JP2015125129A - Spent fuel pool water level monitoring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spent fuel pool water level monitoring system that enables an operator to easily and promptly determining the water level of cooling water.SOLUTION: A spent fuel pool water level monitoring system comprises: a plurality of temperature detectors arranged vertically at predetermined intervals in a spent fuel pool storing spent fuel assemblies in a spent fuel rack and filled with cooling water; a radio wave detector installed above the spent fuel pool and for measuring a water level of the cooling water in the spent fuel pool; and a processing device for displaying first measured water levels obtained based on measured temperatures by the temperature detectors and second measured water levels by the radio wave detector from the past to the present as a history 22 on the same screen of a display device. Furthermore, in a display area 21 on the screen, a block having a height set to the interval between the adjacent temperature detectors is displayed.

Description

  The present invention relates to a system for monitoring cooling water in a spent fuel pool of a nuclear power plant.

  Conventionally, as a method for monitoring the level of spent fuel pool in a nuclear power plant, a displacer type detector capable of monitoring a fixed point of the water level has been used. However, in recent years, continuous monitoring of the water level that can be used even under severe environments such as high temperature conditions has been required. The water level measurement method that enables continuous monitoring of the water level is to reflect radio waves and ultrasonic waves on the water surface, receive the reflected waves with a radio wave detector or ultrasonic detector, and from the propagation time until reception to the water surface There are known a method for measuring the distance of water and a method for measuring the position of the water surface from the difference between the temperature in water and the temperature in the air using a temperature detector.

  Japanese Patent Laying-Open No. 2012-47757 (Patent Document 1) discloses a highly reliable spent fuel pool monitoring device capable of continuously monitoring the water level of fuel pool water. Moreover, the water level detector which comprises it is a radio wave type detector or an ultrasonic type detector.

  Japanese Patent Laid-Open No. 10-153681 (Patent Document 2) discloses a water level measuring device for a pressure suppression pool using a temperature detector. In order to quickly and accurately measure the transition of the pressure suppression pool used in a nuclear reactor plant, etc., this device is equipped with a heating device having a cladding tube filled with an insulating material and a heating wire disposed in the cladding tube, And a thermocouple device having a junction point arranged in the heating region by the heating wire and a junction point arranged outside the heating region in the cladding tube. The water level detection unit is arranged in the pressure suppression pool so that these cladding tubes are offset vertically.

JP 2012-47757 A Japanese Patent Laid-Open No. 10-153681

  As described above, continuous monitoring of the water level is required in the spent fuel pool, and water level detectors using ultrasonic detectors, radio wave detectors, and temperature detectors are used to meet the requirements. Yes.

  However, the ultrasonic detector and radio wave detector described in Patent Document 1 propagate in the gas phase due to environmental fluctuations in the spent fuel pool, for example, temperature, humidity or pressure changes in the gas phase. The ultrasonic waves or microwaves that are received are affected, and errors may occur in the measurement results.

  In addition, in the method of detecting the water level using the temperature detector described in Patent Document 2, since the plurality of temperature detectors are offset up and down, the detected water level becomes discrete and the operator It is difficult to determine the water level easily and quickly.

  Accordingly, the present invention provides a spent fuel pool water level monitoring system in which an operator can easily and quickly determine the coolant level.

  In order to solve the above-described problems, the present invention provides a plurality of temperature detectors arranged at predetermined intervals in the spent fuel pool in the vertical direction, and the spent fuel pool installed above the spent fuel pool. The same screen of the display device shows a water level measuring device that measures the water level of the cooling water, a first measured water level that is obtained based on the temperature measured by the plurality of temperature detectors, and a second measured water level that is obtained by the water level measuring device It has the processing apparatus displayed on the top.

  ADVANTAGE OF THE INVENTION According to this invention, the water level monitoring system of the spent fuel pool which an operator can judge the water level of a cooling water easily and rapidly can be provided.

