Detection sensitivity calibration system for mobile detector

Abstract

To suitably calibrate the detection sensitivity of a mobile detector.SOLUTION: A detection sensitivity calibration system 100 comprises: a position control unit 104 that controls the positions of a plurality of gamma-ray detectors (SPGD 110) used as mobile detectors (TIP detectors 111) for measuring the neutron flux distribution in a core axial direction in a nuclear reactor; a signal detection unit 103 that detects signals from the gamma-ray detectors; a temperature detection unit 102 that detects the temperature in the reactor; and a calibration unit 105 that calibrates the detection sensitivity of the gamma-ray detectors. The position control unit moves the gamma-ray detectors as the mobile detectors and arranges the gamma-ray detectors at specific portions that are arbitrarily determined. The calibration unit compares the signals from the gamma-ray detectors detected by the signal detection unit, and calibrates the detection sensitivity of the gamma-ray detectors on the basis of a result of the comparison and the temperature in the reactor detected by the temperature detection unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a system for calibrating the detection sensitivity of a mobile detector. [Background technology]

[0002] A core power detector that detects the core power is installed inside the reactor. The core power detector deteriorates due to reaction with neutrons. Therefore, a mobile in-core instrumentation system is used to measure the gamma ray dose inside the reactor and calibrate the sensitivity of the deteriorated core power detector according to the neutron flux distribution around the core power detector. The mobile in-core instrumentation system is a device that measures the neutron distribution inside the reactor using a mobile detector that moves inside the reactor.

[0003] Patent Document 1 discloses a method of calibrating the detection sensitivity of a mobile detector using a drive unit that can accommodate one mobile detector (TIP detector), replacing the mobile detector each time it is inserted or removed, inserting or removing the detector the number of times equal to the number of mobile detectors, and detecting signals based on the data. Patent Document 2 also discloses a system using a self-powered gamma ray detector (hereinafter referred to as "SPGD"). An SPGD is a detector that uses lead-bismuth as the gamma ray sensitive element. By using lead-bismuth as the gamma ray sensitive element, an SPGD can be manufactured without using nuclear material. Furthermore, because an SPGD utilizes the ionization reaction of metals due to gamma rays rather than the neutron reaction of nuclear material, it is believed that there is almost no loss of sensitivity due to degradation of the sensitive material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-164338 [Patent Document 2] Japanese Patent Publication No. 2020-067312 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, it is conceivable to use a self-powered gamma ray detector (SPGD) in a mobile detector (TIP detector). For example, it is conceivable to use an SPGD disclosed in Patent Document 2 in the TIP detector disclosed in Patent Document 1. However, since lead bismuth has a melting point lower than 300°C, which is the reactor temperature during operation, it is solid at room temperature but liquefies inside the reactor. Therefore, when a self-powered gamma ray detector (SPGD) is used in a mobile detector, the lead bismuth changes from solid to liquid when the mobile detector moves from the outside to the inside of the reactor. At this time, separation of sensitive substances occurs, and the volume of the lead bismuth changes. This may cause a change (deterioration) in the detection sensitivity of the mobile detector.

[0006] The present invention has been made to solve the above-mentioned problems, and its main object is to provide a detection sensitivity calibration system for a mobile detector that suppresses deterioration of the detection sensitivity of the mobile detector and stabilizes it. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present invention comprises a position control unit that controls the positions of multiple gamma ray detectors used as mobile detectors for measuring the neutron flux distribution in the axial direction of the reactor core, a signal detection unit that detects signals from the gamma ray detectors, a temperature detection unit that detects the temperature inside the reactor, and a calibration unit that calibrates the detection sensitivity of the gamma ray detectors, wherein the position control unit moves the gamma ray detectors as the mobile detectors to place each gamma ray detector at an arbitrarily determined specific location, and the calibration unit compares the signals from each gamma ray detector detected by the signal detection unit, and calibrates the detection sensitivity of each gamma ray detector based on the comparison result and the temperature inside the reactor detected by the temperature detection unit. Other means will be described later. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress deterioration in the detection sensitivity of a mobile detector and stabilize it. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a detection sensitivity calibration system for a mobile detector according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram of a calibration database of the detection sensitivity calibration system for the mobile detector according to the first embodiment. [Figure 3] FIG. 10 is a schematic configuration diagram of a detection sensitivity calibration system for a mobile detector according to a second embodiment. [Figure 4] FIG. 1 is a graph showing changes in reactor power. [Figure 5] FIG. 10 is an explanatory diagram of a calibration database of the detection sensitivity calibration system for the mobile detector according to the second embodiment. [Figure 6] FIG. 1 is a schematic diagram of a mobile in-core instrumentation device according to a comparative example. [Figure 7] FIG. 2 is a schematic diagram of a horizontal cross section of the core. [Figure 8] FIG. 1 is a block diagram of a computer. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings. Note that each drawing is merely a schematic illustration to allow a sufficient understanding of the present invention. Therefore, the present invention is not limited to the illustrated examples. Furthermore, in each drawing, common or similar components are given the same reference numerals, and redundant explanations thereof will be omitted.

[0011] [First embodiment] <Configuration of a mobile detector detection sensitivity calibration system> The configuration of the detection sensitivity calibration system 100 according to the first embodiment will be described below with reference to Figures 1 and 2. Figure 1 is a schematic diagram of the detection sensitivity calibration system 100 according to the first embodiment. Figure 2 is an explanatory diagram of the calibration database 151. Here, the case where the nuclear reactor is a boiling water reactor will be described as an example.

