JP2013104757A - Water level detection system and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water level detection system which can be additionally installed by small-scaled installation work to existing facilities and has excellent radiation resistance.SOLUTION: According to one embodiment, a water level detection system comprises: a reference gamma ray source 24 which is installed in a water tank 21 in reactor facilities and generates a reference gamma ray; a gamma ray detecting sensor 1 which is disposed at the same height as that of the reference gamma ray source 24 in the vicinity thereof in the water tank 21 and detects gamma rays; a signal processing section 3 to which a gamma ray detecting signal output from the gamma ray detecting sensor 1 is input, performs count processing for defining a detection number of the gamma rays per unit time as a counting rate and outputs the counting rate; a threshold value storage section 5 for storing a threshold value of the counting rate therein beforehand; and a comparison determining section 4 for, in a case where the counting rate output from the signal processing section 3 exceeds the threshold value, determining the gamma ray detecting sensor 1 to be in an exposed state to air from underwater.

Description

  Embodiments of the present invention relate to a water level detection system and method for detecting the water level of a pool installed in a nuclear reactor facility such as a spent fuel storage pool.

  FIG. 7 is a block diagram showing a conventional spent water storage pool water level monitoring device. As shown in FIG. 7, stored fuel 25 that is used fuel is installed in the water of the spent fuel storage pool 21. The liquid level 26 of the spent fuel storage pool 21 is monitored by a float type level switch 31 installed in the vicinity of the normal liquid level 26. The float type level switch 31 includes a water level high switch 32 and a water level low switch 33.

  Thus, since the conventional water level monitoring device does not assume monitoring of the liquid level 26 when the liquid level 26 abnormally decreases, the liquid level 26 lower than the level of the low water level switch 33 cannot be grasped. . The liquid level 26 of the spent fuel storage pool 21 is an important monitoring target for ensuring the soundness of the stored fuel 25. Recently, it has been required to install an additional water level gauge for monitoring the level of the liquid level 26 in the existing spent fuel storage pool 21.

  As a general water level meter, for example, as described in Patent Document 1, there is a differential pressure type level meter applied to a water level meter of a reactor pressure vessel. However, it is difficult to apply this differential pressure type level meter to a spent fuel storage pool because it is necessary to draw the pressure guiding piping outside the reactor pressure vessel.

  Further, since the spent fuel storage pool when the water level is significantly lowered becomes a high radiation environment, it is desired that the structure of the detection unit is simplified as much as possible.

  Furthermore, as a mechanical water level meter excellent in radiation resistance, there are a float type level meter and an air purge type level meter. However, this float type level meter has a seismic problem. Further, the air purge type level meter has a problem in that gaseous secondary waste is generated.

JP-A-5-302840

  By the way, an apparatus for detecting an abnormally lowered water level in an existing spent fuel storage pool is required as follows. That is, as the device, firstly, it is not necessary to form a penetration part on the wall surface of the spent fuel storage pool, and secondly, it is a detection part having a simple structure having radiation resistance, In addition, there is a need for a water level gauge that satisfies the constraints such as small installation work.

  The problem to be solved by the embodiments of the present invention is to provide a water level detection system and method which can be additionally installed in existing equipment by a small-scale installation work and which is excellent in radiation resistance. To do.

  In order to achieve the above object, a water level detection system according to an embodiment of the present invention includes a reference gamma ray source that is installed in a water tank in a nuclear reactor facility and generates a reference gamma ray, and the vicinity of the reference gamma ray source in the water tank. The gamma ray detection sensor that detects gamma rays and the gamma ray detection signal output from the gamma ray detection sensor are input at the same height, and the counting process is performed with the number of gamma ray detections per unit time as the count rate. A signal processing unit that outputs a count rate, a threshold value storage unit that stores a threshold value of the count rate in advance, and the gamma ray detection sensor when the count rate output from the signal processing unit exceeds the threshold value, A comparison / determination unit that determines that the air is exposed from the water to the air, and a determination output unit that receives an air exposure determination result from the comparison / determination unit and outputs an air exposure determination signal. , Characterized in that it comprises a.