1 is a schematic configuration diagram of a spent fuel pool water level monitoring system according to Embodiment 1, which is an embodiment of the present invention. FIG. 2 is a screen display example of the display device of FIG. It is an example of a screen display of the display apparatus of FIG. It is a spent fuel pool water level monitoring system calibration flow figure concerning Example 2 which is one example of the present invention. It is a flowchart explaining the correction process of the measurement water level by the detector which concerns on Example 2 of this invention. It is a calibration flow figure of the water level monitoring system of the spent fuel pool concerning Example 3 which is one example of the present invention. It is a flowchart explaining the correction process of the measurement water level by the detector which concerns on Example 3 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a spent fuel pool water level monitoring system according to a first embodiment which is an embodiment. As shown in FIG. 1, a plurality of spent fuel assemblies 17 are accommodated in a spent fuel rack 18 in a spent fuel pool 11 of a nuclear power plant and filled with cooling water. The cooling water is circulated in the spent fuel pool 11 by a circulation pump (not shown). When the height b of the spent fuel rack 18 and the height a of the spent fuel assembly 17 are set, the reference water level of the cooling water in the spent fuel pool 11 cools the decay heat of the spent fuel assembly 17. The amount of cooling water is managed to be sufficient. The spent fuel pool water level monitoring system 10 of this embodiment includes a plurality of temperature detectors 12a to 12h, a radio wave detector 16 as a water level measuring device installed above the spent fuel pool and measuring the water level of cooling water, A temperature measuring device 13 that takes in signals from a plurality of temperature detectors 12a to 12h and measures the temperature, a processing device 14 that processes the measurement signal from the radio wave detector 16 and the measured temperature from the temperature measuring device 13, and the processing device 14 It is comprised from the display apparatus 15 which displays the process result by.

  The temperature detectors 12a to 12h of the present embodiment are configured, for example, by arranging a thermocouple and a heater facing the thermocouple in a cladding tube and filling the inside with an insulating material. The heater is energized for a predetermined time (for example, 10 seconds), and the area around the contact point of the thermocouple disposed in the cladding tube is heated. When the thermocouple contact position in the temperature detector is in the cooling water, the heat is diffused by the surrounding cooling water, and the temperature detected by the thermocouple contact is low. On the other hand, when the contact position of the thermocouple in the temperature detector is located above the coolant level, that is, in the gas phase, the heat generated by the heater is not diffused and detected compared to the coolant. The temperature is close to the heating temperature. As described above, the temperature detectors 12a to 12h use spent fuel as shown in FIG. 1 to measure the water level of the cooling water by utilizing the temperature difference due to the difference in thermal diffusion between the gas phase and the cooling water. The pool 11 is offset up and down. In addition, although the case where eight temperature detectors are installed is illustrated in FIG. 1, it is not restricted to this. By increasing the number of installed temperature detectors and narrowing the arrangement interval in the vertical direction, it becomes possible to obtain the measurement water level in more detail. Further, by using a temperature detector in which a thermocouple and a heater are arranged in the cladding tube, it is possible to detect a change in water level even when the temperature difference between the coolant temperature and the gas phase is low.

  In the present embodiment, a temperature detector in which a thermocouple and a heater are arranged in the cladding tube is used. However, the present invention is not limited to this, and a temperature detector in which only the thermocouple is arranged in the cladding tube may be used. In this case, when the change in temperature measured by each temperature detector exceeds a predetermined threshold value (for example, 5 ° C.), the installation position of the temperature detector has changed from the cooling water to the gas phase, A change in the water level is detected. However, if the temperature of the cooling water is 100 ° C., a temperature gradient is generated as it goes upward from the surface of the cooling water. Therefore, it is difficult to detect the water level in a region where the temperature difference between the coolant temperature and the temperature in the gas phase is less than 5 ° C. However, if the temperature detector is only a thermocouple, the heating time by the heater is unnecessary, and the measurement can be performed in real time.