[0012] The detection sensitivity calibration system 100 according to the first embodiment is configured to calibrate the detection sensitivity of each SPGD 110 (self-powered gamma ray detector) during rated reactor operation. The detection sensitivity calibration system 100 moves each SPGD 110 (self-powered gamma ray detector) so that all gamma ray detectors to be calibrated pass the same position. The detection sensitivity calibration system 100 compares the gamma ray dose measurement values ​​(SPGD signals SG103) of each SPGD 110 measured at the same position, and uses the comparison results to calibrate the detection sensitivity of each SPGD 110. Since the first embodiment is performed during rated reactor operation, the lead-bismuth of the SPGD 110 used in the TIP detector 111 is in a liquefied state. In the first embodiment, the output is in a steady state.

[0013] Generally, the neutron flux of a boiling water reactor is monitored by a local power range monitor (LPRM). A traversing in-core probe (TIP) system is installed in the reactor. The TIP system measures the neutron distribution in the reactor by moving a traversing in-core probe (TIP) in the reactor core.

[0014] As shown in Fig. 1, a pressure vessel 119 in which fuel assemblies are loaded and a mobile in-core instrumentation unit 109 that measures the axial (vertical) neutron flux distribution in a reactor core 120 are housed inside a containment vessel 118. A core power detector 121 that detects the reactor core power is housed inside the pressure vessel 119. A penetration 125 is provided at the bottom of the pressure vessel 119 for inserting a calibration TIP detector 111 from the outside into the reactor and withdrawing it from the inside of the reactor to the outside. The TIP detector 111 is a mobile detector that moves inside the reactor.

[0015] A plurality of pipe-shaped LPRM strings 122 are provided inside the core 120 of the pressure vessel 119. Each LPRM string 122 includes a TIP guide tube 126 extending in the axial direction of the core 120. The TIP guide tube 126 is a pipe-shaped movable in-core instrumentation guide tube within which the TIP detector 111 moves. The TIP guide tube 126 is arranged to penetrate the containment vessel 118 and extend into the pressure vessel 119. A plurality of core power detectors 121 (four core power detectors 121a to 121d in this embodiment) are arranged inside the TIP guide tube 126. The core power detectors 121 are arranged at predetermined intervals in the axial direction of the core 120.

[0016] The detection sensitivity of the core power detector 121 varies depending on the surrounding neutron flux distribution. Therefore, the mobile in-core instrumentation device 109 is used to measure the gamma ray dose inside the reactor, and the detection sensitivity of the core power detector 121 is calibrated based on the gamma ray dose according to the neutron flux distribution around the core power detector 121.

[0017] The mobile in-core instrumentation system 109 has a TIP detector 111 inside a pressure vessel 119. The mobile in-core instrumentation system 109 also has a drive unit 112, an indexer 113, and a TIP drive cable 114 outside the pressure vessel 119.

[0018] The driving device 112 is a device that moves the TIP detector 111 via a TIP driving cable 114 . The indexer 113 is a device that selects which TIP detector 111 to insert into which LPRM string 122. The TIP drive cable 114 is a member that connects the TIP detector 111 and the drive device 112 .

[0019] The TIP detector 111 moves inside and outside the reactor through the inside of the TIP guide tube 126 and the penetration part 125 by the driving device 112 driving the TIP driving cable 114 .

[0020] In this embodiment, the mobile in-core instrumentation system 109 uses an SPGD 110 as the TIP detector 111. The SPGD 110 is a self-powered gamma ray detector. The SPGD 110 can be manufactured without using nuclear materials by using lead-bismuth as the gamma ray sensitive part.

[0021] In this embodiment, the mobile in-core instrumentation system 109 has three or more SPGDs 110 as TIP detectors 111 to measure the neutron flux distribution in the axial direction of the reactor core. The three or more SPGDs 110 measure the neutron flux distribution at a high location, an intermediate height location, and a low location of the reactor. In this embodiment, the detection sensitivity calibration system 100 will be described as having four SPGDs 110a to 110d. The four SPGDs move sequentially in the height direction to change locations, thereby performing gamma ray measurements in the axial direction of the core, and the neutron flux distribution is determined from the results.

[0022] Here, the following description will be given assuming that, of the four SPGDs 110a to 110d, SPGD 110a is the first SPGD 110 to be inserted into the reactor, and SPGD 110d is the last SPGD 110 to be inserted into the reactor. Although the detection sensitivity calibration system 100 includes four SPGDs 110 in this embodiment, there is no limit to the number of SPGDs 110, as long as it is three or more. It is desirable to arrange the SPGDs 110 so as to satisfy the following conditions.

[0023] The installation intervals of the SPGDs 110 are known in advance. In this embodiment, the SPGDs 110 are spaced apart at the same installation interval Δh. However, the installation intervals of the SPGDs 110 do not necessarily have to be equal. It is desirable that the interval between the SPGD 110a, which is inserted first into the core, and the SPGD 110d, which is inserted last into the core, be within the distance from the top to the bottom of the core.

[0024] The spacing between the SPGDs 110 is stored in advance in the storage unit 106. In this embodiment, the SPGDs 110 maintain the same installation spacing Δh while moving inside the reactor. Note that the spacing between the SPGDs 110 may be changed during movement outside the reactor by providing a bending structure such as a hinge between the SPGDs 110.

[0025] The detection sensitivity calibration system 100 includes a main control unit 101, a temperature detection unit 102, a signal detection unit 103, a position control unit 104, a calibration unit 105, a memory unit 106, a time monitoring unit 107, and a temperature sensor 108.

[0026] The main control unit 101 is a component that controls the overall operation. The temperature detection unit 102 is a component that detects the temperature inside the furnace based on the output signal from the temperature sensor 108 . The signal detection unit 103 is a component that detects the amount of gamma rays based on the output signal from the TIP detector 111 (each SPGD 110).