  Further, in the water level detection method according to the embodiment of the present invention, the reference gamma ray source and the gamma ray detection sensor are installed in the vicinity of the water tank in the reactor facility at the same height, and the gamma ray irradiated from the reference gamma ray source is used. The gamma ray detection step of detecting the gamma ray detection sensor, the gamma ray detection signal output in the gamma ray detection step is input, and the counting process is performed with the number of gamma ray detections per unit time as the count rate. A signal processing step for outputting, a threshold value storing step for preliminarily storing a threshold value of the counting rate, and the gamma ray detection sensor is evacuated from the water when the counting rate output in the signal processing step exceeds the threshold value. A determination step of determining that the state is exposed inside, and a determination of outputting an air exposure determination signal in response to the air exposure determination result determined in the comparison determination step And having a force step.

  According to the embodiment of the present invention, a water level detection system can be additionally installed in an existing facility by a small-scale installation work, and the radiation resistance is excellent.

1 is a block diagram showing a first embodiment of a water level detection system according to the present invention. It is a block diagram which shows 2nd Embodiment of the water level detection system which concerns on this invention. It is a block diagram which shows 3rd Embodiment of the water level detection system which concerns on this invention. It is a block diagram which shows the automatic operation at the time of the water level normal of 3rd Embodiment. It is a block diagram which shows the automatic operation at the time of the water level fall of 3rd Embodiment. It is a block diagram which shows 4th Embodiment of the water level detection system which concerns on this invention. It is a block diagram which shows the water level monitoring apparatus of the conventional spent fuel storage pool.

  Embodiments of a water level detection system according to the present invention will be described below with reference to the drawings. 1 to 6, the structure of the spent fuel storage pool is the same as that in FIG. Further, each of the following embodiments will be described with respect to a case where the present invention is applied to a water level detection system that detects the water level of a spent fuel storage pool in a nuclear reactor facility.

(First embodiment)
FIG. 1 is a block diagram showing a first embodiment of a water level detection system according to the present invention.

  As shown in FIG. 1, the water level detection system of the present embodiment includes a fixed gamma ray detection sensor 1, a reference gamma ray source 24, a signal processing unit 3, a comparison / determination unit 4, a threshold storage unit 5, and a determination output. Unit 6 and a threshold rewriting operation input unit 41.

  The fixed gamma ray detection sensor 1 is installed in the water of a spent fuel storage pool 21 as a water tank in which water 22 is stored in a nuclear reactor facility. The fixed gamma ray detection sensor 1 is installed in a state of being positioned at a predetermined height with respect to the vertical direction in the spent fuel storage pool 21. The fixed gamma ray detection sensor 1 detects gamma rays emitted from the reference gamma ray source 24 and outputs a gamma ray detection signal.

  The reference gamma ray source 24 generates a reference gamma ray. The reference gamma ray source 24 is connected to the fixed gamma ray detection sensor 1 via the support member 23. The reference gamma ray source 24 is disposed in the vicinity of the fixed gamma ray detection sensor 1. The reference gamma ray source 24 is installed at the same height as the height of the fixed gamma ray detection sensor 1.

  The fixed gamma ray detection sensor 1 and the reference gamma ray source 24 are suspended from an operation floor (not shown) of the open end of the spent fuel storage pool 21 by a guide rod or the like, for example, and these are suspended on the inner wall surface of the spent fuel storage pool 21. Positioning is ensured by a positioning means on a projection provided in advance.

