In-core measuring instrument for providing both core protection signal and core monitoring signal

Abstract

According to the present invention, the in-core measuring instrument that provides both a core protection signal and a core monitoring signal includes a self-powered neutron detector (SPND) for measuring neutron flux, wherein the neutron detector (SPND) includes an emitter, a welding point, a signal wire, a sheath, an insulator, and a resin. The emitter of the neutron detector for measuring neutron flux includes a delayed-response rhodium (Rh) or vanadium (V) emitter and a prompt-response cobalt (Co) emitter, wherein the rhodium (Rh) or vanadium (V) emitter is used for core monitoring by detecting delayed electron generation after a predetermined time due to a half-life of a compound nucleus generated by a reaction with neutrons, and the cobalt (Co) emitter is used for core protection by detecting an immediate change in neutron flux of a core through prompt electron generation caused by a material reaction, the cobalt (Co) emitter being used for core protection against rapid heating or cooling of the core by detecting a change in the temperature difference (ΔT) between a core inlet thermocouple (CIT) and a core outlet thermocouple (CET). A nuclear fuel assembly includes a nuclear fuel rod, a nuclear fuel control rod guide tube, and an in-core measuring instrument guide tube positioned at a central portion where the nuclear fuel rod and the nuclear fuel control rod guide tubes are arranged. The in-core measuring instrument, which is disposed in the in-core measuring instrument guide tube and includes two types of neutron detectors for measuring neutron flux and two thermocouples for measuring core inlet temperature and core outlet temperature, is configured to simultaneously perform core protection and core monitoring by measuring neutron flux, perform core protection by using a core inlet–outlet temperature difference (ΔT), and calibrate neutron flux measured by the cobalt emitter using the rhodium or vanadium emitter.

Description

In-core instrumentation that provides both core protection signals and core monitoring signals

[0001] The present invention relates to an in-core instrument employing a self-powered neutron detector (SPND, hereinafter referred to as the neutron detector) using a rhodium (Rh) or vanadium (V) emitter with delayed response characteristics and a neutron detector (SPND, self-powered neutron detector) using a cobalt (Co) emitter with prompt response characteristics, and employing a core exit thermocouple (CET) for measuring the temperature of the core exit and a core inlet thermocouple (CIT) for measuring the temperature of the core inlet, comprising: one type of core protection signal using a prompt response neutron detector that detects a rapid change in neutron flux; one type of core protection signal that detects a rapid increase or decrease in core temperature from the difference between the core inlet temperature and the core exit temperature; The present invention relates to an in-core instrument that provides two types of core protection signals and one type of core monitoring signal, capable of simultaneously performing core protection and monitoring using a delayed-response neutron detector.

[0002] Korean Registered Patent Publication No. 10-1445557 discloses a hybrid in-core instrumentation assembly that can simultaneously perform core monitoring and core protection functions, and extends the instrumentation life by changing the instrumentation emitter material that reacts with neutrons to a low-depleting material.

[0003] A hybrid in-core instrumentation assembly capable of simultaneously performing core monitoring and core protection functions is equipped with a vanadium instrument and a background instrument to perform core monitoring, a platinum instrument to perform core protection, and a single integrated core outlet thermocouple.

[0004] The signal generated by the vanadium detector is input into the core monitoring system and used to calculate the three-dimensional core power distribution, thereby performing the core monitoring function.

[0005] The vanadium detectors consist of five units, each with a certain length, and are positioned at heights of 10, 30, 50, 70, and 90% of the height of the fuel assembly within the core.

[0006] The signal generated by the platinum detector is input into the core protection system to perform core protection functions, and the platinum detector is configured with three units, each positioned to cover one-third of the core.

[0007] [Prior Art Literature]

[0008] [Patent Literature]

[0009] (Patent Document 1) Korean Registered Patent Publication KR 10-1445557 B1 (2014.09.29)

[0010] The present invention aims to provide an in-core instrument capable of simultaneously performing core protection and monitoring using two types of core protection signals and one type of core monitoring signal by using a rhodium or vanadium emitter with delayed response characteristics and a cobalt emitter with immediate response characteristics together in a neutron detector (SPND) that measures multiple neutron fluxes, and simultaneously employing a core inlet thermocouple (CIT) and a core outlet thermocouple (CET) for measuring the temperature of the core inlet and outlet.

