JP2002341083A - In-core nuclear instrumentation detector aggregate and reactor output monitoring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reactor output monitoring device capable of always monitoring a three-dimensional neutron flux distribution in a reactor. SOLUTION: A fixed type neutron detector, a mobile type neutron detector, and a gamma thermo detector are arranged in the axial direction in this detector aggregate. The fixed type neutron detector can be complemented by the gamma thermo detector, to thereby facilitate monitoring of the three-dimensional reactor output distribution. The gamma thermo detector can be easily calibrated by the mobile type neutron detector, to thereby dispense with a calibration heater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-core nuclear instrumentation detector assembly for measuring the power inside a reactor of a nuclear reactor, and to a reactor power monitoring device for monitoring the power inside the reactor of the reactor.

[0002]

2. Description of the Related Art A fixed neutron detector and a movable neutron detector movable in the axial direction of a fuel rod are used in a reactor power monitoring apparatus. FIG. 6 shows a conventional reactor power monitoring device. As shown in FIG. 6, a conventional reactor power monitoring device includes a plurality of LPRM detectors 111 for measuring neutrons.
And a signal processing unit 112 for processing a signal from the LPRM detector 111, an interface unit 113 for outputting a signal from the signal processing unit 112, and a computer 114 for calculating burnup distribution and the like. Computer 11 is used to measure the neutron flux in the axial direction of the fuel rod.
4 includes a TIP (movable in-core probe monitor) detector 121 for moving and measuring neutrons and a TIP detector 1
A signal processing unit 122 for processing a signal from the signal processing unit 21 and an interface unit 123 for outputting a signal from the signal processing unit are further connected.

FIGS. 7A and 7B show an LPRM detector 1.
11 is a schematic diagram illustrating a state of a vertical cross section and a horizontal cross section of an LPRM assembly 116 accommodating 11; FIG. Further, as shown in FIG. 7C, a plurality of LPRM assemblies 116 are inserted into the core along the fuel rod axial direction of the reactor. As a result, the LPRM detector 111 is located at axial and radial points in the core. The signal processing unit 112
An average output signal in the reactor is output based on local output signals in the core axis direction and the radial direction from the PRM detector 111. The TIP detector 115 moves inside the TIP calibration tube 117 and is used for calibration of the LPRM detector 111 in addition to the measurement of the neutron flux distribution.

[0004] In addition to the TIP system using the TIP detector 121 described above, the reactor power monitoring device uses an LPRM detector 111 using a fixed gamma thermometer (thermocouple thermometer, hereinafter referred to as a GT detector). There is a GT system that performs calibration of This corresponds to the TIP detector 121, signal processing unit 112, interface unit 11 of FIG.
3. The computer 114 is connected to a GT detector 131 as shown in FIG.
Signal processing unit 132, interface unit 1
33, a computer 134, and a calibration heater 135 (for example, see Japanese Patent Application Laid-Open No. 9-212136).

The GT detector 131 outputs a potential difference generated by heat generated by gamma rays in the core. The signal processing unit 132 converts the potential difference output from the GT detector 131 into a temperature difference, further converts the temperature difference into a gamma ray heat generation amount, and controls a calibration heater. The interface unit 133 outputs an output signal from the signal processing unit 132 to the computer 134 or the like. The computer 134 further converts the calorific value of the gamma ray into the amount of neutron flux to calculate the power inside the reactor. Note that the calibration heater 135 is a GT detector 131.
It is a heat source for calibrating.

FIGS. 9A and 9B are a partial perspective view and a longitudinal sectional view, respectively, showing the structure of the GT detector 131.
As shown in FIGS. 9A and 9B, the GT detector 131 is housed in a GT (gamma thermo) detection tube 136 together with the calibration heater 135. The GT detector 131 includes a high-temperature side contact 138 surrounded by a heat insulating portion 137 and a heat insulating portion 137.
And a thermocouple set having a low-temperature side contact 139 which is not surrounded by a circle. The temperature difference between the high-temperature side contact 138 and the low-temperature side contact 139 is converted into a voltage and output.

FIGS. 10A and 10B show a GT detector 13.
1A and 1B are a vertical cross-sectional view and a horizontal cross-sectional view of an LPRM assembly 116 accommodating a GT, respectively, and show an example of arrangement of a GT detector 131. Each GT detector 131 is housed in the LPRM assembly 116 together with the LPRM detector 111, and is disposed in the reactor core. Then, the GT detector 131 outputs the LPRM
It is arranged at an axial height in the core corresponding to the detector 111,
Used for calibration of the LPRM detector 111.