  The following measurement system including the signal processing unit 3 is installed outside the spent fuel storage pool 21. The signal processing unit 3 is electrically or optically connected to the fixed gamma ray detection sensor 1 through the signal transmission line 2. Although not shown, the signal processing unit 3 includes an amplification unit, a waveform shaping unit, a peak value discrimination unit, a counting unit, and the like. The amplifying unit amplifies the gamma ray detection signal detected by the fixed gamma ray detection sensor 1. The waveform shaping unit shapes the amplified gamma ray detection signal into a signal pulse. The peak value discriminating unit compares and determines the signal pulse obtained by the waveform shaping unit with a preset threshold value, and sets a pulse exceeding the threshold value as a signal pulse. The counting unit counts the number of the signal pulses. Therefore, the signal processing unit 3 receives the gamma ray detection signal output from the fixed gamma ray detection sensor 1, performs a counting process using the number of detected gamma rays per unit time as a count rate, and outputs the count rate.

  The threshold storage unit 5 stores in advance a threshold of a count rate that is the number of detected gamma rays per unit time. This threshold value is a count rate when the liquid level 26 is at the same height as the fixed gamma ray detection sensor 1.

  The comparison determination unit 4 compares the count rate threshold value stored in advance in the threshold storage unit 5 with the count rate output from the signal processing unit 3. The comparison determination unit 4 determines that the fixed gamma ray detection sensor 1 is exposed from the water to the air when the count rate output from the signal processing unit 3 exceeds the threshold value.

  The determination output unit 6 receives an air exposure determination result from the comparison determination unit 4 and outputs an air exposure determination signal. In this case, the determination output unit 6 displays an image on a monitor or the like or gives a sound notification that the output contact is turned on and the liquid level 26 is at a lower position than the fixed gamma ray detection sensor 1.

  The threshold value rewriting operation input unit 41 is a calibration unit and includes an operation unit such as a push button (not shown). That is, the threshold rewriting operation input unit 41 receives a threshold rewriting operation input from the outside and rewrites the threshold stored in the threshold storage unit 5 to the count rate output from the signal processing unit 3. Specifically, the threshold rewriting operation input unit 41, when confirming that the liquid level 26 is at the same height as the fixed gamma ray detection sensor 1 by visual observation or other water level measurement means, The above push button of the threshold rewriting operation input unit 41 that is an operation input is pressed. Thereby, the threshold value rewriting operation input unit 41 overwrites the threshold value stored in the threshold value storage unit 5 with the count rate output from the signal processing unit 3 at that time. As a result, the relationship between the counting rate and the liquid level 26 can be calibrated.

  Next, the operation of this embodiment will be described.

  For example, it is assumed that the liquid level 26 of the spent fuel storage pool 21 is lower than the vertical height at which the fixed gamma ray detection sensor 1 is installed.

  Then, the water between the fixed gamma ray detection sensor 1 and the reference gamma ray source 24 disappears and becomes air. Here, water has a larger shielding ability of gamma rays than air. Therefore, the gamma rays incident on the fixed gamma ray detection sensor 1 increase due to the absence of water. Thereby, the count rate output from the signal processing unit 3 increases.

  Note that this count rate may be output to the outside of the measurement system as necessary, and referred to as a radioactivity level index in water.

  The count rate when the liquid level 26 is at the same height as the fixed gamma ray detection sensor 1 is stored in the threshold storage unit 5 as a threshold. Since the count rate monotonously increases as the liquid level 26 decreases, the count rate output from the signal processing unit 3 is determined to be larger than the threshold value stored in the threshold value storage unit 5 in the comparison determination unit 4. The

  When the count rate output from the signal processing unit 3 is larger than the threshold value stored in the threshold value storage unit 5, the output contact of the determination output unit 6 is turned on, and the liquid level 26 is at a position lower than the fixed gamma ray detection sensor 1. Information indicating that there is an image is displayed on a monitor or the like, or voice notification is given. As a result, the operator can recognize that the liquid level 26 is at a position lower than the fixed gamma ray detection sensor 1.

  On the other hand, when the liquid level 26 is at a position higher than the fixed gamma ray detection sensor 1, the above-described operation is reversed. In the comparison determination unit 4, it is determined that the count rate output from the signal processing unit 3 is smaller than the threshold value stored in the threshold value storage unit 5.

