JPH0821892A - Inspecting method for unexpected gap in fuel assembly for boiling water reactor - Google Patents

Abstract

PURPOSE:To quickly and easily obtain a numerical inspection result with high accuracy and prevent the danger that a channel fastener is dropped during irradiation by providing a method for inspecting whether an unexpected gap is generated between the corner hook of a channel box and the corner rod of an upper tie plate in a fuel assembly for a boiling water reactor with an ultrasonic wave. CONSTITUTION:An ultrasonic wave U1 is emitted while an ultrasonic probe 4 is vertically moved by a lift drive section 6, it is reflected on a corner hook 2a, the inside face 2d of a channel box 2, and a corner rod 1b. A reflected ultrasonic wave U2 on an unexpected gap G is selected according to the magnitude of the time required for the reflected ultrasonic wave U2 to be received by the ultrasonic probe 4. The vertical shift distance of the ultrasonic probe 4 during the reception duration when the ultrasonic wave U1 is emitted and its reflected ultrasonic wave U2 is received by the ultrasonic probe 4 is measured, the unexpected gap G can be numerically detected, and the dropping of a channel fastener is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a boiling water reactor (BW).
Between the bottom of the corner hook of the channel box and the upper surface of the corner rod of the upper tie plate when the channel boss is fitted to the fuel assembly used in R) and attached to the upper tie plate by the channel fastener. In addition, if an unexpected gap remains, the channel fastener may fall off during irradiation, which is dangerous. Therefore, the present invention relates to improvement of an inspection method using ultrasonic waves for inspecting the presence or absence of the unexpected gap.

[0002]

2. Description of the Related Art As is well known, as shown in FIG. 5 (A), a square tubular channel box 2 is first inserted into a fuel assembly 1 for a boiling water nuclear reactor to push the fuel into the fuel assembly 1. In the upper tie plate 1a of the assembly 1, on the upper surface 1b 'of each corner rod 1b protruding from the opposite corners on the diagonal line thereof, in the channel box 2,
The lower surface 2a 'of the triangular plate-shaped corner hook 2a provided at each corner corresponding to each corner rod 1b is pressed.

Next, when the contact state between the upper surface 1b 'and the lower surface 2a' is confirmed, as shown in FIG. 5B, the corner hook 2a is attached to the corner rod 1b by the channel fastener 3. Although it will be fixed, the illustrated channel fastener 3 fits the spring holder 3a, the leaf spring 3b, and the washer 3c, which are sequentially stacked on the corner hook 2a, and the fixing bolt 3d into the female screw hole 1c of the corner rod 1b. The fixing bolt 2 is configured to be screwed and fastened, and 2b is a fixing bolt insertion hole formed in the corner hook 2a for inserting the fixing bolt 3d.

In FIG. 5A, 1c is a fuel rod, 1d is a spacer, 1e is a water pipe, 1f is a lower plate, 1g is a lower end plug of the fuel rod 1c, and 1h is a lower type. A rate 1f finger spring, 1i is a handling portion of the upper tie plate 1a, and 1j is a rod spring. The role of the channel box 2 mounted in this way is to secure a flow path for cooling the fuel rod 1c with a coolant as known, and to provide a flow path for cooling the control rods, in-core instrumentation, etc. And further guide the control rods to protect the fuel rods 1c.

Therefore, when the channel box 2 is fitted and pushed into the fuel assembly 1 as described above, it is located between the upper surface 1b 'of the above-mentioned corner rod 1b and the lower surface 2a' of the corner hook 2a of the channel box 2. If there is an unexpected gap due to insufficient push-in, the fastening by the channel fasteners 3 will be insufficient, and the channel fasteners 3 during the irradiation of fuel.
It is dangerous because it will fall out due to relaxation.

[0006] For this reason at the absolutely unexpected state where there is no gap, not must be fastening work of the channel fastener 3 is completed, therefore, after the fitted closet of the channel box 2, need to be examined for the presence or absence of the unforeseen gap In the inspection, as shown in FIG. 5, in order to prevent the coolant from leaking from the lower end of the channel box 2, the lower tie plate 1f to the finger springs 1h spring outward. This is an extremely important and indispensable step, considering that the channel box 2 is not likely to be pushed sufficiently by the finger spring 1h because it is provided so as to project force.

The following three methods are already known as the above-mentioned inspection method, and the first method is the measurement by the depth cage, that is, the upper surface 1a 'of the upper tie plate 1a.
And the lower surface 2a 'of the corner hook 2a having the triangular plate shape.
The distance between and is measured with a depth gauge, and whether or not there is an unexpected gap is determined by whether or not this is a normal value.

