JP6115289B2 - Debris position detection method and position detection apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for determining the position of debris in a reactor pressure vessel or a containment vessel in a situation where cooling water is filled.

  One of the severe accidents at nuclear power plants is core melting. Core melting means that the fuel melts and collapses. In the core melting, the state in which the fuel falls in the reactor pressure vessel is called meltdown, and the state in which the bottom of the reactor pressure vessel is melted and dropped to the reactor containment vessel is called melt-through. When meltdown or meltthrough occurs, so-called debris is generated, in which the nuclear fuel and the melt of the furnace structure are mixed.

  Patent Document 1 describes a configuration in which a core catcher made of a heat-resistant material is laid in a cavity portion under a reactor pressure vessel. In Patent Document 1, a low-melting point oxidation material that contacts and melts with debris is provided on the top of the heat-resistant material, and a high-heat conductive material that is connected to the heat radiating portion is provided under the heat-resistant material, so that the structure is simple and the strength is strong. It states that it can provide a core catcher for a nuclear reactor with excellent cooling effect.

  Patent Document 2 proposes a configuration in which a cavity capable of supplying cooling water in an emergency is provided below the reactor, and an inclined plate for diffusing the melt (debris) from the reactor is provided in the cavity as a cooling promoting device. ing. In Patent Document 2, it is stated that the safety can be improved by accelerating the cooling of the melt falling from the nuclear reactor and cooling it early.

Japanese Unexamined Patent Publication No. 09-2111166 JP 2010-266286 A

  The debris generated by the core melting must be finally recovered from the reactor pressure vessel or reactor containment vessel and appropriately processed. However, nuclear fuel generates strong radiation and high decay heat even when the nuclear reaction is stopped (subcritical state). Therefore, in the collection work, it is necessary to collect the debris preferentially prior to other debris, and for that purpose it is necessary to specify the position of the debris. However, since the position of the debris varies depending on the situation of the accident, the position of the debris cannot be estimated uniformly, and some detection method for specifying the position needs to be considered.

  The problem here is that the position of the debris must be specified in a situation where the reactor is filled with cooling water. When water is filled in the nuclear reactor, radiation attenuates rapidly in water, so it is difficult to specify the position of the gamma ray generation source (debris) using a γ radiation dosimeter or a Compton camera. Moreover, since water absorbs infrared rays well, it is difficult to specify the position of the heat source (debris) with a radiation thermometer or an infrared camera.

  Further, when the lid of the reactor containment vessel cannot be opened, the equipment is inserted using an inspection hole (hereinafter referred to as “inspection hole”) installed on the wall of the reactor containment vessel. However, the inspection hole is as small as about 10 cm in diameter, and a large-scale device cannot be inserted. In addition, when it is desired to observe the inside in a suppression chamber or the like that is not provided with an inspection hole in advance, it is necessary to drill on the wall surface or ceiling surface from the outside. Even in this case, a very large hole cannot be provided in order to prevent radiation leakage, and a small hole of about 10 cm, which is the same as the inspection hole, is formed.

  Accordingly, an object of the present invention is to propose a debris position detection method and apparatus capable of specifying a debris position with a compact apparatus configuration in a situation where cooling water is applied.

  As a result of investigations by the inventors, if the debris generates decay heat, the heated water expands and the refractive index changes, causing fluctuations in the surrounding cooling water (so-called schlieren phenomenon). I thought it was. That is, even if the debris itself cannot be detected or observed, the inventors have focused on the possibility that the position of the debris can be specified using the cooling water that makes measurement difficult. And further investigations have led to the completion of the present invention.

  That is, a typical configuration of the debris position detection method according to the present invention is a method for detecting the position of nuclear fuel debris in water, which is projected onto a screen by irradiating an object with light and projected onto the screen. The present invention is characterized in that light is photographed, a position where fluctuation is present is determined from the photographed image, and a position of debris is detected from the position where fluctuation is present.