  When the count rate output from the signal processing unit 3 is smaller than the threshold value stored in the threshold value storage unit 5, the output contact of the determination output unit 6 is turned off and the liquid level 26 is positioned higher than the fixed gamma ray detection sensor 1. Information indicating that there is an image is displayed on a monitor or the like, or voice notification is given.

  As described above, the present embodiment functions as a water level measurement level switch using the fixed gamma ray detection sensor 1. According to the present embodiment, the members to be installed in the water may be small-sized members including only the fixed gamma ray detection sensor 1 and the reference gamma ray source 24, and only need to be installed in the water. Therefore, a large installation work becomes unnecessary when applied to the existing spent fuel storage pool 21. Moreover, since the detection part is the fixed gamma ray detection sensor 1, it is excellent in radiation resistance. Furthermore, if the fluctuation | variation of a water level is grasped | ascertained by the other water level measurement means, the increase in the radioactivity of pool water can be monitored.

  In addition, according to the present embodiment, the threshold value rewriting operation input unit 41 that receives a threshold value rewriting operation input from the outside and rewrites the threshold value stored in the threshold value storage unit 5 to the count rate output from the signal processing unit 3 is provided. Therefore, the relationship between the counting rate and the liquid level 26 can be easily calibrated.

  The support member 23 of the present embodiment is not limited to a member that connects the fixed gamma ray detection sensor 1 and the reference gamma ray source 24. For example, a shielding container in which the fixed gamma ray detection sensor 1 and the reference gamma ray source 24 are disposed is provided. It may be used. The shielding container is formed with communicating holes at the top and bottom, and the water 22 is configured to freely enter and exit according to the surrounding liquid level 26 through these communicating holes.

(Second Embodiment)
FIG. 2 is a block diagram showing a second embodiment of the water level detection system according to the present invention. Note that the same components as those in the first embodiment are denoted by the same reference numerals and redundant description is omitted.

  As shown in FIG. 2, the water level detection system of the present embodiment uses a movable gamma ray detection sensor 7 instead of the fixed gamma ray detection sensor 1 of the first embodiment. This movable gamma ray detection sensor 7 is installed so as to be movable vertically in the spent fuel storage pool 21 in which water 22 is stored in the reactor facility. The movable gamma ray detection sensor 7 detects gamma rays irradiated from the reference gamma ray source 24 and outputs a gamma ray detection signal.

  The reference gamma ray source 24 is connected to the movable gamma ray detection sensor 7 via the support member 23. The reference gamma ray source 24 is disposed in the vicinity of the movable gamma ray detection sensor 7. The reference gamma ray source 24 is movable together with the movable gamma ray detection sensor 7. The movable gamma ray detection sensor 7 and the reference gamma ray source 24 are always in the same mutual positional relationship and are always in the same vertical vertical position.

  In the present embodiment, in addition to the measurement system of the first embodiment installed outside the spent fuel storage pool 21, a drive unit 8, a drive control unit 9, a sensor position manual input unit 14, and a drive amount The detection part 10, the sensor position information conversion part 11, the water level calculation part 12, and the water level output part 13 are provided.

  The movable gamma ray detection sensor 7 is connected to the drive unit 8 via the drive force transmission unit 51. The driving unit 8 is a driving unit such as a motor, and moves the movable gamma ray detection sensor 7 and the reference gamma ray source 24 in the vertical vertical direction via the driving force transmission unit 51.

  The driving force transmission unit 51 is, for example, a rotational force transmission unit such as a gear or a chain attached to the output shaft of the motor that is the driving unit 8, and the rotational force is transmitted from the rotational force transmission unit, and the spent fuel storage pool 21. A ball screw that is vertically installed, a ball nut that is screwed to the ball screw and to which the movable gamma ray detection sensor 7 and the reference gamma ray source 24 are fixed, and a guide rail that guides the movement of the ball nut. ing.

