JP2015219163A - Nuclear instrumentation sensor system and nuclear reactor output monitoring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nuclear instrumentation sensor system capable of preventing degradation in the accuracy of a gamma thermometer due to the generation of heat from a self-powered detector, and a nuclear reactor output monitoring system using the nuclear instrumentation sensor system.SOLUTION: A nuclear instrumentation sensor system 1, comprises: a gamma thermometer section 8 configured to have at least two junctions including a cold junction 4 located outside of upper and lower ends of a heat insulator 7; a self-powered detector 11 disposed generally at the same height as that of the heat insulator 7; and a sheath 12 for storing therein the gamma thermometer section 8 and the self-powered detector 11. In the nuclear instrumentation sensor system 1, the self-powered detector 11 is disposed outside of the heat insulator 7. When the gamma thermometer and the self-powered detector are formed integrally to be able to be installed in a narrow space, it is possible to prevent degradation in the accuracy of the gamma thermometer due to the heat generation from the self-powered detector.

Description

  The present invention relates to a nuclear instrumentation sensor system and a reactor power monitoring system.

  In a boiling water reactor or the like, a system in which a radiation sensor is installed in a reactor is widely used as a system for monitoring reactor power (called nuclear instrumentation). For example, in a conventional boiling water reactor, a fission ionization chamber is placed in the gap of the fuel assembly in order to monitor the output in the reactor, and a signal is drawn from the lower part of the pressure vessel with a cable to the central control room. A system that performs measurement and display with an installed monitoring device is common. The fission ionization chamber is obtained by applying uranium as a fission material to the cathode or anode of the ionization chamber. When neutrons are applied to the coated uranium, the uranium undergoes fission, and the fission fragments ionize the gas between the anode and cathode to produce a current signal. Therefore, uranium is lost during operation due to neutron irradiation, and sensitivity is lowered. Usually, to calibrate the decrease in sensitivity during operation, a scanning detector capable of scanning the vicinity of the fission ionization chamber is used, and based on the output signal when the scanning detector is located adjacent to the fission ionization chamber. Sensitivity is calibrated.

  For such a conventional system, a method that does not use a scanning detector has also been proposed. For example, Japanese Patent Laid-Open No. 3-65696 (Patent Document 1) discloses a configuration for calibrating the sensitivity of adjacent fission ionization chambers using a gamma thermometer.

Furthermore, in JP-A-4-18796 (Patent Document 2), a self-output type detector is used instead of the fission ionization chamber, and a thermocouple and a self-output type detector are arranged inside the heat insulating part inside the gamma thermometer, An output distribution measuring device that calibrates the sensitivity of a self-powered detector based on an output signal of a gamma thermometer is disclosed.

JP-A-3-65696 JP-A-4-18796

  Since the above-described scanning detector is inserted into and removed from the guide tube, a certain thickness or more is required to ensure mechanical strength. In addition, since it is necessary to arrange two types of detectors, a fission ionization chamber and a scanning detector, adjacent to each other, an assembly in which these sensor systems are housed in one outer cylinder has a large outer diameter. For this reason, the conventional sensor system can only be installed in a gap having a certain space.

  When a gamma thermometer is used, it is not necessary to ensure the strength when the detector is put in and out, and the outer diameter can be reduced. Furthermore, as shown in Patent Document 2, by integrating a self-output type detector with a gamma thermometer, the outer diameter of the sensor system can be reduced and installed in a narrower region.

  However, such a sensor system has a problem that it is difficult to ensure measurement accuracy as it is. The problem will be described below.

  A gamma thermometer is a sensor for measuring gamma rays, and its measurement principle is to measure the heat generation of gamma rays by temperature. That is, when a heat generating part formed of metal or the like is irradiated with gamma rays, gamma heat is generated. The heating part is in thermal contact with the cooling water flowing outside the sensor at a certain height, and the temperature is kept near the coolant temperature, while the heat insulating part is formed at a different height. Since the heat generating part is thermally isolated from the cooling water flowing outside, the temperature rises. And the gamma ray is calculated | required by measuring the temperature difference between these two points with a differential type thermocouple.