  According to the above configuration, it is possible to specify the position of the debris as a heat source even in a situation where the cooling water is stretched. Further, the device only needs to have a light source and a photographing unit, and since the light irradiation direction and the photographing direction of the photographing unit are the same, these elements can be made extremely close to each other and a compact device configuration can be obtained. . Since the work can be performed in the cooling water, the position can be specified and taken out while removing heat from the debris, and the takeout work can be proceeded safely and efficiently.

  Light may be irradiated from above, and the accumulated rubble or floor may be used as a screen. Thereby, the position in a plane direction can be specified quickly.

  Moreover, light may be irradiated from a horizontal direction and the wall surface of a facility may be used as a screen. Since the wall surface is flat, it is easier to judge fluctuations than accumulated rubble, and detection can be performed with higher accuracy.

  The light is preferably parallel light. As a result, even when the distance between the debris and the screen is large, the fluctuation can be determined with higher accuracy.

  A typical configuration of the debris position detection device according to the present invention is a device that detects the position of nuclear fuel debris in water, and projects a light source that projects light onto a screen by irradiating an object with light. And a position determining unit that detects a position of the debris from the position where the fluctuation is present, and a position determination unit that detects the position where the fluctuation is present from the captured image. .

  Said position detection apparatus may be further equipped with the trolley | bogie which mounts a light source and an imaging | photography part and can drive | work the inner wall face of a facility. As a means for traveling on the wall surface, for example, a magnet that does not contact the wall surface (traveling surface) can be used. Moreover, since the attitude | position of a light source and an imaging | photography part is stabilized by drive | working a wall surface, it can detect with high precision.

  The position detection device may further include an underwater ship equipped with a light source and a photographing unit. The underwater ship is suitable for shooting from above. Further, since the moving speed is fast, it is advantageous when scanning a wide range.

  According to the debris position detection method and apparatus according to the present invention, the position of debris can be specified with a compact apparatus configuration in a situation where cooling water is applied.

It is a figure explaining the schematic structure of a nuclear reactor. It is a figure explaining schematic structure of a position detector. It is a figure explaining an imaging | photography direction. It is a figure which shows the state by which the fluctuation was projected on the screen. It is a figure explaining other embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a diagram illustrating a schematic configuration of a nuclear reactor. Hereinafter, a boiling water reactor (BWR) will be described as an example for easy understanding, but the present embodiment can also be applied to an improved boiling water reactor (ABWR).

  A reactor containment vessel 102 is installed in the reactor building 100, and a reactor pressure vessel 104 is installed therein. A suppression pool 106 (also referred to as a pressure suppression chamber) is provided below the reactor containment vessel 102, and the pressure can be lowered by injecting excess steam into the water in the suppression pool 106.

  The reactor containment vessel 102 and the reactor pressure vessel 104 are both sealed vessels and have a sealed space inside. The reactor pressure vessel 104 has a height of about 20 m and a diameter of about 6 m, and the reactor containment vessel 102 is a large facility having a height of about 40 m and a diameter of about 18 m.

  The reactor pressure vessel 104 accommodates a fuel assembly 108 in which fuel rods made of uranium or the like are bundled. The fuel assembly 108 accommodated in the reactor pressure vessel 104 reaches criticality, and heats water (reactor water) filled in the vessel to generate steam.

  FIG. 1 shows the state at the time of the accident. In the drawing, water is drawn in the bottom of the reactor containment vessel 102, the inside of the reactor pressure vessel 104, and the room of the suppression pool 106. During normal operation, the reactor containment vessel 102 is filled with nitrogen, and an appropriate amount of water is held inside the suppression pool 106. Under severe accident conditions, cooling water is injected into the reactor containment vessel 102 and the reactor pressure vessel 104 in order to shield radiation and cool the reactor core. 110 and 112 stay.