[0027] The position control unit 104 is a component that controls the position of the TIP detector 111 in the axial direction (vertical direction) within the core 120. The position control unit 104 controls the drive unit 112 and the indexer 113 with the TIP position control signal SG104 in accordance with instructions (TIP position signal SG101) from the main control unit 101, and controls the selection of the LPRM string 122 into which the TIP detector 111 is inserted and the position of the TIP detector 111. The calibration unit 105 is a component that calibrates the detection sensitivity of the TIP detector 111 (mobile detector).

[0028] The storage unit 106 is a component that stores various types of data. The storage unit 106 stores a calibration database 151 used to calibrate the detection sensitivity of the TIP detector 111 (mobile detector). The time monitoring unit 107 monitors the operation time of each unit. The temperature sensor 108 is a sensor that detects the temperature inside the reactor. The temperature sensor 108 is disposed inside the pressure vessel 119. For example, since a nuclear reactor is designed so that the temperature inside the reactor is low near the penetration 125, the detection sensitivity calibration system 100 can reliably confirm that the temperature exceeds the melting temperature of lead-bismuth by disposing the temperature sensor 108 near the penetration 125.

[0029] The detection sensitivity calibration system 100 calibrates the detection sensitivity of the TIP detector 111 (mobile detector) about once a month, for example. At this time, in the detection sensitivity calibration system 100, the main control unit 101 outputs a TIP position signal SG101 to the position control unit 104 to instruct the movement of the TIP detector 111 (each SPGD 110). The position control unit 104 outputs a TIP position control signal SG104 to the driving device 112, which indicates to which position the TIP detector 111 specified by the TIP position signal SG101 should be moved.

[0030] Then, the driving device 112 cooperates with the indexer 113 to move the TIP detector 111 designated by the TIP position control signal SG104 to a designated position. At this time, the designated TIP detector 111 is inserted from the outside to the inside of the reactor through the penetration 125, or is withdrawn from the inside to the outside of the reactor. At this time, the mobile in-core instrumentation device 109 withdraws the TIP detector 111, for example, from the top to the bottom of the reactor core 120. At this time, the TIP detector 111 generates a gamma ray measurement signal (TIP measurement value signal) corresponding to the movement distance and outputs it to the detection sensitivity calibration system 100. The detection sensitivity calibration system 100 measures the axial neutron flux distribution inside the reactor core 120 by reading the TIP measurement value signal in synchronization with the TIP position signal SG101.

[0031] All the LPRM strings 122 are divided into five groups, and each TIP detector 111 is assigned to approximately ten LPRM strings 122. Which TIP detector 111 is inserted into which LPRM string 122 is selected by rotating the rotating cylinder of the indexer 113. Each TIP detector 111 detects neutron flux using an SPGD 110.

[0032] However, the lead-bismuth of the SPGD 110 used in the TIP detector 111 changes from a solid to a liquid when the TIP detector 111 moves from the outside to the inside of the reactor. At this time, separation of sensitive substances occurs, and the volume of the lead-bismuth changes. This may cause the detection sensitivity of the TIP detector 111 to change (deteriorate). Therefore, in this embodiment, the detection sensitivity calibration system 100 calibrates the detection sensitivity of each TIP detector 111.

[0033] At this time, the temperature sensor 108 outputs an output signal corresponding to the detected furnace temperature to the temperature detection unit 102. The output signal of the temperature sensor 108 is a current value, which increases or decreases according to the furnace temperature. A sensitivity coefficient for the furnace temperature is measured in advance and stored in the memory unit 106. The temperature detection unit 102 detects the furnace temperature based on the output signal from the temperature sensor 108, and outputs a furnace temperature signal SG102 representing the detected furnace temperature to the main control unit 101.

[0034] Furthermore, each SPGD 110 used in the TIP detector 111 outputs an output signal corresponding to the detected gamma ray dose (i.e., the gamma ray measurement signal (TIP measurement value signal) described above) to the signal detection unit 103. The output signal of the SPGD 110 is a current value, which increases or decreases according to the gamma ray dose. The sensitivity coefficient for the gamma ray dose is measured in advance and stored in the memory unit 106. The signal detection unit 103 detects the gamma ray dose at the placement position of each SPGD 110 based on the output signal from each SPGD 110, and outputs an SPGD signal SG103 representing the detected gamma ray dose to the main control unit 101.

[0035] The main control unit 101 receives an in-furnace temperature signal SG102 from the temperature detection unit 102, and also receives an SPGD signal SG103 from each SPGD 110 (TIP detector 111). Then, the main control unit 101 associates the TIP position signal SG101, the in-furnace temperature signal SG102, and the SPGD signal SG103 output from the main control unit 101 to the position control unit 104, and stores them in the calibration database 151 of the storage unit 106.

[0036] The main control unit 101 reads the SPGD signal SG103 in synchronization with the TIP position signal SG101, as in the case of the TIP measurement value signal (gamma ray measurement signal). As a result, the main control unit 101 measures the neutron flux distribution in the axial direction (vertical direction) inside the reactor core 120. Then, the detection sensitivity calibration system 100 measures the in-core temperature signal in synchronization with the TIP position signal SG101.