[0008]

SUMMARY OF THE INVENTION LPRM detector 111
Has a certain size, and measurement locations are limited in both the axial direction and the radial direction. Therefore, it has been difficult for the conventional reactor power monitoring device to constantly monitor the three-dimensional neutron flux distribution in the reactor. For this reason, it is also difficult to determine a control rod insertion pattern for realizing efficient combustion of the nuclear fuel continuously in time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reactor power monitoring apparatus capable of constantly monitoring a three-dimensional neutron flux distribution of a reactor in order to solve such a problem. Another object of the present invention is to provide a reactor power monitoring device that can easily perform sensitivity calibration. Still another object of the present invention is to provide a reactor power monitoring device having a high time response speed and high reliability.

[0010]

(1) In order to achieve the above object, an in-core nuclear instrumentation detector assembly according to the present invention comprises a plurality of fixed neutron detectors installed at different positions in a predetermined axial direction. A plurality of fixed neutron detectors, a plurality of gamma thermo detectors installed at substantially the same positions in the predetermined axial direction, and the plurality of fixed neutron detectors, and the plurality of fixed neutron detectors are moved in the predetermined axial direction. And a mobile neutron detector capable of calibrating the plurality of gamma thermo detectors. Reactor power can be measured with both fixed neutron and gamma thermo detectors. For this reason, highly reliable measurement is possible.

Here, the plurality of fixed neutron detectors may further include a plurality of gamma thermo detectors installed at different positions in the predetermined axial direction. Gamma thermo detectors are smaller than stationary neutron detectors and can be arranged in large numbers in the axial direction. As a result, for example, a change in the output of the nuclear reactor in the axial direction when the control rod is pulled out can be monitored in detail.

Further, the gamma thermo detector may not have a heater for calibration. Gamma thermo detector
Since calibration can be performed by a mobile neutron detector, a heater for calibration can be omitted. As a result, it is possible to reduce the size of the gamma thermodetector and to arrange a large number thereof. Also,
The miniaturization of the gamma thermo detector leads to an improvement in response speed due to a decrease in heat capacity.

(2) A reactor power monitoring apparatus according to the present invention converts an output signal from the core nuclear instrumentation detector assembly described in (1) and the gamma thermo detector into a neutron detection value. And a signal conversion unit.
The output signal from the gamma thermo detector can be converted into a neutron detection value to monitor the reactor power.

The signal conversion by the signal converter is performed by using a conversion table for converting an output signal of the gamma thermodetector into a value corresponding to a neutron detection value based on a measurement result of the mobile neutron detector, for example. I can do it. By using the measurement result of the mobile neutron detector, more accurate calibration can be performed, for example, using a heater. Here, a power distribution monitoring unit may be further provided, and the power distribution of the nuclear reactor may be monitored based on the measurement result of the core instrumentation detector assembly. With the three-dimensional arrangement of the gamma thermo detectors, the power distribution of the reactor can be monitored three-dimensionally.

Further, the detected value of neutrons converted from the output signal of the gamma thermo detector is compared with the detected value of neutrons based on the output signal of the fixed neutron detector,
When the difference between the detection values is larger than a predetermined value, the detector may include a detector deterioration determination unit that determines that one of the gamma thermodetector and the fixed neutron detector has deteriorated. Since the deterioration of the detector is automatically detected, the reliability of the measurement data is high.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a reactor power monitoring device 10 according to a first embodiment of the present invention. A plurality of LPs as fixed neutron detectors in an LPRM assembly (core instrumentation detector assembly in a core) 20
RM (Local Power Range Moni)
tor: local output monitor) detector 30, TIP (Traveling In-Co) as mobile neutron detector
re Probe) detector 40 and a plurality of GT detectors 50 as gamma thermo detectors. Each of the plurality of LPRM detectors 30, the TIP detector 40, and the plurality of GT detectors 50 includes a signal processing unit 61, 62,
63 and interface units 71, 72, 73
(Computer) 80 is connected via the.

The LPRM detector 30 and the TIP detector 40 both detect neutrons, and the GT detector 50 detects gamma rays. The signal processing units 61 to 63 respectively
LPRM detector 30, TIP detector 40, GT detector 5
Process the signal from 0 and output the measurement result. At this time, the signal processing units 61 to 63 can output a signal representing an average output based on each local output in the core axis direction and the radial direction. The interface units 71 to 73 output the output signals from the signal processing units 61 to 63 to the computer 80, respectively. The calculator 80 calculates the burnup distribution and the like.

