Ultrasonic control system for nuclear reactor reference space

Abstract

The invention relates to nuclear engineering and can be used to control the state of the space above the nuclear reactor zone with liquid metal coolant. The working principle of the ultrasonic control system is based on the excitation and response of ultrasonic signals, which are reflected from structural components located in the space (controlled gap) between the upper level of the fuel assembly head and the lower level of the nuclear reactor rotating plug, cooled by an opaque coolant, such as liquid sodium. The system is used to detect obstacles in the controlled space (controlled gap) of the rotating plug during reloading operations. In order to improve the reliability of detecting obstacles in the controlled space above the core and determine the location of said obstacles, the ultrasonic reflectors are configured in the form of a ring on which at least one row of vertical cylindrical rods is arranged, the ring being attached to a heat shield surrounding the reactor core, preferably one close to the nuclear reactor, wherein the spacing of the cylindrical rods in a row is smaller than the spacing between the components.

Description

[0001] The invention relates to nuclear engineering and can be used to control the state of the space above the nuclear reactor zone with liquid metal coolant. The working principle of the ultrasonic control system is based on the excitation and response of ultrasonic signals, which are reflected from structural components located in the space (controlled gap) between the upper level of the fuel assembly head and the lower level of the nuclear reactor rotating plug, cooled by an opaque coolant, such as liquid sodium. The system is used to detect obstructions of the rotating plug in the controlled space (controlled gap) during reloading operations.

[0002] Systems in which a scanning ultrasound beam propagates in the horizontal direction are called horizontal acoustic vision systems. They are used to obtain the analogue of an optical image of an object located or trapped in a spatial region of a reactor cooled by an opaque liquid metal coolant. Control of the spatial region of the reactor over the optically opaque region can be performed by using ultrasound propagating in a liquid metal heat carrier. In this case, the ultrasonic signal is suitable for reactors with heat carriers opaque to light (sodium, lead, etc.) and can provide an optical image of the object with good resolution.

[0003] In order to improve the reliability of detecting structural components, special ultrasonic reflectors are installed in nuclear reactors, and by reducing the signal from it, it is determined whether there are objects that fall into the range of the ultrasonic beam.

[0004] Typically, control systems for the space above the reaction area are developed with a specific reactor design in mind and cannot be transferred to another reactor without certain changes associated with adapting the design features of the space above the reaction area to each specific device.

[0005] A horizontal sound-visual system for determining the gap between the lower part of the CPS organ and the FA head is known (application N° 58-34799, Japan). The device contains an ultrasonic transducer placed on a rod, connected to an ultrasonic generator and connected through an amplifier to a signal processing and recognition device, an ultrasonic reflector. In the device, the rod with the ultrasonic transducer rotates at a constant angular velocity and moves in height after each revolution. During one revolution, ultrasonic pulses are emitted in unison, and in the intervals between them, they receive reflected pulses.

[0006] The disadvantage of this technical solution is that when the rays reflected from the object do not fall into the plane of the converter, it is not always possible to determine whether there is an object in the area space.

[0007] A system for ultrasonically monitoring the position of structural components in space above the nuclear reactor region with liquid metal coolant is known (US Patent No. 4290849), which includes an ultrasonic transducer for transmitting and receiving pulsed ultrasonic signals, the incident ultrasonic wave is sequentially reflected from the additional ultrasonic reflector, the main reflector and the object (if any) located in the gap between the CPS organ and the FA head, and then returns to the ultrasonic converter along the path it has traveled. In order to avoid interference between the incident and reflected ultrasonic signals, the plane of the reflector is placed at different distances from the transducer.

[0008] In the known technical solution, two straight line segments corresponding to the path of the ultrasonic beam from the ultrasonic source to the ultrasonic reflector and from the ultrasonic reflector to the ultrasonic receiver are indicated as the position of the detected obstacle. At the same time, no answer is given on which segment the obstacle is located.

[0009] The purpose of this technical solution is to increase the reliability of detecting obstacles in space on a controlled mixed area and determining their positions.

[0010] In order to solve this problem, in an ultrasonic control system for the space above a nuclear reaction zone with liquid metal coolant, there is provided an ultrasonic reflector and a scanning ultrasonic mechanism with a driver, comprising a sealed ultrasonic transducer - in a controlled gap between a lower mark of an uncoupled CPS organ and an upper mark of a fuel assembly head, the ultrasonic reflector being made in the form of a ring having at least one row of vertical cylindrical rods thereon, the ring being attached to one of the heat shields surrounding the core, primarily one of the heat shields closest to the nuclear reactor body, the cylindrical rods being arranged in a row with a step smaller than the step between assemblies (step of the reactor grid).

