JP5024936B2 - Inspection method for graphite-containing ceramic containers - Google Patents

Description

  The present invention relates to a method for inspecting a graphite-containing ceramic container used for melting treatment of low-level radioactive waste or the like.

  Nuclear facilities represented by nuclear power plants generate low-level radioactive solid waste such as metals, glass, concrete, filters, and incineration ash. As a final treatment method of these radioactive miscellaneous solid wastes, a method in which they are housed in a ceramic container, subjected to high-frequency induction heating in a melting furnace, and melted and solidified is mainly used. The ceramic container for this purpose is a graphite-containing ceramic container containing about 8 to 40% of graphite as described in Patent Document 1, and the container itself generates heat by providing conductivity with graphite. Yes.

  Methods for inspecting this graphite-containing ceramic container include hammering inspection method, ultrasonic inspection method, X-ray fluoroscopic inspection method, water pressure inspection method, foaming inspection method (Patent Document 2), visual inspection method, etc. In Japan, products without defects are shipped by a combination of these inspection methods.

  However, even if there is no defect at the time of shipment from the factory, the graphite-containing ceramic container may be defective in the transportation stage after shipment or the handling stage such as mounting in the melting furnace at the place of use. This is a defect that occurs when the graphite-containing ceramic container is collided with an obstacle in the middle of conveyance, and is not a defect inside the ceramic structure such as laminar cracks or lack of compactness called lamination, but the mouth of the graphite-containing ceramic container Most of the cracks generated in Although this crack may be detected visually, it may be a fine hair crack that cannot be detected visually. When such cracked graphite-containing ceramic containers are used for high-frequency induction heating of radioactive miscellaneous solid waste, cracks expand due to the heat generated during melting, leading to damage. There is a possibility of a hot water leak that leaks into the furnace.

  In order to avoid such hot water leakage during the use of the graphite-containing ceramic container, it is possible to find defects by performing the same inspection as that performed at the time of factory shipment at the place of use. However, since the hammering inspection method, the ultrasonic inspection method, and the visual inspection method all depend on the skill of the individual, there is a possibility that an inspection failure may occur. In addition, since a large inspection device is required to perform the fluoroscopic inspection method, the water pressure inspection method, and the foam inspection method, it is necessary to carry out these inspection methods at the radioactive waste disposal site that is the place of use. It is difficult both economically and equipment.

Moreover, in order to prevent oxidation of the graphite contained in the graphite-containing ceramic containers currently used, an anti-oxidizing glaze is applied to the surface at the time of factory shipment. For this reason, the ultrasonic inspection method, the hydraulic pressure inspection method, and the foaming inspection method are difficult to implement due to the glaze layer being an obstacle, and further visual inspection is difficult.
Japanese Patent No. 3499868 Japanese Patent No. 2955191

Therefore, the object of the present invention is to easily and reliably find defects that can lead to leakage of graphite-containing ceramic containers at the place of use without requiring a large inspection device and without being affected by the anti-oxidant glaze. It is to provide a method for inspecting a graphite-containing ceramic container.
In order to solve this problem, the present inventor completed the present invention by paying attention to the fact that the graphite-containing ceramic container has electrical conductivity and that the generation site of cracks is concentrated in the container mouth.

The inspection method for a graphite-containing ceramic container according to the present invention based on the above knowledge is that the sensor unit equipped with the eddy current sensor is moved along the mouth edge of the graphite-containing ceramic container, and there is no crack in the container mouth. The sensor unit has a reverse U-shaped body straddling the mouth of the graphite-containing ceramic container, a roller in contact with the upper surface of the mouth of the graphite-containing ceramic container, and a roller in contact with the inner surface of the mouth. And the roller in contact with the outer surface of the mouth are provided in two stages. The eddy current sensor is mounted inside the sensor unit, and the roller in contact with the outer surface of the mouth is springed toward the outer surface of the mouth by a spring. The presence or absence of cracks is inspected from the inner surface of the mouth while keeping the distance from the eddy current sensor to the container surface constant .

  The method for inspecting a graphite-containing ceramic container according to the present invention performs an eddy current flaw inspection of a container mouth utilizing the fact that a graphite-containing ceramic container has conductivity, and uses a small sensor unit to The presence or absence of cracks in the part can be easily and accurately inspected without being influenced by the antioxidant glaze. This inspection does not require a large inspection device and can be easily performed at a radioactive waste disposal site or the like. In addition, defects inside the ceramic structure are inspected at the factory shipment stage, and most of the defects that occur during the subsequent transport are concentrated at the container mouth, so inspection of only the mouth may lead to water leaks. Defective containers can be almost completely eliminated.

