JP2005172474A - Nuclear reactor core thermal output monitoring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately derive a nuclear reactor thermal output when a detector is troubled in a heat balance system. <P>SOLUTION: This nuclear reactor thermal output monitoring device has a plurality of fixed neutron detectors 5 provided with a prescribed interval along an axial direction in a protection tube 4 penetrated along the axial direction between fuel assemblies in a nuclear reactor core, a nuclear reactor output measuring instrument provided with gamma thermometers 8 with a larger number than the neutron detectors along the axial direction, an average output area monitor (APRM) for finding a core average output using measured values in the neutron detectors, and a nuclear reactor thermal output calculator 18 for finding a core thermal output, from the detector such as a thermometer and a flowmeter installed in a supply water flow rate system, using a heat balance. The core thermal output is derived by using measured values by the gamma thermometers 8, when the detector such as the thermometer and the flowmeter is troubled in the supply water flow rate system. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reactor core thermal output monitoring device such as a boiling water reactor (BWR), and more particularly to a reactor core thermal output monitoring device that improves measurement accuracy and reliability.

  In general, in boiling water reactors, as a constant monitoring device, at least a device that evaluates and monitors the power distribution in the core (reactor core monitoring device), a horizontal cross section of the core, and a neutron flux over the height direction. A local power range monitor (LPRM) and an average power range monitor (APRM) for monitoring the average power level of the core are provided.

  The above-mentioned apparatus for evaluating and monitoring the power distribution in the core is designed to obtain the thermal output of the nuclear reactor by calculating the thermal balance of the core, and to perform the thermal evaluation in the core. LPRM is a neutron The neutron flux detector is configured to monitor the neutron flux at the installation position of the neutron flux detector and provide information such as a local output increase. The APRM calculates the core average output level equivalent value by averaging the output signals of the LPRM, and when the calculated value exceeds a predetermined set value, has a role of outputting a signal such as an alarm or a scrum. Is.

  That is, FIG. 4 is a plan view showing a schematic configuration of the core of the BWR, in which a large number of fuel assemblies 1 are arranged in a square lattice shape, and a cross-like shape is formed at the center of the four fuel assemblies 1. The control rod 2 is disposed so as to be movable in the axial direction. In consideration of the symmetry of the arrangement of the fuel assemblies 1 installed in the core, a plurality of detector assemblies 3 are arranged in the core so that the entire core can be measured uniformly. As shown in FIG. 5, this detector assembly 3 includes a local output region monitor (LPRM) 5 for detecting the amount of neutrons composed of fission ionization chambers in a protective tube 4 penetrating the core along the axial direction. Four bodies are arranged at predetermined intervals, and a mobile neutron detector (TIP) 7 for sensitivity calibration of the LPRM5 is inserted into a guide tube 6 provided adjacent to the LPRM5. These LPRM5 Is input to the output monitoring device via the signal cable to perform the reactor power measurement and control. The LPRM signals are collected in an average output region monitor (APRM), and the average value of the signals is used to monitor the change in neutron flux in the core.

  The neutron flux detector used as the LPRM uses a fission counter in which a fission material such as uranium 235 is applied to an electrode and an ionized gas is enclosed in the tube. For this reason, since the detection sensitivity deteriorates due to a decrease in fission material due to neutron irradiation, calibration is performed using the TIP. The TIP is the same neutron flux detector as the LPRM, but is usually kept outside the reactor and moved inside the detector assembly only when the LPRM is calibrated to calibrate the LPRM.

  Since the value of the APRM is an average of the indicated values of the LPRM as described above, it is approximately proportional to the core average neutron flux and approximately proportional to the core thermal output. Therefore, the thermal output of the core can also be monitored by the value of APRM.

  As described above, there are two methods for monitoring the core thermal output: a method using a value obtained by heat balance calculation (heat balance method) and a method using an APRM value (APRM method). In the APRM method, the absolute value cannot be expressed as it is, so that the APRM value is calibrated in a timely manner so as to indicate the ratio (%) of the core heat output to the rated value as compared with the heat balance method.

In the reactor core monitoring device, the core thermal output by the heat balance method is usually used, but when the measuring device related to the heat balance centering on the reactor is out of order, the core thermal output is obtained by the heat balance method. I can't. For example, since the water supply system dominates about 99% of this heat balance, the failure of the detector related to the water supply flow rate system has a great influence. Therefore, in the reactor core monitoring device, when a detector related to the feed water flow rate system fails, the value of APRM is used as the input value of the core thermal output. That is, when both the core thermal output by the heat balance method and the APRM method are normally obtained, their proportional constants (referred to as calibration constants) CAP (I) are obtained by the equation (1).
FRP = CAP (I) ・ RAP (I) (1)
FRP: Core thermal power rating ratio (based on heat balance method)
CAP (I): Calibration constant for APRM channel I
RAP (I): APRM value of APRM channel I and when the detector related to the feed water flow system fails, the rated value of the core thermal power is obtained from the right side of equation (1) using the APRM value. This value is used as an input value for the core thermal output.