  The radio wave detector 16 installed above the spent fuel pool 11 irradiates microwaves toward the water surface of the cooling water, and detects the reflected wave from the water surface, thereby detecting the radio wave detector 16 and the water surface. It measures the distance between them. The distance d between the radio wave detector 16 and the water surface shown in the cross-sectional view of the spent fuel pool 11 in FIG. 1 is the time from the start of microwave irradiation to the time when the reflected wave from the water surface is detected. From time t and the propagation velocity c of the microwave, it is obtained by d = c × (t / 2). In the present embodiment, the case where the radio wave detector 16 is used will be described, but the same can be done when an ultrasonic detector is used. In the case of an ultrasonic detector, the time from the start of ultrasonic irradiation to the detection of a reflected wave from the water surface is the ultrasonic propagation time t and the ultrasonic propagation velocity c, and the radio wave detector 16 described below is used. What is necessary is just to perform like a process.

  The radio wave detector 16 is installed at a position where it does not interfere with a crane (not shown) provided for transporting the spent fuel assembly 17 into the spent fuel pool 11.

  Outputs from the temperature detectors 12 a to 12 h are input to the processing device 14 via the temperature measurement device 13. The temperature measuring device 13 continuously measures the temperature. The distance d between the radio wave detector 16 and the water surface obtained by the radio wave detector 16 is input to the processing device 14.

  Here, the processing device 14 includes a storage unit such as a RAM and a ROM, and a CPU, and the CPU reads and executes various programs stored in the ROM. The temperature detected by the temperature detectors 12a to 12h and the temperature detection time input from the temperature measuring device 13 correspond to the installation position of each temperature detector in a storage unit (not shown) or an external storage device provided in the processing device 14. And stored.

  The processing device 14 executes a water level determination process based on the detected temperature and the detection time stored in the storage unit or the external storage device. Specifically, for each temperature detector, the presence or absence of a water level change is determined from the difference between the detected temperature at the previous measurement time and the current detected temperature, and the determination result is associated with the installation position of each temperature detector. Store in the storage unit or the external storage device. In the case of the above-described thermocouple and heater temperature detector, the determination of whether or not the water level has changed is based on the difference between the detected temperatures at the previous measurement time, and in the case of the thermocouple temperature detector, the previous time. This is performed depending on whether or not the difference between the detected temperatures at the measurement time exceeds a predetermined threshold.

Here, instead of the difference between the detected temperature at the previous measurement time and the current detected temperature for each temperature detector, the current detected temperature between adjacent temperature detectors, for example, the temperature detector 12h and the temperature detector 12g. The water level determination process may be performed using the difference between the two. In this case, if a temperature detector using a thermocouple and a heater is used, even if there is a temperature gradient in the gas phase and fluctuations in temperature distribution due to convection of the cooling water, at the interface between the gas phase and the cooling water, The water level can be determined from the difference between the detected temperatures.
Further, the processing device 14 is based on the distance d between the radio wave detector 16 and the water surface inputted at a predetermined sampling period, and the distance L between the radio wave detector 16 stored in advance and the bottom surface of the spent fuel pool 11. The water level (Ld) is obtained and stored together with the measurement time in a storage unit (not shown) or an external storage device.

  The processing device 14 displays the water level determination result for each temperature detector and the water level measured by the radio wave detector 16 on the display device 15.

Below, the display example of the water level determination result displayed on the display device 15 and the display example of the measured water level will be described. FIG. 2 shows a screen display example of the display device 15. As shown in FIG. 2, on the screen of the display device 15, a diagram simulating a cross section of the spent fuel pool 11 is displayed with time on the horizontal axis and water level on the vertical axis. Further, on the screen, usually water level (reference level) 25, the upper end position 24 of the spent fuel rack 18 shown in FIG. 1, measuring the water level at the current time t _A by electric-wave detector 16 is digitally displayed 23.