[0011] Placing an ultrasonic reflector (a ring with cylindrical rods) on the heat shield at the closest distance to the reactor vessel allows the position of the standard structure to be controlled. It also provides detection of obstructions to the rotation of the rotating plug in the entire controlled volume of the area space.

[0012] The cylindrical rods are arranged in rows at equal distances from the center of this ring and evenly around its circumference (to facilitate automatic control of the level of reflected signal when scanning the ultrasound beam of the ultrasound reflector from the central cell):

[0013] The height of the cylindrical rods is such that they cover the entire gap between the upper level of the head of the fuel assembly and the lower level of the rotating plug of the reactor and the lower mark of the uncoupled CPS mechanism. They also provide the ability to perform layer-by-layer scanning throughout the controlled space.

[0014] One of the cylindrical rods is located at a selected distance from the center of the ring (smaller or larger than the other rods) and is uniquely determined by the arrival time of the echo pulses through the ultrasound scan. The axis direction of the ultrasound transducer is conveniently taken with this rod as a reference point to facilitate the rotation angle of the ultrasound transducer so that its rotation angle can be more accurately calculated during the scanning process.

[0015] The steps of the cylindrical rods arranged in a row on the ring are smaller than the steps between the components. Otherwise (with a larger step), those pop-up components will not be detected, and when the ultrasound beam is scanned by the ultrasound reflector, these pop-up components will appear in the inner cavity between the cylindrical rods.

[0016] In the case where the surfacing assembly does not cover the entire controlled gap, but only brings the upper narrow part (head) to the height of one layer of ultrasonic scanning, the shadow of the head may fall between the cylindrical rods. To avoid this, the cylindrical rods of the next row are located in the gaps between the cylindrical rods of the previous row.

[0017] In order to be able to clearly determine the reference point for the ultrasound transducer's rotation angle and to calculate its rotation angle more accurately during scanning, one of the cylindrical bars is located at a specified distance from the center of this ring. The distance is chosen to be smaller or greater relative to the other bars.

[0018] The cylindrical rods are fixed to the ring in such a way that they are located in the extension of a line passing through the center of the core and the center of the head of the remote fuel assembly.

[0019] The side of the cylindrical rod is roughened, for example in the form of cross knurling, which increases the reflectivity of the cylindrical rod. It also ensures that during the control process, the ultrasonic signal is returned to the ultrasonic transducer regardless of the position of the ultrasonic transducer (in the center or periphery of the controlled space).

[0020] During long-term operation of the reactor, the geometric dimensions and shapes of its components change, including an increase in the deviation of the shaped cylindrical surfaces of the rods from the vertical. This leads to a significant decrease in the amplitude of the echo signal and, as a result, a decrease in the probability of detecting distant components.

[0021] The presence of roughness increases the possibility of detecting distant components.

[0022] When using an ultrasonic inspection system for spatial area in a "large" reactor, it is best to form an angle reflector on the side of a cylindrical rod, which has the effect of returning the ultrasonic beam incident on it in the opposite direction. When forming the ultrasonic reflector, it is necessary to place vertical cylindrical rods on the ring so that the axis of the angle reflector points to the center of the ring.

[0023] As a corner reflector on the side of the cylindrical rod, at least one conical groove with a right angle at the top is made, ending with a through hole. The axis of the right angle coincides with the axis of the conical groove and the axis direction of the ultrasonic transducer and forms a right angle with the axis of the cylindrical rod.

[0024] The cylindrical rods may be arranged in two (or more) annular rows, offset relative to each other such that the rods of an outer row are oriented relative to the center of the annulus between adjacent rods of an inner row.

[0025] A scanning ultrasonic mechanism with a driver, comprising a carrier bar with a sealed ultrasonic transducer (transmitter and receiver of ultrasonic signals), is mounted under the FA overload channel located on the periphery of the reactor's small rotating plug. In addition, this device is placed in the space released after removing the embedded pipe from the reactor, and is intended for the placement of a loop channel or other irradiation equipment in the center of the core.

[0026] The cylindrical rods are mounted on the ring at a certain spacing so that when they scan alternately, the ultrasonic signals reflected from adjacent rods and reaching the ultrasonic transducer overlap in space at least at a level of 0.707. This is to avoid losing information signals about the presence of obstacles in the space between the directions pointing to adjacent rods, such as the presence of a pop-up component.