  Further, in FIG. 1, the debris 140 is depicted as being deposited below the reactor containment vessel 102 and the reactor pressure vessel 104. When the fuel (fuel pellet) is overheated due to a severe accident, the case (channel box) of the fuel cladding tube and the fuel assembly 108 is melted (core melting: meltdown). As a result, so-called debris is generated in which a melt of the fuel and the furnace structure is mixed. Although debris is considered to be deposited in the lower part of the reactor pressure vessel 104, depending on the degree, the bottom of the reactor pressure vessel may be melted and dropped to the reactor containment vessel 102 (melt-through). Therefore, as shown in FIG. 1, it is considered that the debris 140 is deposited on the bottom of the reactor pressure vessel 104 and the reactor containment vessel 102.

  Although the debris 140 needs to be recovered, even if the nuclear reaction is stopped (subcritical state), high decay heat and strong radiation are generated, so a cooling period of several years must be waited. Then, when collecting the debris 140, it is necessary to specify the position of the debris 140 as accurately as possible. This is because it is difficult to think that only the debris 140 is deposited on the bottom of the reactor containment vessel 102 or the reactor pressure vessel 104, and many other collapsed structures and other non-radioactive materials are also deposited. This is because the debris 140 having strong radioactivity is preferentially taken out.

  However, when recovering, the cooling water 110 is used to shield radiation and cool the core. At the same time, there is a high possibility that the debris 140 is underlayed by another structure or buried in a melt of another material, which makes it more difficult to specify the position.

  As described above, since the debris 140 generates a high decay heat, the heated water expands and the refractive index changes, and fluctuations (so-called Schlieren phenomenon) occur in the surrounding cooling water 110. Therefore, by detecting the fluctuation in the cooling water 110, the fluctuation position can be detected as the debris position. That is, the position of debris is detected by irradiating light into the flow and photographing it, and determining the position of fluctuation in the video.

  Here, the Schlieren method is known as a method for visualizing the Schlieren phenomenon. In the Schlieren method, light from a point light source is converted into parallel rays by a collimator lens, passed through a target object, and condensed again at one point through a collimator. If there is uneven refractive index in the vicinity of the object, the focal point shifts. Therefore, the uneven refractive index is visualized as bright and dark by installing a knife edge at the focal position to block out of focus light.

  However, since the lid of the reactor containment vessel cannot be opened under severe accidents, it is necessary to insert equipment from the inspection hole 114 provided in the wall surface of the reactor containment vessel 102. The problem here is that the inspection hole 114 is as small as about 10 cm in diameter, and a large-scale device cannot be inserted. As described above, the Schlieren method requires a light source and a camera on both sides of the object. Therefore, the apparatus for carrying out the Schlieren method is relatively large, and it is virtually impossible to insert it from the small inspection hole 114 as described above.

  On the other hand, the present invention uses only a light source and a photographing unit (camera) as a device to be inserted in the field. In addition, since the light irradiation direction and the photographing direction of the photographing unit are the same, these elements can be extremely close to each other. From these things, it can be set as a very compact apparatus structure, and it enables it to insert an apparatus from a test | inspection hole or a small hole equivalent to this.

  First, as shown in FIG. 1, a debris position detection device (hereinafter referred to as “position detection device 120”) includes an image analysis device 122, an insertion tube 124 inserted into the inspection hole 114, and a distal end of the insertion tube 124. And a head 126 connected to the head. The insertion tube 124 is a flexible tube having flexibility, and is capable of inserting an optical cable or a signal cable connecting between the image analysis device 122 and the head 126 and moving and supporting the head 126 to an arbitrary position. it can.

  FIG. 2 is a diagram illustrating a schematic configuration of the position detection device 120. The head 126 is provided with a light source 128 that irradiates light onto an object and projects it onto a screen, and a photographing unit 130 (camera) that photographs light projected onto the screen. The light irradiation direction of the light source 128 and the imaging direction of the imaging unit 130 (the optical axis direction of the camera lens) are substantially parallel.

  Objects to be irradiated with light by the light source 128 are debris and debris deposited on the bottom surfaces of the reactor pressure vessel 104, the reactor containment vessel 102, the suppression pool 106, and the like. The image capturing unit 130 captures a range irradiated with light, but the purpose of capturing is not the object itself but the shadow reflected on the screen behind the object.

