JP2003177193A - Nuclear reactor output monitoring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nuclear reactor output monitoring device capable of improving the evaluation accuracy by making use of an LPRM detector which coexists with a γ-ray dosage detector. <P>SOLUTION: In the nuclear reactor equipped with an in-furnace fixed type neutron flux detector and an in-furnace fixed type γ-ray dosage detector, readings of the γ-ray dosage detector are utilized during a constant output states without output variation and readings of the neutron flux detector are utilized during an output varying states in order to monitor reactor core characteristics by evaluating output distribution in the nuclear reactor. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor output monitoring device for monitoring the output distribution of a reactor by utilizing the measurement results of a thermal neutron flux detector and a γ-ray detector fixed in the reactor. In particular, the present invention relates to a reactor power monitoring device that selectively uses a measurement result of a thermal neutron flux detector and a measurement result from a γ-dose detector according to whether the reactor power is in a constant state or is changing.

[0002]

2. Description of the Related Art In a boiling water nuclear power plant (BWR),
A traveling-type in-core instrumentation (TIP) detector that has traveled in the reactor to measure thermal neutrons, and a fixed-type local power range monitor (LPR) that is fixed in the reactor and measures the amount of thermal neutrons.
M) The detector is used to monitor the power distribution in the reactor. An example of the arrangement of the TIP detector and LPRM detector in the nuclear reactor is shown in FIGS. 2 and 3. FIG. 2 shows a horizontal plane cross section of the core, and shows the positional relationship among the fuel assemblies 12, the control rods 13, and the TIP strings 14. The control rods 13 are arranged in the center of the four fuel assemblies 12. And in addition,
A plurality of TIP strings 14 are fixedly installed in the reactor on the control rod non-insertion side of the fuel assembly 12.

FIG. 3 shows a height positional relationship between the TIP string 14, the TIP detector 15 and the LPRM detector 16. Here, the TIP string and the LPRM string mean the same thing. The LPRM detector 16 is
The TIP detector 15 is fixedly loaded at four positions in the height direction of the TIP string 14, and the TIP detector 15 is provided so as to be able to move in the TIP guide tube 17 in the TIP string 14. . That is, the TIP detector 15 can measure the continuous neutron flux distribution in the height direction by moving from the lower part to the upper part of the core. Moreover, the TIP detector 15 does not run only in one TIP string, but the TIP detector can be taken out from one TIP string and run in another TIP string in the same manner. Therefore,
There are only 3 to 5 TIP detectors 15 per reactor. However, each TIP detector 15 can run on a common string 18 near the center of the core. That is, the neutron flux distribution at the same place can be measured by each TIP detector 15. With this structure, the characteristic difference between each TIP detector can be calibrated, and the neutron flux distribution data equivalent to the case where the whole core is measured by one TIP detector can be obtained.

Usually, the TIP detector 15 is extracted outside the core in order to prevent the detector from being consumed, and is inserted into the core only when the detailed power distribution in the core is measured. On the other hand, since the LPRM detector is always installed in the core, it constantly measures the power distribution in the core. However, the number of measurement points is smaller than that of the TIP detector. LPRM
Since the detectors are independent of each other, the LPRM detector alone cannot calibrate the characteristic difference of the individual LPRM detectors. Therefore, by calibrating so that the distribution of the measured values by the TIP detector and the distribution of the measured values by the LPRM detector may match when the TIP detector is running, the measured values by the individual LPRM detectors are as if they were the same detector. It is designed so that it can be treated in the same way as when it is measured. Further, this calibration method also makes it possible to associate the measured value of the TIP detector with the measured value of the LPRM detector.

The power distribution of a nuclear reactor can be evaluated by calculating a neutron flux balance formula based on basic data relating to the nuclear reactor, such as core heat output, core flow rate, and control rod insertion state. From the power distribution in the reactor obtained by this method, T
The measurements of the IP and LPRM detectors can be calculated. However, this calculation requires various approximations inside the reactor to be modeled and calculated.
The calculated value of the detector and the calculated value of the LPRM detector do not always match the measured value. The present reactor output monitoring device has a function of comparing the calculated TIP value and LPRM calculated value with each measured value and adjusting the output distribution so that the calculated value matches the measured value. Enables the core to be monitored with sufficient accuracy.

