JPS6145167B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a horizontal perspective ultrasonic fluoroscopy system capable of locating obstacles such as fuel assemblies and control rods floating above the core of a sodium-cooled nuclear reactor.

FIGS. 1 and 2 show examples of conventionally used ultrasonic fluoroscopes. FIG. 1 is a diagram conceptually showing a longitudinal section of a sodium-cooled nuclear reactor using metallic sodium as a coolant, and FIG. 2 is a diagram showing a cross section of FIG. 1 taken along the plane A-A'. In FIG. 1, a reactor vessel 1 houses a reactor core 2, a core upper mechanism 3, metallic sodium, etc., and a rotating plug 4 in the upper part.
have. There are fuel assemblies and control rods (not shown) inside the reactor core 2, which generate heat through nuclear fission reactions.
or in control. This heat heats the sodium flowing in from the sodium inlet 5 provided at the bottom of the furnace vessel 1, and the heated sodium flows out from the sodium outlet 6 provided at the top of the furnace vessel 1. The heated sodium flowing out of the furnace vessel 1 passes through a heat exchanger (not shown) to convert thermal energy into electrical energy, is cooled, and enters the sodium inlet 5 again. Sodium flows through the core 2 from bottom to top. For this reason, there is a possibility that a portion of the fuel assembly or control rod may float up from the reactor core 2 and become a floating fuel assembly 7.

The upper core mechanism 3 located at the upper part of the reactor core 2 includes a control rod drive mechanism, fuel exchange, etc. (not shown), and the upper core mechanism 3 must be moved during fuel exchange. In this case, either the fuel assembly replaced and inserted in the fuel exchanger was not inserted sufficiently downward, or the upper core mechanism was moved while the floating fuel 7 caused by the above reason still existed. , there is a risk that the fuel assembly 7 may be destroyed.

For this reason, before moving the core upper mechanism, it is necessary to know the position and floating amount of the floating fuel assembly 7, and to push it down according to the floating amount. In order to locate the position of the floating fuel assembly and measure the floating amount, a device that can see through the horizontal direction is required just above the reactor core 2. Since sodium is optically opaque, a fluoroscopy device using ultrasonic waves that is highly transparent even in sodium is required.

In FIG. 2, if there are no obstacles on the reactor core 2, the ultrasonic waves emitted from the ultrasonic transducer 8 immersed in sodium will pass through the gap, be reflected by the reflector plate 9, and then be reflected again. Return to the ultrasonic transducer 8. Here, if there is a fuel assembly 7 or other obstacle floating into the gap, the light will not be reflected to the ultrasonic transducer 8. Therefore, when the transducer 8 is rotated left and right to change the direction of transmitting and receiving ultrasonic waves, the ultrasonic waves do not return from the position where the obstacle was.
If the rotation angle φ at this time is known, the direction can be determined. Here, the reflecting plate 9 has a circumferential wall with the ultrasonic transducer 8 at its center, and small pieces of reflecting surfaces are arranged in a step-like manner so that the distances from the ultrasonic transducer are different within the ultrasonic beam. These are reflector plates arranged periodically at

Figure 3 is an example of measuring echoes reflected from a small reflective surface of a reflector that enters the ultrasonic beam.
In the same figure a, the small reflective surface that enters the beam is 3 in the horizontal direction.
When there are two stages in the vertical direction and a total of six surfaces, each surface is named a to f, and Figure b shows the echo obtained at this time. Here, when an ultrasonic wave is emitted at time O, Ta, Tb... After Tc, a, b to f
Echoes Ea, ...Ef reflected from each surface of are received. Here, taking the reflecting surface a as an example, if the distance from the transducer 8 to a is La, and the speed of sound in sodium is v, then Ta=La/v. If the reflecting surfaces of the reflecting plate are arranged regularly as a whole under such conditions that the distances from the transducer 8 are different within the ultrasonic beam, the transducer When rotating horizontally to scope the entire upper part of the core,
As shown in b, six echoes are obtained at the same time on the time axis, regardless of the horizontal position of the transducer. If there is an obstacle between the reactor core and the upper core mechanism and the reflecting surfaces e and f are masked, the echoes Ee and Ef that return from there will not be detected.
The number of echoes measured is four. This allows us to determine which reflective surfaces in the beam are masked from the time at which the unmeasured echoes should be present, and at the same time to determine the size of the obstruction and the gap it forms with the upper core structure. I can do it. Although it is easy to detect obstacles by regularly arranging the reflecting surfaces as described above, the following problems arise in putting this into practical use. In other words, in order to arrange the distances from the transducer to each reflective surface regularly, the reflective surfaces must be arranged at circular positions centered on the transducer position. As a result, the reactor core becomes larger, the space between it and the reactor vessel becomes narrower, the transducer position is limited, and due to the arrangement of other core equipment, it is not possible to install a circular reflecting wall inside the reactor. It may be possible. For this reason, it is extremely difficult to increase the size of the furnace vessel and downsize or eliminate other equipment.
As described above, the conventional arrangement of the reflector plate causes serious inconvenience.

