JPS58122404A - Measuring method of thickness of copper film on inside surface of clad pipe for nuclear fuel - Google Patents

Abstract

PURPOSE:To measure the thickness of copper films non-destructively and continuously in a short time by inserting insertion type eddy current measuring elements of a diameter smaller by a prescribed size than the inside diameter of a clad pipe for nuclear fuel and sweeping the measuring elements along the inside surface of the pipe while applying test frequencies in a prescribed range thereupon. CONSTITUTION:Two pieces of eddy current measuring elements 5 are inserted into a clad pipe for nuclear fuel of 12.5mm. outside diameter, 10.8mm. inside diameter and 4m length having no copper films on the inside surface, and the output terminals thereof are connected to the bridge circuit of an eddy current measuring device 1 so that the equil. thereof is taken. A clad pipe 2 for nuclear fuel provided with a copper film of 1-10mu thickness on the inside surface is fixed to a stand 3 by means of fixing jigs 4. One of the eddy current measuring elements in the clad pipe having no copper film is drawn out and is inserted into the pipe 2 having the copper film. Air pressure is applied thereto from a compressor 6 with a dryer 7 to feed the element up to the position of a stopper plate 8. This element 5 is drawn out by a sweeping device 9 at a prescribed speed until it comes to the position of a beam switch 10, whereby the pipe 2 is swept and the results are recorded with a recorder 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to measuring the thickness of a copper coating, and more particularly to a method and apparatus for measuring the thickness of a copper coating formed on the inner surface of a nuclear fuel cladding tube.

Traditionally, nuclear fuel cladding tubes are typically several meters long.

It is a long and narrow tube with a diameter of approximately 110 mm, and zirconium alloy is generally used as the material, and a satisfactory effect has been obtained. However, if the load fluctuation of the nuclear reactor in which it is used is large, 1.1 the zirconium alloy has a tendency to be affected by nuclear fission products and to cause stress corrosion. Therefore, special consideration was required to avoid sudden changes in the load on the F11 Song reactor. In order to solve this problem, a fluoronium oxide film was formed on the inner wall of the cladding tube made of silconi and ram alloy, and a copper film was further provided on top of it. The use of so-called copper barrier type cladding has been proposed. In other words, the copper coating in the copper barrier type rupture tube functions as a barrier against fission products. Therefore, the thicker the copper film, the better the barrier function. However, from the standpoint of operating efficiency of the nuclear reactor, since the neutron absorption cross-sectional area of copper material is large, it is better to have a smaller thickness.

A thickness of 5 μm is recommended as a compromise between these conflicting requirements, and if the thickness deviates from this value, the function as a barrier and the operating efficiency of the reactor will be greatly affected depending on the direction of the deviation. Therefore, this thickness must be controlled extremely accurately.

On the other hand, the thickness of the provided copper coating is measured by destroying the nuclear fuel cladding and using the 1 gravimetric method, the metallurgical method, or the electrochemical method, but these methods are not only destructive measurements but also This process takes time and is uneconomical.

On the other hand, fluorescent X-ray method and ultrasonic method are used as non-destructive measurement methods. Although the fluorescent X-ray method has good accuracy and is a measurement method that has become rapidly popular in recent years, there are many problems in its application to the inner surface of tubes. On the other hand, since the ultrasonic method uses reflected waves, it can be easily applied to the inner surface of a tube.

However, the accuracy of the results obtained using this method is problematic. In any case, these conventional non-destructive measurement methods cannot effectively measure a copper coating of about 5±1 mm on the inner surface of a nuclear fuel cladding tube.

An object of the present invention is to provide a method and apparatus for measuring the copper film thickness on the inner surface of a nuclear fuel cladding tube continuously in a short period of time by a non-destructive method.

According to the present invention, the eddy current method is applied to the thickness measurement of a copper coating formed on the inner surface of a nuclear fuel cladding tube having a length of several meters and an inner diameter of about 10 mm.

The eddy current method utilizes the fact that when a coil to which an alternating magnetic field is applied is brought close to metal, the impedance of the coil itself changes, and mainly utilizes the skin effect. In other words, the specific resistance ratio of copper and zirconium alloy is approximately 2.
5 = 1 and is relatively thick, and this difference makes it different from the case with copper coating.

This is based on the fact that the impedance of the coil is clearly different from that of the ruconium alloy alone, and that the change in impedance shows a clear correlation with the thickness of the copper coating under certain conditions. The present invention is configured as follows.

One of the specific conditions above is the test frequency. If this test frequency is too low, it will be strongly influenced by the underlying zirconium alloy, such as the wall thickness of the tube, thereby reducing measurement accuracy. On the other hand, if the test frequency is too high, linearity cannot be obtained in the relationship between the change in impedance and the thickness of the copper film. Therefore, the selection of this test frequency is important. That is, it is necessary to select a frequency that has good linearity for the copper coating thickness in question and that provides sufficient measurement accuracy even if the wall thickness of the zirconium alloy tube varies somewhat.

