JPS59214794A - Method of measuring cladding thickness of composit type fuelcan - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a composite fuel cladding tube, and to a measurement method suitable for measuring the cut thickness in percent.

[Background of the invention]

Currently, the fuel cladding that houses the nuclear fuel in a nuclear reactor is (1)
Zirconium alloys are widely used because they are required to have excellent corrosion resistance, (2) good thermal conductivity, (3) high toughness and ductility, and (4) small neutron absorption cross section. There is.

However, although zirconium alloy cladding is an excellent cladding under steady-state conditions in a nuclear reactor, when rapid load-following operation is attempted, it suffers from corrosion due to iodine gas released from the fuel pellets and corrosion of the fuel pellets themselves. Stress corrosion cracking occurs due to the stress caused by the expansion of the steel, leading to damage.

In recent years, in order to prevent stress corrosion cracking, a composite type of storage in which a zirconium alloy cladding tube is entirely lined with a layer of pure zirconium has been developed (Japanese Patent Laid-Open Publication No. 54-59600).

The thickness of the pure zirconium layer is approximately 5 to 30 qb of the cladding tube wall thickness.
I'll go. Compared to zirconium alloys (for example, Zircaloy-2), pure zirconium maintains its softness during neutron irradiation, reduces local strain generated in the cladding, and has the effect of preventing stress corrosion cracking.

Since the cladding tube is manufactured into a small diameter and thin walled tube by hot extrusion, cold pressing, etc., the total wall thickness of the cladding tube can be made to the desired thickness. However, there is no guarantee that the extremely thin pure zirconium layer can be made to the desired thickness. Considering the reliability of fuel cladding tubes used in nuclear reactors, a technology that non-destructively measures the pure zirconium thickness over the entire length of all cladding tubes is essential.

However, the physical properties of zirconium alloy and pure zirconium are almost similar, and cannot be measured by conventional ultrasonic dimension measurement methods. Currently, measurements must be taken by cutting the end of the cladding tube and observing the entire cross section under a microscope, which is destructive and takes a lot of time.

[Purpose of the invention]

An object of the present invention is to provide a method for measuring the thickness of pure zirconium of a composite type stored material simply, accurately, and non-destructively.

[Summary of the invention]

FIG. 1 shows a cross-sectional view of the composite storage device. 1
is a zirconium alloy, and 2 is a pure zirconium layer. The present invention o1 Noting that there is a slight difference in the resistance ratio of pure zirconium and zirconium alloy at 1:2, we used the eddy current flaw detection method to apply a magnetic field fluctuation from the outside of the camphor tube to detect the eddy currents generated in the tube. This method measures the thickness of pure zirconium by detecting the size. The eddy current method utilizes the fact that when a coil applied with an alternating magnetic field is brought close to metal, the impedance of the coil itself changes. Widely used for thickness measurements, etc.

The present invention has devised the following when applying this eddy current method.

(1) Use a through-type coil to avoid scratching or contaminating the pure zirconium layer. Furthermore, by using a through-type coil, the thickness distribution in the length direction of the cladding tube can be continuously measured.

(2) The tube to be measured has a small diameter and a thin wall. In order to accurately measure the thickness of pure zirconium in a thin wall, a calibration curve within the wall thickness tolerance is provided so that it is not affected by the wall thickness.

(3) Since the difference in specific resistance between zirconium alloy and pure zirconium is small, select the entire test frequency range.

If the test frequency is too low, the measurement accuracy will be reduced due to the strong influence of wall thickness. If the thickness is too low, the linearity between the amount of change in impedance and the thickness is not good. As a result of studies conducted by the present inventors, it has been found that the test frequency range that can guarantee a measurement accuracy of ±5 μm at an eddy current penetration depth of 1 to 5 M is 5 to 130 KH2.

The calibration curve for the wall thickness change described in (2) above is obtained as follows. First, prepare the following test piece. The upper limit wall thickness (Tmax) and lower limit wall thickness (T
m1n)'lc, in which the thickness of each pure zirconium is changed in stages (for example, 30~
120 μm). Determine the amount of change in eddy current for each test piece under the same eddy current test conditions. Then, T shown in FIG.
A complete diagram of the relationship between the amount of change in eddy current and the thickness of pure zirconium with respect to max and Tm1n is prepared.

As a result, the eddy current change (jt) of the tube to be measured is measured, and a straight line shown in the same figure is drawn.@The point X indicating the pure zirconium thickness of the tube to be measured on the line is determined by the following formula.TX is the wall thickness of the tube to be measured, and is a value measured in advance by some method.

