JPS5834799B2 - Reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear reactor equipped with an ultrasonic device for detecting a gap between the upper end surface of a nuclear fuel assembly in the core of a fast reactor and an upper reactor mechanism.

In fast reactors, there is a possibility that fuel assemblies within the core may float during reactor operation, or that control rods may not be completely separated from the drive device when the reactor is shut down.

Due to these two causes, there is a possibility that the reactor core and upper reactor mechanism remain mechanically connected.

On the other hand, during refueling, it is necessary to move the upper core mechanism in order to use the refueling machine in the upper part of the core.

At this time, if the upper core mechanism is connected to the reactor core due to the above two causes, an accident may occur in which the fuel assembly, control rod, or measurement sensor at the lower end of the upper core mechanism is damaged.

Therefore, it is necessary to detect the presence of a gap between the reactor core and the upper reactor mechanism.

Conventionally, a method has been proposed that utilizes the propagation of ultrasonic waves in liquid sodium used as a coolant.

Figure 1 shows the configuration of this type of nuclear reactor. 1 is a furnace vessel, and the opening of this furnace vessel 1 is hermetically closed by a rotating flag 2.

Inside the reactor vessel 1, there are provided a reactor core section 3 configured by a plurality of nuclear fuel assemblies arranged in a row, and an upper reactor mechanism 4 used when operating control rods.

The reactor core section 3 includes a reactor core 5 and a blanket section 6 surrounding it.
It is composed of.

Also, inside the reactor vessel 1 is a coolant 7 typified by liquid sodium.
is arranged to flow from the bottom to the top of the furnace vessel as shown by solid line arrows A and B in the figure.

Note that 8 in the figure indicates the handling head portion of the floating fuel assembly.

An ultrasonic transducer 10 and an acoustic separate body 9 for transmitting and receiving ultrasonic waves are provided at an obliquely upper position of the reactor core 3.

This anti-separate body, 9, has a right angle 3 on one side as shown in Figure 2A.
It is a plate-shaped body provided with rectangular grooves (1) to (2), and is arranged facing the ultrasonic transducer 10 along the inner surface of the furnace vessel 1 with one side inclined.

In such a configuration, the principle of the gap detection method between the reactor core 3 and the upper reactor mechanism is as follows.

That is, the ultrasonic transducer 10 is excited by the transmitting device 11 and emits ultrasonic pulses 17 into the coolant 7 .

The ultrasonic wave 17 propagates through the gear G, reaches the acoustic repellent body 9, is repelled, and returns to the transducer 10.

At this time, if there is a floating fuel assembly 8 in the cap G, the echo from the fouler 9 becomes weaker, and the output voltage of the transducer 10 becomes smaller.

Using this relationship, the size of the gap G is detected from the value of the output voltage of the transducer.

The transducer 10 is rotated in a horizontal plane by a control device 15 mounted on a rotation axis 16 of a drive device 14 .

Then, the output voltage from the transducer 10 and the transducer rotational position signal from the drive device 14 are processed by the signal processing device 12 and guided to the display device 13.
The gap value for the entire reactor core can be detected.

In such an apparatus, a large number of plate bodies each having a groove with a right triangular cross section or a groove with a hemispherical cross section on one side are used as the repellent body 9, for example, as shown in FIG. 2A.

For example, if the mirror plate 9 is tilted at an angle θ with respect to the incident direction of the ultrasonic wave as shown in FIG. 2A without using the mirror plate, there will be problems even if the setting error of the deflector 9 is large. This is because it has the advantage that it can be eliminated.

However, in the above device, the transducer emits burst waves of ultrasonic waves, receives echoes from the fouling plate, and simply detects this peak value to determine the gap value, which is related to the levitation of the fuel assembly. Since echoes that do not occur are also detected as peak values, the minimum value of the detection gap is large. For example, when a normal gap is 50 mm, the minimum gap becomes 30 mm.

Therefore, it is strongly desired to lower the minimum value of this detection gap.

The purpose of the present invention is to provide a safe nuclear reactor that is distantly related to the above-mentioned object by improving the signal processing method of the above-mentioned device.