The computer 80 includes a signal conversion unit 81, an output distribution monitoring unit 82, a GT calibration unit 83, a detector deterioration determination unit 84,
An input / output unit 85 is provided. The signal converter 81 converts the signal of the gamma ray heating value into an output in the reactor. The power distribution monitoring unit 82 monitors a three-dimensional power distribution of the reactor. The GT calibration section 83 performs calibration of the GT detector 50.
The detector deterioration determination unit 84 determines whether the LPRM detector 30 and the GT detector 50 have deteriorated. The input / output unit 85 includes input devices such as a mouse and a keyboard, a CRT, and an LCD.
And a recording device such as a hard disk.

The LPRM assemblies 20 are inserted at different positions along the axial direction of the fuel rods of the nuclear reactor when viewed from the radial direction. As a result, the computer 80 includes the LPRM detector 3
0 and signals relating to three-dimensional measurement results in the reactor from the GT detector 50 are input. FIG. 2 (A), (B)
Is a schematic sectional view showing a state in which the LPRM assembly 20 is cut in the axial direction and the radial direction, respectively. LP
A TIP detector 40 is arranged on the central axis of the RM assembly 20. Around the LPRM detector 30 and the GT detector 50
Are all arranged in a plurality. The plurality of LPRM detectors 30 are arranged at different heights in the axial direction. In addition, the plurality of GT detectors 50
In addition to being arranged so as to have almost the same height as the detector 30, it is also arranged at a different height from the LPRM detector 30.

The GT detector 50 and the LPRM detector 30
Since the reactors are arranged at almost the same height and the output of the reactor can be monitored by both the LPRM detector 30 and the GT detector 50, the reliability is improved. When the GT detector 50 is L
Since the GT detector 50 is also arranged at a different height from the PRM detector 30, the GT detector 50 has L
The PRM detector 30 can be complemented. GT detector 50 is L
Compared to the PRM detector 30, it is structurally simple and easy to miniaturize. For this reason, a large number of GT detectors 50 can be easily arranged in the same string of the LPRM assembly 20, and local outputs can be measured at a large number of measurement points as compared with the related art. As a result, a fine power distribution can be measured in the axial direction of the fuel rod.

The TIP detector 40 has a G
The T-detector 50 and the LPRM detector 30 can be moved to the respective installed heights. Therefore, the GT detector 50 and the LPRM detector 30 can be calibrated by the TIP detector 40. As described above, the GT detector 50 can perform the sensitivity calibration by the TIP detector 40, and thus does not require the sensitivity calibration using a heater as in the related art. Therefore, G
It is possible to further reduce the size of the T detector 50 and improve the response speed.

The normal use of the LPRM detector 30 is an ionization chamber type detector in which fission material (uranium) is applied to the inner surface of the outer wall of the LPRM detector 30, and a high voltage is applied between the outer wall and the center electrode. Things. LPRM detector 3
Inside 0, an ionizing gas, for example, Ar is sealed. In such an ionization chamber type LPRM detector 30, the characteristics of electronic circuits such as an amplifier and a wave height discrimination filter connected to the latter change with time, causing a so-called drift phenomenon. Further, the neutron detection sensitivity also changes due to a decrease in the amount of U235 of uranium applied to the inner surface of the outer wall of the LPRM detector 30. Since the TIP detector 40 requires a TIP drive mechanism, it is difficult to measure many points simultaneously.

In a nuclear reactor such as a boiling water reactor, γ-rays are generated in proportion to the fission amount of nuclear fuel loaded in a core in a reactor pressure vessel, and the generated γ-ray flux is used to construct the GT detector 50. Heat. This heating amount is proportional to the γ-ray flux, and the γ-ray flux is proportional to the amount of fission in the vicinity. The GT detector 50 is configured such that a structural material such as stainless steel constituting a sensor unit absorbs energy by absorbing radiation (especially gamma rays) and inelastic scattering in a nuclear reactor, generates heat, and generates heat by an external coolant. The temperature distribution formed at the time of the outflow into the chamber is measured with a thermocouple or the like. Accordingly, unlike the fission chamber, the GT detector 50 does not involve a neutron absorption reaction, so that the sensor sensitivity does not deteriorate in principle.