[0037] Furthermore, when the main control unit 101 has finished moving each SPGD 110 (TIP detector 111) for calibration, it instructs the calibration unit 105 to start calibration. In response to this, the calibration unit 105 reads out the TIP position signal SG101, the furnace temperature signal SG102, and the SPGD signal SG103 from the calibration database 151. The calibration unit 105 then compares the SPGD signals SG103 from each SPGD 110 (TIP detector 111) detected by the signal detection unit 103. Next, the calibration unit 105 calibrates the detection sensitivity (detection sensitivity of gamma rays) of each SPGD 110 (TIP detector 111) based on the comparison result between the SPGD signals SG103 and the furnace temperature (furnace temperature signal SG102) detected by the temperature detection unit 102. That is, the calibration unit 105 uses, as a comparison for calibration, the SPGD signals SG103 from each SPGD 110 (TIP detector 111) at which the temperature inside each furnace is deemed to exceed the melting temperature of lead-bismuth. At this time, the calibration unit 105 calibrates the detection sensitivity (detection sensitivity of gamma ray dose) of each SPGD 110 (TIP detector 111) using a sensitivity coefficient for gamma ray dose stored in advance in the storage unit 106. Then, the calibration unit 105 stores the calibration result SG105 in the storage unit 106.

[0038] Note that "when the temperature inside each reactor exceeds the melting temperature of lead-bismuth" means that the lead-bismuth in each SPGD 110 (TIP detector 111) has melted and changed from a solid to a liquid state. Regarding this point, the reactor core temperature (water temperature) rises to the rated temperature before power is increased at the start of operation. However, even if the reactor core temperature rises to the rated temperature, the reactor temperature (water temperature) does not necessarily exceed the melting temperature of lead-bismuth at all locations inside the reactor. Taking this into consideration, the detection sensitivity calibration system 100 excludes from comparison the SPGD signals SG103 from SPGDs 110 for which lead-bismuth is not considered to be melted, based on the reactor temperature (inner reactor temperature signal SG102) detected by the temperature detector 102. In other words, the detection sensitivity calibration system 100 excludes from comparison the SPGD signals SG103 from SPGDs 110 for which the reactor temperature does not exceed the melting temperature of lead-bismuth. As a result, the detection sensitivity calibration system 100 prevents the SPGD signal SG103 from the SPGD 110 in a state where lead-bismuth is molten from being mixed with the SPGD signal SG103 from the SPGD 110 in a state where lead-bismuth is not molten, as a comparison target. The detection sensitivity calibration system 100 then compares the SPGD signals SG103 from the SPGDs 110 in which lead-bismuth is deemed to be molten (i.e., the furnace temperature exceeds the melting temperature of lead-bismuth) to obtain the comparison result. Thereafter, the detection sensitivity calibration system 100 identifies a sensitivity coefficient for the gamma ray dose stored in advance in the memory unit 106 based on the comparison result, and multiplies the detection sensitivity value of each SPGD 110 by the identified sensitivity coefficient. In this way, the detection sensitivity calibration system 100 can suitably calibrate the detection sensitivity (detection sensitivity of gamma ray dose) of each SPGD 110.

[0039] The detection sensitivity calibration system 100 calibrates the detection sensitivity of each SPGD 110 each time the SPGD 110 (TIP detector 111) is inserted into or removed from the reactor. In other words, the detection sensitivity calibration system 100 calibrates the detection sensitivity of each SPGD 110 for gamma ray amounts each time the SPGD 110 is inserted into or removed from the reactor.

[0040] Thereafter, the main control unit 101 uses the calibration result SG105 stored in the storage unit 106 to calibrate the detection sensitivity of the core power detectors 121a to 121d.

[0041] Such a detection sensitivity calibration system 100 can calibrate the detection sensitivity of the TIP detector 111. The calibration database 151 is stored in the storage unit 106 for each TIP detector 111. After the TIP detector 111 is pulled out of the reactor, the detection sensitivity calibration system 100 calibrates the detection sensitivity of the TIP detector 111 every time it is inserted into the reactor.

[0042] In the example shown in Fig. 2, the rows are arranged in the order in which they were stored in calibration database 151. Note that in the example shown in Fig. 2, the output is assumed to be in a steady state, and therefore calibration database 151 does not include time information (period information). However, in the example shown in Fig. 5 (described later), for example, the output is assumed to change, and therefore calibration database 151b includes time information (time information). The SPGD number 401 represents a number that identifies the SPGD 110 . TIP position 402 indicates the TIP position where the data was acquired. Because the TIP detector 111 travels back and forth along a route determined for each LPRM string, it can be expressed as a one-dimensional coordinate for calibration. However, here, it is expressed as an integer value in units of the installation interval Δh of the SPGD 110, and the larger the value, the higher the position inside the reactor. Temperature 403 represents the temperature inside the furnace. The SPGD signal 404 represents a current value.

[0043] If the gamma ray dose rate at TIP position x is γ(x), the sensitivity function of the κth SPGD 110 is g_n(γ), and the relative sensitivity of the SPGD 110 due to liquefaction is S_n, the SPGD signal I(x) is expressed by the following equation (1): I(x)=S_n g_n(γ(x)) …(1)

[0044] 2, for example, when the melting temperature of the emitter is set to 200°C, the calibration unit 105 obtains measurement values ​​for all four SPGDs 110 at tip positions 4 and 5. Assuming that the gamma ray dose rate is the same at each tip position, the signal ratio of the SPGDs 110 represents the relative sensitivity ratio.

[0045] Here, for example, the relative sensitivity ratios for the maximum value of the output signal of the SPGD 110 are calculated at tip positions 4 and 5. As an example, assume that the relative sensitivity ratio at tip position 4 is "S_1:S_2:S_3:S_4 = 0.798:0.996:1.00:1.00." Also, assume that the relative sensitivity ratio at tip position 5 is "S_1:S_2:S_3:S_4 = 0.795:0.992:0.998:1.00." In this case, the relative sensitivity S_1 has deteriorated to approximately 0.8.

