JPS6122883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear reactor configured to quickly detect abnormalities in the reactor core, particularly abnormalities in the loading state of nuclear fuel assemblies.

For example, a nuclear reactor such as a fast breeder reactor, as shown in FIG. The upper furnace mechanism 4 and the container 1
The coolant 9 is configured to flow from a lower inlet a to an upper outlet b.

Between the reactor core 3 and the upper mechanism 4, there is an ultrasonic transducer 7 for detecting, for example, the position and state of the nuclear fuel assembly 5, and a reflector 6 is located opposite the transducer 7. It is provided. Note that the transducer 7 is connected to a cable c, and the cable c is connected to a drive device 8. Note that the transducer 7 is vertically and rotationally driven by a drive device 8 so that the ultrasonic signal crosses the vicinity of the upper part of the reactor core 3 . By the way, when replacing the nuclear fuel assembly, the upper reactor mechanism 4 is moved from the reactor core 3, but in order to do so,
It is necessary to confirm that the upper reactor mechanism 4 and the reactor core 3 are mechanically separated. On the other hand, during operation of the nuclear reactor, the core 3 is damaged due to thermal deformation and force from the coolant 9.
The nuclear fuel assembly 5 loaded on the lifts up,
The reactor upper mechanism 4 may have reached the reactor upper mechanism 4, or the reactor upper mechanism 4 and the reactor core 3, which are connected by control rods during operation but are separated during heat exchange, are incompletely separated. 4 may be in a dangerous situation if rotated.

Therefore, as a means of confirming that the reactor upper structure 4 and the reactor core part 3 are completely separated, the propagation characteristics of ultrasonic waves in the liquid sodium coolant 9 are used to separate the reactor core part 3 and the reactor upper structure 4. A means of checking whether there is a gap between the two has been devised. This principle allows ultrasonic waves to propagate between the reactor core 3 and the upper reactor mechanism 4, and depending on the presence or absence of obstacles between them and the echo level from the obstacles or the echo level from the reflector 6. This is an attempt to detect gaps. First, in the case of the method of confirming the presence or absence of an obstacle (such as a nuclear fuel assembly or control rod) based on the echo level from the obstacle, the performance of the system is greatly influenced by the shape of the obstacle. For example, the nuclear fuel assembly 5 has a hexagonal prism shape, and its reflecting surface is limited to the sound waves in six directions, so it is very rare that a floating nuclear fuel assembly 5 can be detected. As a means to improve this problem, there is a method of checking the presence or absence of obstacles based on the echo level from the reflector. For example, as shown in FIG. 1, a reflector 6 is installed at a position facing the ultrasonic transducer 7 and the center of the furnace. When there is no obstacle, an echo from the reflector 6 can be obtained, but if there is an obstacle, no echo from the reflector 6 can be obtained. Since this means uses the shadow of the obstacle as information, it has the advantage of not being affected by the shape or inclination of the obstacle.
In the case of an echo from an obstacle, if the obstacle is raised and tilted from the direction of sound wave propagation like the nuclear fuel assembly 5', the echo will be transmitted and received by ultrasonic waves as shown by the dotted line X in Figure 1. Since the signal cannot be received at 7, it is determined that there is no obstacle.

However, a major problem with this means is that the mounting conditions for the reflector 6 are strict. Conventionally,
As the reflector 6, a specular reflector having a radius of curvature centered on the ultrasonic transducer 7 is used. That is, when the reflector 6 is in a normal position directly facing the ultrasonic transducer 7 shown by the solid line as shown in FIG. The ultrasonic waves from the transducer 7 are reflected by the reflector 6 and return to the ultrasonic transducer 7, but the reflector 6 may deviate from its normal position and tilt due to the installation of the reflector or due to thermal deformation. tilted reflector 6'
The reflected ultrasonic waves will not return to the ultrasonic transducer 7. For example, in a nuclear reactor on the scale of a DEMO reactor, if the reflector 6 is tilted by 1 degree, the ultrasonic transducer 7
The reflected waves will be shifted by a large width depending on the location, and the echo level will drop significantly, making it difficult to detect obstacles. Therefore, requirements regarding the installation of the reflector 6 and aging thereof are very strict. Therefore, there is a need for a nuclear reactor equipped with a means to alleviate this requirement.