  On the other hand, the self-powered detectors that measure neutrons are the β-ray type and the capture γ-ray type. In either case, it is assumed that the neutron is absorbed by the emitter and causes transmutation. Yes. That is, a substance sensitive to neutrons is lost due to neutron irradiation, and the sensitivity changes. A gamma thermometer is required to calibrate this sensitivity change.

  If a self-output type detector is built in such a gamma thermometer, heat generation of the self-output type detector is detected in addition to the gamma heat generation in the gamma thermometer heat generating part. Here, the heat generation of the self-powered detector depends on the number of transmutation by neutrons, but the transmutation number varies with the loss of sensitive material even in the same neutron irradiation environment. Therefore, since the measurement value of the gamma thermometer serving as a calibration reference depends on the sensitivity of the self-output detector that is the calibration target, there arises a problem that the accuracy cannot be improved.

  Alternatively, in order to avoid such problems, it can be considered that the height of the gamma thermometer and the self-output detector are sufficiently separated so as not to be affected by the heat generated by the self-output detector. In that case, since the sensitivity of the self-output type detector is calibrated by a gamma thermometer installed at a distant position, an error due to a difference in position occurs, and there is a problem that the accuracy deteriorates for another reason.

The present invention has been made to solve the above-described problems, and its purpose is to provide a self-output type detection when a gamma thermometer and a self-output type detector can be integrally formed and installed in a narrow space. It is an object of the present invention to provide a nuclear instrumentation sensor system that does not cause a decrease in accuracy of the gamma thermometer due to heat generation of the reactor, and a reactor power monitoring system using this nuclear instrumentation sensor system.

The present invention includes a calibration heater, a differential thermocouple installed around the heater, a heating unit arranged to be in thermal contact with the heater and the differential thermocouple, the calibration heater, The differential thermocouple includes a heat insulating portion disposed so as to surround a certain height range of the heat generating portion, and the differential thermocouple includes a hot junction positioned between upper and lower ends of the heat insulating portion. A gamma thermometer unit configured to have at least two contacts with a cold junction located outside the upper and lower ends of the heat insulating unit, and a self-output detector disposed at substantially the same height as the heat insulating unit And a nuclear instrumentation sensor system comprising a sheath for housing the gamma thermometer unit and the self-powered detector, wherein the self-powered detector is disposed outside the heat insulating portion.

When the gamma thermometer and the self-output type detector are integrally molded so that the gamma thermometer can be installed in a narrow space, the accuracy of the gamma thermometer due to heat generation of the self-output type detector can be prevented.

It is a longitudinal cross-sectional view with respect to an example of a nuclear instrumentation sensor system. It is a cross-sectional view with respect to an example of a nuclear instrumentation sensor system. It is the figure which showed the structural example of the nuclear reactor power monitoring system using the nuclear instrumentation sensor system of Example 1. FIG.

  The present invention relates to an in-core radiation sensor system for monitoring the output of a nuclear reactor and a reactor output monitoring system using the sensor system.

  Hereinafter, each embodiment will be described with reference to the drawings.

  FIG. 1 is a longitudinal sectional view showing a configuration example of a nuclear instrumentation sensor system according to the present embodiment. The nuclear instrumentation sensor system 1 includes a calibration heater 2, a differential thermocouple 5 including a hot junction 3 and a cold junction 4, a heat generating unit 6, and a gamma thermometer unit 8 including a heat insulating unit 7, an emitter 9 and a collector. 10 includes a self-output type detector 11 constituted by 10, a gamma thermometer unit 8 and a self-output type detector 11, and a connector 13 attached to the lower part of the metal sheath 12. Although only two sets of the gamma thermometer unit 8 and the self-output type detector 11 are shown in FIG. 1, they are also installed at the lower part of these, and have four sets as a whole.