The TIP detector can measure the continuous neutron flux distribution in the height direction, but it is not always resident in the nuclear reactor to measure the inside of the reactor core, and only about once a month in the reactor. The neutron flux distribution is measured by traveling inside. On the other hand, the LPRM detector has a number of measurement points in the height direction of T
Although it is smaller than the IP detector, it is always resident in the reactor, so the neutron flux distribution in the reactor is constantly measured. The reactor power monitoring device uses the value when the measurement by the TIP detector is performed to improve the evaluation accuracy,
In the time between the time point of measurement by the P detector and the time point of measurement by the next TIP detector, the LPRM detector is used to maintain the evaluation accuracy. Where TIP detector and LPR
The prerequisites for using the M detector in combination are:
This is a calibration for establishing the relationship between the TIP detector and the LPRM detector described above.

The TIP detector is a moving type γ-dose detector (γ-T which measures γ-rays instead of neutron flux).
IP) also exists.

In recent years, a fixed type in-reactor γ-dose detector has been developed in place of the TIP detector. This detector is
It uses the fact that the temperature rises by irradiation with a wire, and measures the temperature with a thermocouple. As shown in the example of FIG. 4, the fixed γ dose detector in the reactor is
It is installed in the string 14 instead of the TIP detector, and the installation place is fixed. For example, nine gamma dose detectors 20 are installed in one string. However, in FIG. 4, only one line for capturing the signals of the LPRM detector and the γ-dose detector is simply shown. T
The IP detector measures the continuous neutron flux distribution or the γ-dose distribution in the height direction, whereas the γ-dose detector has the measurement point only at the installation point of the detector. More than four of them are installed so that the distribution in the axial direction can be detected as much as possible.

In the reactor output monitoring device in the reactor in which the γ dose detector is installed, the γ dose detector is different from the TIP detector.
Since the dose detector 20 is always resident in the reactor,
Only the dose detector 20 can be used to evaluate and monitor the power distribution in the reactor. However, some gamma rays are generated immediately in response to the nuclear fission of fuel and some are delayed. Prompt γ rays that are generated immediately γ
Rays and those that occur late are called delayed γ rays. When the output of the reactor is changing, this delayed γ ray causes
There is a time delay in the tracking of the γ-ray dose with respect to the output change.
The response to the output of the γ dose has a larger time delay than the response to the neutron flux. For this reason, in the reactor output monitoring device, in order to use the measured value of the γ-dose detector when the output is changing, it is necessary to correct the time delay before use. As a method of this correction, for example, JP-A-2000-258585 or 2001-
As shown in Japanese Patent Laid-Open No. 83280, these corrections are carried out in the measuring device of the γ dose detector 20, that is, in the device for amplifying the signal. of course,
These corrections should be made in γ
There may be a method implemented in the reactor power monitoring device that uses the measured value of the dose detector.

As with the LPRM detector, the γ-dose detector 20 is an independent detector. For this reason, it has a heater calibration function for correlating the detectors. By performing this calibration, the measured value of each gamma dose detector can be treated as if it was measured by one detector.

[0011]

As described above, in the reactor output monitoring apparatus using the side constant value of the γ dose detector, when the output is changing, the measured value of the γ dose detector is delayed. It is necessary to use the measured values of the gamma dose detector corrected by evaluating the time delay effect of emitted gamma rays. However, when the output changes in a relatively simple form, the time delay effect of this delayed γ-ray can be evaluated accurately, but when the output change becomes complicated for some reason, However, the accuracy of the evaluation value of the time delay effect is reduced.

By the way, since the LPRM detector has an extremely good response to the output change, even if the γ-dose detector is used in place of the TIP detector, it can be used as a safety device such as an average output area monitor (APRM). The LPRM detector is still in use. Therefore, since the γ-dose detector and the LPRM detector are used together, the measured value of the γ-dose detector and the measured value of the LPRM detector are both in a state where they can be used in the reactor power monitor. However, gamma dose detector and LP
In order to use the measured value of the RM detector in the reactor output monitoring device, the distribution of the measured value of each γ-dose detector and the distribution of the measured value of each LPRM detector must correspond to each other. That is, it is necessary to be able to calibrate the measured value of the LPRM detector.