[0046] Therefore, the calibration unit 105 can maintain the detection accuracy of the current value by providing the reciprocal of each relative sensitivity (i.e., "1 / relative sensitivity") as the calibration value. The more SPGDs 110 used as TIP detectors 111 are increased, and the more the number of TIP position samples is increased, the more the detection accuracy of the detection sensitivity calibration system 100 can be improved.

[0047] Note that here, the reactor temperature at each TIP position is shown as a different value, but this is an example in which an individual temperature sensor 108 is placed at each TIP position. If a temperature sensor 108 is placed at only one location inside the reactor, or only in the SPGD 110d that is inserted last into the reactor, all the values ​​will be the same. Even in this case, the detection sensitivity calibration system 100 performs the same processing.

[0048] <Comparative Example> Here, in order to clearly explain the configuration of the mobile in-core instrumentation system 109 according to this embodiment, the configuration of a comparative mobile in-core instrumentation system 109Z will be explained with reference to Figures 6 and 7. Figure 6 is a schematic diagram of the comparative mobile in-core instrumentation system 109Z. Figure 7 is a schematic diagram of a horizontal cross section of a reactor core 120. The comparative mobile in-core instrumentation system 109Z is an apparatus to which the detection sensitivity calibration system 100 according to this embodiment is not added.

[0049] As shown in Figure 6, the comparative example mobile in-core instrumentation system 109Z differs from the mobile in-core instrumentation system 109 of this embodiment (Figure 1) in that it has a TIP detector 131 using an SPGD 110 instead of the TIP detector 111.

[0050] The mobile in-core instrumentation system 109Z calibrates the detection sensitivity of the TIP detector 131 (mobile detector), for example, about once a month. At this time, the mobile in-core instrumentation system 109Z inserts the calibrating TIP detector 131 from the outside of the reactor to the inside and withdraws it from the inside of the reactor through the penetration 125 using the driving device 112. The TIP detector 131 moves inside and outside the reactor through the inside of a TIP guide tube 126. A plurality of pipe-shaped LPRM strings 122 are provided inside the core 120. Each LPRM string 122 includes a TIP guide tube 126 extending in the axial direction of the core 120. Inside the TIP guide tube 126 of each LPRM string 122, four core power detectors 121a to 121d are arranged at predetermined intervals in the axial direction of the core 120. The indexer 113 selects which TIP detector 131 to insert into which LPRM string 122. The driver 112 drives the TIP drive cable 114, causing the TIP detector 131 to move from the outside to the inside of the reactor through the TIP guide tube 126. When the driver 112 pulls out the TIP detector 131 from the top to the bottom of the reactor core 120, the TIP detector 131 generates a gamma ray measurement signal (TIP measurement value signal) corresponding to the movement distance and outputs it to a control device (not shown). The control device (not shown) measures the axial neutron flux distribution inside the reactor core 120 by reading the TIP measurement value signal in synchronization with the gamma ray measurement signal (TIP measurement value signal).

[0051] However, the lead-bismuth of the SPGD 110 used in the TIP detector 111 changes from solid to liquid when the TIP detector 111 moves from the outside to the inside of the reactor. At this time, separation of sensitive materials occurs, and the volume of the lead-bismuth changes. This may cause the detection sensitivity of the TIP detector 111 to change (deteriorate). Therefore, in the mobile in-core instrumentation system 109Z, the detection sensitivity of each TIP detector 131 is calibrated as follows.

[0052] 7, the mobile in-core instrumentation system 109Z is provided with a pipe-shaped string called a common string 31, which can introduce all of the TIP detectors 131, at only one location among the multiple control rods 32. The mobile in-core instrumentation system 109Z calibrates the detection sensitivity between different TIP detectors 131 by inserting and removing each TIP detector 131 into and from the common string 31 one by one in sequence.

[0053] However, the mobile in-core instrumentation system 109Z is not equipped with the detection sensitivity calibration system 100 according to this embodiment. Therefore, the mobile in-core instrumentation system 109Z cannot calibrate the change (deterioration) in the detection sensitivity of the TIP detector 131 caused by the lead-bismuth of the SPGD 110 constituting the TIP detector 131 changing from a solid to a liquid.

[0054] In contrast, the mobile in-core instrumentation system 109 according to this embodiment is equipped with a detection sensitivity calibration system 100. Therefore, the mobile in-core instrumentation system 109 according to this embodiment can calibrate the change (deterioration) in the detection sensitivity of the TIP detector 111 caused by the lead-bismuth of the SPGD 110 constituting the TIP detector 111 changing from a solid to a liquid.

[0055] <Main features of the detection sensitivity calibration system> The detection sensitivity calibration system 100 according to this embodiment can be configured to have the following features. (1) A detection sensitivity calibration system 100 according to this embodiment is a system for calibrating the detection sensitivity of a plurality of SPGDs 110 (self-powered gamma ray detectors) used as TIP detectors 111 (mobile detectors) for measuring the neutron flux distribution in the axial direction of the core of a nuclear reactor. As shown in FIG. 1 , the detection sensitivity calibration system 100 includes a position control unit 104, a signal detection unit 103, a temperature detection unit 102, and a calibration unit 105. The position control unit 104 is a component that controls the position of the SPGDs 110. The signal detection unit 103 is a component that detects a signal (SPGD signal SG103) representing the measured gamma ray dose from the SPGDs 110. The temperature detection unit 102 is a component that detects the furnace temperature (furnace temperature signal SG102). The calibration unit 105 is a component that calibrates the detection sensitivity of the SPGDs 110. The position control unit 104 moves the SPGDs 110 serving as TIP detectors 111 and places each SPGD 110 at an arbitrarily determined specific location (specific single location). The calibration unit 105 compares the SPGD signals SG103 from each SPGD 110 detected by the signal detection unit 103, and calibrates the detection sensitivity of each SPGD 110 based on the comparison result and the furnace temperature (furnace temperature signal SG102) detected by the temperature detection unit 102.