A second inspection method is visual observation with an underwater camera. In a state where the spot of the unexpected gap is illuminated, the spot is projected on a mirror and artificially observed by the camera. Of.

As a third detection method, ultrasonic measurement has been carried out. This is that ultrasonic waves are emitted vertically from above the upper tie plate 1a toward an unexpected gap, and the ultrasonic waves are channeled. An attempt is made to observe the ultrasonic waves reaching the upper surface 1b 'of the corner rod 1b in the upper tie plate 1a through the corner hooks 2a of the box 2 and reflected by the ultrasonic probe through the corner hooks 2a again. Is.

[0010]

According to the first method in the above-mentioned prior art, the length is measured by the depth gauge, but since the upper tie plate 1a is actually a casting product, each molded body is individually processed. , With some error, so from the upper surface 1a ′ of the upper tie plate 1a,
There is variation in the length of the corner rod 1b to the upper surface 1b ', which makes it difficult to measure an unexpected gap that satisfies the required accuracy (± 0.1 mm), and the measurement work itself requires labor and time. I have to spend.

Next, in the second method, since the presence or absence of the unexpected gap is checked by the image of the camera, the unexpected gap cannot be quantified and a highly reliable inspection result is obtained. In addition to not being able to obtain it, the observation environment changes due to inconvenience of lighting, and as a result, errors due to human visual acuity are likely to occur, automation is difficult, and work efficiency should be satisfactory. It is not a kimono.

In the case of the third ultrasonic method, since an unexpected gap is to be detected by the reflected echo generated by the ultrasonic wave emitted from above, it is incident on the ultrasonic probe as the reflected echo. Is not only from the upper surface 1b 'of the corner rod 1b, but also from the echoes from the corner hooks 2a and the like in the channel box 2, especially when an attempt is made to inspect when the channel fastener 3 is fastened. Since there are reflection echoes emitted from various members of the channel fastener 3, the reference reflection echo to be detected must be analyzed from among these various reflection echoes, which makes the analysis complicated and Judgment by will also be accompanied by considerable difficulty.

In view of the above-mentioned defects of the conventional method, the present invention attempts to inspect an unexpected gap by using ultrasonic waves. However, while moving the ultrasonic probe in the vertical direction, the ultrasonic probe horizontally moves toward the unexpected gap. The ultrasonic waves reflected from various target members such as the corner hooks of the channel box and the corner rods of the upper tie plate are emitted from the ultrasonic waves until the reflected ultrasonic waves are incident. The reflected ultrasonic waves due to the unexpected gap are sorted from the reflected ultrasonic waves from other various members depending on the length of time required for.

Further, by detecting how much the ultrasonic probe has moved up and down within the reception duration of the reflected ultrasonic wave specified as described above by the ultrasonic probe, the unexpected gap is detected. To avoid the disadvantages of the above-mentioned first and second conventional methods, and to facilitate and highly accurately analyze the reflected echo that serves as a reference in the third method. The purpose is to enable quick inspection of seeds, to make it possible to quantify with high reliability, and to facilitate automation.

[0015]

In order to achieve the above-mentioned object, the present invention provides an ultrasonic probe of an ultrasonic oscillator by an elevation drive unit driven by an electric controller.
The upper tie plate is moved in the vertical direction toward the corner rod side, and in the movement process, ultrasonic waves are emitted from the ultrasonic probe and reflected by various target members. Depending on the time required until the sound wave is received by the ultrasonic probe, a reflected ultrasonic wave based on an unexpected gap between the corner hook of the channel box to be inspected and the corner rod in the upper tie plate is selected, and this is selected. Within the duration of reception of reflected ultrasonic waves by the ultrasonic probe, the ultrasonic probe is adapted to measure the displacement distance moved by the elevating and lowering drive unit. It seeks to provide a method of testing for unexpected gaps in the body.

[0016]

When the elevating and lowering drive section controlled by the electric controller is operated, the ultrasonic probe connected thereto is vertically moved. Now, assuming that the ultrasonic probe is moving downward, the ultrasonic wave emitted from this is first reflected by the inner end surface of the corner hook of the channel box and is incident on the reflected ultrasonic probe. It Furthermore, when the ultrasonic probe descends,
If there is an unexpected gap, the reflected ultrasonic waves from the inner surface of the channel box below the corner hook will be received by the ultrasonic probe.