[0027] The step between the cylindrical rods is related to the step between the components and the diameter of the ultrasonic beam at the level of 0.707, which depends on the equipment of the transducer, the frequency of the ultrasonic waves used, their propagation speed in the medium, and the distance to the irradiated object, that is, the distance to the adjacent rods, that is, the step between the cylindrical rods is set to be smaller than the step between the components and is selected so that the ultrasonic waves reflected from the adjacent rods overlap on the receiving surface of the ultrasonic transducer.

[0028] This ensures that in the presence of an obstacle in the path of the ultrasound beam there is an informative signal (reduction of the signal from the ultrasound reflector). This is independent of the distance at which the obstacle appears from the ultrasound transducer and the slope of its surface.

[0029] The ultrasonic control system in the space above the nuclear reaction area is shown in the figure.

[0030] Figure 1 A vertical section of the reactor is shown with the components of the sound-visual system placed outside the rotating plug, where:

[0031] 1-large rotating plug; 2-small rotating plug with CPS organ; 3-CPS guide tube; 4-cylindrical rod; 5-ring; 6-heat shield; 7-fuel assembly; 8-sound and visual probe; 9-liquid-metal coolant; 10-overload channel; 11-reactor vessel; 12-ultrasonic transducer.

[0032] Figure 2 A horizontal section of a reactor in the upper space of the region of a nuclear reactor with components of an ultrasonic control system, located outside the rotating plug, wherein:

[0033] 4-cylindrical rod; 5-sealing ring; 11-reactor; 12, 13-ultrasonic transducers. A, B, C, D-sectors detect obstacles to the rotation of the rotary plug, located in an area away from the corresponding power protection device.

[0034] Figure 3 A horizontal cross section of a nuclear reactor is shown, with components of an ultrasonic control system arranged in the zone space. Among them:

[0035] 1 - large rotating tube (schematically shown); 2 - small rotating tube (schematically shown); 4 - cylindrical rod; 5 - ring; 11 - reactor vessel; 14 - central pipe; 15 - processing channel; Ultrasonic transducers 12 and 13 are installed in channels 14 and 15 respectively.

[0036] Figure 4-7 Different variations of conical grooves in the sides of the cylindrical rods are shown, which are particularly important for large reactors (core diameter 4-9m).

[0037] The working principle of the device is as follows.

[0038] The ultrasonic transducers 12 and 13 emit a series of ultrasonic signals into the liquid metal coolant 9, propagating along the acoustic axis of each ultrasonic transducer through the liquid metal coolant 9, and are spatially localized in the form of an ultrasonic beam in a controlled gap between the upper level of the fuel assembly head and the lower level of the rotating plug (the lower mark of the device installed on the rotating plug). By reducing the amplitude of the echo signal from the cylindrical rod 4 (the so-called bottom signal), they judge whether there is an obstacle blocking the ultrasonic beam, and by fixing the ultrasonic transducer 12 at different heights and rotating the probe 8 at the same time during the time interval between the radiation and the bottom signal, the regional space is scanned layer by layer with the ultrasonic beam.

[0039] There are two possible options for placing the acoustic and visual probe 8 in the reactor:

[0040] - stationary (in specially designated places outside rotating traffic jams 1 and 2);

[0041] - a groove (from the central channel of the reactor, the embedded pipe is removed, in which during the micro-movements the irradiation device is located, and in its place the acoustic-visual probe 8 is installed).

[0042] An example of a stationary placement of the acoustic and visual probe 8 in a reactor is shown in Figure 1 and 2 , an example of a grooved version is shown in Figure 3 .

[0043] Before the start of the core assembly overload, an ultrasonic monitoring system of the position of the structural components in the space above the nuclear reactor area is activated on the stopped reactor. This is done to confirm that there is no mechanical connection between the rotating plug and the core.

[0044] When the acoustic and visual probe 8 is stationary in the reactor, the ultrasonic transducer 12 emits a series of ultrasonic signals to the liquid metal coolant 9 and receives the reflected signal from the opposite direction (the echo from one of the cylindrical rods 4). Foreign matter. The position of the object, that is, the path of the ultrasonic beam, is determined by the propagation time of the echo signal and the azimuth of the ultrasonic transducer 12. If this object does not produce an echo signal released from the background noise, it is detected by reducing the amplitude of the "bottom" signal, and only the azimuth of the ultrasonic transducer 12 is used to determine the position. In the case of a significant drop in the amplitude of the "bottom" signal recorded when scanning the space above the above area with the ultrasonic transducer 13, the intersection of the ultrasonic rays will indicate the most likely position of the object. The intersection of the ultrasonic beam corresponds to a fixed azimuth.