FIG. 3 is a partial perspective view showing the structure of the GT detector 50 and a longitudinal sectional view. GT detector 50 is G
It is housed in a T (gamma thermo) detection tube 51. G
The T detection tube 51 includes a cover tube 52 and a core tube 53.
Calibrated with a double structure. GT detector 50 is a heat insulating part 5
It is the same as the related art in that it is configured by a thermocouple set having a high-temperature side contact 55 surrounded by 4 and a low-temperature side contact 56 not surrounded by the heat insulating portion 54. Note that heat generated by gamma rays is generated from the core tube 53, for example. Where GT
The detector 50 does not include the calibration heater shown in the conventional example,
Only one GT detection tube 51 is housed. If there is a heater for calibration, the necessity of installing a plurality of GT detectors 50 around the heater for calibration increases in order to save space and the like.

Thus, a single GT detector 50 is
It can be easily installed in the detection tube 51, and the GT detector 5
0 can be further reduced in size. As a result, GT
The time response is faster because the heat capacity per detector 50 is smaller. Further, the GT detector 50 can be calibrated by the TIP detector 40 with higher accuracy than the conventional case using a heater. The only thing that can be calibrated by the heater is the relationship between the amount of generated heat and the voltage rise (temperature difference) of the thermocouple, and the direct relationship between the gamma ray irradiation amount and the voltage rise cannot be calibrated. By using the TIP detector 40, the relationship between the amount of generated neutrons (corresponding to the output of the reactor) and the voltage rise (temperature difference) of the thermocouple can be obtained.

The signal processing unit 63 includes the GT detector 50
Is converted into a signal of a temperature difference, and further, a signal of a calorific value of a gamma ray and output. Then, the signal conversion unit 81 converts the signal of the calorific value of the gamma ray output from the signal processing unit 63 into the local output of the reactor such as the intensity of the gamma ray, the neutron flux value, and the burnup (for example, when the GT detector 50 (The output around the placed control rod). At the time of this conversion, a conversion table representing the correspondence between gamma ray intensity and neutron ray intensity is used. The method of creating the conversion table will be described later.

The output signal of the reactor output from the signal conversion section 81 is input to an output distribution monitoring section 82 and is constantly monitored. At this time, the measurement signal of the neutron flux from the LPRM detector 30 is also converted into a local output of the reactor by the signal conversion unit 81 and is monitored by the output distribution monitoring unit 82. The power distribution monitoring unit 82 displays the three-dimensional output of the reactor on a display device and records the output on a recording device.
The output distribution is analyzed, and a warning is issued when the output distribution deviates from a predetermined range. As described above, in the present embodiment, the three-dimensional output of the nuclear reactor can always be monitored using the GT detector 50.

Since the plurality of GT detectors 50 are arranged in the LPRM assembly 20 at different heights in the axial direction, for example, the power distribution can be finely monitored in the axial direction of the fuel rod. By arranging a large number of GT detectors 50 in the axial direction of the fuel rod, it is possible to continuously monitor a change in output when the control rod is pulled out. In other words, the power distribution can be closely monitored in the axial direction of the fuel rod without using the TIP detector 40, and the output change in the axial direction when the control rod is pulled out is monitored to quickly change the control rod insertion pattern. it can. Therefore, efficient combustion of fuel becomes possible.

FIG. 4 is a flowchart showing a procedure of calibrating the GT detector by the GT calibrating section 83. TIP detector 40
Are moved to the same height as viewed from the axial direction of the GT detector 50 and the LPRM assembly 20, so that the TIP detectors 40 and G
The inside of the reactor is simultaneously measured by the T detector 50. As a result,
The measurement result of the gamma ray flux from the GT detector 50 and the measurement result of the neutron flux by TIP are obtained. The GT detector 50 can be calibrated by rewriting the conversion table of the signal conversion unit 81 based on the measurement result. This calibration is G
The measurement may be performed assuming that the measurement result of the gamma ray flux from the T detector 50 and the measurement result of the neutron flux by TIP are proportional. Further, different amounts of gamma ray flux and neutron flux may be measured by the TIP detector 40 and the GT detector 50. G
By performing the sensitivity calibration of the T detector 50 by the TIP detector 40, the calibration can be performed with higher accuracy than the calibration using a heater.

FIG. 5 shows the LP determined by the detector deterioration determining unit 84.
It is a flowchart showing the procedure of the deterioration determination of RM detector 30 and GT detector 50. As shown in FIG.
The measurement result of the neutron flux obtained from 0 is compared with the measurement result of the neutron flux obtained from the GT detector 50 (Step S).
21). If this difference is greater than a predetermined value, LPR
It is determined that either the M detector 30 or the GT detector 50 has deteriorated (step S22), and a warning by sound or image is issued as necessary. If the difference between the measurement results is smaller than a predetermined value, it is determined that the measurement result is valid (step S23).