Screen, the display area 21 to the left in the spent fuel pool, which is displayed level determination processing result of each temperature detector 12a~12h at the current time t _A. In the display area 21, seven blocks are displayed in a row in the vertical direction, the fourth block from the lower side is hatched, and the upper three blocks are outlined. Each block has a temperature detector 12a and 12b, a temperature detector 12b and 12c, a temperature detector 12c and 12d, a temperature detector 12d and 12e, a temperature detector 12e and 12f, and a temperature detector 12f from the top to the bottom. 12g, and the temperature detectors 12g and 12h correspond to the installation height intervals in the spent fuel pool 11.

The display state of the display area 21 in FIG. 2 shows a state in which it is determined that the water level has changed as a result of the water level determination process by the temperature detector 12d. The temperature detectors 12a to 12c indicate no change in the water level and in the gas phase, and the temperature detectors 12e to 12h indicate that there is no change in the water level and is in the cooling water. Border extending horizontally respectively is displayed at a position corresponding to the upper and lower ends of the fourth block from the bottom corresponding to the spacing of the installation height of the temperature detector 12d and 12e, the water level of the cooling water at the current time t _A Visibility to operators in the range is improved. In order to further improve the visibility, the area within the frame line may be highlighted.

The measurement level by electric-wave detector 16, history 22 from the past to the current time t _A is continuously displayed. Thus, the operator is on the screen easily and quickly determine that the measured water level due to electric-wave detector 16 at the current time t _A is within the measurement level range by the temperature detector 12a to 12h.

FIG. 3 shows another screen display example of the display device 15. As in FIG. 2, a diagram simulating the cross section of the spent fuel pool 11 is displayed on the screen of the display device 15, with the horizontal axis representing time and the vertical axis representing the water level. The normal water level (reference water level) 25 is used. The upper end position 24 of the spent fuel rack 18 is displayed. Screen display example of the different 2 is that measuring the water level by the electric-wave detector 16 at the current time t _B deviates the measured water level range of the temperature detector 12a to 12h. The measured water level range at the current time t _B by the temperature detector indicates that it is within the interval between the installation heights of the temperature detectors 12d and 12e, similar to the measured water level range at the time t _A shown in FIG. A state in which the water level measured by the radio wave detector 16 is further measured as a low water level is shown. The operator can immediately determine that adjustment of either the temperature detector or the radio wave detector 16 is necessary, and can quickly perform maintenance.

  In the present embodiment, the case where the processing device 14 determines the presence or absence of a water level change by each temperature detector has been described as an example. However, the present invention is not limited to this, and the temperature measuring device 13 may be configured to execute this processing. good. In this case, the processing device 14 receives from the temperature measurement device 13 the presence or absence of a water level change by each temperature detector, and the other processing may be executed in the same manner as described above.

  According to the present embodiment, the water level measurement result by the temperature detectors 12a to 12h and the water level measurement result by the radio wave detector 16 can be grasped on the same screen, and even when the environmental fluctuation in the spent fuel pool 11 occurs. It becomes possible to quickly determine the coolant level.

  The overall configuration of the spent fuel pool water level monitoring system 10 of this embodiment is the same as that of the first embodiment shown in FIG. The difference from the first embodiment is that it is possible to cope with environmental changes in the spent fuel pool, for example, changes in humidity and temperature in the gas phase, and pressure changes.

  FIG. 4 shows a calibration flow of the radio wave detector 16 of the present embodiment. Similarly to the first embodiment, the processing device 14 determines whether or not the water level has changed for each of the temperature detectors 12a to 12h, and determines whether the water level has changed in any of the temperature detectors (step S1). If it is determined in step S1 that the water level has changed, it is determined which temperature detector has passed the water surface (step S2). Specifically, the temperature detector determined to have a water level change is specified, and the installation position of the specified temperature detector is stored in the storage device 14 or external storage provided in the processing device 14 as described in the first embodiment. Read from the device. Here, the installation positions of the temperature detectors 12 a to 12 h stored in advance in the storage unit or the external storage device are stored as distances from the bottom surface of the spent fuel pool 11. And since the contact of the thermocouple arrange | positioned in the cladding tube of each temperature detector is located in the bottom part of a cladding tube, the installation position of the temperature detector determined with the water level change corresponds to a water level. Then, the distance d between the radio wave detector 16 and the water surface is determined from the difference between the installation position of the obtained temperature detector and the distance L between the radio wave detector 16 stored in advance and the bottom surface of the spent fuel pool 11. Ask for.