  Therefore, when the motor that is the driving unit 8 is rotationally driven, the driving force transmission unit 51 transmits the rotational force to the ball screw via the rotational force transmission unit. Then, this ball screw rotates around the axis, so that the ball nut moves along the guide rail. As a result, the movable gamma ray detection sensor 7 and the reference gamma ray source 24 move vertically upward or downward, for example.

  The drive control unit 9 receives a manual operation input from the sensor position manual input unit 14 and controls the drive of the motor as the drive unit 8. Specifically, the drive control unit 9 receives the manual operation input and controls the moving direction of the movable gamma ray detection sensor 7 and the reference gamma ray source 24 vertically upward or downward, as well as the motor that is the drive unit 8. Performs on / off control. Here, when the moving direction of the movable gamma ray detection sensor 7 and the reference gamma ray source 24 is converted, the rotation direction changing means configured to rotate the motor as the drive unit 8 in the reverse direction or to include a gear, a cam and the like. Thus, by making the rotation direction of the ball screw reverse, it can be moved in the reverse direction.

  The drive amount detection unit 10 detects the drive amount of the drive unit 8. Specifically, the drive amount detection unit 10 detects the rotational drive amount of the motor that is the drive unit 8.

  The sensor position information conversion unit 11 converts the rotational drive amount of the motor serving as the drive unit 8 into position information of the movable gamma ray detection sensor 7 and the reference gamma ray source 24 in the vertical vertical direction in the spent fuel storage pool 21.

  The water level calculation unit 12 is based on the position information of the movable gamma ray detection sensor 7 and the reference gamma ray source 24 output from the sensor position information conversion unit 11 when the air exposure determination signal from the determination output unit 6 changes. Calculate the water level. That is, the water level calculation unit 12 determines that the output from the sensor position information conversion unit 11 at the time when the contact signal of the determination output unit 6 is switched is the height of the liquid level 26.

  The water level output unit 13 displays an image of the value of the liquid level 26 calculated by the water level calculation unit 12 on a monitor or is notified by voice.

  Next, the operation of this embodiment will be described.

  It is assumed that the threshold value stored in the threshold value storage unit 5 is calibrated so as to have a counting rate when the liquid level 26 is at the same height as the movable gamma ray detection sensor 7.

  Then, when the movable gamma ray detection sensor 7 is moved up and down in the vertical direction by manual operation, the contact signal of the determination output unit 6 is switched when the level becomes equal to the liquid level 26, and the sensor position information conversion unit at that time The water level calculation unit 12 calculates that the output from 11 is the height of the liquid level 26, and the water level output unit 13 displays an image as a water level or provides voice notification.

  As described above, this embodiment functions as a water level measurement level meter using the movable gamma ray detection sensor 7 and capable of continuous water level monitoring. According to the present embodiment, members other than the movable gamma ray detection sensor 7 and the reference gamma ray source 24 can be installed apart from the spent fuel storage pool 21. Therefore, the periphery of the spent fuel storage pool 21 can be a small-scale structure. Therefore, a large installation work becomes unnecessary when applied to the existing spent fuel storage pool 21. Moreover, since the detection part is the fixed gamma ray detection sensor 1, it is excellent in radiation resistance. Furthermore, if the fluctuation | variation of a water level is grasped | ascertained by the other water level measurement means, the increase in the radioactivity of pool water can be monitored.

  The support member 23 is not limited to a member that connects the movable gamma ray detection sensor 7 and the reference gamma ray source 24. For example, a shielding container in which the movable gamma ray detection sensor 7 and the reference gamma ray source 24 are disposed may be used. . The shielding container is formed with communicating holes at the top and bottom, and the water 22 is configured to freely enter and exit according to the surrounding liquid level 26 through these communicating holes. This can also be applied to the following embodiments described later.

