JPS59137807A - Method and apparatus for measuring gap between fuel rod - Google Patents

Abstract

PURPOSE:To display the gap between fuel rods at the outer part in two dimensions, by detecting the response times from the fuel rods and the height of echo by an ultrasonic wave sensor. CONSTITUTION:A fuel assembly 1 is suspended from a suspending jig 2 and arranged at a specified position in the vicinity of a sensor device 4 under this state. The sensor 4 is composed of a driving motor part 5, a carrier 6, an ultrasonic wave probe sensor 7, and a cable 8, and attached to a supporting table 3. The response time period from the time when the ultrasonic wave, which is transmitted from the sensor 4, is reflected by the fuel rod 1 to the time when the wave is received by the sensor depends on the distance between the ultrasonic wave sensor to the fuel rod, which is an object. The sensor is moved at a constant speed and performs the transmission and reception. The sensor detects the response time of the ultrasonic wave from each fuel rod, and detects the height of echo and the position of the sensor from the fuel rod. Based on the measured value of the displacement and the gap, the positions of the fuel rods can be displayed in two dimensions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates primarily to a method and apparatus for measuring fuel rod gaps in irradiated fuel for light water reactors.

[Conventional technology and problems]

Fuel rod gap of irradiated fuel is an important factor in fuel integrity assessment. Conventionally, the fuel assembly that has been irradiated and scheduled to be loaded during the next cycle of operation is displayed on a monitor television, and the gap between the fuel rods is measured from the reproduced image on the monitor. However, when using a monitor TV, the fuel rod gap is evaluated as a projection onto a reference plane, so the orientation of the fuel rods in a direction parallel to the observation direction cannot be detected, which has the disadvantage that it cannot be detected as a true fuel rod gap. Ta.

[Structure of the invention]

The present invention provides a fuel rod IT/IJ gap measurement method color measurement system that is designed to eliminate the above-mentioned drawbacks.

The fuel rod gap measuring method and device according to the present invention will be explained below based on the drawings.

FIG. 1 is an illustration showing a method and apparatus for measuring fuel rod gaps. (a) In the figure, the fuel assembly 1 is placed in a predetermined position near the sensor device 4 while being suspended by a hanging jig 2. The above-mentioned sensor device 4 includes a drive motor section 5. as shown in FIG. Key? ! It consists of a J-26, an ultrasonic probe sensor 7, and a cable 8, and is attached to a support stand 3 as shown in the figure (A).

FIG. 2 is a schematic diagram showing the arrangement of the fuel assembly 1 and the sensor 7. An ultrasonic probe used as a sensor scans the surface of the fuel rod 9 parallel to the side surface of the fuel assembly to perform measurements. Note that X,,X, is the position of the sensor.

FIG. 3 is a diagram (A) showing the waveform received by the sensor.

(b) In the figure, tI + tx is the time it takes for the ultrasonic wave emitted by the sensor to be reflected by the fuel rod and received by the sensor again. This response time is the distance from the ultrasonic sensor to the target fuel rod. Depends on. The sensor transmits and receives signals while moving at a constant speed, and detects the ultrasonic response time of each fuel rod, the echo height from the fuel rod, and the sensor position at that time, and plots the graph in Figure 4 (I2P). )I;
,↑,su.

From the relationship between the ultrasonic response time and the sensor position, we can measure the displacement of the fuel and feed rate at the outer periphery, and from the relationship between the echo height of the fuel rods and the sensor position, we can measure the spacing between the fuel rods at the outer periphery. , the position of the fuel rods can be displayed in two dimensions from the displacement and spacing measurements.

When measuring the spacing between fuel rods on the outer periphery, if the position of the target fuel rod is read from the sensor position at the tip of the echo from the fuel rod, it is possible to accurately capture the echo due to changes in the surface condition of the fuel rod. /d from the tip value, which is an echo that does not change due to the surface condition of the fuel rod.
It is preferable that the average value of the sensor positions that generate echoes reduced by B or more is taken as the position of the fuel rod.

Also, if the frequency of the sensor used is lower than 51 pigeons, the directivity of the ultrasonic beam will be poor, and the frequency /!
;M) If the frequency is lower than Iz, the attenuation of the ultrasonic wave before it reaches the fuel rod is severe, and the echoes cannot be captured accurately in either case, so the frequency of the sensor used should be set!
; should be limited between MH2 and 1sHH.

The sensor can not only move parallel to the fuel assembly (horizontal direction), but also vertically (in the axial direction of the fuel assembly), so the position of the fuel rod can be displayed in three dimensions. It can also be extended to measure bending of fuel rods and torsion of fuel assemblies.

(Example) Using irradiated light water reactor fuel as a fuel assembly and an ultrasonic probe with a frequency of 10 MHz as a sensor, the fuel assembly and sensor were placed 1100 M apart in water, and the sensor was moved by a drive motor. I moved it and measured it.

The position signal of the sensor was taken from the drive motor, and the signal of the reflected echo from the fuel rod was detected with a normal ultrasonic probe. When the spacing between the fuel rods was set to 3 and measurements were taken, a female value could be obtained for 3.0±θ/run, indicating that it was possible to measure the gap between the fuel rods on the outer periphery of the fuel assembly. Ta.

(Effects of the invention) With the conventional method using underwater television, the fuel rod gap could only be evaluated by projecting it onto a reference surface, but now we can evaluate the response time and echo height from the fuel rods using an ultrasonic sensor. This allows the gap between the fuel rods at the outer periphery to be displayed two-dimensionally.

Furthermore, when an ultrasonic sensor is used, information is obtained in the form of electrical signals, so data processing can be performed easily and quickly.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the method and device for measuring the fuel rod gap, (a) is an overall explanatory diagram, (b) is a detailed explanatory diagram of the sensor device, and Fig. 2 shows the arrangement of the fuel assembly and sensor. The explanatory diagram, Figure 3, is the received waveform of the sensor (A). (B) is a diagram of received waveforms at x, , , x, respectively; FIG. 4 is a graph plotting the output signal measured according to the present invention with respect to sensor position 1; (0) indicates the echo height. DESCRIPTION OF SYMBOLS 1... Fuel assembly, 2... Hanging jig, 3... Support stand, 4...: Sensor device, 5... Drive motor part, 6...
・Career, age 2 and age 3

Claims (1)

[Claims] 1. A fuel rod gap measurement method that uses an ultrasonic sensor to detect and measure the reflection response time from the fuel rods on the outer periphery of the fuel assembly, the reflection echo from the fuel rods, and the position of the sensor. . 2. Set the frequency of the sensor to 5H7~/! ; MHz is the fuel rod gap measurement method according to claim 1. 6. The fuel rod gap according to claim 1 or 2, wherein the fuel rod position is the average value of the positions of sensors that generate echoes that are lower than the tips of reflected echoes from the fuel rods by /dB or more. Measurement method. 4. Drive motor, carrier, ultrasonic probe sensor,
A fuel rod gap measuring device equipped with a sensor device consisting of a cable.