[0056] In the detection sensitivity calibration system 100, the position control unit 104 moves the TIP detector 111 to place each SPGD 110 at a specific location (a specific single location). At this time, the TIP detector 111 is inserted from the outside to the inside of the nuclear reactor. This causes the lead-bismuth in each SPGD 110 used in the TIP detector 111 to liquefy. In the detection sensitivity calibration system 100, while the lead-bismuth is in a liquefied state, the calibration unit 105 compares SPGD signals SG103 representing the measured gamma ray doses from each SPGD 110 detected by the signal detection unit 103. The detection sensitivity calibration system 100 calibrates the detection sensitivity of each SPGD 110 based on the comparison result and the furnace temperature (furnace temperature signal SG102) detected by the temperature detection unit 102. The detection sensitivity calibration system 100 according to this embodiment can suppress deterioration of the detection sensitivity of the TIP detector 111 and stabilize it.

[0057] (2) In the detection sensitivity calibration system 100 according to this embodiment, the signals (SPGD signals SG103) from each SPGD 110 at which the furnace temperature detected by the temperature detection unit 102 is deemed to exceed the melting temperature of lead-bismuth are used as comparison targets. The calibration unit 105 may then be configured to compare the signals to be compared to obtain a comparison result, identify a sensitivity coefficient based on the comparison result, and multiply the sensitivity coefficient by the detection sensitivity value of each gamma-ray detector, thereby calibrating the detection sensitivity of each SPGD 110.

[0058] The detection sensitivity calibration system 100 according to the present embodiment prevents the SPGD signal SG103 from the SPGD 110 in a state where lead-bismuth is dissolved and the SPGD signal SG103 from the SPGD 110 in a state where lead-bismuth is not dissolved from being mixed together as a comparison target. This allows the detection sensitivity calibration system 100 to suitably calibrate the detection sensitivity (detection sensitivity of gamma ray dose) of each SPGD 110.

[0059] (3) As shown in FIG. 1, in the detection sensitivity calibration system 100 according to this embodiment, the temperature detection unit 102 detects the temperature inside the reactor using a temperature sensor 108 installed near the SPGD 110d, which was the last to be inserted inside the reactor.

[0060] The vicinity of the SPGD 110d is a relatively low temperature location, and therefore, is a location within the reactor where the temperature is likely to be stable. The detection sensitivity calibration system 100 according to this embodiment can stably perform the calibration process by treating the temperature near the SPGD 110d as the reactor temperature. Note that the detection sensitivity calibration system 100 may be configured such that the temperature sensor 108 is directly attached to the SPGD 110d. This allows the detection sensitivity calibration system 100 to obtain accurate reactor temperature information.

[0061] (4) As shown in Fig. 1, the detection sensitivity calibration system 100 according to this embodiment has a driving device 112 that moves each SPGD 110. The driving device 112 moves each SPGD 110 so that all SPGDs 110 to be calibrated pass the same position at an output change rate that is equal to or less than an arbitrarily determined calibration accuracy relative to the output increase rate at the start of operation.

[0062] The detection sensitivity calibration system 100 according to this embodiment uses a driving device 112 to move each SPGD 110 so that all of the SPGDs 110 to be calibrated pass the same position. The detection sensitivity calibration system 100 according to this embodiment can compare the measured values ​​of the gamma ray doses of the SPGDs 110 with each other, and therefore can suitably calibrate the detection sensitivity of the TIP detector 111. This also enables the detection sensitivity calibration system 100 to suppress deterioration of the detection sensitivity of the TIP detector 111 and stabilize it.

[0063] As described above, according to the detection sensitivity calibration system 100 according to the first embodiment, the detection sensitivity of the TIP detector 111 can be stabilized by suppressing deterioration of the detection sensitivity.

[0064] [Second embodiment] The second embodiment provides a detection sensitivity calibration system 100A that accurately calibrates the detection sensitivity of each SPGD 110 even when the amount of change in output due to the time difference between the SPGD signals SG103 to be compared is sufficiently small relative to the calibration accuracy. The configuration of the detection sensitivity calibration system 100A according to the second embodiment will be described below with reference to FIGS. 3 to 5. FIG. 3 is a schematic diagram of the detection sensitivity calibration system 100A according to the second embodiment. Some of the components common to the detection sensitivity calibration system 100 according to the first embodiment are omitted in FIG. 3. FIG. 4 is a graph of the change in reactor power output. FIG. 5 is an explanatory diagram of a calibration database 151.

[0065] The detection sensitivity calibration system 100 according to the first embodiment described above is configured so that each TIP detector 111 can be withdrawn to the outside of the reactor during operation, and is configured to calibrate the detection sensitivity of each SPGD 110 (self-powered gamma ray detector) during rated reactor operation. In contrast, the detection sensitivity calibration system 100A according to the second embodiment is configured so that each TIP detector 111 cannot be withdrawn to the outside of the reactor during operation, and is configured to calibrate the detection sensitivity of each SPGD 110 only when the reactor starts operating.