Next, the ultrasonic waves are reflected by the corner rods of the upper tie plate, and the reflected ultrasonic waves are received by the ultrasonic probe as described above. At this time, the above-mentioned three-reflected ultrasonic waves are the reflection surface of the target member on which they are respectively reflected,
There is a difference in size with the ultrasonic probe, and moreover,
Since each of these reflected ultrasonic waves does not enter the ultrasonic probe at the same time, it is easy to determine whether or not the ultrasonic waves are reflected ultrasonic waves based on an unexpected gap only by the required time from the time when the ultrasonic waves are reflected until the ultrasonic waves are incident. Can be sorted into

With respect to the reflected ultrasonic wave thus identified, the ultrasonic probe has moved within a continuation time period during which it is being received by the ultrasonic probe, and by which distance the ultrasonic probe has moved. If such a gap is detected by the output from the electric controller or the like, not only the presence or absence of the unexpected gap but also its length can be automatically known with high accuracy.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to FIGS.
3 is a schematic plan view showing the fuel assembly for the boiling water reactor described above with reference to FIG. 5, and FIG.
A vertical side view of the IV line is shown, where 1a is the upper tie plate, 1i is its handling part, 2a is the corner hook of the channel box 2, 1b is the corner rod of the upper tie plate 1a, and 2b is the corner hook as described above. 2a is a fixing bolt insertion hole, 1c is a female screw hole of the above-mentioned corner rod 1b, and G is an unexpected hole formed between the lower surface 2a 'of the corner hook 2a and the upper surface 1b' of the corner rod 1b. In the gap, 4 indicated by a virtual line in FIG. 3 is an ultrasonic probe described later.

In order to carry out the present invention, the ultrasonic probe 4 of the ultrasonic oscillator is provided in advance above the upper tie plate 1a in the fuel assembly for a boiling water reactor as described above. Is vertically movable by an elevating / lowering drive unit 6 which can be moved by an electric controller 5. At this time, the ultrasonic probe 4 is moved to the corner rod 1b of the upper tie plate 1a.
Be prepared to emit ultrasonic waves to the side.

Further, in the illustrated example, an analysis operation unit 7 is provided so that the output from the electric controller 5 and the signal from the ultrasonic probe 4 are input thereto, as will be described later in detail. It has become.

Therefore, in order to carry out the method of the present invention, the ultrasonic probe 4 is operated upward or downward. Now, as shown in FIG. 1, the ultrasonic probe 4 is lowered toward the upper tie plate 1a. Then, the ultrasonic wave U ₁ emitted thereby is reflected on the inner end surface 2c of the corner hook 2a in the channel box 2, and the reflected ultrasonic wave U ₂ is received by the ultrasonic probe 4. .

Further, when the ultrasonic probe 4 descends, as shown in FIG. 1, when the channel fastener 3 is not yet applied and the unexpected gap G exists, the ultrasonic wave is unexpected. After passing through the gap G, it is reflected by the inner surface upper portion 2d of the channel box 2, and the reflected ultrasonic waves are received by the ultrasonic probe 4 in the same manner as before. Then, as the movement process progresses, the same ultrasonic wave comes to be reflected by the inner surface 1k of the corner rod 1b of the upper tie plate 1a, and this reflected ultrasonic wave also becomes
Similarly, the ultrasonic probe 4 receives the signal. In the drawing, L indicates the lowest line of the ultrasonic probe 4.

In this way, the reflected ultrasonic waves based on the ultrasonic probe 4 are received one after another and input to the above-mentioned analytical computing unit. In the present invention, however, ultrasonic waves are applied to each of these inputs. After the ultrasonic wave emitted from the probe 4 is reflected by each target member as described above, each of these reflected ultrasonic waves measures the required time until it is received by the ultrasonic probe 4. As a result, whether it is the reflected wave from the inner end 2c of the corner hook 2a located closest to the ultrasonic probe 4 or the inner end surface 2d of the channel box 2 located farthest, Inner surface 1 at corner rod 1b, which is the distance
That is, the reflected wave from k is selected.

Here, in practice, as the ultrasonic sensor adopted for the ultrasonic probe 4, a line type sensor which radiates ultrasonic waves in a beam shape in the horizontal direction is also used. A focus type sensor that emits ultrasonic waves so as to be tied can also be used, but the focus type sensor is preferable when trying to measure the distance to the target member as described above.