  Recently, however, as shown in Japanese Patent No. 3274904, a γ thermometer (γ-ray thermometer) has been used for calibration of LPRM instead of the TIP. This γ thermometer measures the temperature of the γ ray heating element in the detector assembly with a thermocouple, and measures the heat generated when the γ ray emitted from the fuel rod is absorbed by the heating element. Therefore, there is little deterioration in detection sensitivity due to neutron irradiation, and it can be permanently installed in the furnace.

As shown in FIG. 6, the arrangement of the γ thermometer 8 in the core radial direction is the same as that of the LPRM 5, and the arrangement in the height direction is arranged at the same position as the LPRM 5 and further at an intermediate position thereof. 7 to 9 places are arranged in the vertical direction. Therefore, when the γ thermometer 8 is used, the power distribution in the height direction in the furnace can be grasped more accurately than the LPRM 5. However, the measured γ rays include not only the prompt γ rays generated by fission, but also the delayed γ rays generated by the decay of fission products, and the responsiveness due to the time delay of heat generation. There is also a disadvantage that it is slightly inferior to a neutron flux detector in terms of quick response.
Japanese Patent No. 3274904

  Since the APRM value is based on the LPRM value, the accuracy of the core thermal power obtained by the APRM method depends on the ability of the LPRM to express the in-core power distribution. That is, when the change in the shape of the power distribution in the core is small from the time when the calibration constant is obtained by the equation (1), the value of each LPRM changes at the same rate according to the change in the core thermal power, and accordingly, The value of APRM also changes at the same rate. In such a case, the value of the calibration constant CAP (I) in the equation (1) hardly changes. On the other hand, when the power distribution type in the furnace changes, the degree of detection of the change in the LPRM value decreases, and the correspondence relationship with the APRM heat output shifts. That is, the accuracy of the value of the core thermal output by the APRM method is inferior.

  In view of these points, the present invention obtains the core heat output with higher accuracy by using a γ thermometer having more measurement points than LPRM, which is a neutron detector, when a detector of the feed water flow system fails. It is an object of the present invention to provide a reactor core thermal power monitoring apparatus that can perform the above-described process.

  The invention according to claim 1 includes a plurality of fixed neutron detectors installed at predetermined intervals in the axial direction in a protective tube penetrating along the axial direction between fuel assemblies of the nuclear reactor core, and along the axial direction. A reactor power measuring device provided with a number of γ thermometers installed more than the neutron detector, an average output area monitor (APRM) for obtaining a core average output using the measured value of the neutron detector, and water supply A reactor thermal power monitoring device having a reactor thermal power calculation device that calculates a core thermal power using heat balance from a detector such as a thermometer and a flow meter installed in a flow system, wherein the thermometer and the flow meter When such a feed water flow rate detector fails, the core thermal output is derived using the measured value of the γ thermometer.

The invention according to claim 2 is the invention according to claim 1, wherein the quasi-average power region monitor (quasi-APRM) value based on the measured value of the γ thermometer and the rating of the core thermal power based on the heat balance method in the normal state. Find the relationship with the ratio by the following formula,
FRP = GTCAP (I) ・ GTRAP (I)
FRP: Core thermal power rating ratio (based on heat balance method)
GTCAP (I): Quasi-APRM channel I calibration constant
GTRAP (I): APRM value of quasi-APRM channel I When the detector of the feed water flow rate system fails, the core thermal output is obtained based on the right side of the above equation.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein a plurality of γ thermometers installed in the core is divided into a plurality of groups, and the local power in the core can be measured for each group, When the detector of the feed water flow rate system fails, the core thermal output is obtained for each group.

  According to a fourth aspect of the present invention, in the third aspect of the invention, a correct / incorrect determination in which the core thermal output for each group is obtained from the measured value of the γ thermometer for each group and the correct / incorrect determination is performed based on these values. A device is provided.

  As described above, when the measuring instrument of the feed water flow rate system fails, the core thermal output cannot be obtained by the heat balance method, so the core thermal output is derived based on the value of APRM. The number of neutron detectors installed in the LPRM that constitutes this APRM is four in the axial direction, and changes in the power distribution of the core cannot be fully captured. Therefore, in the present invention, it is used for derivation of the core thermal power by using a γ thermometer, which is usually used for measuring the power distribution or calibrating the neutron detector, which is installed 7 to 9 points in the axial direction. It is what you do.