  FIG. 2 is a cross-sectional view showing a configuration example of the nuclear instrumentation sensor system of the present embodiment. Elements that are the same as those shown in FIG. 1 are given common numbers. The gamma thermometer section 8 is formed with a heat insulating section 7 in which a rare gas (Ar, etc.) is enclosed so as to surround the heating heater 6 for calibration, the differential thermocouple 5, and the heat generating section 6 formed of metal, ceramic, etc. ing. The self-output type detector 11 is disposed outside the heat insulating portion 7 and is thermally isolated from the gamma thermometer portion 8.

  A calibration heater 2 and a differential thermocouple 5 are arranged inside the heat insulating portion 7 formed in a cylindrical shape. In particular, the hot junction 3 of the differential thermocouple 5 is arranged within the height range from the upper end to the lower end of the heat insulating portion 7, and the cold junction 4 is the height range from the upper end to the lower end of the heat insulating portion 7. Placed outside. In addition, the entire emitter 9 that is the sensitive part is arranged outside the heat insulating part 7 and within a height range from the upper end part to the lower end part of the heat insulating part 7.

  Hereinafter, the operation of the sensor system will be described. This sensor system is attached to a narrow part in a nuclear reactor and is irradiated with neutrons emitted from nuclear fuel by fission. Neutrons that have reached the emitter 9 in the self-output detector 11 are captured by the nuclei in the emitter 9 and emit gamma rays. This trapped gamma ray knocks out orbital electrons of surrounding atoms. By taking out the knocked-out electrons as current from the collector 9, a signal corresponding to the neutron flux in the reactor can be obtained. Since the time from neutron capture to obtaining a signal is very short, use this signal for reactor power monitoring, etc., and to operate an emergency stop (scram) in the event of excessive power. Can do. Substances such as cobalt, cadmium, platinum, erbium, hafnium, and gadolin can be used as substances that emit trapped γ rays. In the self-powered detector 11 based on such a principle, since a signal is output by nuclear transmutation in the emitter, the nucleus that causes the nuclear transmutation is lost during operation, and the signal level for the same neutron irradiation decreases. To go.

  When the gamma thermometer unit 8 is irradiated with gamma rays emitted by nuclear fission in the reactor core, the gamma thermometer unit 8 absorbs the gamma rays and the heat generating unit 6 generates heat. This calorific value depends on the fission amount, that is, the output of the reactor. At this time, the temperature of the portion surrounded by the heat insulating portion 7 increases according to the amount of heat generation, but the temperature does not increase due to heat dissipation at the cold junction not surrounded by the heat insulating portion 7. The temperature difference between the two is detected by the hot junction 3 and the cold junction 4, and the output of the differential thermocouple 5 is in accordance with the reactor output. The output of the differential type thermocouple 5 is based on heat generation, and is accompanied by a time delay of several seconds or more with respect to changes in the core output, so it is suitable for use in order to generate signals such as emergency stop (scram). Absent. However, it can be used for calibration of the self-output detector 11 whose output decreases with operation. In this sensor system, the signal of the self-output detector 11 can be calibrated based on the output of the differential thermocouple 5 and used for operations such as emergency stop (scram) throughout the operation period.

  Further, the gamma thermometer unit is provided with a calibration heater 2, and the output signal of the differential thermocouple 5 can be calibrated so that the same output signal is obtained with respect to a specified calorific value.

  As described above, the gamma thermometer unit 8 is based on the principle of measuring the output by heat generation. If there is heat generation not directly correlated with the output, an error factor is caused. The self-output type detector 11 generates heat based on the nuclear reaction of neutron absorption, but since the amount of generated heat changes with the loss of the nuclear reactant, if this generated heat propagates to the heat generating part 6, it becomes an error factor. In this sensor system, the heat generated by the self-output detector 11 is blocked by the heat insulating unit 7 and is not transmitted to the heat generating unit 6, and the gamma thermometer unit 8 can maintain accurate measurement.