That is, the present invention includes a reactor core housed in a reactor vessel, an ultrasonic transceiver installed near the upper end of the reactor core and transmitting an ultrasonic signal across the upper part of the reactor core, and an ultrasonic transceiver arranged at a predetermined angle. a means for rotating; a repellent body provided near an upper end of the core and opposite the ultrasonic transmitter/receiver; a means for electrically energizing the ultrasonic transmitter/receiver; means for obtaining an output signal proportional to the energy of the signal; and means for displaying the output signal in synchronization with the scanning span of the ultrasonic transducer; means for obtaining an output signal proportional to the difference between a signal proportional to the energy and a signal proportional to the energy of the received signal from the fouling body in a reference state; This nuclear reactor is characterized by comprising means for synchronously displaying the information.

An embodiment of the nuclear reactor according to the present invention is shown in FIGS. 2 to 4 below.
This will be explained with reference to the figures.

FIG. 3 is a block diagram showing the signal processing device 12 that processes the signals transmitted from the transducer 10 and the drive device, which are the main parts of the present invention. In the figure, 22 is an amplifier, 23 is an AM detector, 24 is an integrator, 25 is a counter, and 26 is a D/A converter.

In this signal processing device 12, the signal from the transducer 10 is a burst waveform with a frequency on the MHz order as a carrier, but it is amplified by the amplifier 22, then converted to an envelope waveform by the AM detector, and then integrated. to the display device 13.

On the other hand, the position signal of the transducer 10 is
4 is sent as a digital signal, counted by a counter 25, converted to an analog signal according to the count number by a D/A converter 26, and guided to a display device 13.

Now, when the transducer 10 emits a burst wave of ultrasonic waves, receives the echo from the fouling plate 9, and performs AM detection, the detected echo has a pulse waveform as shown in the second diagram.

Fig. 2 shows the correspondence between the fouling plate and the fouling wave of the nuclear reactor according to the present invention, where A is a cross-sectional view showing a unit of the fouling plate provided on the inner wall of the reactor vessel, and B is a floating C is an amplitude distribution diagram of the ultrasonic beam, D is a diagram showing echoes from the fouling plate when the nuclear fuel assemblies are normally arranged, and Sl is a cross-sectional view schematically showing the nuclear fuel assembly. In the groove, S2 shows the echo corresponding to the groove I, S3 shows the echo corresponding to the groove A, and S4 shows the echo corresponding to the groove a.

E shows the echo from the separate plate when the fuel assembly floats up.

As is clear from FIG. 2, the repelling plate 9
It is installed at an angle θ from a position perpendicular to the direction of movement of the right triangular grooves, and is tilted so that the distance difference between adjacent right triangular grooves of the right triangular grooves ① to ② is equal to or more than 1/2 of the pulse length of the ultrasonic wave.

Then, as shown in the second diagram, echoes S11, S21,
S31 and S41 are obtained.

The second diagram shows the received signal when the fuel assembly is not floating, but when the fuel assembly is floating, the groove in the reflector plate 9
, ■ are shadows, so the echo level decreases like echoes S22 and S12, as shown in FIG. 2E.

In addition, in the conventional method of measuring the lift (or gap) of the fuel assembly using the peak detection value, the focus is only on the peak value, so in the state shown in Figure 2E, the level of the echo 83 is 832 831 is detected, and the gap value is determined from a signal unrelated to the lifted fuel assembly.

That is, in the conventional peak detection method, as shown in Figure 2 and E, a large number of pulse-like signals are received by the transducer, but the gap value is detected from the echo with the highest level among them, and therefore the fuel assembly The echo S1, which shows a peak level when the body is not lifted, shows a decrease in level S,2 in proportion to the amount of lifting (or gap value) when lifting occurs.

As the levitation progresses further, the level of echo S3, which has the highest level among the echoes unrelated to the levitation of the fuel assembly, is level S32.
When the level S12 of the echo S1 becomes smaller than the level S12 of the echo S1, the level S of the echo S3, which is a peak value unrelated to the lifting amount,
32 will be detected.

In this way, the peak value of the echo level used to detect the amount of uplift is a force that initially decreases in proportion to the amount of uplift. is asymptotic to the level of the echo S3), and the minimum detection gap value is defined at the level S32 of the echo S3.

This is shown in FIG. That is, in the peak detection method, the received signal level does not decrease above the rising amount U\ullJ, so the minimum detection gap value g becomes G-11.