[0066] As described above, the detection sensitivity calibration system 100A according to the second embodiment calibrates the detection sensitivity of each SPGD 110 (self-powered gamma ray detector) only when the reactor starts operating. As described later, the detection sensitivity calibration system 100A is configured such that the driving device 112 limits the movement of each TIP detector 111 so that the TIP detector 111 does not move outside the reactor. This detection sensitivity calibration system 100A can prevent liquefied lead-bismuth from re-solidifying during operation. Since this second embodiment is an operation performed when the reactor starts operating, the lead-bismuth of the SPGD 110 used in the TIP detector 111 changes from solid to liquid. Furthermore, in this second embodiment, the output changes. In this second embodiment, the detection sensitivity calibration system 100A calibrates the detection sensitivity of each SPGD 110 using time 701 ( FIG. 5 ) as time information (time information).

[0067] As shown in FIG. 3, the detection sensitivity calibration system 100A according to this embodiment differs from the detection sensitivity calibration system 100 according to the first embodiment (see FIG. 1) in the following points. (1) A mobile in-core instrumentation system 109A is stored inside the containment vessel 118, and the mobile in-core instrumentation system 109A is equipped with one or more (two in the illustrated example) TIP detectors 111a, 111b (hereinafter collectively referred to as "TIP detectors 111"). (2) The TIP detectors 111a, 111b are provided with connecting parts 501a, 501b (hereinafter collectively referred to as "connecting parts 501") that selectively connect or disconnect the TIP detectors 111a, 111b to the position control part 104 arranged outside the furnace. (3) A TIP detector 111 is always disposed inside each LPRM string 122a, 122b (hereinafter collectively referred to as "LPRM string 122"). (4) The connecting unit 501 connects the TIP detector 111 to be connected and the position control unit 104 only during calibration.

[0068] Although two TIP detectors 111a and 111b are shown in Fig. 3, the number of TIP detectors 111 may be three or more. Furthermore, although two connecting portions 501a and 501b are shown in Fig. 3, the number of connecting portions 501a and 501b may be three or more.

[0069] In this embodiment, a TIP detector 111 is always disposed inside each LPRM string 122. The detection sensitivity calibration system 100A selects one of the coupling units 501 corresponding to the TIP detector 111 to be coupled during calibration. As a result, the coupling unit 501 couples the TIP detector 111 to be coupled to the position control unit 104 only during calibration. A mobile in-core instrumentation device 109A is stored inside the containment vessel 118.

[0070] The detection sensitivity calibration system 100A uses a driving device 112 to move the TIP detector 111 to be connected up and down via an indexer 113. The driving device 112 moves each SPGD 110 so that all SPGDs 110 to be calibrated pass the same position at an output change rate that is equal to or less than the calibration accuracy relative to the output increase rate at the start of operation.

[0071] In this detection sensitivity calibration system 100A, the TIP detector 111 (SPGD 110) can be connected to the position control unit 104 only during calibration by the connection unit 501. In this detection sensitivity calibration system 100A, each SPGD 110 can be placed in a position suitable for the calibration process during calibration.

[0072] The driving device 112 limits the movement of each TIP detector 111 so that the TIP detector 111 does not move outside the reactor. Since the TIP detector 111 does not move outside the reactor during rated reactor operation, the detection sensitivity calibration system 100A prevents the lead-bismuth of the SPGDs 110 used in the TIP detectors 111 from solidifying. This prevents the detection sensitivity calibration system 100A from changing the detection sensitivity of the TIP detectors 111 (SPGDs 110) during operation. Therefore, the detection sensitivity calibration system 100A only needs to calibrate the detection sensitivity of the TIP detectors 111 (SPGDs 110) at the start of operation. However, as shown in FIG. 4, the reactor power output changes at the start of operation. FIG. 4 shows an example 601 of change in reactor power 604. At the start of operation, the change in reactor power causes the power detection of the local power range monitor (LPRM) to exceed 10% of the rated power. Therefore, before this state occurs, the detection sensitivity calibration system 100A must complete the calibration of the detection sensitivity of the TIP detector 111 (SPGD 110).

[0073] Furthermore, at the start of operation, the reactor water temperature rises to the rated temperature inside the reactor before the power is increased, so that the temperature inside the reactor reaches the melting temperature of the emitter when the power increase starts.

[0074] During calibration, the detection sensitivity calibration system 100A operates in the same manner as the detection sensitivity calibration system 100. At that time, the detection sensitivity calibration system 100A creates a calibration database 151b (FIG. 5) and stores the calibration result SG105 in the storage unit 106. The calibration database 151b (FIG. 5) has a configuration in which a time 701 is added to the calibration database 151 (FIG. 2). By adding the time 701 to the calibration database 151b (FIG. 5), the detection sensitivity calibration system 100A can calculate the time difference between the measurement values. Therefore, the detection sensitivity calibration system 100A can limit the measurement values ​​to be compared (the value of the SPGD signal SG103 (the gamma ray dose measurement signal)) obtained under the following conditions, for example:

[0075] When creating the calibration database 151b (FIG. 5), the detection sensitivity calibration system 100A moves each SPGD 110 at a speed that causes all SPGDs 110 to pass the same position within a time period in which the rate of change of the output increase rate v [% / min] is 1% or less. This enables the detection sensitivity calibration system 100A to calibrate the detection sensitivity of each SPGD 110 with an accuracy of 1% or less.

[0076] As described above, the detection sensitivity calibration system 100A according to the second embodiment can suppress and stabilize the deterioration of the detection sensitivity of the TIP detector 111, similar to the detection sensitivity calibration system 100 according to the first embodiment. Moreover, according to the detection sensitivity calibration system 100A of the second embodiment, unlike the detection sensitivity calibration system 100 of the first embodiment, it is only necessary to calibrate the detection sensitivity of the TIP detector 111 (SPGD 110) at the start of operation.