Another condition is the gap between the eddy current measuring element and the inner surface of the nuclear fuel cladding tube, especially when an internal hollow type eddy current measuring element is used. In other words, when sweeping a material using a probe, a certain amount of space is required between the probe and the inner surface of the tube, but this gap reduces noise, improves detection sensitivity, and reduces impedance changes and film lift. From the viewpoint of improving linearity of quantity, it is desirable that it be as small as possible.

These conditions can be determined empirically to some extent using the measurement target as a guide. For example, the zirconium alloy is Zircaloy-2, the length of the cladding tube is 4 meters, and the inner diameter is 10.
8 mm, and the thickness of the copper film is 6 to 7 μm,
The wall thickness tolerance of the cladding tube is ±0.08, and the required measurement accuracy is ±0.08.
When using a 0.2μ door, the test frequency is 100 to 1000.
KHz, the gap between the probe and the inner wall of the cladding tube is 0.2 to 0.7
It turns out that ynx is suitable.

These points will be made clear by the following examples shown in the drawings.

Example 1 Outer diameter 12.5 Ill Inner & 10.8 m, length 4 m
2 inserted into a nuclear fuel cladding tube that does not have a copper coating on its inner surface.
Connect the output terminals of the eddy current probes (5) to the eddy current measuring device (
Connect to the bridge circuit in 1) to maintain balance. Next, a nuclear fuel cladding tube (2) similar to the above with a copper coating of 1 μm to 10 μm thick on the inner side (1) is attached to a fixing jig (4) on a pedestal (3).
) to fix it.

Next, one of the eddy current probes in the nuclear fuel cladding tube that does not have the copper coating is taken out and inserted into the nuclear fuel cladding tube that has the copper coating, and air pressure is applied from the compressor (6) via the dryer (7). By doing so, it is fed to the position of the stop plate (8).

Next, this eddy current measuring element (5) is
Pull it out at a speed of WL/f+ until it reaches the beam switch (10) position, sweep the cladding tube, and record it on the recording device (10).
Record according to 1).

Table 1 shows the results of examining the linearity between the impedance change and the copper film thickness using the test frequency as a parameter in the above operation, along with the measurement accuracy when the wall thickness variation is ±0.0811.

Table 1 450~9 ±0.6 90 0~8 ±0.2 2700~8 ±0.2 5400~8 ±0.2 1080 0~7 ±0.2 2160, 0~5 ±0.1 or more From the results, it can be seen that the test frequency range with good linearity between 6 and 7 μm and good measurement accuracy is 100 to 1000 KHz.

Example 2 A copper film of 1 to 10 μm was formed on the inner surface of the nuclear fuel cladding tube with a gap of 0.1 to 0.5 between the measuring element (5) and measurements were carried out at a test frequency of 540 KHz using the same procedure as in Example 1. went. Table 2 shows whether the probe (5) can be transported and swept.

It shows the noise during sweeping, the sensitivity during measurement, that is, the amplitude per 1 μm of film, and the film thickness range showing linearity.

0.1 No ---〇, 2
Possible 0.05 10 0~8
0.3 Possible 0.05 10
0-80.4 Town 0.05
10 0~80.5 #
0.05 9 0~70.7
Town 0.06 8 0~71.0
Possible 0.11 5 0
~5 From the above results, it was determined that the gap is 0.2 to 0.7, which allows conveyance and sweeping, has low noise, and has good sensitivity and linearity in the range of copper coating thickness of 6 to 7 μm. Recognize.

As explained above, according to the present invention, the nuclear fuel cladding tube can be provided on the inner surface of the nuclear fuel cladding tube without destroying it.

The copper coating thickness in the range of 6 to 7 μm can be measured continuously in a short period of time, and work efficiency can be greatly improved.

Although the above description is limited to the measurement of the thickness of the copper coating, the present invention also makes it possible to detect defects in the copper coating and defects in the 0.zirconium oxide layer.

In other words, regarding defects in the copper film, copper is not partially deposited and the exposed defect surface of the underlying Zircaloy-2 is 0.
It is possible to detect the missing surface of the zirconium oxide layer to a minimum of 1 x m and about 2 mm.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus used to measure copper film thickness according to the present invention. l... Full current measuring device 2... Nuclear fuel cladding tube 3.
... Frame 4 ... Fixing jig 5 ... Eddy current probe 6
...Compressor 7...Dryer 8...Stop plate 9...Measure head sweep device 10...Beam switch 1
1...Recorder 12...Guide

Claims (1)

[Claims] An inner hollow type eddy current probe having an outer diameter 0.2 to 0.7 myx smaller than the inner diameter is placed inside a nuclear fuel cladding tube having a copper coating of 1.6 to 7 μm on the inner surface, and a 1.
The thickness of the copper coating on the inner surface of the nuclear fuel cladding tube is continuously measured by sweeping the measuring element along the inner surface of the cladding tube while supplying a test frequency in the range of 00 to 1000 KHz. Measuring method.