  FIG. 3 shows a configuration example of a reactor power monitoring system using the nuclear instrumentation sensor system of the present invention. The nuclear instrumentation sensor system 1 is inserted into the core 19 of the boiling water reactor pressure vessel 14 in a direction parallel to the fuel assembly. Inside the pressure vessel 14, in addition to the core 19, a core support plate 20 that supports the core at the lower part, an upper lattice plate 18 that fixes the upper part of the fuel, a shroud 17 that contains the core, and a steam separator attached to the upper part of the shroud 16, steam dryer 15 etc. are installed. The tip of the nuclear instrumentation sensor system 1 is supported by the upper lattice plate 18, and the lower portion passes through the core support plate 20 and is inserted into the guide tube and the housing 21 and guided to the outside of the pressure vessel 14. The guide tube and housing 21 have a water seal (not shown in FIG. 3) so that the cooling water in the pressure vessel 14 does not leak to the outside. Outside the pressure vessel 14, the connector 13 and the cable 22 are connected to a self-output detector measuring device 23 and a gamma thermometer measuring device 24. The self-output detector measuring device 23 and the gamma thermometer measuring device 24 are connected to an output monitoring device 25. In addition to the above, the output monitoring device 25 is connected to a core flow rate measuring device 31 including a flow rate sensor 30 for measuring the core flow rate. A control rod 27 is installed inside the pressure vessel 14, and its drive mechanism 28 is connected to a control rod control device 29. The output monitoring device 25 and the control rod control device 29 are connected to the safety protection system 26.

  As a form of connecting the gamma thermometer 8 and the self-output detector 11 to each measuring device, a first signal cable connected to the gamma thermometer 8 and a second signal cable connected to the self-output detector 11 are used. Signal cable, a gamma thermometer measuring device 24 connected to the first signal cable to generate a local output signal in the reactor, and a local output signal of the reactor connected to the second signal cable A self-output type detector measuring device 23 may be arranged.

  The operation of this system will be described below. In a boiling water reactor, the core 19 generates heat due to a fission reaction that occurs in the core 19, and heats cooling water (not shown in FIG. 3) that flows in the core. The coolant passes through the core 19 from the lower part toward the upper part, but is slightly subcooled at the lower inlet of the core 19 and absorbs heat to be vaporized. The generated steam reaches the steam separator 16 from the upper part of the shroud 17, and the moisture is removed and enters the steam dryer 15. Droplets are removed in the steam dryer 15, and the dried steam is sent to a turbine (not shown in FIG. 3) connected to the outside of the pressure vessel. The nuclear instrumentation sensor system 1 is installed in a gap between fuels in a core 19, and a coolant flows around from the lower part to the upper part. The nuclear instrumentation sensor 1 that has been irradiated with neutrons outputs a signal corresponding to the neutron flux from the internal self-output detector 11. This signal reaches the self-output type detector measuring device 23 from the lower part of the pressure vessel 14 via the connector 13 and the cable 22. In the self-output type detector measuring device 23, the input signal is converted into an output and transmitted to the output monitoring device 25 as an analog signal or a digital signal. In order to maintain the thermal safety of the core, the output monitoring device 25 is set with an output value corresponding to the core flow rate output from the flow sensor 30 and the core flow rate measuring device 31, and the output signal described above is excessive. When judged, a trip signal is output to the safety protection system 26. The safety protection system 26 receives a trip signal from a plurality of channels (not shown in FIG. 3) to prevent erroneous operation, and when a predetermined condition is satisfied according to a built-in logic circuit, a reactor emergency stop (scram) Generate a signal. The control rod control device 29 that has received the scram signal fully inserts all the control rods 27 into the core via the control rod drive mechanism 28.