[0045] In order to ensure the amplitude of the "bottom" signal, which is many times higher than the background noise level, the axis of the cylindrical rod 4 is directed by the conical groove to the axis of the ultrasonic transducer. The angle of the top of the conical groove is made straight to provide a mirror reflection of the scanning beam (Scheme 6). The axis of the conical groove of the cylindrical rod 4 located in sector B points alternately: even numbers point to the ultrasonic transducer 12, and odd numbers point to the ultrasonic transducer 13. The axis of the conical groove of the cylindrical rod 4 located in sector D is directed to the ultrasonic transducer 13. The axis of the conical groove of the cylindrical rod 4 located in sector B points alternately: even numbers point to the converter 13, and odd numbers point to the converter 12. The axis of the conical recess of the cylindrical rod 4, located in sector A, is directed to the converter 12.

[0046] The ultrasonic reflector, made in the form of an intermittent series of cylindrical rods, provides a more accurate calculation of the ultrasonic reflector rotation angle than a continuous ultrasonic reflector made in the form of a solid cylindrical screen.

[0047] In order to minimize the probability of losing the signal about foreign objects located in the above-mentioned area space, the steps between the cylindrical rods should be proportional to the steps of the reactor grid. In this case, the diameter of the cylindrical rods must be proportional to the diameter of the fuel assembly head.

[0048] The diameter of the focal spot, where the main energy of the ultrasound beam is concentrated, should be chosen to be proportional to the apparent size of the conical recess. It depends on the size of the ultrasonic transducer, the frequency of the ultrasound used, the propagation speed of ultrasound in the medium and the distance to the cylindrical rods. The minimum permissible step size between the cylindrical rods covered simultaneously by the focal spot corresponds to the Pearson criterion, according to which the echo signals from these rods are considered distinguishable. If the combination of influencing factors makes it difficult to distinguish the echo signals from adjacent cylindrical rods, the step size between adjacent rods is increased. Still a second row of such rods is added, located on a concentric circle of larger diameter in the gaps between the rods of the first row.

[0049] If the height of the space above the controlled area allows, two or more conical recesses can be made in the cylindrical rod, each directed to its own ultrasonic transducer ( Figure 7 ).

[0050] With the groove for placing the acoustic and visual probe 8 in the reactor ( Figure 3 ), ultrasonic transducers 12 and 13 are installed in the central channels 14 and 15 respectively. Figure 1 In. Figure 3 As shown, the large cock 1 and the small cock 2 are shown conditionally. The cylindrical rod 4 can be made smooth, with a conical recess oriented to the central channel 14, or with a partial side with a right-angled triangular recess at the top and made in relief, for example, in the form of a cross knurling ( Figure 5-7 ). The use of a relief shape for the side of a cylindrical rod allows the use of a mirror image method for the ultrasound transducer 13, located in the overload 15 or any other channel suitable for mounting the probe 8.

Claims

1. A system for ultrasonically monitoring the space above the core of a nuclear reactor, wherein the space is filled with a liquid metal coolant (9), the system comprising: Ultrasonic reflectors, and A scanning ultrasonic mechanism with a driver, the scanning ultrasonic mechanism comprising a support rod with ultrasonic transducers (12, 13), each of the ultrasonic transducers having an acoustic ultrasonic axis coinciding with a horizontal plane intersecting the space filled with the liquid metal coolant (9), wherein the space is made to be a gap between a height below a control rod guide pipe (3) of the nuclear reactor and a height above a head of a fuel assembly (7) of the nuclear reactor that can be monitored by the scanning ultrasonic mechanism, The invention is characterized in that the ultrasonic reflector has the shape of a ring (5) on which a row of vertical cylindrical rods (4) are arranged, a heat shield (6) surrounds the core (11) of the nuclear reactor, the ring (5) is attached to the heat shield (6) of the nuclear reactor, wherein the distance between adjacent cylindrical rods (4) in a row is smaller than the distance between adjacent fuel assemblies (7) of the nuclear reactor.

2. The system according to claim 1, characterized in that One of the cylindrical rods (4) is located at a smaller distance from the center of the ring (5) than the other cylindrical rods.

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