In view of the above-mentioned problems, the present invention provides a reactor power monitoring apparatus utilizing the measured value of the γ dose detector,
Using the LPRM detector that coexists with the dose detector,
It is an object of the present invention to provide a reactor power monitoring device that improves the evaluation accuracy by using the measured value of the LPRM detector, which has better followability to the power change when the power is changing.

Further, in a reactor power monitoring device having a function of evaluating the reactor power distribution by utilizing the measured value of the γ-dose detector, the LPRM detector can be calibrated so that the measured value of the LPRM detector can be calibrated. An object is to obtain a reactor output monitoring device having a function of calculating a value to be instructed.

[0015]

The invention according to claim 1 is
A local power range monitor detector for measuring thermal neutron flux in a nuclear reactor, and a fixed γ-ray detector for measuring γ-rays are mounted in the same detector assembly, and the detector assembly is In a reactor power monitoring device that installs multiple reactors, measures the reactor power, evaluates the power distribution in the reactor, and monitors the thermal characteristics of the reactor, it is assumed that the reactor power is operating at a substantially constant level. When it can be considered, the measurement result from the γ-ray detector is used, and when it can be considered that the reactor output is changing, the measurement result from the local power range monitor detector is used.

According to a second aspect of the invention, in the invention according to the first aspect, the output of the nuclear reactor is kept constant or the output is changed by the time series change of the measurement result from the thermal neutron flux detector. It is characterized by automatically controlling whether the measurement result from the γ-ray detector or the measurement result from the thermal neutron flux detector is used.

The invention according to claim 3 is the same as the invention according to claim 1, wherein the time series change of the measurement result from the thermal neutron flux detector is compared with the time series change of the measurement result from the γ-ray detector. By doing so, it is determined whether the reactor output is operating at a constant level or whether the output is being changed, and the measurement result from the γ-ray detector is used or the measurement result from the thermal neutron flux detector is used. It is characterized by automatically controlling whether to use.

The invention according to claim 4 is, in the invention according to claim 2 or 3, characterized in that it has an output change judging means for judging a change in output by using an operation signal of the control rod. To do.

The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the measurement result from the γ-ray detector when the reactor power can be regarded as operating at a substantially constant level. Evaluate the power distribution of the reactor by using the, and evaluate the thermal neutron flux at the thermal neutron flux detector position based on the output distribution that is the evaluation result, and It is characterized in that it has means for calculating a value to be indicated by the neutron flux detector.

According to a sixth aspect of the invention, in the invention according to the first aspect, the reactor output is sampled from the thermal neutron flux detector in time series, and the rate of change of the reactor output is evaluated to delay the delay. Reactor power evaluation processor that judges whether the delay of time-tracking with respect to output change of γ-dose is significant, and whether the measured value of neutron flux measurement device is used for evaluation of reactor power distribution based on that judgment , Or an LPRM / GT switching command generation processing device for selecting whether to use the measurement value of the γ-ray detector,
A core power distribution evaluation processing device for evaluating the power distribution of the core based on a command from the PRM / GT switching command generation processing device and utilizing the measured value of the local power range monitor detector or the γ-dose detector. To do.

[0021]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows an overall configuration diagram of a reactor power monitoring device according to an embodiment of the present invention. The reactor power monitoring device 1 includes a core power change evaluation processing unit 2 and an LPRM.
It includes a / GT switching command generation processing unit 3, a core power distribution evaluation processing unit 4, and an evaluation processing unit 5 for the value to be instructed by LPRM.

In the core output change evaluation processing unit 2, the LPRM
LP which is the measured value of the detector 6 and the output signal of the APRM 7.
RM signal a and APRM signal b are taken in time series,
Remember. Here, the APRM is called an average power range monitor, and LPs installed at various locations in the core
The RM detector signal is acquired and averaged, and is calibrated to correspond to the core heat output. APRM is
Usually, 4 to 6 channels are installed as an independent system and supply signals to the safety control system. By evaluating the change rate of the time series data of the APRM detector, it is possible to detect the output change of the entire core. In addition, by evaluating the rate of change of the time series data of the LPRM detector, it is possible to detect a local change in the core output. For example, when a small number of control rods are dipped in a small amount, the output may change at the tip of the control rods and may not change much in the entire core. Of course,
If many LPRM values in the core are changing, it can be determined that the output of the entire core is changing, and the LPRM can also detect the output change of the entire core.