The thickness of pure zirconium is obtained by reading the thickness corresponding to the point X.

As described above, the present invention determines the thickness of pure zirconium on the inner circumferential surface of a composite fuel camphor tube using an eddy current coil installed on the outer circumferential surface.

The wall thickness of the cladding tube can be measured easily and accurately using conventional methods. Ultrasonic dimension measurement is the most preferred method for quickly measuring the entire length of the pipe.

Note that the pure zirconium thickness can also be measured using an interpolated coil or a globe-shaped coil, but this is inconvenient with respect to the above item (1).

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be explained. Zircaloy-2
A tube to be measured was prepared by lining the inner surface of the tube with a layer of pure zirconium. This cladding tube has an outer diameter of 12.27 mm and an inner diameter of 10 mm.
55 fermentation, wall thickness is 810±70μm.

First, the wall thickness of the tube to be measured was measured over the entire length using an ultrasonic dimension measuring device. Next, as shown in FIG.
was attached to the coil holder 4. The inner diameter of the coil holder 4 is 13.5 m.

As shown in FIG. 4, the coils 5 are self-comparison type through-hole coils, each having a coil winding width of 4 mm and a coil spacing of 2 m. The magnetic flux influence range of this is 12 to 15 mm wide.

In the measurement, the coil holder 4 was fixed and slid along the entire length of the tube 3 to be measured, and the amount of change in eddy current in the length direction (output was DC voltage) was recorded on a chart. The measuring box speed is 1.5-”/
s, and the measurement length was about 4 m.

The test frequency was 64KHz.

Figure 5 shows the suspended load and flow change h1 prepared in advance.
FIG. 2 is a diagram showing the relationship between wall thickness and pure zirconium thickness. Table 1 shows the measurement results of the pure zirconium thickness determined from the above relationship diagram. The pure zirconium jv thickness was 54 to 60 □m. After the measurement, the cross section of the same porcelain was polished and the thickness of pure zirconium was measured from a microscopic photograph. As a result, for each average value, the measured values of the present invention are in good agreement with an accuracy of ±5 μn1? Indicated.

〔Effect of the invention〕

As described above, according to the present invention, the thickness of pure zirconium can be easily determined.
Since measurements can be made with high accuracy, a nuclear fuel element can be obtained using a composite fuel cladding tube having a pure zirconium layer of a desired thickness, and a highly reliable nuclear fuel assembly can be obtained.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a composite fuel cladding tube, Figure 2 is an explanatory diagram of the method for determining the thickness of pure zirconium according to the present invention, and Figures 3 and 4 are eddy currents caused by the through-type coil of the present invention. FIG. 5, which is an explanatory diagram of the measurement method, is a diagram showing the relationship between the thickness of pure zirconium and the amount of change in eddy current in Examples. 1... Cladding tube made of Zircaloy-2 alloy, 2...
Pure zirconium layer. Diagram 2 Yahiso 1 Shitsutsunium R → Diagram 65 Yahizo 1 Conium Thickness μm

Claims (1)

[Claims] 1. A method for measuring the thickness of a pure zirconium layer of a composite fuel cladding tube in which a pure zirconium layer is provided on the inner circumferential surface of a cladding tube made of a zirconium alloy, in which the wall thickness of the cladding tube is measured, and then The amount of change in eddy current is measured using a penetrating eddy current coil installed on the outer circumferential surface of the zirconium alloy, and the thickness of pure zirconium is determined from the relation diagram between the amount of change in eddy current obtained in advance, the cladding tube wall thickness, and the pure zirconium thickness. A method for measuring the cladding thickness of a composite fuel cladding tube, which is characterized by quantifying the cladding thickness of a composite fuel cladding tube. 2. In claim 1, the method for quantifying the pure zirconium thickness involves changing the pure zirconium thickness stepwise at the upper and lower limits of the wall thickness tolerance of the cladding tube. A composite fuel cladding tube characterized in that the pure zirconium thickness is determined by inserting the measured values of the eddy current change amount and the cladding tube wall thickness into the obtained diagram of the eddy current change amount and pure zirconium thickness. Method for measuring coating thickness. 3. Scope of % Allowance Required Item 1, a method for measuring the thickness of a composite fuel cladding tube, characterized in that the wall thickness of the cladding tube is measured by an ultrasonic dimension measurement method;