  The microwave pulse propagation time t measured by the radio wave detector 16 at the time measured by the temperature detector determined to have a water level change in step S1 is read out from the storage unit in the processing device 14 or an external storage device. (Step S3).

  Based on the microwave pulse propagation time t acquired in step S3 and the distance d between the radio wave detector 16 and the water surface obtained in step S2, the value after calibration of the microwave propagation velocity c is expressed as c = Obtained by d / (t / 2) (step S4). The obtained macro wave propagation velocity c after calibration is stored in a storage unit provided in the processing device 14 or an external storage device, and the calibration processing of the radio wave detector 16 is completed.

  Thereafter, by using the calibrated microwave propagation velocity c, the radio wave detector 16 obtains the distance d = c × (t / 2) between the radio wave detector 16 and the water surface, thereby obtaining a more accurate water level. Measurement is possible.

  This calibration is automatically performed when there is a water level change in the water level monitoring by the temperature detector. For example, when the temperature of the cooling water suddenly rises due to the decay heat of the spent fuel assembly 17 and the amount of vapor in the gas phase above the surface of the cooling water increases, the radio wave detector 16 moves toward the water surface. The microwaves irradiated and the reflected waves from the water surface are decelerated by the influence of this vapor. The microwave propagation velocity c is calibrated by the distance d between the radio wave detector 16 and the water surface based on the change in the water level of the temperature detector that is not affected by the amount of vapor in the gas phase. The fluctuation can be absorbed, and the water level measurement by the radio wave detector 16 can be performed with high accuracy.

  According to the present embodiment, the water level measurement result by the radio wave detector 16 becomes more accurate, and the operator can easily and quickly determine the water level of the cooling water. In this embodiment, an ultrasonic detector may be used instead of the radio wave detector 16.

Hereinafter, correction of the measured water level by the radio wave detector 16 will be described. FIG. 5 shows a flow of correction processing of the measured water level by the radio wave detector 16. The microwave propagation speed c calibration process from step S1 to step S4 is the same as the flow shown in FIG. Here, at step S1, the measurement time by the temperature detector when it is determined that there is water change due to the temperature detector and t _A. The water level measured at time t _A by the radio wave detector 16 is corrected by the corrected microwave propagation velocity c obtained in step S4 (step S5). By correcting the measurement water level at the measurement time t _A in this way, the measurement water level at the current time obtained using the calibrated microwave propagation velocity c displayed on the screen, and the measurement time t _A By displaying the corrected water level on the screen, the history 22 of the measured water level by the radio wave detector 16 becomes more accurate, and the operator can accurately grasp the fluctuation of the measured water level. .

  The overall configuration of the spent fuel pool water level monitoring system 10 of this embodiment is the same as that of the first embodiment shown in FIG. In addition, the second embodiment is different from the second embodiment in that it can cope with environmental fluctuations in the spent fuel pool, for example, humidity and temperature fluctuations in the gas phase, and pressure changes. In this embodiment, it is possible to cope with a change in the mounting state of the radio wave detector 16 due to a disturbance such as an earthquake.

  FIG. 6 shows a calibration flow of the radio wave detector 16 of the present embodiment. The processing device 14 determines whether or not the water level has changed for each of the temperature detectors 12a to 12h, and determines whether the water level has changed in any of the temperature detectors (step S11). Step S11 is repeatedly executed until a water level change is detected by any one of the temperature detectors. If it is determined in step S11 that the water level has changed at the measurement time tc, it is determined which temperature detector the water surface has passed (step S12). Specifically, the temperature detector determined to have a water level change is specified, and the installation position of the specified temperature detector is stored in the storage device 14 or external storage provided in the processing device 14 as described in the first embodiment. Read from the device. Similar to the second embodiment, the measured water level h1 by the temperature detector is obtained from the installation position of the specified temperature detector.