(Third embodiment)
FIG. 3 is a block diagram showing a third embodiment of the water level detection system according to the present invention. FIG. 4 is a configuration diagram showing an automatic operation when the water level is normal according to the third embodiment. FIG. 5 is a block diagram showing an automatic operation when the water level is lowered in the third embodiment.

  In addition, the same code | symbol is attached | subjected to the component same as the said 1st Embodiment and 2nd Embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 3, in this embodiment, the sensor position manual input unit 14 is deleted from the configuration of the second embodiment, and a sensor position control calculation unit 15 and a sensor position control program storage unit 16 are added. .

  The drive control unit 9 receives the automatic operation input signal output from the sensor position control calculation unit 15 and controls the drive unit 8.

  The sensor position control program storage unit 16 moves the movable gamma ray detection sensor 7 vertically in the spent fuel storage pool 21 over the entire measurement range, and the air exposure signal output from the determination output unit 6 A program for stopping the movable gamma ray detection sensor 7 at the changing position is stored.

  Specifically, in the sensor position control program storage unit 16, as shown in FIG. 4, the position where the contact switching signal of the determination output unit 6 is switched after the movable gamma ray detection sensor 7 scans the entire measurement range once. The program that stops at is stored.

  The sensor position control calculation unit 15 executes the program stored in the sensor position control program storage unit 16 at regular intervals and outputs a control instruction signal to the drive control unit 9. That is, the sensor position control calculation unit 15 calls and executes the program at regular intervals.

  Next, the operation of this embodiment will be described.

  As shown in FIG. 4, the sensor position control calculation unit 15 executes the above program at regular intervals, thereby re-searching the position where the contact switching signal of the determination output unit 6 is switched. Therefore, the water level output from the water level output unit 13 is updated.

  For example, as shown in FIG. 5, when the height of the liquid level 26 is lower than the height of the movable gamma ray detection sensor 7 before the execution of the above program, the height of the liquid level 26 is decreased after scanning the measurement range. The movable gamma ray detection sensor 7 is stopped, and the lowered water level information is output from the water level output unit 13 and is displayed as an image or notified by voice.

  Thus, according to the present embodiment, the water level information can be periodically and automatically acquired in the continuous water level monitoring method using the movable gamma ray detection sensor 7.

(Fourth embodiment)
FIG. 6 is a block diagram showing a fourth embodiment of the water level detection system according to the present invention.

  In addition, the same code | symbol is attached | subjected to the component same as the said 1st Embodiment-3rd Embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 6, the present embodiment is obtained by adding a count rate distribution recording unit 17, a count rate distribution change detecting unit 18, and a radioactivity increase information output unit 19 to the configuration of the third embodiment.

  As shown in FIG. 6, the count rate distribution recording unit 17 includes a count rate output from the signal processing unit 3 and a sensor position information conversion unit during the execution of the program stored in the sensor position control program storage unit 16. The position information of the movable gamma ray detection sensor 7 output from 11 is input, and the count rate distribution history of the measurement range of the movable gamma ray detection sensor 7 is recorded.

  Specifically, the count rate distribution recording unit 17 converts the count rate output from the signal processing unit 3 and sensor position information every time scanning is performed according to the program stored in the sensor position control program storage unit 16. A count rate distribution relating the height position of the movable gamma ray detection sensor 7 output from the unit 11 is recorded as history information.

  The count rate distribution change detection unit 18 compares the latest count rate distribution recorded in the count rate distribution recording unit 17 with the previous count rate distribution. That is, the count rate distribution change detection unit 18 compares the latest count rate distribution history with the previous count rate distribution history.

  The radioactivity increase information output unit 19 outputs radioactivity increase information when the counting rate distribution change detection unit 18 detects that the underwater radioactivity is increasing. That is, the radioactivity increase information output unit 19 outputs radioactivity increase information when there is a characteristic increase in underwater radioactivity.

  Next, the operation of this embodiment will be described.

