JPH07119563B2 - Plenum length measuring device for nuclear fuel rods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" The present invention relates to the length of a plenum portion of a nuclear fuel rod for a nuclear reactor, which is accommodated in a reactor core, in which a coil spring is accommodated.
The present invention relates to a plenum length measuring device for nondestructive measurement from the outside of a nuclear fuel rod.

"Prior Art" Fig. 3 shows an example of nuclear fuel rods housed inside the core of a PWR (pressurized water reactor), which is a type of nuclear reactor for power generation. This nuclear fuel rod A includes a hollow rod-shaped fuel cladding tube 1,
A plurality of uranium dioxide fuel pellets 2 filled in the inside, and a coil spring 3 for pressing the fuel pellets 2,
It is mainly composed of an upper end plug 4 and a lower end plug 5 for sealing both ends of the fuel cladding tube 1. The fuel cladding tube 1 and the end plugs 4 and 5 are made of Zircaloy-4 alloy material, and the coil spring 3 is made of stainless steel material. The coil spring 3 is provided between the upper end plug 4 and the fuel pellet 2. The coil spring 3 is provided inside the fuel cladding tube 1 so as to press the fuel pellet 2 and prevent its movement. The purpose is to prevent the unnecessary pressure from being applied to the fuel cladding tube 1 and the end plugs 4 and 5 due to the influence of the fission product gas released from the fuel pellet 2 and the thermal expansion of the fuel pellet 2, This is due to the purpose of forming P).

[Problems to be Solved by the Invention] By the way, in the final stage of the manufacturing process of the nuclear fuel rod A described above, the length dimension of the plenum P, that is, the plenum length PL shown in FIG. It has to be inspected whether or not there are formed. Therefore, conventionally, the plenum length PL of the nuclear fuel rod A was measured by an X-ray fluoroscope. That is, the transmission image of the plenum P of the nuclear fuel rod A is projected on the fluorescent screen by the X-ray fluoroscope, the transmission image projected on the fluorescent plate is captured by the television camera, and the video signal output from the television camera is subjected to image processing. Processed by the device, which results in fuel pellets 2
The plenum length PL by detecting the position of the boundary between the coil spring 3 and
Was being measured. However, in the above-described conventional apparatus for measuring the plenum length PL, since an X-ray fluoroscopic apparatus is used, shielding is required for radiation protection, the apparatus becomes bulky, and an image processing apparatus is also required. Therefore, there is a drawback that the entire apparatus becomes expensive. Furthermore, in order to capture a stable image of a part of the plenum P, the nuclear fuel rod A must be kept stationary, and there is also the time required for image processing, so it takes time before the measurement results are obtained. there were.

On the other hand, in Japanese Patent Laid-Open No. 56-55801, a detection unit composed of a magnetic sensor and a permanent magnet for bias is moved on the surface of an object to be inspected to detect a change in output value of the magnetic sensor, With this, a technique for measuring the position of the shape change portion inside the inspection object has been proposed.

However, this technique has a problem in that the surface of the object to be measured may be damaged because the detection unit has to be moved in contact with the surface of the object to be measured.

And such a defect is an important matter that must be avoided especially in the above-mentioned nuclear fuel rod.

The present invention has been made in view of the above-mentioned circumstances, and by incorporating it into the transport path of a nuclear fuel rod, the plenum length of the nuclear fuel rod can be measured at high speed and continuously.
An object of the present invention is to provide a plenum length measuring device which can be detected in a non-contact state and which can be further downsized and inexpensive.

"Means for Solving Problems" The present invention provides a self-comparison coil which is provided in a transport path for transporting nuclear fuel rods and through which the nuclear fuel rods penetrate, and an AC voltage of a predetermined frequency is supplied to the self-comparison coil. At the same time, the electromagnetic induction measurement for measuring the impedance change of the self-comparison type coil caused by the change of the effective magnetic permeability when the nuclear fuel rod penetrates the self-comparison type coil, and outputting the voltage corresponding to the measurement result. And a peak of the output voltage from the electromagnetic induction measuring means corresponding to the impedance change of the self-comparison coil due to the fact that the boundary between the plenum portion of the nuclear fuel rod and the fuel pellet filling portion reaches inside the self-comparison coil. Peak detecting means for detecting
At the time when the peak detection means detects the peak, the tip position measuring means is arranged at a predetermined distance from the self-comparison type coil in the moving direction of the nuclear fuel rod and measures the position of the end face of the nuclear fuel rod. And a calculating means for calculating the length of the plenum portion based on the position information supplied from the tip position detecting means.