  What is referred to here as a screen does not have a banner. FIG. 3 is a diagram for explaining the photographing direction. When light is irradiated from above as shown in FIG. 3A, the accumulated rubble or floor corresponds to the screen. When the light is irradiated from the horizontal direction as shown in FIG. 3B, the inner wall surface of the facility such as the reactor pressure vessel 104 or the reactor containment vessel 102 corresponds to the screen.

  FIG. 4 is a diagram showing a state in which the fluctuation is projected on the screen. FIG. 4A is a photograph of the experiment, and FIG. 4B is an explanatory diagram thereof. In FIG. 4, the slanted rod 146 is a heater assuming a fuel rod. Referring to FIGS. 4A and 4B, fluctuation cannot be observed around the rod 146. However, it can be seen that fluctuations (brightness unevenness) are reflected around the shadow of the bar 146 in the portion of the back wall (screen) irradiated with light. In FIG. 4B, a portion that can be determined as fluctuation is indicated by a broken line. From this, it can be seen that it is difficult to distinguish the fluctuation even if the object is simply photographed, but it can be discriminated if it is projected onto the screen.

  The light emitted from the light source 128 is preferably parallel light. Although there is a case where the distance from the object to the screen is far away, fluctuations can be determined with higher accuracy by using parallel light. However, fluctuations can be detected without difficulty even if the light is diffused to some extent. There is a merit that the image on the screen becomes larger if the light is expanded more than the parallel light. However, if the light is spread too much, there is a demerit that the amount of light weakens, and it is necessary to allow it. As the parallel light, spotlight, diffuse parallel light obtained by spreading laser light with a collimator lens, or diffuse quasi-parallel light can be used.

  The image analysis device 122 includes a fluctuation determination unit 132, a position specifying unit 134, and an output unit 136.

  The fluctuation determination unit 132 determines a position where there is fluctuation from the photographed image. The determination of fluctuation can be made by capturing a change in the image on the premise that the photographing unit 130 is kept stationary. For example, image data is continuously acquired from the imaging unit 130 of the head 126, the luminance of each pixel is compared between images (between frames), and it is determined that there is fluctuation in a pixel having a change of a predetermined value or more. be able to. Also, a known technique such as motion detection in a video compression technique such as mpeg may be used.

  The position specifying unit 134 detects the debris position from the fluctuation position detected by the fluctuation determination unit 132. The process of the position specifying unit 134 is coordinate conversion if it is described very simply. When light is irradiated from above, the position with fluctuation can be regarded as the position of debris, so the process is simple. When light is irradiated from the horizontal direction, debris exists at any position on the optical axis. Therefore, when irradiating light from the horizontal direction, it is necessary to perform imaging from at least two directions. For example, scanning is performed so as to look around the facility from one position, and then scanning from a different position. The position specifying unit 134 can specify the position of fluctuation on the plane coordinates, that is, the position of debris by multiplying the positions of fluctuation determined from two directions.

  The output unit 136 outputs the detected debris position as an image or a numerical value. The output signal can be displayed on a monitor 142 or a printer (not shown), image data or numerical data can be stored in a recording medium, or transmitted from a network.

  According to the above configuration, it is possible to specify the position of the debris 140 as a heat source even in a situation where the cooling water is stretched. Further, the device only needs to have the light source 128 and the photographing unit 130, and since the light irradiation direction and the photographing direction of the photographing unit 130 are the same, these elements can be made extremely close to each other, and a compact device configuration is obtained. be able to. Since the work can be performed in the cooling water, it is possible to specify the position and take out the work while removing heat from the debris 140, and the work can be carried out safely and efficiently.

  FIG. 5 is a diagram for explaining another embodiment. In the embodiment described above, the head 126 is moved and supported by the insertion tube 124. However, depending on the positional relationship between the inspection hole 114 and the debris 140, the insertion tube 124 may be too long, and the posture of the head 126 may not be stable. In addition, when the range becomes wide like the suppression pool 106, the range that can be photographed by the insertion tube 124 may not be covered.