  Each time scanning is performed according to the program stored in the sensor position control program storage unit 16, the count rate distribution on the measurement range is recorded in the count rate distribution recording unit 17. For example, consider the case where the stored fuel 25 is damaged in FIG. 6 and the radioactive material is released into water. At this time, the count rate distribution increases as a whole, but in the case of the fluctuation of the water level, the distribution change occurs only in the vicinity of the fluctuation range of the liquid level 26, so that it can be distinguished from the influence of the fluctuation of the water level.

  This distribution change is detected by the count rate distribution change detection unit 18 and the radioactivity increase information output unit 19 indicates that the underwater radioactivity has increased and its level is output to the outside and displayed as an image, or by voice notification. Is done.

  As described above, according to the present embodiment, continuous automatic water level measurement and radioactivity level monitoring can be performed at the same time, and damage of the stored fuel 25 in the spent fuel storage pool 21 can be detected. Can do.

  As described above, the embodiments of the present invention have been described. However, these embodiments are presented as examples, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  For example, in each of the above-described embodiments, the case where the fuel tank is applied to the spent fuel storage pool 21 as a water tank in the reactor facility has been described. However, the present invention is not limited to this, and can be applied to a suppression chamber pool, for example.

DESCRIPTION OF SYMBOLS 1 ... Fixed gamma ray detection sensor 2 ... Signal transmission line 3 ... Signal processing part 4 ... Comparison determination part 5 ... Threshold storage part 6 ... Determination output part 7 ... Movable gamma ray detection sensor 8 ... Drive part 9 ... Drive control part 10 ... Drive amount detection unit 11 ... sensor position information conversion unit 12 ... water level calculation unit 13 ... water level output unit 14 ... sensor position manual input unit 15 ... sensor position control calculation unit 16 ... sensor position control program storage unit 17 ... count rate distribution recording unit 18 ... Count rate distribution change detection unit 19 ... Radioactivity increase information output unit 21 ... Spent fuel storage pool (water tank)
22 ... Water 23 ... Support member 24 ... Reference gamma ray source 25 ... Storage fuel 26 ... Liquid level 31 ... Float type level switch 32 ... Water level high switch 33 ... Water level low switch 41 ... Threshold rewriting operation input unit 51 ... Driving force transmission unit

Claims (10)