In such output monitoring during operation, the gamma thermometer unit 8 of the nuclear instrumentation sensor system 1 is irradiated with gamma rays accompanying fission generated in the core 19, and a voltage corresponding to the gamma dose rate is a differential thermocouple 5. Is output by. This voltage is converted into an output signal by the gamma thermometer measuring device 24 and output to the output monitoring device 25. The output monitoring device 25 compares the output signal from the gamma thermometer measurement device 24 with the output signal from the self-output detector measurement device 23 periodically or at the request of the operator to measure the self-output detector. The output signal of the device 23 is calibrated. Thereby, even during operation, the output of the self-output type detector measuring device 23 can be instructed to be the original output without being affected by the impairment.

DESCRIPTION OF SYMBOLS 1 Nuclear instrumentation sensor system 2 Heater for calibration 3 Hot junction 4 Cold junction 5 Differential thermocouple 6 Heat generation part 7 Heat insulation part 8 Gamma thermometer part 9 Emitter 10 Collector 11 Self-output type detector 12 Metal sheath 13 Connector 14 Pressure vessel 15 Steam dryer 16 Steam / water separator 17 Shroud 18 Upper lattice plate 19 Core 20 Core support plate 21 Guide tube and housing 22 Cable 23 Self-output detector measuring device 24 Gamma thermometer measuring device 25 Output monitoring device 26 Safety protection System 27 Control rod 28 Drive mechanism 29 Control rod control device 30 Flow rate sensor 31 Core flow rate measurement device

Claims (5)

Calibration heater, differential thermocouple installed around the heater, a heat generating portion arranged to be in thermal contact with the heater and the differential thermocouple, the calibration heater, and the differential type A thermocouple, and a heat insulating part arranged so as to surround a certain height range of the heat generating part,
The differential thermocouple has a gamma configured to have at least two contacts, a hot junction located between upper and lower ends of the heat insulating portion and a cold junction located outside the upper and lower ends of the heat insulating portion. A thermometer section;
A self-powered detector disposed at substantially the same height as the heat insulating part;
In a nuclear instrumentation sensor system comprising a sheath that houses the gamma thermometer unit and the self-output detector,
The nuclear instrumentation sensor system, wherein the self-output detector is disposed outside a heat insulating portion.   In Claim 1, The said heat insulation part is longer than the length of the emitter of the said self-output type detector, and is arrange | positioned so that the whole of the said emitter may be settled in the height range to the upper and lower ends of a heat insulation part. A featured nuclear instrumentation sensor system.   2. The nuclear instrumentation sensor system according to claim 1, wherein a cold junction of the gamma thermometer unit is disposed at a position lower than the lower end of the emitter of the self-output detector or a position higher than the upper end of the emitter. .   2. The nuclear instrumentation sensor system according to claim 1, wherein the self-powered neutron detector is composed of any one of cobalt, cadmium, platinum, erbium, hafnium, gadlium, or a combination thereof as an emitter material. Calibration heater, differential thermocouple installed around the heater, a heat generating portion arranged to be in thermal contact with the heater and the differential thermocouple, the calibration heater, and the differential type A thermocouple, and a heat insulating part arranged so as to surround a certain height range of the heat generating part,
The differential thermocouple has a gamma configured to have at least two contacts, a hot junction located between upper and lower ends of the heat insulating portion and a cold junction located outside the upper and lower ends of the heat insulating portion. A thermometer section;
A self-powered detector disposed at substantially the same height as the heat insulating part;
A sheath for housing the gamma thermometer unit and the self-output detector;
The self-powered detector is disposed outside the heat insulating portion,
A first signal cable connected to the gamma thermometer unit, a second signal cable connected to the self-powered detector, and a local output signal in the reactor connected to the first signal cable. A gamma thermometer measurement device to be generated, a self-output detector measurement device connected to a second signal cable to generate a local reactor output signal, a gamma thermometer measurement device, and a self-output detector measurement A reactor power monitoring system comprising: an output monitoring device that is connected to the device and calculates calibration information of sensitivity of the self-powered detector from local output signals generated by both devices.