This comparison is made by using the LPRM detector 30 and the GT detector 50 which are at the same height in the axial direction of the LPRM assembly 20. To neutron flux. As the predetermined value, for example, 20
% And 50% can be adopted. Further, different measures can be taken according to the difference in the measurement results. Since the deterioration of the detector can be immediately recognized by the detector deterioration determination unit 84,
For example, the LPRM detector 30 and the GT detector 50 are set to TI
By calibrating with the P detector 40, the reliability of the measurement data can always be ensured.

(Other Embodiments) The present invention is not limited to the above embodiment, but can be extended and modified. Further, the extended and modified embodiment is also included in the technical scope of the present invention.
For example, in the above embodiment, a fixed GT detector is used, but instead or in addition to this, a GT detector movable in the axial direction can be used. At this time, L
For each PRM aggregate or for multiple LPRM aggregates,
One or more mobile GT detectors can be installed. Since this mobile GT detector can be prevented from being constantly exposed to radiation, it has high reliability as a detector and can be used as a reference detector for calibration.

[0033]

As described above, according to the present invention,
A reactor power monitoring device capable of constantly monitoring three-dimensional neutron flux distribution of a reactor can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a reactor power monitoring device according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a state in which the LPRM aggregate according to the present invention is cut in an axial direction and a radial direction.

FIG. 3 is a partial perspective view and a longitudinal sectional view illustrating an example of the structure of a GT detector according to the present invention.

FIG. 4 is a flowchart showing a procedure of calibrating a GT detector by a GT calibrator.

FIG. 5 shows an LPRM detector and G by a detector deterioration determination unit.
It is a flowchart showing the procedure of the deterioration determination of a T detector.

FIG. 6 is a block diagram showing a conventional reactor power monitoring device.

FIG. 7 is a schematic cross-sectional view showing a state where a conventional LPRM assembly is cut in an axial direction and a radial direction, and LP.
FIG. 3 is a schematic cross-sectional view illustrating an example of disposing an RM assembly in a nuclear reactor.

FIG. 8 is a block diagram showing a conventional reactor power monitoring device using a GT detector.

FIG. 9 is a partial perspective view and a longitudinal sectional view showing the structure of a conventional GT detector.

FIG. 10 is a schematic cross-sectional view illustrating a state in which a conventional LPRM assembly using a GT detector is cut in an axial direction and a radial direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Reactor power monitoring apparatus 20 ... LPRM assembly 30 ... LPRM detector 40 ... TIP detector 50 ... GT detector 51 ... GT detection tube 52 ... Cover tube 53 ... Core tube 54 ... Heat insulation part 55 ... High temperature side contact 56 ... Low temperature side contacts 61,62,63 ... Signal processing unit 71,72,73 ... Interface unit 80 ... Calculator 81 ... Signal conversion unit 82 ... Output distribution monitoring unit 83 ... Calibration unit 84 ... Detector deterioration judgment unit 85 ... Input / output Department

Claims (7)

[Claims] A plurality of fixed neutron detectors installed at different positions in a predetermined axial direction; and a plurality of fixed neutron detectors installed at substantially the same position in the predetermined axial direction as the plurality of fixed neutron detectors. A gamma thermo detector, and a mobile neutron detector that can move in the predetermined axial direction to calibrate the plurality of fixed neutron detectors and the plurality of gamma thermo detectors. In-core nuclear instrumentation detector assembly. 2. The apparatus according to claim 1, further comprising a plurality of gamma thermo detectors installed at different positions in the predetermined axial direction from the plurality of fixed neutron detectors.
A core instrumentation detector assembly in a core as described in the above. 3. An in-core nuclear instrumentation detector assembly according to claim 1, wherein said gamma thermo detector does not have a heater for calibration. 4. An in-core nuclear instrumentation detector assembly according to claim 1, further comprising: a signal conversion unit that converts an output signal from the gamma thermodetector into a neutron detection value. A reactor power monitoring device, comprising: 5. A signal conversion unit comprising: a conversion table for converting an output signal of the gamma thermo detector into a value corresponding to a neutron detection value based on a measurement result of the mobile neutron detector. The reactor power monitoring device according to claim 4, wherein 6. The reactor power monitoring device according to claim 4, further comprising a power distribution monitoring unit that monitors a power distribution of the reactor. 7. A neutron detection value converted from an output signal of the gamma thermo detector and a neutron detection value based on an output signal of the fixed neutron detector, and a difference between the detection values is determined. 5. The reactor power monitoring device according to claim 4, further comprising a detector deterioration determination unit that determines that one of the gamma thermodetector and the fixed neutron detector has deteriorated when the value is larger than the value of .