A reference gamma ray source that is installed in a water tank in the reactor facility and generates a reference gamma ray;
A gamma ray detection sensor that is disposed at the same height in the vicinity of the reference gamma ray source in the water tank and detects gamma rays;
A signal processing unit that inputs a gamma ray detection signal output from the gamma ray detection sensor, performs a counting process using the number of detected gamma rays per unit time as a count rate, and outputs the count rate;
A threshold storage unit for storing in advance the threshold of the counting rate;
A comparison determination unit that determines that the gamma ray detection sensor is exposed to the air from the water when the count rate output from the signal processing unit exceeds the threshold;
A determination output unit that receives an air exposure determination result from the comparison determination unit and outputs an air exposure determination signal;
A water level detection system comprising:   The threshold rewriting operation input part which receives the threshold rewriting operation input from the outside and rewrites the threshold value memorize | stored in the said threshold value memory | storage part into the count rate output from the said signal processing part is provided. Water level detection system. The gamma ray detection sensor is a movable gamma ray detection sensor installed so as to be movable together with the reference gamma ray source in the vertical direction in the water tank,
A drive unit for moving the movable gamma ray detection sensor in a vertical direction;
A drive control unit that drives and controls the drive unit;
A drive amount detection unit for detecting a drive amount of the drive unit;
A sensor position information conversion unit that converts the drive amount into position information of the movable gamma ray detection sensor in a vertical direction in the water tank;
A water level calculation unit that calculates a water level based on the position information of the movable gamma ray detection sensor output from the sensor position information conversion unit at the time when the air exposure determination signal from the determination output unit changes;
A water level output unit for outputting the water level calculated by the water level calculation unit;
The water level detection system according to claim 1, comprising: A program for moving the movable gamma ray detection sensor in the vertical direction in the water tank over the entire measurement range and stopping the movable gamma ray detection sensor at a position where an air exposure signal output from the determination output unit changes is stored. A sensor position control program storage unit,
A sensor position control calculation unit that executes the program at regular intervals and outputs a control instruction signal to the drive control unit;
The water level detection system according to claim 3, further comprising: During the execution of the program stored in the sensor position control program storage unit, the count rate output from the signal processing unit and the position information of the movable gamma ray detection sensor output from the sensor position information conversion unit are displayed. A count rate distribution recording unit that records the history of the count rate distribution of the measurement range of the movable gamma ray detection sensor,
A count rate distribution change detection unit that compares the latest count rate distribution recorded in the count rate distribution recording unit with the previous count rate distribution;
A radioactivity increase information output unit that outputs radioactivity increase information when the counting rate distribution change detection unit detects that radioactivity in the water is increasing;
The water level detection system according to claim 3 or 4, characterized by comprising: A gamma ray detection step in which a reference gamma ray source and a gamma ray detection sensor are installed in the vicinity and at the same height in a water tank in the reactor facility, and the gamma ray irradiated from the reference gamma ray source is detected by the gamma ray detection sensor;
A signal processing step of inputting a gamma ray detection signal output in the gamma ray detection step, performing a counting process with the number of detected gamma rays per unit time as a count rate, and outputting the count rate;
A threshold value storing step for storing the threshold value of the counting rate in advance;
A comparison and determination step of determining that the gamma ray detection sensor is exposed from the water to the air when the count rate output in the signal processing step exceeds the threshold;
A determination output step of receiving an air exposure determination result determined in the comparison determination step and outputting an air exposure determination signal;
A water level detection method characterized by comprising:   The water level detection method according to claim 6, further comprising a threshold rewriting operation input step of receiving a threshold rewriting operation input from the outside and rewriting the stored threshold value to the count rate output in the signal processing step. The gamma ray detection sensor is a movable gamma ray detection sensor installed so as to be movable along with the reference gamma ray source in the vertical direction in the water tank, and the gamma ray irradiated from the reference gamma ray source together with the reference gamma ray source. A movable gamma ray detection step in which a movable gamma ray detection sensor detects the movable gamma ray while moving in the vertical direction of the pool;
A driving step of moving the movable gamma ray detection sensor in a vertical direction;
A drive control step for controlling the drive step;
A driving amount detecting step for detecting a driving amount in the driving step;
A sensor position information conversion step of converting the drive amount into position information of the movable gamma ray detection sensor in the vertical direction in the water tank;
A water level calculation step of calculating a water level based on the position information of the movable gamma ray detection sensor output in the sensor position information conversion step when the air exposure determination signal output in the determination output step changes. When,
A water level output step for outputting the water level calculated in the water level calculation step;
The water level detection method according to claim 6, comprising: A sensor position control program storage for storing a program for moving the movable gamma ray detection sensor over the entire measurement range and stopping the movable gamma ray detection sensor at a position where the air exposure signal output in the determination output step changes. Process,
A sensor position control calculation step of executing the program at regular intervals and outputting a control instruction in the drive control step;
The water level detection method according to claim 8, comprising: While the program stored in the sensor position control program storage step is being executed, the count rate output in the signal processing step and the movable gamma ray detection sensor output in the sensor position information conversion step A count rate distribution recording step of inputting position information and recording a history of count rate distribution of the measurement range of the movable gamma ray detection sensor;
A count rate distribution change detecting step for comparing the latest count rate distribution recorded in the count rate distribution recording step with the previous count rate distribution;
Radioactivity increase information output step of outputting radioactivity increase information when it is detected that the radioactivity in water is increased in the counting rate distribution change detection step;
The water level detection method according to claim 8 or 9, characterized by comprising:

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