means for measuring the length of the fuel channel 5.

The ultrasonic position detector 18 is connected to a pair of upper and lower ultrasonic sensors 20 and 21 attached to the frame 15 and connected to the outside of the fuel storage boule 11! ! It consists of a signal processing device 22 whose position is shifted between lt. Note that the arithmetic processing unit 19 is also placed outside the fuel storage boule 11 at a separate position.

The upper ultrasonic sensor (hereinafter referred to as upper sensor) 20 is attached to the upper part of the frame 15 so as to be inclined downward.

The sensor mounting angle, that is, the intersection angle θ1 of the upper sensor 20 with respect to the vertical plane is set to a constant angle in the range of 10 to 40'. Thereby, an ultrasonic output wave is oscillated from an oblique direction to the upper edge portion 5a of the fuel channel 5 supported by the support device 13, and an end echo from the upper edge portion 5a is received.

In addition, the lower ultrasonic sensor (hereinafter referred to as the lower sensor)
21 is attached to the lower part of the frame 15 so as to be inclined upward. The sensor installation angle of the lower sensor 21, that is, the intersection angle θ2 with the vertical plane is also set within the range of 10 to 40 degrees, and the ultrasonic output wave is oscillated from an oblique direction to the lower end portion 5b of the fuel channel 5, and the ultrasonic output wave is The end echo from the end face 5b is received.

FIG. 3 shows a system configuration of the signal processing device 22 and the arithmetic processing device 19.

As shown in FIG. 3, the signal processing device 22 includes an ultrasonic detection circuit 23 and a signal processing circuit 24.

The ultrasonic detection circuit 23 controls the intensity of the ultrasonic output waves oscillated by the upper and lower sensors 20 and 21, and furthermore,
Ultrasonic signal 101.1 received by lower sensors 20, 21
02 and outputs detection signals 103 and 104 based on it to the signal processing circuit 24. The signal processing circuit 24 includes, for example, an AD conversion circuit, performs waveform processing on the detection signals 103 and 104, and outputs device detection signals 105 and 106 to the arithmetic processing unit 19.

The arithmetic processing device 19 includes an arithmetic processing circuit 25, a storage device 26,
The configuration includes a printer 27, a CRT 28, a keyboard 29, and the like. For example, the sensor 20 is stored in the storage device 26.
．． 21, etc. are stored. The arithmetic processing circuit 25 calculates the length of the fuel channel 5 based on the device detection signals 105 and 106 configured from the signal processing device 22 and the data signal 107 output from the storage device 26. Arithmetic processing signal 108
．． 109 is output to the printer 27 and CRT 28.

Next, the measurement method will be explained.

First, the spent fuel assembly 1 is transported underwater to the fuel storage boule 11 by a crane or the like of a fuel exchange device (not shown).

As shown in FIG. 1, this fuel assembly 1 is suspended from a support device 13 and held vertically.

As described above, the fuel channel 5, which is a length measurement object attached to the fuel assembly 1, has its upper and lower ends exposed. Therefore, this fuel channel 5
The positions of the upper and lower ends of the fuel channel 5 are detected by the upper and lower sensors 20, 21, and the length of the fuel channel 5 is determined by the arithmetic processing unit 19 based on the results.

The measurement concept will be explained with reference to FIG.

Assuming that the length of the fuel channel 5 is 1, this length l is calculated from the relative distance between the centers of the upper and lower sensors 20 and 21.
This is the value obtained by subtracting the sum of the vertical distances 111Y and Y2 between the lower sensors 20 and 21 and the upper and lower end portions of the fuel channel 5. Therefore, the following formula (1) holds true.

ノ=L−(Y+Y2) ・・・・・・(
1) Note that the value of L is stored in the storage device 26 as described above.

On the other hand, if the absolute distance in the diagonal direction between the upper sensor 20 and the upper end of the fuel channel 5 is 81, then Yl is as follows (2
) is obtained by the formula.

Yl-81cosθ1 ・・・・・・(2
) Similarly, if the absolute distance in the diagonal direction between the lower sensor 21 and the lower end of the fuel channel 5 is 82, then Y2 is determined by the following equation (3).

Y 2- S 2 CO2O3 (3) Note that the values of cos θ and cos θ2 are also stored in the storage device 26.

FIG. 4 shows in detail how the upper sensor 20 detects Sl. Assume that the fuel channel 5 is now in the state shown by the solid line in FIG. In this state, the ultrasonic waves emitted from the upper sensor 20 are reflected by the upper edge portion 5a of the fuel channel 5, as indicated by the arrow W. Take the reflection path shown by . This reflection path W. A reflected wave along the line, ie, an edge echo, is detected by the upper sensor 20 along with the output wave. The waveform at this time is shown in FIG. Note that since the peak value of the reflected wave is smaller than the peak value of the output wave, the sensitivity of the ultrasonic detection circuit 23 must be made sufficiently high in this case. 81 as shown below (
4) It is determined by the formula.

s = v −to ・・・・・・(
4) This obtained Sl is input as the calculation element of the above equation (2).

In addition, regarding the mounting angle of the upper sensor 20, θ1-45°
When we set it up nearby and conducted an experiment, we found that it was affected by surface waves.
It was observed that the edge echo was disturbed. As mentioned above, it was found that good end echoes appeared in the range of θ=10'' to 40°.

By the way, if the effective diameter of the upper sensor 20 is Dl, then the upper end edge portion 5 of the fuel channel 5 whose axial length changes.
The measurable range for a is this Dl and the mounting angle θ1
It will be determined by. Therefore, regarding the above device configuration, the measurement range of the upper edge portion of the fuel channel 5 is determined in consideration of the dimensional tolerance of the fuel assembly 1 and the maximum elongation due to irradiation growth of the fuel channel 5, and according to this, D , θ1 Select.