[0011] The emitter of the neutron detector for measuring neutron flux according to the present invention is configured to include a rhodium (Rh) or vanadium (V) emitter with delayed response characteristics and a cobalt (Co) emitter with immediate response characteristics. The rhodium (Rh) or vanadium (V) emitter is used for core monitoring by detecting a current caused by delayed electrons generated after a certain period of time due to the half-life of synthetic nuclei produced by reacting with neutrons, and the cobalt (Co) emitter is used for core protection by detecting a current caused by immediate electrons generated by reacting with neutrons.

[0012] The present invention is configured to perform core protection by detecting a rapid increase and decrease in core temperature from the temperature difference (ΔT) between the core inlet and the core outlet, using a core inlet thermocouple (CIT), which is a thermocouple-type temperature detector that measures temperature at a hot junction location, to measure the temperature at the core inlet, and using a core exit thermocouple (CET) to measure the temperature at the core outlet.

[0013] The center positions of the five axial arrays of rhodium (Rh) or vanadium (V) emitters of the neutron detector (SPND) of the present invention are positioned at 10%, 30%, 50%, 70%, and 90% from the bottom of the active core to measure the neutron flux at the corresponding core height and provide a signal to the core monitoring system.

[0014] The center position of the emitter axial array can be changed to calculate the accurate axial power distribution of the core.

[0015] The center position of the cobalt (Co) emitter of the neutron detector (SPND) of the present invention is configured in any one of the following forms: three positions (30%, 50.0%, 80%), four positions (20%, 40%, 60%, 80%), or five positions (10%, 30%, 50%, 70%, 90%) in the core axis direction, to measure the neutron flux at the corresponding core height and provide a signal to the core protection system.

[0016] The center position of the cobalt emitter can be changed by the axial arrangement position of the rhodium (Rh) or vanadium (V) emitter.

[0017] The emitter length of the neutron detector (SPND) of the present invention is a length ranging from one-third to one-twentieth of the total length of the reactor core, and the emitter length is selected to match the magnitude of the current signal suitable for processing in the neutron detector (SPND) signal processing system, and the emitter center position can be changed according to the emitter length.

[0018] The present invention is characterized by two types of core protection functions and one type of core monitoring function, wherein a neutron flux signal measured by a neutron detector (SPND) using a cobalt (Co) emitter with immediate response characteristics is used to immediately detect rapid changes in the neutron flux of the core to perform core protection, a change in the temperature difference (ΔT) between the core inlet and core outlet is used by a core inlet thermocouple and a core outlet thermocouple to perform core protection against rapid heating or rapid cooling, and a neutron flux signal measured by a neutron detector (SPND) using a rhodium (Rh) or vanadium (V) emitter with delayed response characteristics is used to calculate a detailed output distribution to perform core monitoring.

[0019] In the present invention, the calibration of the cobalt neutron detector neutron flux using the core neutron flux calculated by the rhodium or vanadium neutron detector is characterized by: ① synthesizing the axial neutron flux distribution using the rhodium (Rh) or vanadium (V) neutron detector signal; ② separating the synthesized axial neutron flux distribution into fine nodes; ③ calibrating the cobalt emitter neutron flux using the average neutron flux of the nodes in ①, which is identical to the nodes corresponding to the length of the cobalt (Co) emitter; and performing the calibration online at regular intervals.

[0020] The present invention enables simultaneous core protection and monitoring using an in-core instrument, and allows core protection to be performed by simplifying system equipment without using an ex-core instrument; thus, it offers advantages in design, installation, and maintenance due to equipment simplification, as well as economic benefits in reducing purchasing costs.

[0021] In addition, since core inlet and outlet temperatures are measured using core inlet thermocouples (CIT) in conjunction with core outlet thermocouples (CET), resistance thermometer-type temperature detectors installed in the high-temperature and low-temperature tubes of the reactor coolant system can be eliminated, thereby enabling simplification of the system equipment.

[0022] FIG. 1 illustrates the configuration of a magnetic output type neutron detector (SPND) for monitoring neutron flux according to the present invention.

[0023] FIG. 2 illustrates the configuration of an in-core instrumentation that uses a core outlet thermocouple (CET) and a core inlet thermocouple (CIT) according to the present invention, and a neutron detector (SPND) with a cobalt (Co) emitter and a neutron detector (SPND) with a rhodium (Rh) or vanadium (V) emitter together.