"Operation" When an AC voltage of a predetermined frequency is supplied to the self-comparison coil provided in the transport path of the nuclear fuel rods to pass the nuclear fuel rods,
The effective permeability differs depending on the difference in the internal structure and material of the nuclear fuel rods. Therefore, the effective permeability differs between the plenum part where the coil spring is housed and the fuel pellet filling part, and the self-comparison that accompanies this effective permeability change. The impedance change of the die coil is measured by the electromagnetic induction measuring means,
The voltage corresponding to the measurement result is output. Then, the peak of the output voltage from the electromagnetic induction measuring means corresponding to the impedance change of the self-comparison coil due to the boundary between the plenum portion of the nuclear fuel rod and the fuel pellet filling portion reaching inside the self-comparison coil is At the time point detected by the peak detecting means, the calculating means calculates the length of the plenum portion based on the position information of the end face position of the tip portion of the nuclear fuel rod supplied from the tip position detecting means.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

In the figure, reference numerals 6 and 6 denote transport rollers which are provided along the transport path and are rotatably supported by horizontal shafts 6a and 6a, respectively. The loaded nuclear fuel rod A is conveyed in the direction of arrow F. Reference numeral 7 denotes a cylindrical coil portion provided on the conveyance path, and is arranged so that the nuclear fuel rod A moving on the conveyance roller 6 penetrates through it. This coil portion 7 is an inspection coil 7a
And a comparison coil 7b are integrated into a self-comparison type coil, and this coil portion 7 is connected to an electromagnetic induction measuring circuit 8. The electromagnetic induction measuring circuit 8 is composed of an oscillating circuit for supplying a high frequency voltage of 5 to 8 kHz to the coil section 7, a detecting circuit for detecting a change in impedance of the coil section 7, and the like. The detection signal S corresponding to the material is output. That is, since the effective permeability differs between the plenum P portion of the nuclear fuel rod A and the portion filled with the pellets 2, the impedance of the coil portion 7 changes, and this impedance change is converted into a voltage signal by the electromagnetic induction measuring circuit 8. It is output as the detection signal S.

Here, as shown in FIG. 2A, when the nuclear fuel rod A is moved in the direction of the arrow F and inserted into the central portion of the coil portion 7, the detection signal S output from the electromagnetic induction measuring circuit 8 is output. Changes as shown in FIG. That is, the detection signal S has a voltage of 0 when the tip of the nuclear fuel rod A is not inserted in the coil portion 7, and when the boundary portion A ₁ between the upper end plug 4 and the coil spring 3 reaches the coil portion 7, ,
The voltage drastically decreases from 0 to −V _1, and when the plenum portion PA reaches the coil portion 7, the voltage rises to 0, and the coil portion 7 further includes the coil spring 3 and the pellet 2.
At the time point when the boundary A ₂ of A reaches, the voltage sharply rises to the voltage V ₂ . The voltage becomes 0 when the coil portion 7 is located in the pellet filling portion PB. in this case,
The inspection coil 7a and the comparison coil are located at the boundaries A ₁ and A _2.
When the middle of 7b coincides, the voltage of the detection signal S becomes the highest and appears as a peak.

The detection signal S output from the electromagnetic induction measurement circuit 8 is supplied to the positive peak voltage detection circuit 9, and when the peak voltage is supplied, the boundary detection signal KS of "H" level is supplied to the arithmetic processing unit 11. It The electromagnetic induction measurement circuit 8 and the positive peak voltage detection circuit 9 constitute a boundary detection circuit 10. In this case, when the boundary detection signal KS output from the positive peak voltage detection circuit 9 reaches the coil portion 7 at the boundary portion A ₁ between the end plug 4 and the coil spring 3 as shown in FIG. Does not output, but remains at the “L” level, and when the boundary portion A ₂ between the coil spring 3 and the pellet 2 reaches, the “H” level boundary detection signal KS is output. Therefore, when the boundary detection signal KS rises, the boundary A ₂ between the plenum portion PA of the nuclear fuel rod A and the pellet filling portion PB is detected.

On the other hand, 12 and 13 are a floodlight and a line sensor which are arranged so as to face each other so as to sandwich the nuclear fuel rod A moving on the transport roller 6, and the center C of the projector and the line sensor is located from the position where the coil portion 7 is arranged to the nuclear fuel rod A. In the moving direction, the reference dimension PL and the length TL of the end plug 4 are separated from each other by a total dimension L (see FIG. 2A). The line sensor 13 is driven by the drive signal supplied from the line sensor control circuit 14,
A scan is performed along the moving direction of the nuclear fuel rod A, and a bright / dark signal obtained by this scan is supplied to the tip position measuring circuit 15 via the line sensor control circuit 14. That is, the line sensor control circuit 14 outputs the dark signal in the period in which the light emitted from the projector 12 is blocked by the nuclear fuel rods A and in the period in which it is not blocked each time the line sensor 13 scans once. Is a bright signal at the tip position measurement circuit 15
Supply to. The tip position measuring circuit 15 measures the position of the tip of the nuclear fuel rod A based on the light / dark signal supplied from the line sensor control circuit 14.
A counter that mainly counts the period during which the dark signal is supplied is configured for each scanning period, and the measurement result is supplied to the arithmetic processing unit 11 as position data D. The arithmetic processing unit 11 includes a CPU (central processing unit) and a ROM (read only memory) in which a program used in this CPU is stored.
And a RAM (random access memory) for temporarily storing data, an input / output interface, and the like. At the time when the boundary detection signal KS of “H” level supplied from the boundary detection circuit 10 is supplied, Based on the position data D supplied from the position measurement circuit 15, the plenum length
PL is calculated, and it is determined whether the calculated plenum length PL is a reference length. Further, 16 is a display device for displaying the determination result of the plenum length PL determined by the arithmetic processing device 11, and 17 is a printer for printing the determination result of the plenum length PL.