Next, according to the present invention, the reference reflected ultrasonic waves selected as described above are within the continuous time when they are received by the ultrasonic probe 4, and the ultrasonic probe 4 concerned. However, it measures the displacement distance moved downward. As a means for performing such a measurement, of course, any measuring means may be used, but in the illustrated example, the input from the ultrasonic probe 4 is processed by the analytic computing unit 7 so as to reflect the reflected ultrasonic wave corresponding to the unexpected gap G. The sound wave is selected as described above, and the signal related to the moving distance of the ultrasonic probe 4 is input from the electric controller 5 to the analysis calculator 7, so that the ultrasonic probe 4 can detect the reflected ultrasonic wave. The displacement distance moved within the sound wave reception duration can be automatically displayed.

Here, in the case of measuring the unexpected gap G as described above, in order to improve the measurement accuracy in practice, the ultrasonic probe is used in various cases in which the unexpected gap is known with high accuracy in advance. The relationship between the displacement distance of 4 and the length of the known unexpected gap is measured,
It is preferable to obtain a calibration curve between the two and use it to perform the correction.

Next, referring to FIG. 2, the corner hook 2a of the channel box 2 is moved by the channel fastener 3.
Is tightened to the corner rod 1b of the upper tie plate 1a, and the unexpected gap G is inspected. Even in this case, the inner end surface 2c and the inner surface 1k are also inspected.
Although the reflected ultrasonic waves from and are received by the ultrasonic probe 4 as in the case of FIG. 1, the reflected ultrasonic waves related to the unexpected gap G are not reflected from the inner side surface 2d, but the fixing bolt. It will be reflected from the spiral portion in 3d.

However, even in this case, since the distances from the ultrasonic probe 4 to the inner end face 2c, the fixing bolt 3d, and the inner side face 1k are different from each other, the fixing bolt 3d reflects the same distance as before. It is possible to specify the reflected ultrasonic wave that has been generated, and by measuring the displacement distance of the reflected ultrasonic wave that serves as a reference based on this, it is possible to determine the presence or absence of the unexpected gap G and to quantify it.

[0030]

Since the present invention is carried out as described above, since the unexpected gap is directly measured, it is not affected by the height of the corner rod having variations such as the depth gauge method. High-accuracy measurement is possible, and unlike the visual observation with an underwater camera, it is possible to quantify an unexpected gap, and it is difficult to analyze the reference ultrasonic wave, which is a problem in the ultrasonic measurement method from the vertical direction. It is possible to solve the problems of reliability, labor, accuracy, and measurement time, and with high reliability, prevent the risk of the channel fastener falling off during irradiation.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view in the vicinity of an upper tie plate of a fuel assembly for a boiling water reactor, showing a state of use of an apparatus for carrying out the method for inspecting an unexpected gap according to the present invention. .

FIG. 2 is a vertical sectional side view in the vicinity of an upper tie plate of the same fuel assembly under a condition different from that of FIG. 1, which shows a usage state of the device for carrying out the inspection method.

FIG. 3 is a schematic plan view showing the fuel assembly of the above.

FIG. 4 is a vertical sectional side view taken along the line IV-IV of FIG. 3, showing the fuel assembly of the above.

FIG. 5 (A) is an overall perspective view showing a fuel assembly for a boiling water reactor by cutting out a part of the fuel assembly, and FIG. 5 (B) is an upper corner portion of a channel box in the fuel assembly.
It is an exploded side view of a partially cutaway showing a channel fastener to which this is applied.

[Explanation of symbols]

1a Upper tie plate 1b Corner rod 2 Channel box 2a Corner hook 4 Ultrasonic probe 5 Electric controller 6 Lifting drive unit U ₁ Ultrasonic U ₂ Reflected ultrasonic G G Unexpected gap

Claims (1)

[Claims] 1. An ultrasonic probe of an ultrasonic oscillator is moved by an elevation drive unit driven by an electric controller.
The upper tie plate is moved in the vertical direction toward the corner rod side, and in the movement process, ultrasonic waves are emitted from the ultrasonic probe and reflected by various target members. Depending on the time required until the sound wave is received by the ultrasonic probe, a reflected ultrasonic wave based on an unexpected gap between the corner hook of the channel box to be inspected and the corner rod in the upper tie plate is selected, and this is selected. Within the duration of reception of reflected ultrasonic waves by the ultrasonic probe, the ultrasonic probe is adapted to measure the displacement distance moved by the elevating and lowering drive unit. Inspection method for unexpected gaps in the body.