Also, interference between the fuel channel 5 and the upper sensor 20 can be prevented by a.
The outer peripheral surface of the fuel channel 5 and the upper sensor 2
Determine the distance x 1 between the 0° tip edge and set the sensor mounting position.

In the above example, 81 was measured at the center of the sensor using the upper hinge 20 installed in a predetermined position. 81 measurements are often taken at off-center positions.

That is, let us now consider a case where the upper end of the fuel channel 5 has been extended to the position shown by the imaginary line in FIG. 4 due to irradiation growth.

In this case, the path of the ultrasonic wave deviates from the center of the sensor by a certain amount in the vertical direction as shown by the arrow W1, so it is necessary to input this δ to the arithmetic processing unit 25 as a correction value.

FIG. 6 shows the relationship between the displacement Δy of the end of the fuel channel 5 based on the output value of the upper sensor 20 and the actual value Δy' measured by a micrometer. Δy like this
The difference δ between and Δy' is input as a correction value. In addition, ff
! As shown in FIG. 6, if the path of the ultrasonic wave deviates, the sound pressure level etc. will change, and δ will also change slightly, so it is necessary to find this value empirically.

FIG. 7 shows the detection action of S2 by the lower sensor 21 in detail. This is substantially the same as the detection of Sl by the upper sensor 20, except that the ultrasonic wave is reflected by the lower end surface 5b of the fuel channel 5 and the outer peripheral surface of the lower tie plate 4. That is, the path of the ultrasonic wave becomes as shown by W or W4.

In this case, even if the path of the ultrasonic wave changes, the reflection time via the lower end surface of the fuel channel 5 is always constant.
The diagonal distance measured by the edge echo is always 8
It becomes 2. Furthermore, since the reflected wave intensity is large, the sensor output is controlled to be smaller than in the case of the upper sensor 20. Regarding the edge echo detection by the lower sensor 21,
It has been found that it is most preferable for the sensor mounting angle θ2 to be in the range of 10° to 40°. Note that D2 in the figure indicates the sensor effective diameter.

Based on S and S2 detected as described above, the calculations of equations (1), <2), and (3) are performed to determine the length l of the fuel channel 5, and the output signal 108. 1
09 is input to the printer 27 or CRT 28 or the like.

According to the embodiments described above, the positions of the upper and lower ends of the fuel channel 5 are detected by the ultrasonic sensors 20 and 21, and the distance between the ultrasonic sensors 20 and 21 is calculated as a reference. The total length of the fuel assembly 1 can be easily and accurately measured by remote control while attached to the fuel assembly 1.

In addition, the device configuration is relatively simple as it does not have complicated moving parts, and since the ultrasonic sensors 20 and 21 are arranged at an angle, the width dimension is small and the cable is long. , the space within the fuel boule 11 can be used effectively. Further, the operation can be performed efficiently in a short time using, for example, an existing fuel exchanger, and it is also effective for large-volume measurements. Furthermore, maintenance is easy and effective in reducing radiation exposure.

Especially regarding measurement accuracy, high accuracy (for example, total length 424
±1# for 0IIIM measurement! It was confirmed that 1 or less) was obtained.

In the above embodiments, the present invention was applied to the measurement of fuel channels, but it goes without saying that the present invention can be widely applied to the measurement of various radioactive members as long as the ends have sharp edges or reflective surfaces.

〔Effect of the invention〕

As described above, according to the method and device for measuring the length of a radioactive member according to the present invention, the length of a long radioactive member can be efficiently measured without requiring a large work space.
And it can be done with high precision.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is an enlarged view of the main parts of FIG. 1, and FIG. 3 is a block diagram showing the circuit configuration of the device shown in FIG. 1. , FIG. 4 is a diagram showing the measurement method using the upper sensor, FIG. 5 is a diagram showing the ultrasonic waveform, FIG. 6 is a graph showing the correction value, and FIG. 7 is a diagram showing the measurement method using the lower sensor. FIG. 8 is a side view showing a partial cross section of the object to be measured. 5...Fuel channel, 11...Fuel storage pool,
13... Support device, 19... Arithmetic processing device, 20.
21... Ultrasonic sensor, 22... Signal processing device. Applicant's agent Hisashi Hatano Figure 1 Figure 2 Figure 3 Figure 4 Figure 7 o1020 (mm) Travel amount calculated from sen + j output value Δy Figure 6

Claims (1)

[Claims] 1. A method for measuring the length of a long radioactive member under a radiation-shielded state by immersing it in water, the method comprising: supporting the radioactive member vertically in water; Ultrasonic waves are applied to the lower end from diagonally above and diagonally from below, and the reflected waves are detected to determine the diagonal distance from each ultrasonic oscillation position to the upper and lower ends of the radioactive member, and calculate each distance. By converting each into a vertical distance, and subtracting the sum of the vertical distances from the vertical relative distance between each ultrasonic oscillation position set in advance,
A method for measuring the length of a radioactive member, comprising measuring the length of the radioactive member. 2. A support device that supports a radioactive member vertically in water; a pair of upper and lower ultrasonic sensors provided on the upper and lower ends of the supported radioactive member, respectively, facing each other from diagonally above and below; A signal processing device that is connected to each ultrasonic sensor and is provided at a position separated from the support device, and that controls the output waves of each of the sensors and performs signal processing of the reflected waves; Find the diagonal distance from each sensor to the top and bottom ends of the radioactive member, convert each value to a vertical distance, and calculate the sum of the vertical distances from the preset vertical relative distance between each sensor. 1. An apparatus for measuring the length of a radioactive member, comprising: an arithmetic processing device that calculates the length of the radioactive member by subtraction.