In order to perform an eddy current flaw inspection, it is necessary to keep the distance from the eddy current sensor to the container surface constant. However, if the sensor unit described above is used, the entire edge of the mouth is maintained while keeping the above distance constant. Defect inspection over the entire circumference is possible.

Embodiments of the present invention will be described below.
In FIG. 1, reference numeral 1 denotes a graphite-containing ceramic container used for high-frequency melting of radioactive miscellaneous solid waste. This graphite-containing ceramic container is made of alumina as a basic component and contains about 8 to 40% of graphite so as to have conductivity. As described above, an anti-oxidant glaze for preventing oxidation of graphite is applied to the surface.

  In the present invention, an eddy current flaw inspection of the graphite-containing ceramic container 1 is performed using a small sensor unit 2 equipped with an eddy current sensor. Eddy current flaw detection utilizes the fact that an AC magnetic field is generated when a high-frequency voltage is applied to a coil, and the eddy current generated in a metal material placed inside the magnetic field changes due to the influence of material, defects, shape changes, etc. Thus, a non-destructive inspection of a metal material is performed. This eddy current flaw inspection itself is a well-known inspection method and has been conventionally used in the field of nuclear power in order to confirm the soundness of fuel cladding tubes, steam generator heat transfer tubes, and the like. However, conventionally, this method has been used exclusively for inspection of metal materials.

  The sensor unit 2 used in the present embodiment is one in which an eddy current sensor 4 is mounted on a main body 3 having an inverted U-shaped cross-section straddling the mouth of a graphite-containing ceramic container 1. The eddy current sensor 4 is connected to a power supply device (not shown) and a detection signal analyzer, and can generate an alternating magnetic field and detect an eddy current. However, since the detection signal changes when the distance from the eddy current sensor 4 to the container surface changes, it is necessary to move along the container mouth while keeping this distance constant.

  Therefore, the sensor unit 2 is provided with a roller 5 in contact with the upper surface of the mouth of the graphite-containing ceramic container 1 as shown in FIGS. 2 and 3, a roller 6 in contact with the inner surface of the mouth, and a roller 7 in contact with the outer surface of the mouth. It is. The roller 5 is for maintaining the body 3 of the sensor unit 2 at a constant height, and the two rollers 5 and 5 are arranged on the circumference of the graphite-containing ceramic container 1 so that the roller 5 can run on the upper surface of the mouth of the graphite-containing ceramic container 1. It is installed with an angle in the direction. In addition, if the height adjustment mechanism with respect to the main body 3 of the sensor unit 2 is provided on the roller 5 in contact with the upper surface of the mouth portion, the inspection height can be adjusted by the eddy current sensor 4. It is sufficient that the adjustment width is about 50 mm.

  As shown in the drawing, a total of four rollers 6 in contact with the inner surface of the mouth are provided on the left and right of the upper and lower two stages. And the eddy current sensor 4 is provided in those center positions. Since both the roller 6 and the eddy current sensor 4 are fixed to the main body 3 of the sensor unit 2, if the roller 6 is brought into contact with the inner surface of the mouth of the graphite-containing ceramic container 1, the mouth meat of the graphite-containing ceramic container 1. Regardless of the thickness or distortion in the circumferential direction, the distance between the eddy current sensor 4 and the container surface is always constant.

  On the other hand, a total of four rollers 7 in contact with the outer surface of the mouth are provided on the left and right sides of the upper and lower stages, and these rollers 7 are roller holding shafts 8 supported by bearings 9 fixed to the main body. A spring 10 is provided between the bearing 9 and the roller 7. The spring 10 is a compression coil spring and repels the roller 7 toward the outer surface of the mouth. By the reaction, the main body 3 of the sensor unit 2 is always urged toward the outside of the container, and the roller 6 is always in contact with the inner surface of the mouth of the graphite-containing ceramic container 1, and the sensor unit 2 and the eddy current sensor. 4 can be kept constant.