The present invention has been made to eliminate the above-mentioned drawbacks, and is particularly capable of detecting obstacles present in the upper part of the core and measuring gaps in any reactor, without making any changes to the reactor vessel or equipment within the core. An object of the present invention is to provide an ultrasonic fluoroscopy device that enables the following.

An embodiment of the present invention will be described with reference to FIGS. 4 to 6.

FIG. 4 is a cross-sectional view of the device of the present invention. The reflecting plate 9' is a reflecting plate which is made by directly attaching a reflecting surface to the inside of the reactor vessel that satisfies the condition that each reflecting surface in the ultrasonic beam θ is at a different distance from the transducer. In this way, the reflection plate can be set in any shape of furnace.

FIG. 5 is an example of an echo signal obtained by FIG. 4. In other words, a represents the reflecting surfaces present in the beam, and b represents the echo group obtained from each surface at this time. Here, since there is no regularity in the arrangement of the reflecting surfaces, it is difficult to simply detect obstacles from the temporal arrangement of the echo signals.

FIG. 6 is a block diagram of the present invention. The echo sorting circuit 11 sequentially inputs the echo signal k of the ultrasonic transducer 8 via the ultrasonic transmitting/receiving circuit 10, and also inputs the transducer position signal j, and divides the echo group of k. Make each echo correspond to the time of arrival.

The signal that has passed through the echo separation circuit 11 is guided to the echo comparison and determination circuit 12 together with the transducer position signal j. The echo comparison and determination circuit 12 stores combinations of a plurality of small reflecting plates corresponding to the position of the transducer 8, the time of the echoes to return from each small reflecting plate, and the number of echoes. In other words, all the echo patterns of each small reflective surface that make up the reflector are memorized, and by comparing them with this, it becomes clear to which small reflective surface the measured echo corresponds. It is possible to detect objects and measure voids.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view showing an example of a conventional ultrasonic fluoroscope installed in a nuclear reactor, and Figure 2 is A--A in Figure 1.
A cross-sectional view taken along the direction of arrow A′,
FIG. 3 is a diagram showing the relationship with the ultrasonic echoes reflected from the reflector, FIG. 4 is a cross-sectional view showing an embodiment of the reflector according to the present invention, and FIG. 5 is the reflection of FIG. 4. FIG. 6 is a block diagram of an ultrasonic fluoroscope according to the present invention, which is a diagram showing an example of a reflector echo obtained with a plate configuration. 1...Reactor vessel, 7...Fuel assembly, 8...Ultrasonic transducer, 9,9'...Reflector, 10
. . . Ultrasonic wave transmission/reception circuit, 11 . . . Echo classification circuit, 12 . . . Echo comparison/determination circuit, 13 .

Claims (1)

[Claims] 1. An ultrasonic reflector is provided on the inner wall of a reactor vessel that uses liquid metal coolant, and a transducer that emits and receives ultrasonic waves is placed in a position facing this reflector, and the reflector and transducer are placed in a position facing the reflector. In an ultrasonic fluoroscopy device that sees between users, the reflecting plate is divided into a large number of small reflecting plates, and the distances between each of the small reflecting plates and the transducer that enter the ultrasonic beam are different. 3 shows arranged reflection plates, a group of echo signals obtained when the ultrasonic waves emitted from the transducer are reflected by each of the small reflection plates and returned to the transducer sequentially, and the orientation of the transducer. an echo separation circuit that corresponds to the arrival time of each echo signal in the group of echo signals from the transducer position signal; a small reflector corresponding to the transducer position signal; and an echo to be returned from the small reflector. A combination of the signal time and the number of its echo signals is stored in advance, and the signal from the echo separation circuit and the transducer position signal are input to determine the correspondence between each echo signal and its corresponding small piece reflector. 1. An ultrasound fluoroscope, comprising: an echo comparison and determination circuit for making a determination.