That is, in the same way as configuring APRM from the value of LPRM, a quasi-APRM based on the measured value of the γ thermometer is constructed, and the core thermal output is obtained using this quasi-APRM. This will be referred to as a quasi-APRM method. Therefore, when there is no failure in the instruments, the relationship between the heat balance method and the quasi-APRM method is obtained from the following equation (2) corresponding to equation (1).
FRP = GTCAP (I) / GTRAP (I) (2)
FRP: Core thermal power rating ratio (based on heat balance method)
GTCAP (I): Quasi-APRM channel I calibration constant
GTRAP (I): APRM value of quasi-APRM channel I When the detector of the feed water flow rate system fails using the calibration constant of equation (2), the core thermal output is obtained from the right side of equation (2).

  Since the γ thermometer 8 is installed at 7 to 9 points in the axial direction and the number of power measurement points in the core is increased, the axial power distribution shape can be expressed more accurately. For this reason, the amount of fluctuation accompanying the change in the core power distribution of the calibration constant GTCAP (I) of the quasi-APRM in the equation (2) is smaller than the calibration constant CAP (I) of the APRM. This improves the calculation accuracy of the core thermal output.

  Further, in the configuration of the quasi-APRM, reliability can be improved by grouping the output monitor devices of the γ thermometer in the core and associating it with a plurality of channels.

  When three or more channels are set, it is possible to provide an error signal self-determination function. That is, if two or more of the three channels have the same numerical value, it can be determined that the value is correct.

  According to the present invention, when the detector of the feed water flow system fails, the measurement value of the γ thermometer, which is installed more than the LPRM, is used, so that the detection accuracy of the reactor heat output can be improved. it can.

  Embodiments of a reactor thermal power monitoring apparatus according to the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows an embodiment of a reactor thermal power monitoring apparatus according to the present invention. In the reactor core thermal power monitoring apparatus of the present embodiment, a plurality of detector assemblies 3 are installed in the core 11 of the reactor pressure vessel 10. In FIG. 1, only one body is shown, but this detector assembly 3 can be measured uniformly throughout the core in consideration of the symmetry of the arrangement of the fuel assemblies 1 installed in the core. Several are arranged. As described above, the detector assembly 3 is installed at a position opposite to the control rod insertion position with respect to the fuel assembly having a configuration in which a plurality of fuel rods are bundled, and penetrates the core in the axial direction. Four local output region monitors LPRM5, which are fixed neutron detectors composed of fission ionization chambers, are installed in the protective tube 4 as the first output detector, and second output detection as calibration means for the LPRM5 As a device, a γ thermometer 8 for detecting heat generation of γ rays is provided. As shown in FIG. 1, the LPRM 5 is arranged at a predetermined interval in the axial direction of the core, and these output signals are input to the APRM 12 via a cable. On the other hand, as shown in FIG. 1, the γ thermometer 8 has a larger number than the LPRM 5 in the protective tube 4 and is installed at predetermined intervals in the axial direction. is set up. In the present invention, the output signal from the γ thermometer 8 is input to the quasi-APRM 13 that obtains an average output with the same logic as the APRM, via a cable, similarly to the LPRM 5.

  On the other hand, the heat output of the nuclear reactor is usually obtained by calculating the balance of heat to the core 11. The heat balance calculation is based on the temperature, flow rate, pressure, etc. measured by the detector 15 installed near the coolant inlet 14 and the detector 17 installed near the coolant outlet 16. Derived by the output calculation device 18. This heat balance accounts for about 99% of the heat balance in the water supply system.

  Using this reactor heat output, the APRM value is calibrated at a certain time frequency. In the present invention, similar to APRM, the quasi-APRM value is also calibrated with this core thermal output.

  The APRM value composed of the measured values of LPRM5 installed at four locations in the axial direction and the quasi-APRM value composed of the measured values of γ thermometer 8 installed at four or more locations in the axial direction more accurately represent the output distribution. The quasi-APRM value that can be made has a more stable calibration factor. In particular, when the coolant flow rate or the control rod loading pattern is changed and the output distribution shape changes greatly, the calibration coefficient is likely to cause an error. That is, when the detector of the feed water flow rate system fails for some reason, the reactor thermal power output by the reactor thermal power calculation device by the heat balance method becomes an inaccurate value. Based on the above, the correct reactor thermal output is derived using the calibration coefficient obtained and stored immediately before the failure.

That is, when there is no failure in the instruments, the relationship between the heat balance method and the quasi-APRM method is obtained by the following equation (2).
FRP = GTCAP (I) / GTRAP (I) (2)
FRP: Core thermal power rating ratio (based on heat balance method)
GTCAP (I): Quasi-APRM channel I calibration constant
GTRAP (I): APRM value of quasi-APRM channel I When the detector of the feed water flow rate system fails using the calibration constant of equation (2), the core thermal output is obtained from the right side of equation (2).