  Thus, in this embodiment, the eddy current sensor 4 is provided inside the sensor unit 2, and the mouth of the graphite-containing ceramic container 1 is inspected from the inner surface. According to the inventor's investigation, cracks that occur when the graphite-containing ceramic container 1 collides with an obstacle are often generated from the top of the mouth and penetrate from the inner surface to the outer surface. Although it progresses from the top of the mouth to the inner surface, it may not penetrate to the outer surface. On the contrary, there are almost no cracks that propagate only from the top of the mouth to the outer surface. For this reason, if the eddy current sensor 4 is moved along the lip of the graphite-containing ceramic container 1 and the presence or absence of cracks is inspected from the inner surface of the mouth of the container, most of cracks including fine hair cracks can be detected. In particular, cracks that cause hot water leakage can be completely detected. However, the present invention is not limited to this, and cracks may be inspected from the outer surface of the mouth or the upper surface of the mouth.

  The sensor unit 2 may manually move the mouth of the graphite-containing ceramic container 1 over the entire circumference. However, the sensor unit 2 is equipped with a traveling motor, and the roller 5 is in contact with the upper surface of the mouth and the roller is in contact with the inner surface of the mouth. 6 may be driven to cause the sensor unit 2 to self-run. It is also possible to inspect the entire circumference while the graphite-containing ceramic container 1 is placed on a rotary table and rotated to hold the sensor unit 2 at a fixed position. Since power lines and signal lines are connected to the sensor unit 2, a method of rotating the graphite-containing ceramic containers 1 is convenient when inspecting all of the many graphite-containing ceramic containers 1.

  FIG. 4 shows an example of a detection signal of the eddy current sensor 4 at a position where there is a crack, and FIG. 5 shows an example of a detection signal of the eddy current sensor 4 in the case of a healthy product. Thus, there is a clear signal change depending on the presence or absence of cracks, and there is no obstacle due to the anti-oxidant glaze. If the inspection according to the present invention is carried out at the place of use, it is possible to reliably detect cracks in the mouth of the graphite-containing ceramic container 1 due to handling mistakes during transportation, and eliminate the risk of hot water leakage during the melting process. It becomes possible.

  A graphite-containing ceramic container having an electrical resistivity of 5000 μΩcm was turned over to generate a crack from the upper end of the mouth to a height of 100 mm on the inner surface. This crack is a hair crack that does not penetrate the outer surface. With respect to this graphite-containing ceramic container and a sound product without cracks, the sensor unit shown in the embodiment was run manually to measure the detection signal of the eddy current sensor. As a result, the amplitude value of the detection signal was 0.15 mV in the healthy product, whereas it was 0.85 mV in the container in which the crack was generated, and it was possible to detect the crack.

  Similarly, a graphite-containing ceramic container having an electrical resistivity of 5000 μΩcm was turned over to generate a through crack from the upper end of the mouth to a height of 200 mm on the inner surface and a height of 100 mm on the outer surface. With respect to the graphite-containing ceramic container and the healthy product, the sensor unit shown in the embodiment was manually moved to measure the detection signal of the eddy current sensor. As a result, while the amplitude value of the detection signal was 0.15 mV for the healthy product, it was 1.5 mV for the container in which the through crack was generated, and the crack was detected. In addition, although the anti-oxidant glaze was apply | coated to any graphite containing ceramic container, it has also confirmed that it was not influenced at all.

It is a perspective view which shows embodiment of this invention. It is a vertical sectional view showing an embodiment of the present invention. It is a horizontal sectional view showing an embodiment of the present invention. It is a graph which shows an example of the detection signal of an eddy current sensor in case there exists a crack. It is a graph which shows the detection signal of the eddy current sensor in the case of a healthy article.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Graphite containing ceramic container 2 Sensor unit 3 Main body 4 Eddy current sensor 5 Roller in contact with the upper surface of the mouth 6 Roller in contact with the inner surface of the mouth 7 Roller in contact with the outer surface of the mouth 8 Roller holding shaft 9 Bearing 10 Spring

Claims (1)

A sensor unit equipped with an eddy current sensor is moved along the mouth of a graphite-containing ceramic container, and the presence or absence of cracks in the container mouth is inspected ,
The sensor unit has an inverted U-shaped body straddling the rim of the graphite-containing ceramic container, a roller in contact with the upper surface of the mouth of the graphite-containing ceramic container, a roller in contact with the inner surface of the mouth, and a roller in contact with the outer surface of the mouth. Is provided in two stages,
The eddy current sensor is mounted inside the sensor unit,
It is characterized by inspecting the presence or absence of cracks from the inner surface of the mouth while keeping the distance from the eddy current sensor to the container surface constant by springing the roller in contact with the outer surface of the mouth toward the outer surface of the mouth by a spring. Inspection method for graphite-containing ceramic containers.

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