As a criterion for determining whether or not the output is changing, for example, 0.5% / hour can be set from the output increase rate at the time of reactor startup at present. If the absolute value of the output change rate is larger than this value, it is judged that the output is changing, and conversely, if the absolute value of the output change rate is smaller than this value, it is judged that the output is operating at almost constant. can do. This judgment reference value may be set to a larger value and used in consideration of the output response of the measurement value of the γ-dose detector.

From the core output change evaluation processing unit 2 to LPRM /
A signal as to whether or not the output change is recognized is issued to the GT switching command generation processing unit 3. When the LPRM / GT switching command generation processing unit 3 receives a signal that the output does not change or is small, the output of the core is output to the core power distribution evaluation processing unit 4 by using the signal c from the γ dose detector 8. Instruct to evaluate the distribution. When a signal indicating that the output change is large is received, an instruction is issued to evaluate the output distribution of the core using the measured value of the LPRM detector 6.

The core power distribution evaluation processing unit 4 has a function of evaluating the reactor power distribution with high accuracy by utilizing the measurement values of the γ-dose detector 8 or the LPRM detector 6.
When the signal from the PRM / GT switching command generation processing unit 3 is received,
The core power distribution is evaluated using the measured value of either the dose detector 8 or the LPRM detector 6.

When the output change is small or during constant output operation, the core power distribution evaluated by the core power distribution evaluation processing unit 4 using the measured value of the γ dose detector 8 is used to calculate the LPRM detector 6. Evaluation processing unit 5 for values to be instructed
Then, the calculated value of LPRM corresponding to the core power distribution is calculated. Normally, the calculated LPRM value represents only the relative distribution among the LPRMs, but it is preferable to calculate a value suitable for the LPRM device system including the LPRM value display system and the like. As such a value, for example, the average value of the surface heat flux of the four fuel rods 19 closest to the LPRM in each of the four fuel assemblies 12 adjacent to the LPRM detector is expressed. There is a method to standardize.

The value to be instructed by the LPRM calculated by the evaluation processing unit 5 for the value to be instructed by the LPRM detector is set to LPRM.
By adjusting the LPRM system as indicated by the detector measurements, the LPRM detector measurements can be properly calibrated. By performing this calibration, it is possible to make a relationship between the individual LPRM measurement values and also a relationship between the LPRM value and the measurement value of the γ-ray detector. Due to this relationship, the core power distribution evaluation processing unit 4 can evaluate the consistent core power distribution by utilizing the measurement values of the γ-ray detector or the LPRM detector.

In the evaluation of core power change in the example of FIG.
Although the measured value of the PRM detector and the output signal of the APRM are used, it does not matter which one makes the judgment of the core output change. Alternatively, a control rod operation signal may be used. It is also possible to use the measured value of the generator output. Furthermore, since most changes in the core heat output correspond to changes in the feed water flow rate, it is possible to use measured values of the feed water flow rate. Of course, these may be used in combination.

As a method of evaluating the output change, a method of comparing the time change of the LPRM value with the time change of the measured value of the γ dose detector installed corresponding to the position of the LPRM detector can be considered. In this case, when the time change rates of the measured values of the LPRM detector and the γ dose detector are equal, it is determined that the influence of the time delay of the delayed γ ray is small, and the core power distribution evaluation processing unit 4 The core power distribution may be evaluated by the γ-ray detector 8. In addition, if there is a significant difference in the rate of change between the measured values of the LPRM detector and the γ dose detector, the delayed γ
It may be determined that the influence of the time delay of the line is large, and the core power distribution evaluation processing unit 4 may evaluate the core power distribution by the LPRM detector.