This value is compared to the normal gap value G = 50 mm.
t=30mm.

However, this invention aims to reduce the value of this minimum detection gap, and its principle is based on the fact that when there is no obstacle in the gap such as a fuel assembly, the sum of the energies of the echoes S1...S4 is constant. are doing.

In other words, it is.

Now, the difference in the integral value △■ for the second diagram and the echo of E
If we calculate this and write it using the gap g and the uplift amount U (Fig. 1), we get the following.

This formula calculates the amount of energy that cannot be returned, as part of the echo energy returns to the transducer due to the lifting of the fuel assembly.
The left side calculates "the difference between the energy/S□ldt of the echo S1 when it is not floating and the energy f812dt of the echo 81 when it is floating."

The right side is ``Of the energy of the echo 81 when there is no uplift and the gap is G, the energy masked by the uplift corresponds to the uplift amount U, and this is approximated as being approximately proportional.''I'm asking you to let me.

That is, the right side holds true as the amount of the total energy fS11dt of the echo 81, u/G=u/g+u, is not detected as an echo.

Also, Echo S2゜S3. Regarding S4, the foul board structure ■,
■, ■, ■The degree of contribution of the sound wave diffraction phenomenon in the fuel assembly to the echo level differs depending on the positional relationship between the transducer and the fuel assembly, so the above equation that holds for echo S1 remains the same relationship. However, since the above-mentioned diffraction phenomenon can be easily solved, S2. S
3. In S4, when the reduction in the energy of the echo is assumed to be due to floating, the following equation holds true.

Since g+u=G and the integral value is constant, △■ is proportional to the lifting amount U.

The integral value ■ is I=I −△I=Io Ku Here, k is a constant value and is a proportional coefficient.

If this is shown in Figure 4, it becomes a solid line (integral method), and ■/■o
The value of corresponds perfectly to the gap value, and the minimum detected gap value is O.

Further, if it is indicated by △■, it will look like a two-dot chain line, and the minimum detection gap will be O.

As described above, according to the present invention, by providing an integral circuit using an integral method and processing signals, the gap between the lower end surface of the reactor upper mechanism and the upper end surface of the handling head of the floating nuclear fuel assembly is minimized. Therefore, the minimum detection gap value has become smaller, which improves the operating rate of one nuclear reactor.

■ It has the effect of allowing nuclear reactor maintenance and inspection to be carried out safely and quickly.

[Brief explanation of drawings]

Figure 1 is a diagram of the constituent countries for schematically explaining this type of nuclear reactor, and Figure 2 is a sectional view and distribution diagram for explaining the correspondence between the reactor reflector and reflected waves according to the present invention. , 3rd
FIG. 4 is a block diagram showing a signal processing device of the present invention, and FIG. 4 is a graph showing a comparison between the relationship between the ultrasonic echo level and the lifting amount of a fuel assembly in the present invention and the peak value detection method. DESCRIPTION OF SYMBOLS 1... Reactor vessel, 2... Rotating plug, 3... Reactor core stand 4... Reactor upper mechanism, 5... Reactor core, 6... Blanket part, 7... Coolant, 8 . . . Floating fuel assembly, 9. Acoustic anatomical body, 10. Ultrasonic transducer, 11. ... Drive device, 15
...Control device, 16...Rotation axis, 17...Ultrasonic wave, 18...Envelope of ultrasonic beam, 22...
Amplifier, 23... Amplitude detection, 24... Integrator, 25
...Counter, 26...D/A converter.

Claims (1)

[Claims] 1. A reactor core housed in a reactor vessel, an ultrasonic transmitter/receiver provided near the upper end of the reactor core and crossing above the reactor core,
means for rotating the ultrasonic transceiver by a predetermined angle; a separate body provided near the upper end of the core and facing the ultrasonic transceiver; and electrically energizing the ultrasonic transceiver. a signal processing means for processing a received signal from the anti-separate body to obtain an output signal; and a display means for displaying the output signal in synchronization with the scanning span of the ultrasonic transceiver. wherein the signal processing means generates a signal proportional to the energy of the received signal from the anti-separate body;
an integrating circuit for obtaining an output signal proportional to a difference between a received signal from the anti-separate body in a reference state and a signal proportional to the energy; A nuclear reactor characterized in that it is a means for displaying in synchronization with an angular position.