  Therefore, as shown in FIG. 5A, instead of the insertion tube 124 and the head 126, the light source 128 and the imaging unit 130 may be mounted on a cart 150 that can travel on the wall surface 102a of the facility. The cart can be run remotely by means of wheels 152. Furthermore, by including the magnet 154 supported at a position where it does not come into contact with the wall surface 102a (the ground contact surface), it can be attracted to the wall surface 102a to travel. The light source 128 and the photographing unit 130 are preferably attached to a movable pan head 156 so that the light irradiation direction and the photographing direction can be adjusted by remote control.

  Since the postures of the light source 128 and the photographing unit 130 are stabilized by traveling on the wall surface 102a by the carriage 150 as in the above configuration, detection can be performed with high accuracy. Note that the cable 160 connecting the carriage 150 and the image analysis device 122 does not need to support the head unlike the insertion tube 124, and therefore, a cable that is much thinner, lighter, and more flexible (soft) can be used. Further, instead of the cable 160, a wireless connection may be used.

  FIG. 5B shows an example in which the light source 128 and the imaging unit 130 are mounted on the underwater ship 170 instead of the insertion tube 124 and the head 126. The underwater ship 170 is suitable for photographing from above. Further, since the moving speed is fast, it is advantageous when scanning a wide range. However, since the posture of the underwater boat 170 is difficult to stabilize, it is preferable to increase the frame rate of the video imaged by the imaging unit 130 (for example, 60 fps or 120 fps).

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  In the above-described embodiment, the inside of the reactor containment vessel 102 is described as an example. However, it is also possible to observe the inside of the reactor pressure vessel 104 and the suppression pool 106 in exactly the same manner.

  INDUSTRIAL APPLICABILITY The present invention can be used as a method and an apparatus for identifying the position of debris in a reactor pressure vessel or a containment vessel in a situation where cooling water is filled.

DESCRIPTION OF SYMBOLS 100 ... Reactor building, 102 ... Reactor containment vessel, 102a ... Wall surface, 104 ... Reactor pressure vessel, 106 ... Suppression pool, 108 ... Fuel assembly, 110 ... Cooling water, 112 ... Cooling water, 114 ... Inspection hole, DESCRIPTION OF SYMBOLS 120 ... Position detection apparatus, 122 ... Image analysis apparatus, 124 ... Insertion tube, 126 ... Head, 128 ... Light source, 130 ... Imaging | photography part, 132 ... Fluctuation judgment part, 134 ... Position specification part, 136 ... Output part, 140 ... Debris , 142 ... monitor, 146 ... rod, 150 ... trolley, 152 ... wheel, 154 ... magnet, 156 ... pan head, 160 ... cable, 170 ... underwater ship

Claims (7)

A method for detecting the position of nuclear fuel debris in water,
Irradiate the object with light and project it onto the screen,
Photographing the light projected on the screen,
Judge the position where there is fluctuation from the photographed image,
A debris position detection method, wherein the position of the debris is detected from a position where the fluctuation exists. The light is irradiated from above,
The debris position detection method according to claim 1, wherein accumulated debris or a floor surface is used as the screen. The light is emitted from the horizontal direction,
The debris position detection method according to claim 1, wherein a wall surface of a facility is used as the screen.   The debris position detection method according to claim 1, wherein the light is parallel light. A device for detecting the position of nuclear fuel debris in water,
A light source that projects light onto a screen by irradiating the object with light;
A photographing unit for photographing the light projected on the screen;
A fluctuation determination unit that determines a position where fluctuation is present from the captured image;
A debris position detection apparatus comprising: a position specifying unit that detects a position of debris from a position where the fluctuation exists.   The debris position detection device according to claim 5, further comprising a carriage that is mounted with the light source and a photographing unit and is capable of traveling on an inner wall surface of a facility.   The debris position detection device according to claim 5, further comprising an underwater ship equipped with the light source and a photographing unit.