  In the present invention, as described above, the APRM is composed of the measured values of the LPRM5 installed at four locations in the axial direction, but the γ thermometer 8 has a large number of installed points from 7 to 9 locations in the axial direction. The γ thermometer 8 is more accurately monitoring the core power distribution than the LPRM 5. Therefore, the reactor heat output can be derived with higher accuracy when the quasi-APRM value is used than when the APRM value is used.

  Next, a second embodiment of the reactor thermal power monitoring apparatus according to the present invention will be described. FIG. 2 shows another example of a reactor thermal power monitoring device, in which the quasi-APRM is multi-channeled. In consideration of the symmetry of the fuel assembly arrangement, a plurality of detector assemblies 3 are uniformly installed in the reactor core. Among these, the γ thermometer 8 connected to the multi-channel type quasi-APRM 19 with a cable is divided into a plurality of groups while maintaining a uniform arrangement in the core. The present invention is characterized in that the cables from these grouped γ thermometers are assigned so as to correspond to the respective channels of the multi-channel type semi-APRM 19. As a result, even if some of the γ thermometers 8 in the core fail, the measured values of other channels can be used, and the reliability of the system can be further improved while improving the accuracy of deriving the reactor heat output.

  FIG. 3 is a diagram showing a third embodiment of a reactor thermal power monitoring apparatus according to the present invention. A correctness determination device 20 is added to the reactor thermal power monitoring apparatus described in the second embodiment. ing. As an example of the correctness determination apparatus 20, when the number of channels of the multi-channel quasi-APRM is 3 or more, the reactor heat output derived from each channel can be determined using the principle of majority vote. That is, in the case of 3 channels, a method in which two or more values are the same is regarded as positive, and the others are erroneous. As described above, in the present embodiment, by automatically determining whether the reactor heat output that is an input value to the online simulator is correct or not, occurrence of a human error or the like can be suppressed, and the reliability of the system can be further improved.

The figure which shows 1st Embodiment in the reactor thermal power monitoring apparatus of this invention. The figure which shows 2nd Embodiment in the reactor thermal power monitoring apparatus of this invention. The figure which shows 3rd Embodiment in the reactor thermal power monitoring apparatus of this invention. The figure which shows an example of radial direction arrangement | positioning of LPRM. The figure which shows an example of the axial direction arrangement | positioning of LPRM. The figure which shows an example of axial arrangement | positioning of (gamma) thermometer.

Explanation of symbols

1 Fuel Assembly 2 Control Rod 3 Detector Assembly 4 Protective Tube 5 Local Output Area Monitor (LPRM)
8 γ Thermometer 11 Core 12 Average Power Range Monitor (APRM)
13 Semi-APRM
14 Coolant inlet 15 Detector 16 Coolant outlet 17 Detector 18 Reactor thermal power calculation device 19 Multi-channel quasi-APRM
20 Correctness judgment device

Claims (4)

  A plurality of fixed neutron detectors installed at predetermined intervals in the axial direction in a protective tube penetrating along the axial direction between the fuel assemblies of the nuclear reactor core, and more than the neutron detectors along the axial direction Reactor output measuring device provided with an installed γ thermometer, an average output region monitor (APRM) for obtaining a core average output using measured values of the neutron detector, and a thermometer installed in the feed water flow system A reactor thermal output monitoring device having a reactor thermal output calculation device for obtaining a core thermal output using heat balance from a detector such as a flow meter, etc., in the feed water flow system detector such as the thermometer and the flow meter A reactor core thermal power monitoring apparatus, wherein when a fault occurs, a core thermal power is derived using a measured value of the γ thermometer. The relationship between the quasi-average power region monitor (quasi-APRM) value based on the measured value of the γ thermometer and the rated ratio of the core thermal power based on the heat balance method in a normal state is obtained by the following formula,
FRP = GTCAP (I) ・ GTRAP (I)
FRP: Core thermal power rating ratio (based on heat balance method)
GTCAP (I): Quasi-APRM channel I calibration constant
GTRAP (I): APRM value of quasi-APRM channel I Reactor core heat according to claim 1, characterized in that when the detector of the feed water flow system fails, the core thermal output is obtained based on the right side of the above equation. Output monitoring device.   Multiple gamma thermometers installed in the core are divided into multiple groups, and the local power in the core can be measured for each group, and when the detector in the feed water flow system fails, The reactor core thermal power monitoring apparatus according to claim 1, wherein the power is obtained.   The atom according to claim 3, further comprising a correct / incorrect determination device that determines a core thermal output for each group from a measurement value of the γ thermometer for each group and makes a correct / incorrect determination based on these values. Reactor core thermal output monitoring device.

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