In the above configuration, when the nuclear fuel rod A moves on the conveying roller 6 in the direction of arrow F shown in FIG. 1 and the boundary portion A ₂ between the coil spring 3 and the pellet 2 reaches the coil portion 7, the boundary detection circuit 10 outputs “ The H "level boundary detection signal KS is output, and at the time when the" H "level boundary detection signal KS is output, the arithmetic processing circuit 11 outputs the plenum based on the position data D supplied from the tip position measuring circuit 15. The length PL is calculated, it is determined whether or not the calculated plenum length PL is a regular length, and the determination result is displayed on the display device 16 and printed by the printer 17. Such an operation is continuously performed every time the nuclear fuel rod A passes through the place where the coil portion 7 and the line sensor 13 are installed.

Although the self-comparison type coil is used in the above-described embodiment, the present invention is not limited to this, and a separate type coil may be used to form a similar device.

[Advantages of the Invention] As described above, according to the present invention, a self-comparison coil through which a nuclear fuel rod penetrates is provided in a transport path for transporting a nuclear fuel rod, and the self-comparison coil extends in the moving direction of the nuclear fuel rod. A tip position measuring means for measuring the position of the tip end face of the nuclear fuel rod is provided at a position separated by a predetermined distance, and an AC voltage of a predetermined frequency is supplied to the coil to pass through the nuclear fuel rod. The impedance change of the coil due to the change of is measured by the electromagnetic induction measuring means, and the voltage corresponding to the measurement result is output. Then, the peak of the output voltage from the electromagnetic induction measuring means corresponding to the impedance change of the self-comparison coil due to the boundary between the plenum portion of the nuclear fuel rod and the fuel pellet filling portion reaching inside the self-comparison coil is At the time of detection, since the length of the plenum portion is calculated based on the position information of the end face position of the tip of the nuclear fuel rod supplied from the tip position detecting means, the nuclear fuel rod moving along the transport path is calculated. The plenum length can be measured at high speed and continuously, and the entire apparatus can be made compact and inexpensive as compared with the one using the conventional X-ray fluoroscopic apparatus, and since X-rays are not used. The safety is ensured and the measurement operation can be performed in a non-contact state with respect to the nuclear fuel rods, so that the effect of not damaging the nuclear fuel rods can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention,
FIG. 2 is a diagram for explaining the operation of the embodiment, and FIG. 2 (a) is a diagram for explaining the positional relationship between the nuclear fuel rod A and the coil portion 7, FIGS. 2 (b) and (b). C) is nuclear fuel rod A
And a graph showing changes in the detection signal S and the boundary detection signal KS with changes in the relative position of the coil portion 7, and FIG. 3 is a cross-sectional view showing one structural example of a nuclear fuel rod. 1 ... Fuel cladding tube, 2 ... Pellet, 3 ... Coil spring, 4 ... Upper end plug (end end plug), A ... Nuclear fuel rod, PA ... Plenum part, PB ... Pellet filling part, P
…… Plenum, PL …… Plenum length, A ₂ …… Coil spring 3
And pellet 2 boundary, 6 ... conveying roller, 7 ... coil part, 7a ... inspection coil, 7b ... comparison coil, 8 ... electromagnetic induction measurement circuit, 9 ... positive peak voltage detection circuit, 10 ... …
Boundary detection circuit, 11 ... Arithmetic processing unit, 12 ... Emitter, 13
...... Line sensor, 14 ...... Line sensor control circuit, 15 ...
... Tip position measurement circuit.

Claims (1)

[Claims] 1. A fuel cladding tube filled with fuel pellets,
The coil spring of the nuclear fuel rod is composed of an end plug for sealing the tip and the base end of the fuel cladding tube, and a coil spring provided between the end plug of the fuel cladding tube and the fuel pellet. In a plenum length measuring device for measuring a length of a stored plenum portion, a self-comparison coil which is provided in a transport path for transporting the nuclear fuel rods, and through which the nuclear fuel rods penetrate, and a predetermined frequency of the self-comparison coil. While supplying an AC voltage, measuring the impedance change of the self-comparison coil caused by the change in effective permeability when the nuclear fuel rod penetrates the self-comparison coil,
Corresponding to the impedance change of the self-comparison coil due to the boundary between the plenum portion and the fuel pellet filling portion of the nuclear fuel rod reaching the inside of the self-comparison coil, the electromagnetic induction measuring means outputting a voltage corresponding to the measurement result. The peak detection means for detecting the peak of the output voltage from the electromagnetic induction measuring means and the self-comparison type coil are arranged at a predetermined distance in the moving direction of the nuclear fuel rod, and the position of the end face of the nuclear fuel rod is set. A tip position measuring means for measuring; and a computing means for calculating the length of the plenum portion based on the position information supplied from the tip position detecting means when the peak detecting means detects the peak. Plenum length measuring device for nuclear fuel rods.