  Next, the microwave pulse propagation time t1 measured by the radio wave detector 16 at the measurement time tc by the temperature detector determined as having a water level change in step S11 is stored in a storage unit or an external storage device in the processing device 14. Is read out and acquired (step S13). Here, the microwave pulse propagation time t1 at the measurement time tc and the water level h1 measured by the temperature detector are stored in the storage unit or the external storage unit, and then whether or not the water level has changed for each temperature detector 12a to 12h. The process proceeds to step S14 where it is determined and it is determined whether any of the temperature detectors has caused a change in the water level. In step S14, similar to step S11, the process is repeatedly executed until a water level change is detected by any one of the temperature detectors. If it is determined in step S14 that the water level has changed at the measurement time td, it is determined which temperature detector the water surface has passed (step S14). A temperature detector determined to have a water level change is specified, and a measured water level h2 by the temperature detector is obtained from the installation position of the specified temperature detector.

  Next, the microwave pulse propagation time t2 measured by the radio wave detector 16 at the measurement time td by the temperature detector determined that the water level has changed in step S14 is stored in the storage unit or the external storage device in the processing device 14. Is read out and acquired (step S16). When the second water level change by the temperature detector is detected in step S14 and the microwave pulse propagation time t2 is acquired in step S16, the measurement water level h2 by the temperature detector and the first water level change detection are detected. The radio wave detector 16 is calibrated using the microwave pulse propagation time t1 stored in the storage unit and the water level h1 measured by the temperature detector (step S17).

  Hereinafter, calibration of the radio wave detector 16 in step S17 will be described. From the distance L between the radio wave detector 16 and the bottom surface of the spent fuel pool 11 and the distance d = c × (t / 2) between the radio wave detector 16 and the water surface, the water level h measured by the radio wave detector 16 is h = L−c × (t / 2). In step S17, c = 2 × (h1-h2) / (t2-t1), L = (h1t2- h2t1) / (t2-t1) is obtained. The obtained microwave propagation velocity c after calibration and the distance L from the bottom of the calibrated radio wave detector 16 and the spent fuel pool 11 are stored in a storage unit provided in the processing device 14 or an external storage device. The calibration process of the equation detector 16 is finished. An ultrasonic detector may be used instead of the radio wave detector 16.

  This calibration is automatically performed when a water level change is detected by the temperature detector and a second water level change is detected from the previous water level change. For example, when there is an n-th water level change, the calibration process is executed using the results of the n, n-1th water level change detection.

  As a result, as in the second embodiment, environmental fluctuations in the gas phase are absorbed, and the water level measurement by the radio wave detector 16 can be performed with high accuracy. Furthermore, according to the present embodiment, the calibration process is executed when the water level change by the temperature detector is detected twice as compared with the first embodiment, so that the timing of the calibration process is delayed by that amount. Even when the mounting position of the radio wave detector 16 or the mounting angle of the radio wave detector 16 is fluctuated due to a disturbance such as an earthquake, the water level can be measured with high accuracy.

  Hereinafter, correction of the measured water level by the radio wave detector 16 will be described. FIG. 7 shows a process flow for correcting the measured water level by the radio wave detector 16. The calibration process of the microwave propagation velocity c and the distance L between the radio wave detector 16 and the bottom of the spent fuel pool 11 from step S11 to step S17 is the same as the flow shown in FIG. The measured water level by the radio wave detector 16 is corrected using the calibrated microwave propagation velocity c obtained in step S17 and the distance L between the calibrated radio wave detector 16 and the bottom surface of the spent fuel pool 11. (Step S18). Here, the correction of the measured water level by the radio wave detector 16 is performed by correcting the measured water level at the measurement time td when the second water level change is detected by the temperature detector, or the first change in the water level is detected by the temperature detector. The measured water level at the measurement time tc may also be corrected. As described above, the corrected water level of the measured water level measured in the past is displayed on the screen, so that the measured water level history 22 by the radio wave detector 16 becomes more accurate, and the operator can observe the fluctuation of the measured water level. It is also possible to grasp accurately.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace the configurations of other embodiments with respect to a part of the configurations of the embodiments.