[0024] Figure 3 illustrates an example configuration in which 45 in-core instruments are installed inside the OPR 1000 reactor, a Korean standard nuclear power plant.

[0025] Figure 4 shows the relationship between neutron flux and current ratio according to the accumulation of neutron irradiation of a cobalt emitter material.

[0026] FIG. 5 illustrates the calibration of a cobalt neutron detector neutron flux using a core neutron flux calculated by a rhodium or vanadium neutron detector according to the present invention.

[0027] The Korean standard nuclear power plants, specifically the OPR 1000 (Optimized Power Reactor 1000) and APR 1400 (Advanced Power Reactor 1400) types, perform core protection using neutron flux measured by ex-core instruments installed outside the reactor and perform core monitoring using neutron flux measured by in-core instruments installed in the fuel guide tubes.

[0028] In-core instruments are a combination of neutron detectors (SPND) and thermocouples (T / C). Neutron detectors using rhodium or vanadium emitters (Rh emitters) are used only for core monitoring because electrons are generated after a certain period of time due to the half-life of the synthetic nucleus produced by the reaction of rhodium or vanadium materials with neutrons.

[0029] The present invention aims to provide an in-core instrument capable of simultaneously performing core protection and monitoring by employing a rhodium or vanadium emitter (Rh or V emitter) with delayed response characteristics and a cobalt emitter with immediate response characteristics as a neutron detector, and employing a core inlet thermocouple (CIT) along with a core exit thermocouple (CET) for measuring the temperature of the core exit to provide two types of core protection signals and one type of core monitoring signal as an in-core instrument.

[0030] The present invention relates to an in-core instrument capable of simultaneously performing core protection and monitoring using two types of core protection signals and one type of core monitoring signal by employing a rhodium or vanadium emitter with delayed response characteristics and a cobalt emitter with immediate response characteristics together, and employing a core outlet thermocouple (CET) for measuring the temperature of the core outlet and a core inlet thermocouple (CIT) for measuring the temperature of the core inlet together, thereby providing two types of core protection signals and one type of core monitoring signal.

[0031] Hereinafter, the in-core instrument providing two types of core protection signals and one type of core monitoring signal according to the present invention will be described in more detail with reference to the attached drawings.

[0032] The in-core instrumentation providing two types of core protection signals and one type of core monitoring signal is configured to include a neutron detector (SPND) that detects neutron flux, comprising a plurality of rhodium or vanadium emitters and a plurality of cobalt emitters arranged along the length of the core to measure neutron flux inside the reactor, a core exit thermocouple (CET) for detecting the core exit temperature, and a core inlet thermocouple (CIT) for detecting the core inlet temperature.

[0033] FIG. 1 illustrates the configuration of a magnetic output type neutron detector (SPND) for monitoring neutron flux according to the present invention.

[0034] The neutron detector (SPND) (100) is configured to include an emitter (110), a signal wire (120), a sheath (130), an insulator (140), a resin (150), and a background signal wire (160).

[0035] The characteristics of self-powered neutron detectors (SPNDs) are classified according to the composition of the emitter, and rhodium (Rh), vanadium (V), cobalt (Co), hafnia (Hf), platinum (Pt), and silver (Ag) are used.

[0036] Among these, rhodium (Rh) and vanadium (V) are generally the most widely used for measuring and observing neutron flux.

[0037] The neutron detector (SPND) (100) is configured to include an emitter (110), a signal wire (120), a sheath (130), an insulator (140), a resin (150), and a background signal wire (160).

[0038] The characteristics of self-powered neutron detectors (SPNDs) according to the use of emitter materials Co, Pt, Rh, Hf, and Ag in nuclear reactors are as shown in Table 1 below (Characteristics of self-powered neutron detectors used in power reactors, William H. Todt).

[0039]

[0040] Neutron detectors (SPNDs) are classified into immediate response neutron detectors and delayed response neutron detectors depending on the emitter material.

[0041] Neutron detectors using rhodium or vanadium emitters are used for core monitoring because they cannot reflect the immediate core state due to the delayed response characteristic in which electrons are generated after a certain period of time due to the half-life of the synthetic nucleus produced by reacting with a neutron.

[0042] The process of delayed beta (β) generation after the neutron reaction of rhodium is as follows, and beta (β) and electron (e) are physically identical.

[0043]

[0044] The process of immediate electron (e) generation after a neutron reaction in cobalt material is as follows.

