JPS6210362B2 - - 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 breeder reactor and an upper reactor mechanism.

In fast breeder reactors, there is a possibility that fuel assemblies in the core may float up during reactor operation, or that control rods may not be completely separated from the drive device when the reactor is shut down. There is a possibility that the reactor core and upper reactor mechanism remain mechanically connected due to these two causes. On the other hand, during fuel exchange, it is necessary to move the upper core mechanism 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 as a detection means that utilizes the propagation of ultrasonic waves in liquid sodium used as a coolant. The configuration will be explained with reference to FIG. 1 is a furnace vessel, and this furnace vessel 1
The opening is hermetically closed by a rotating plug 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 is composed of a reactor core 5 and a bracket section 6 surrounding it. Furnace vessel 1
Inside, a coolant 7 typified by liquid sodium flows from a lower inlet a to an upper outlet b 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 fuel assembly that has been lifted up for some reason due to the flow of the coolant. An ultrasonic transducer 10 for transmitting and receiving ultrasonic waves and a scanning reflector 9 are provided diagonally above the reactor core 3. The reflectors 9 are arranged radially on the inner surface of the furnace vessel 1. In such a configuration,
The principle of the gap detection means between the reactor core 3 and the upper reactor mechanism 4 is as follows. That is, the ultrasonic transducer 10 is excited by the transmitter 11 and emits ultrasonic pulses 17 into the coolant 7 . The ultrasonic wave 17 propagates through the gap, reaches the reflector 9, is reflected, and returns to the ultrasonic transducer 10. At this time, if there is a floating fuel assembly 8 in the gap, the echo from the reflector 9 becomes weaker and the output voltage of the transducer 10 becomes smaller. This relationship is used to detect the size of the gap from the output voltage value of the transducer. The transducer 10 is installed on the rotation shaft 16 of the drive device 14 and is connected to the control device 15.
to rotate it in a horizontal plane. Then, the output voltage from the transducer and the transducer rotational position signal from the drive device are processed by the signal processing device 12 and sent to the display device 13, making it possible to detect gaps throughout the reactor core. ing.

In such an arrangement, the detection gap is determined from the signal level and the position of the obstacle is determined from the signal of the position detector of the drive. On the other hand, the signal level may change due to changes in the sensitivity of the transducer, sensitivity reproducibility when inserted into sodium during use, changes in propagation loss in sodium, changes in electronics over time, etc. This may result in false detection of the presence of an obstacle. In addition, since the length of the transducer's rotation axis is over 10 m, the rotational position of the transducer and the output signal of the position detector do not necessarily match, and the drive mechanism's backlash etc. There is a position detection error due to If you mislocate an obstacle, it will take time to take the next countermeasure.
This will reduce operating efficiency and lead to increased radiation exposure.

These two problems are important, and countermeasures are desired.

An object of the present invention has been made in view of the above points, and is to provide a nuclear reactor equipped with a sodium fluoroscopy device that allows on-line calibration of the sensitivity and position detection device.

That is, as only the main part of this invention is shown in FIG. 2, reference reflectors 18 and 19 are installed at both ends of scanning reflectors 9 and 9b installed in the reactor vessel 1. two reference reflectors 18,
By calibrating the position detector by the signal from 19 and by calibrating the system sensitivity by the echo level from one reflector,
It is about achieving a goal.

The drive device is installed on the rotating plug and is designed to detect the gap between the reactor core and the upper core mechanism, and has a total length of up to 10 meters.
On the other hand, the temperature conditions in the plant are room temperature on the rotating plug, and as high as approximately 200°C near the gap.

At this time, the effects of temperature conditions on the drive device include elongation and bending due to thermal expansion. The ultrasonic transducer, which is usually attached to a drive, swivels and
The rotation position signal is output by a position detector. However, the drive device may not necessarily correspond to its position within the furnace due to installation errors and thermal effects.

In order to achieve the above purpose, two reference reflectors 18 and 19 for calibration are installed at positions where the ultrasonic waves are not affected by the reactor internals, and the reference reflectors 1
Find the peak value of the reflected signal from 8 and 19. The scanning range is calibrated from the obtained peak value.

Note that the reflector used for sensitivity calibration needs to be installed at a position where the upper reactor mechanism 4 and the reactor core 3 are not present between the transducer 10 and the reference reflectors 18 and 19. In addition, 20, 21, 22 in the figure
and 23 are members for attaching the scanning reflectors 9, 9a, 9b and the reference reflectors 18, 19 to the inner wall surface of the furnace vessel 1.

Therefore, in FIG. 2, among the two reference reflectors 18 and 19, one reference reflector 18 is installed at one end of the reflector, and the other reference reflector 19 is installed at one end of the reflector.
is installed in a position where there are no reactor internal structures that may interfere with the ultrasonic waves emitted from the transducer being reflected by the reflecting plate 19 and returning to the transducer.

The angle θs in FIG. 2 indicates the range in which gap detection is required. Calibration is performed as follows. The transducer is rotated and scanned by the drive device to detect the position of the reflector 18 and the reflector 19 from the peak value of the echo level, and the detector output value indicating the peak is the position of the reference reflectors 18 and 19. Calibrate the position sensor output value as

Sensitivity calibration is performed by using the echo level of the reference reflector 19 and adjusting and setting the gain of the signal processing circuit 12 so that the echo level is always equal. Note that this adjustment must be performed using echoes from the reflecting plate 19. In other reflectors, the ultrasonic propagation path interferes with the reactor core 3 or upper reactor mechanism 4, so whether the change in echo level is due to a change in the sensitivity of the equipment system or the state of the reactor core 3 or upper reactor mechanism 4. This is because it is unclear whether this is due to changes.

As explained above, the present invention has the following effects.

(1) Obstacles can now be detected reliably, and the rate of false detection of obstacles will be reduced.
The time required for fuel exchange can be reduced.

(2) Since the position of obstacles can be detected reliably, the time required for the next countermeasure can be shortened, leading to improved operating efficiency and reduced radiation exposure.

[Brief explanation of the drawing]

FIG. 1 is a partial side cross-sectional view schematically showing a conventional nuclear reactor, and FIG. 2 is a partial cross-sectional view schematically showing an embodiment of the nuclear reactor according to the present invention. 1... Furnace vessel, 2... Rotating plug, 3... Reactor core, 4
... Reactor upper mechanism, 5... Core, 6... Blanket part,
7... Coolant, 8... Handling head of floating fuel assembly, 9... Scanning reflector, 10... Ultrasonic transducer, 11... Transmitting device, 12...
Signal processing device, 13... Display device, 14... Drive device, 15... Control device, 16... Rotating shaft, 17... Ultrasonic wave, 18, 19... Reference reflection plate.

Claims (1)

[Claims] 1. A reactor vessel, an ultrasonic transducer that is installed near the upper end of the core in the reactor vessel and transmits and receives ultrasonic waves that cross above the core, and a drive for rotating this ultrasonic transducer at a predetermined angle. a reflector disposed near an upper end of the core and opposite the ultrasonic transceiver; means for obtaining an output signal proportional to a level of a received signal from the reflector; means for displaying an output signal in synchronization with the rotation angle of the ultrasonic transducer; and means for displaying the ultrasonic signal near both ends of the reflector in order to calibrate the received signal level and the rotation angle of the ultrasonic transducer. A nuclear reactor comprising reference reflectors arranged so that the level is not affected by reactor internal structures.