DESCRIPTION OF SYMBOLS 10 Used fuel pool water level monitoring system 11 Used fuel pool 12a-12h Temperature detector 13 Temperature measuring device 14 Processing device 15 Display device 16 Radio wave type detector 17 Used fuel assembly 18 Used fuel rack 21 Display area 22 Radio wave History of the measured water level by the detector 23 Digital display of the measured water level by the radio detector 24 Upper end position of the spent fuel rack 25 Normal water level

Claims (9)

A plurality of temperature detectors arranged at predetermined intervals in the vertical direction in the spent fuel pool;
A water level measuring device that is installed above the spent fuel pool and measures the level of cooling water in the spent fuel pool;
It has a processing device which displays on the same screen of a display device the 1st measurement water level obtained based on the temperature measured by a plurality of temperature detectors, and the 2nd measurement water level by the water level measurement device. Spent fuel pool water level monitoring system. The spent fuel pool water level monitoring system according to claim 1,
The processing device displays the first measured water level by identifying whether or not the temperature detector is in the cooling water corresponding to the position of each temperature detector and displaying the second measured water level. A spent fuel pool water level monitoring system characterized by displaying the history from the past to the present. The spent fuel pool water level monitoring system according to claim 2,
The processing device displays a block having a height between intervals of the adjacent temperature detectors arranged in the vertical direction on the screen, and is the uppermost among the blocks indicating the cooling water. A spent fuel pool water level monitoring system, wherein a frame line extending in a horizontal direction is displayed on the screen at positions corresponding to an upper end and a lower end of a block located. In the spent fuel pool water level monitoring system according to claim 3,
A spent fuel pool water level monitoring system, wherein a region within a frame line extending in a horizontal direction on the screen is highlighted. The spent fuel pool water level monitoring system according to claim 1,
The water level measuring device is a radio wave detector that obtains the second measured water level by irradiating the water surface of the cooling water with microwaves and detecting a reflected wave from the water surface,
The spent fuel pool water level monitoring system, wherein the processing device calibrates the propagation speed of the microwave using the first measured water level. The spent fuel pool water level monitoring system according to claim 5,
The spent fuel pool water level monitoring system, wherein the processing device corrects the second measured water level based on a propagation speed of the microwave after the calibration. The spent fuel pool water level monitoring system according to claim 1,
The water level measuring device is a radio wave detector that obtains the second measured water level by irradiating the water surface of the cooling water with microwaves and detecting a reflected wave from the water surface,
The processor is
After the first measurement time when the first measurement water level was obtained from the change in the measurement temperature by a certain temperature detector, the measurement water level at the first measurement time is different from the change in the measurement temperature by another temperature detector. When the first measurement water level is obtained at the second measurement time,
Using the first measurement water level at the first measurement time and the second measurement time, the distance between the radio wave detector and the bottom surface of the spent fuel pool and the propagation speed of the microwave are calibrated. A spent fuel pool water level monitoring system. The spent fuel pool water level monitoring system according to claim 7,
The processing apparatus corrects the second measured water level based on a distance between the calibrated radio wave detector and a bottom surface of a used fuel pool and a propagation speed of the microwave. Pool water level monitoring system. In the spent fuel pool water level monitoring system according to any one of claims 1 to 8,
The temperature detector has a thermocouple and a heater disposed in the cladding tube so as to face the contact of the thermocouple, heats the surrounding area of the contact by the heater, and measures the temperature after a predetermined time has elapsed. A water level monitoring system for a spent fuel pool.

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