[0045]

[0046] Cobalt materials are used for core protection because they generate immediate electrons through the above (n, r, e) reaction, allowing for the immediate determination of the core's neutron flux levels.

[0047] If an in-core instrumentation is configured using a cobalt neutron detector, core protection can be performed in place of an ex-core instrumentation.

[0048] The emitter length of the neutron detector (SPND) is between one-third and one-twentieth of the total length of the reactor core, and the emitter center position may change depending on the emitter length.

[0049] Two pairs of thermocouples are placed to directly measure the temperatures at the core inlet and outlet locations.

[0050] A thermocouple is a temperature detector that measures temperature at the hot junction.

[0051] Currently, in-core instruments generally use K-type thermocouples in the range of -20℃ to 1200℃ and are positioned to measure only the temperature at the core exit.

[0052] The present invention uses a core exit thermocouple (CET) and a core inlet thermocouple (CIT) together, wherein the heating junctions of the K-type thermocouples are positioned at the core exit and core inlet locations.

[0053] FIG. 2 illustrates the configuration of an in-core instrumentation that uses a core outlet thermocouple (CET) and a core inlet thermocouple (CIT) according to the present invention, and a cobalt (Co) neutron detector together with a rhodium (Rh) or vanadium (V) neutron detector.

[0054] The center positions of the axial array of rhodium (Rh) or vanadium (V) emitters of the neutron detector (SPND) measure the neutron flux at the corresponding core heights at 10%, 30%, 50%, 70%, and 90% from the bottom of the active core and provide a signal to the core monitoring system.

[0055] The center positions of the cobalt (Co) emitters of the neutron detector (SPND) are arranged at four locations (20%, 40%, 60%, 80%) along the core axis to measure the neutron flux at the corresponding core height and provide a signal to the core protection system.

[0056] The center positions of the cobalt (Co) emitters of the neutron detector (SPND) can be configured in the form of three locations (30%, 50.0%, 80%), four locations (20%, 40%, 60%, 80%), or five locations (10%, 30%, 50%, 70%, 90%) along the core axis to measure the neutron flux at the corresponding core height and provide a signal to the core protection system.

[0057] The present invention configures an in-core instrument by installing a core exit thermocouple (CET) and a core inlet thermocouple (CIT) together, and using a cobalt (Co) neutron detector together with a rhodium (Rh) or vanadium (V) neutron detector.

[0058] With a configuration equipped with two types of neutron detectors, it is possible to simultaneously perform core monitoring by detecting a current proportional to the neutron flux from a rhodium (Rh) or vanadium (V) neutron detector and core protection by detecting a current proportional to the neutron flux from a cobalt (Co) neutron detector.

[0059] An in-core instrumentation system consisting of a core exit thermocouple (CET), a core inlet thermocouple (CIT), and two types of neutron detectors (SPND) is installed in the in-core instrumentation guide tube of the nuclear fuel to enable simultaneous temperature measurement and neutron flux measurement.

[0060] The In-Core Instrument Assembly (ICI Assembly), installed in the central instrument guide tube of the reactor's fuel assembly, measures the neutron flux inside the reactor and the reactor outlet temperature of the Nuclear Steam Supply System (NSSS) to analyze the neutron flux output distribution in the core and the degree of supercooling at the core outlet.

[0061] Previously, the configuration, which only had a Core Exit Thermocouple (CET) installed in the core, required temperature detectors of the Resistance Thermometer (RDT) type installed in the hot and cold tubes of the reactor coolant system, respectively.

[0062] In the present invention, by installing a core outlet thermocouple (CET) and a core inlet thermocouple (CIT) together, the resistance thermometer (RDT) type temperature detectors installed in the high-temperature and low-temperature tubes of the reactor coolant system, respectively, are not required.

[0063] Nuclear reactor instrumentation consists of ex-core instrumentation systems installed outside the reactor and in-core instrumentation systems installed inside the reactor; neutron detectors (SPNDs) are primarily used in in-core instruments (ICIs) that monitor neutron flux within the reactor.

[0064] The core exit thermocouple (CET) and core inlet thermocouple (CIT) measure the temperature at the hot junction location.

[0065] At the heating junction of a thermocouple, a thermoelectric power is generated by the Seebeck effect due to the temperature difference resulting from the junction of the two ends of two types of metals, so the thermoelectric power is measured and converted into temperature to measure the temperature.