As a means to solve this problem, a reflector 6b whose surface shape is a right-angled triangular groove or a relief surface is used.
It has been proposed to arrange the reflectors 6b with a distance difference of 1/2 or more of the ultrasonic pulse length so that reflected waves from adjacent right-angled triangular grooves or relief surfaces do not interfere. An example of this proposal will be explained with reference to the drawings below.

FIG. 2 shows an example of such a nuclear reactor, and is a schematic enlarged view of the cross section taken along the line A-A' in FIG. 1. This is Figure 3,
The reflectors 6b and 6c shown in FIGS. 4 and 6 are arranged on an arc centered on the ultrasonic transducer 7 with a constant inclination angle, and the reflectors 6b ₁ and 6b ₂
The step is provided in between to prevent echoes from reaching the ultrasonic transducer 7 at the same time in the ultrasonic beam (Fig. 5). This is to make a difference.

By using the reflectors 6b arranged in this manner and having the above shape, the requirements for the reflectors are relaxed. That is, as shown in FIGS. 3(a), (b), and (c), when the inclination angle θ of the reflector 6b is θ≦45°, in any case, the ultrasonic transducer 7 The transmitted ultrasonic wave is reflected by the reflector 6b, and the echo returns to the transducer 7. Further, when the inclination angle θ is θ>45°, the echo reflected by the reflector 6b does not return to the transducer 7, as shown in FIG. 3(d). In this way, there is a large degree of tolerance regarding the inclination of the reflector 6b. This facilitates the installation of the reflector and eliminates the need for maintenance to resist deformation due to aging or thermal changes.

However, in this example, it is necessary to prevent interference of reflected waves when arranging adjacent right-angled triangular grooves or surface-shaped reflectors, so installation inside the reactor is complicated as shown in Figure 2. It is inevitable that it will become.

The present invention has been made in view of the above points,
When installing the reflector, there is no need for special adjustment of the inclination angle as shown in Figure 2, and there is no need to spend time and effort for adjustment. ) becomes larger,
In order to prevent interference with internal equipment used for maintenance work when the reactor is shut down, the diameter of the reactor must be increased, and the reactor does not have to be enlarged due to the installation of reflectors. It is about providing.

That is, the present invention relates to a reactor core housed in a reactor vessel, an ultrasonic transducer provided near the upper end of the reactor core for transmitting and receiving ultrasonic signals that cross over the reactor core, and means for rotating the transducer by a predetermined angle and scanning it up and down; a reflector provided near the upper end of the reactor core and at a position facing the ultrasonic transducer; and energizing the ultrasonic transducer. and means for displaying the received signal in synchronization with the scanning of the ultrasonic transducer, in which the center of rotation of the ultrasonic transducer and the center of the fuel assembly arranged at the outermost periphery are connected. A nuclear reactor characterized in that a plurality of reflectors are installed in a line, the minimum arrangement interval of the reflectors is equal to or greater than the beam width of the ultrasonic wave, and the aperture dimension of the reflector is equal to or less than the width dimension of the outermost fuel assembly. The reactor is also characterized in that the reflector has a right triangular surface shape, a relief groove, or a corner reflector in its surface shape.

In the present invention, the right triangular grooves or salvage-shaped reflectors are arranged at a pitch equal to or larger than the ultrasonic beam width, compared to the prior art in which the right-angled triangular grooves or salvage-shaped reflectors are arranged without gaps in the rotation angle range of the ultrasonic transducer. It is characterized by