FIG. 1 shows an example in which the LPRM / GT switching command to the core power distribution evaluation processing unit 4 is automatically issued by the LPRM / GT switching command generation processing unit 3, but the operator can give an arbitrary command. It is also possible to add a function that can be set,
It will be beneficial.

FIG. 1 shows the calculation of the value to be instructed by the LPRM in the reactor power monitoring apparatus 1 regarding the calibration of the LPRM, but in recent years, L which can be digitally processed is shown.
PRM devices are beginning to be used, and such LPRM
For the apparatus, even the LPRM calibration processing can be performed in the reactor power monitoring apparatus 1.

[0032]

As described above, according to the present invention,
The evaluation accuracy of the reactor power monitoring system can be improved by taking advantage of the advantages of the fixed γ-dose detector and the fixed neutron flux detector. It is also possible to calibrate the measurement values of the fixed neutron flux detector at a boiling water nuclear power plant equipped with the fixed γ dose detector.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an example of horizontal arrangement of a reactor power distribution measuring device for a boiling water reactor.

FIG. 3 is an example of a vertical arrangement of an in-reactor power distribution measuring device for a boiling water reactor.

FIG. 4 is a vertical arrangement example of a fixed type γ-ray detector in a furnace.

[Explanation of symbols]

1 Reactor power monitor 2 Core output change evaluation processing unit 3 LPRM / GT use switching command generation processing unit 4 Core power distribution evaluation processing unit 5 Evaluation processing unit for values to be instructed by LPRM detector 6 LPRM detector 7 Average output area monitor 8 γ-dose detector a LPRM signal b APRM signal c GT signal 12 Fuel assembly 13 control rod 14 strings 15 TIP detector 16 LPRM detector 17 TIP guide tube 18 common strings 19 fuel rods 20 γ dose detector

Claims (6)

[Claims] 1. A local power range monitor detector for measuring thermal neutron flux in a nuclear reactor and a fixed type γ-dose detector for measuring γ rays are mounted in the same detector assembly, and In a reactor power monitoring device that installs multiple detector assemblies in the reactor, measures the reactor power, evaluates the power distribution in the reactor, and monitors the thermal characteristics in the reactor, the reactor power is almost constant. Characterized by using the measurement results from the γ-ray detector when it can be regarded as operating, and by using the measurement results from the local power range monitor detector when it can be considered that the reactor power is changing. Reactor power monitor. 2. The measurement result from the γ-ray detector is determined by the time series change of the measurement result from the thermal neutron flux detector to determine whether the reactor output is constant or the output is changed. Or automatically controlling whether to use the measurement result from the thermal neutron flux detector,
The reactor power monitoring device according to claim 1. 3. By comparing the time series change of the measurement result from the thermal neutron flux detector and the time series change of the measurement result from the γ-ray detector, whether the output of the reactor is constant, It is characterized by determining whether the output is changed, and automatically controlling whether to use the measurement result from the γ-ray detector or the measurement result from the thermal neutron flux detector, Item 1. The reactor output monitoring device according to item 1. 4. An output change judging means for judging a change in output using the operation signal of the control rod is also provided.
The reactor output monitoring device according to claim 2 or 3. 5. When it can be considered that the reactor output is operating at a substantially constant level, the output distribution of the reactor is evaluated using the measurement results from the γ-ray detector, and the output distribution that is the evaluation result is calculated. Evaluating the thermal neutron flux of the thermal neutron flux detector position based on, having a means for calculating the value to be indicated by the thermal neutron detector for calibration of the thermal neutron flux measuring device, Item 5. The reactor output monitoring device according to any one of items 1 to 4. 6. A reactor output is sampled from a thermal neutron flux detector in time series to evaluate the rate of change in reactor output, and is there a significant delay in time followability with respect to delayed γ-dose output change? A core power evaluation processing device to judge whether or not to use the measurement value of the neutron flux detector or the measurement value of the γ dose detector to evaluate the reactor power distribution based on the judgment An LPRM / GT switching command generation processing device for performing L
Based on a command from the PRM / GT switching command generation processing device, a core power distribution evaluation processing device that evaluates the power distribution of the core by using the measurement value of the local power range monitor detector or the γ-ray detector is characterized. Reactor output monitoring device.