[0066] Figure 3 illustrates, as an example, a configuration in which 45 in-core instruments are installed inside the OPR 1000 reactor, a Korean standard nuclear power plant.

[0067] 177 nuclear fuels are provided inside the reactor, and 45 in-core instruments are provided.

[0068] In the case of the OPR 1000 type, since in-core instruments are installed at 45 locations throughout the core, core protection against local neutron flux changes is possible at 135 (=45×3) locations when three axially arranged neutron detectors and responsive cobalt emitters.

[0069] In addition, core protection against changes in heat generated in the core is possible by utilizing the temperature difference between the core inlet and outlet at 45 locations.

[0070] When five axially arranged rhodium or vanadium emitters with delayed response to neutron detectors are used, core monitoring of local neutron flux changes at 225 (=45×5) positions is possible, and neutron flux correction of the cobalt emitter can be performed.

[0071] Depending on the method of loading in-core instruments into the fuel guide tubes, there are Bottom Mounted In-Core Instruments (Bottom Mounted ICI), which load fuel from the bottom of the reactor, and Top Mounted In-Core Instruments (Top Mounted ICI), which loads fuel from the top of the reactor; both methods can be used depending on the reactor and fuel types.

[0072] In-core instruments are installed in guide tubes positioned in the center of the nuclear fuel and measure neutron flux at a close distance to the fuel, thus having the advantage of lower uncertainty in neutron flux measurement compared to ex-core instruments.

[0073] Figure 4 shows the relationship between neutron flux and current ratio according to the cobalt emitter material.

[0074] As described in the paper by Xinxin Liu, Zhongwei et al. (Current compensation for material consumption of cobalt self-powered neutron detector, Nuc. Eng. & Tech), the cobalt emitter material used is Co-59, which is transformed into Co-60 and Co-61 by neutron irradiation. As the irradiation period increases within the reactor, the current signal generated from Co-59 decreases, while the current signals generated from Co-60 and Co-61 increase.

[0075] Therefore, as the neutron irradiation period increases in the same neutron flux environment, the proportion of current generated in the total cobalt emitter increases, resulting in an effect where the integrated neutron flux calculated from the measured current increases.

[0076] For this reason, the neutron flux calculated by the cobalt neutron detector needs to be calibrated.

[0077] FIG. 5 illustrates the calibration of a cobalt neutron detector neutron flux using a core neutron flux calculated by a rhodium or vanadium neutron detector according to the present invention.

[0078] The neutron flux of a cobalt neutron detector is calibrated using the core neutron flux calculated by a rhodium or vanadium neutron detector as follows.

[0079] ① Synthesize the axial neutron flux distribution using rhodium (Rh) or vanadium (V) neutron detector signals.

[0080] ② Separate the synthesized axial neutron flux distribution into fine nodes.

[0081] ③ The average neutron flux of several nodes in ①, which is identical to several nodes corresponding to the length of the cobalt (Co) emitter, is used to correct to the cobalt emitter neutron flux, and the correction is performed online at regular intervals.

[0082] The immediate response signal generated from the cobalt (Co) emitter of the neutron detector (SPND) detects rapid changes in the neutron flux of the core to perform core protection, and detects changes in the temperature difference (ΔT) between the core inlet and core outlet to perform core protection against rapid heating or rapid cooling.

[0083] By using an immediate response cobalt (Co) neutron detector (SPND), an immediate core protection signal can be obtained, and by using a delayed response rhodium (Rh) or vanadium (V) neutron detector (SPND), a core monitoring signal can be obtained, thereby enabling simultaneous core protection and monitoring.

[0084] The present invention enables simultaneous core protection and monitoring using an in-core instrument, and allows core protection to be performed by simplifying system equipment without using an ex-core instrument; thus, it offers advantages in design, installation, and maintenance due to equipment simplification, as well as economic benefits in reducing purchasing costs.

[0085] Since core inlet and outlet temperatures are measured using core inlet thermocouples (CIT) in conjunction with core outlet thermocouples (CET), resistance thermometer-type temperature detectors installed in the high-temperature and low-temperature tubes of the reactor coolant system can be eliminated, thereby enabling simplification of the system equipment.

[0086] Compared to measuring neutron flux using neutrons leaking out of the reactor, measuring the neutron flux directly at the emitter location inside the reactor significantly improves the uncertainty of neutron flux measurement.