Hereinafter, one embodiment of the present invention will be described with reference to FIG. In FIG. 7, only essential parts of the present invention are shown, and the same parts as those in the previous figures are denoted by the same reference numerals, and the explanation of the overlapping parts is omitted. In the figure,
7 is an ultrasonic transducer, S ₁ to _{S o} are fuel assemblies, R ₁
˜R _o indicate right-angled triangular groove reflectors, respectively. The reflector R is located at the center of the ultrasonic transducer 7 and the fuel assembly S ₁ located at the outermost periphery when viewed from the transducer 7.
The fuel assembly is placed on the line connecting the centers of S ₂ , S ₃ ,...
S ₁ , S ₂ , . . . are arranged with an opening dimension WR smaller than a width dimension WS projected from the transducer 7 to the position of the reflector R. With the reflectors R arranged in this manner, all of the fuel assemblies S can be detected by scanning with an ultrasonic beam whose beam width is smaller than the arrangement pitch of the reflectors R. That is, when the fuel assembly S ₁ rises, it affects the echo level from the reflector R ₁ . Fuel assembly S ₄ ,
The same applies to S ₅ and S ₇ .

In addition, for fuel assemblies S ₂ and S ₅ , reflectors
It is detected by the echo level from R ₂ , and the fuel assemblies S ₃ and S ₆ are detected by the echo level from reflector R ₃ . At this time, the ultrasound beam width is equal to the echoes E ₁ and E ₂ from adjacent reflectors.
It is necessary to have a narrow beam width so as not to obtain both at the same time. In the case of the illustrated right-angled triangular groove reflector, the beam width is satisfied by making it less than or equal to the minimum value _P1 of the reflector arrangement pitch.

However, with the reflector arrangement in the above embodiment, echoes from adjacent reflectors are not received by the ultrasonic transducer at the same time, so it is possible to prevent signal level fluctuations caused by mutual interference. I can do it. As a result, it is not necessary to install the reflector at an angle as in the conventional case, so the space for installing the reflector (indicated by S in FIG. 2) can be minimized.

Furthermore, since the echo level of one right-angled triangular groove reflector has little dependence on the inclination angle, there is no need to make special adjustments to the inclination angle during installation work, which simplifies the work. In addition, changes in echo level due to thermal deformation are also significantly reduced.

Also, when fuel assembly S ₁ rises, only the echo level from reflector R ₁ decreases, but in the case of fuel assemblies S ₅ and S ₁₀ , the echo level from reflector R ₁ and R ₂ decreases. The echo levels of both decrease. Furthermore, at the time of fuel assembly S ₁₁ , the echo levels from reflectors R ₁ , R ₂ , and R ₃ simultaneously decrease, so that the floating fuel assembly is It is also possible to determine whether it is a body or an aggregate located nearby.

It should be noted that the present invention is not limited to the above embodiments, and the shape of the reflector is not limited to the right-angled triangular groove reflector, but can also be used in the same manner as a relief surface or a corner reflector. The distances to the ultrasonic transducer do not need to be equal.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of one of the conventional nuclear reactors, FIG. 2 is a schematic cross-sectional view of another conventional nuclear reactor, and FIGS. 3, 4, and 6 are Fig. 5 is an explanatory diagram showing the reflector used in Fig. 2, Fig. 5 is a pulse waveform diagram showing the output voltage of the transducer when the echo from the reflector in Fig. 3 is detected on the receiving surface, Fig. 7 FIG. 1 is an enlarged and partially in-reactor layout diagram showing only the main parts in one embodiment of the nuclear reactor according to the present invention. 1... Reactor vessel, 2... Rotating plug, 3... Reactor core, 4... Reactor upper mechanism, 5, S... Nuclear fuel assembly, 6, R... Reflector, 7... Ultrasonic transducer ,
8... Drive device, 9... Coolant.

Claims (1)

[Claims] 1. A reactor core housed in a reactor vessel, and an ultrasonic transducer that transmits and receives ultrasonic signals across the upper part of the reactor core, which is provided near the upper end of the reactor core. ,
means for rotating the ultrasonic transducer by a predetermined angle and scanning it up and down, a reflector provided near the upper end of the reactor core and at a position facing the ultrasonic transducer, and the ultrasonic transducer and means for displaying the received signal in synchronization with the scanning of the ultrasonic transducer, in which fuel assemblies are arranged at the center of rotation and the outermost periphery of the ultrasonic transducer. A plurality of the above-mentioned reflectors are installed on a line connecting the centers of A nuclear reactor featuring: 2. The nuclear reactor according to claim 1, wherein the reflector has a right triangular or relief surface groove or a corner reflector in its surface shape.