[0077] Fig. 8 is a block diagram of the computer 980. The detection sensitivity calibration systems 100 and 100A shown in Fig. 1 and Fig. 3 each include one or more computers 980 shown in Fig. 8. The main control unit 101, the memory unit 106, etc. are realized by the functions of the computer 980. 8, a computer 980 includes a CPU 981, a storage unit 982, a communication I / F (interface) 983, an input / output I / F 984, and a media I / F 985. Here, the storage unit 982 includes a RAM 982a, a ROM 982b, and an SSD (Solid State Drive) 982c. The communication I / F 983 is connected to a communication circuit 986. The input / output I / F 984 is connected to an input / output device 987. The media I / F 985 reads and writes data from a recording medium 988.

[0078] The ROM 982b stores an IPL (Initial Program Loader) executed by the CPU, etc. The SSD 982c stores control programs, various data, etc. The CPU 981 executes the control programs, etc. loaded from the SSD 982c to the RAM 982a, thereby realizing various functions. The main control unit 101 and other components of the detection sensitivity calibration systems 100, 100A shown in FIGS. 1 and 3 are primarily shown as blocks representing functions realized by the control programs, etc.

[0079] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of the embodiments with other configurations, and it is also possible to add other configurations to the configuration of the embodiments. Furthermore, it is possible to add, delete, or replace part of each configuration with other configurations.

[0080] <Application to pressurized water reactors> Although the above-described embodiments have been described by taking the case where the reactor is a boiling water reactor as an example, the present invention can also be applied to a pressurized water reactor, since the in-core detector has a mechanism that moves back and forth between the outside and inside of the reactor. [Explanation of symbols]

[0081] 31 Common String 32 control rods 100,100A detection sensitivity calibration system 101 Main control unit 102 Temperature detection unit 103 Signal detection unit 104 Position control section 105 Proofreading Department 106 Storage section 107 Time Monitoring Department 108 Temperature Sensor 109, 109A, 109Z Mobile in-core instrumentation equipment 110, 110a, 110b, 110c, 110d SPGD (Gamma ray detector) 111, 111a, 111b, 131 TIP detector (mobile detector) 112 Drive unit 113 Indexer 114 TIP drive cable 118 Containment Vessel 119 Pressure Vessels 120 reactor core 121, 121a, 121b, 121c, 121d Core power detector 122,122a,122b LPRM strings 125 Penetration 126 TIP guide tube (movable in-core instrumentation guide tube) 151 Calibration Database 401 SPGD Number 402 TIP position 403 Temperature 404 SPGD signal (signal) 501,501a,501b Connection part 601 Example of change 604 Output 701 Time SG101 TIP position signal SG102 Furnace temperature signal SG103 SPGD signal (signal) SG104 TIP position control signal SG105 calibration results

Claims

1. a position control unit that controls the positions of a plurality of gamma ray detectors used as mobile detectors for measuring the neutron flux distribution in the axial direction of the core of the nuclear reactor; a signal detection unit that detects a signal representing a measured gamma ray dose from the gamma ray detector; a temperature detection unit for detecting the temperature inside the furnace; a calibration unit that calibrates the detection sensitivity of the gamma ray detector, the position control unit moves the gamma ray detectors as the mobile detectors and places each gamma ray detector at a specific position that is arbitrarily determined; the calibration unit compares the signals from the gamma ray detectors detected by the signal detection unit with each other, and calibrates the detection sensitivity of each gamma ray detector based on the comparison result and the furnace temperature detected by the temperature detection unit; A detection sensitivity calibration system comprising:

2. 2. The detection sensitivity calibration system according to claim 1, The temperature inside the furnace detected by the temperature detection unit is compared with signals from each gamma ray detector that are deemed to exceed the melting temperature of lead-bismuth used in the gamma ray detector, the calibration unit compares the signals to be compared to obtain a comparison result, identifies a sensitivity coefficient based on the comparison result, and multiplies the detection sensitivity value of each gamma ray detector by the sensitivity coefficient, thereby calibrating the detection sensitivity of each gamma ray detector. A detection sensitivity calibration system comprising:

3. 2. The detection sensitivity calibration system according to claim 1, the temperature detection unit detects the temperature inside the reactor using a temperature sensor installed near the gamma ray detector that was last inserted into the reactor among the plurality of gamma ray detectors inserted into the reactor, A detection sensitivity calibration system comprising:

4. 2. The detection sensitivity calibration system according to claim 1, a connecting part that selectively disconnects or connects the mobile detector disposed inside the nuclear reactor and the position control part disposed outside the nuclear reactor; the coupling unit couples the mobile detector to be coupled with the position control unit only during calibration; A detection sensitivity calibration system comprising:

5. 5. The detection sensitivity calibration system according to claim 1, a drive unit for moving each gamma ray detector; the driving device moves each gamma ray detector so that all gamma ray detectors to be calibrated pass the same position at an output change rate that is equal to or less than an arbitrarily determined calibration accuracy with respect to an output increase rate at the start of operation; A detection sensitivity calibration system comprising:

6. 2. The detection sensitivity calibration system according to claim 1, Each gamma ray detector is designed to be removable from the reactor during operation. the calibration unit calibrates the detection sensitivity of each gamma ray detector during rated operation of the reactor; A detection sensitivity calibration system comprising:

7. 2. The detection sensitivity calibration system according to claim 1, Each gamma ray detector is designed so that it cannot be removed from the reactor during operation. the calibration unit calibrates the detection sensitivity of each gamma ray detector only when the reactor starts operating; A detection sensitivity calibration system comprising:

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