[0087] In the case of the OPR1000 and APR1400 reactor models, an indirect measurement method is used in which core inlet and outlet temperatures are measured in the hot and cold tubes of the reactor coolant system and converted to core inlet and outlet temperatures; however, since measurements are taken directly at the core inlet and outlet, temperature measurement uncertainty is reduced.

[0088] Neutron flux and temperature measurement uncertainties are reduced, and core protection against total or localized output changes is possible.

[0089] Although the present invention has been described in detail through representative embodiments above, those skilled in the art will understand that various modifications can be made to the above-described embodiments within the scope of the present invention.

[0090] Therefore, the scope of the rights of the present invention should not be limited to the described embodiments, but should be determined by the claims set forth below as well as all modifications or variations derived from the claims and equivalent concepts.

[0091] [Explanation of the symbol]

[0092] 100: Neutron detector

[0093] 110: Emitter

[0094] 120: Signal line

[0095] 130: Cover

[0096] 140: Insulator

[0097] 150: Resin filling part

[0098] 160: Background signal line

Claims

1. An in-core instrument that provides both core protection signals and core monitoring signals includes a Self-Powered Neutron Detector (SPND) that measures neutron flux, and A neutron detector (SPND) (100) is configured to include an emitter (110), a signal wire (120), a sheath (130), an insulator (140), a resin (150), and a background signal wire (160). The emitter (110) of the neutron detector for measuring neutron flux is configured to include a rhodium (Rh) or vanadium (V) emitter and a cobalt (Co) emitter. Rhodium (Rh) or vanadium (V) emitters are used for core monitoring by detecting delayed electron currents generated after a certain period of time due to the half-life of synthetic nuclei produced by reacting with neutrons, and Cobalt (Co) emitters are used for core protection by detecting the immediate neutron flux levels of the core using immediate electron currents generated by material reactions, and An in-core instrument comprising a neutron detector that measures two types of neutron flux is characterized by measuring neutron flux to simultaneously perform core protection and core monitoring, and provides a core protection signal and a core monitoring signal together.

2. In Paragraph 1, An in-core instrument that provides both a core protection signal and a core monitoring signal, characterized by measuring the temperature of the core inlet using a core inlet thermocouple (CIT), which is a thermocouple temperature detector that measures the temperature at a hot junction location, and measuring the temperature of the core outlet using a core exit thermocouple (CET), thereby detecting the temperature difference (ΔT) between the core inlet and the core outlet to provide core protection against a sudden increase or decrease in the heat content of the core.

3. In Paragraph 1, The center positions of the axial array of rhodium (Rh) or vanadium (V) emitters of the delayed-response neutron detector (SPND) measure the neutron flux at the corresponding core heights at 10%, 30%, 50%, 70%, and 90% from the bottom of the active core, provide a signal to the core monitoring system, and An in-core instrument that provides both a core protection signal and a core monitoring signal, characterized by configuring the center positions of the cobalt (Co) emitters of the rapid response neutron detector (SPND) in any one of three arrangements along the core axis (30%, 50.0%, 80%), four arrangements (20%, 40%, 60%, 80%), or five arrangements (10%, 30%, 50%, 70%, 90%) to measure the neutron flux at the corresponding core height and provide a signal to the core protection system.

4. In Paragraph 1, An in-core instrument that provides both a core protection signal and a core monitoring signal, characterized by the ability to use a bottom-mounted method in which the in-core instrument is inserted from the bottom to the top of the nuclear fuel and a top-mounted method in which the in-core instrument is inserted from the top to the bottom of the nuclear fuel.

5. In Paragraph 3, An in-core instrument that provides both a core protection signal and a core monitoring signal, characterized in that the emitter length of a neutron detector (SPND) is between one-third and one-twentieth of the total length of the reactor core, and the emitter center position can be changed according to the emitter length.

6. In any one of Paragraphs 3 through 5, Calibration of the cobalt neutron detector neutron flux using the core neutron flux calculated by a rhodium or vanadium neutron detector, ① Synthesize the axial neutron flux distribution using rhodium (Rh) or vanadium (V) neutron detector signals, and ② Separate the synthesized axial neutron flux distribution into fine nodes, and ③ An in-core instrument that provides both a core protection signal and a core monitoring signal, characterized by using the average neutron flux of the several nodes of ① above, which is identical to the length of the cobalt (Co) emitter, to correct to the cobalt emitter neutron flux, and performing the correction online at regular intervals.

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