JP2000346980A - Reactor output measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make convertible the output signal of a γ-ray detector into a fuel assembly output by setting the sum of γ rays being generated from a fuel rod and those other than it to the value of γ rays at the position of the detector and using the sum and the calculation value of adjacent fuel assembly output. SOLUTION: The output signal of a γ-ray detector is sent to an output conversion device 9 via a filter 8. An adjacent fuel assembly output calculation means 10 takes in a parameter for indicating the state of fuel being adjacent to each fixed γ-ray detector 4 from a process computer or the like, and calculates the output of the adjacent fuel assembly by an incorporated evaluation method based on it. A fuel road γ-ray calculation means 11 calculates γrays from the fuel rod of the adjacent fuel assembly by a specific evaluation method based on a parameter for indicating the state of the adjacent fuel similarly. A structure material γ-ray calculation means 12 calculates γ rays from a member other than the inner and outer fuel rods based on a parameter for indicating the state of the adjacent fuel. The output of the adjacent fuel assembly being calculated by them and the value of γ rays are sent to an output conversion device 9 is obtained the calculation values of all γ rays.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a reactor output based on measured values of a fixed neutron detector and a fixed gamma ray detector, and a calculated power distribution calculated from a core physics model.
And a reactor power measuring device for obtaining a power distribution in a reactor.

[0002]

2. Description of the Related Art Reactor power distribution measurement of a boiling water reactor,
It is known to calibrate reactor power measurements with fixed power detectors using fixed γ-ray detectors. In particular, as a known example using a γ-ray thermometer,
There is a reactor power measurement device that converts the output signal of a γ-ray thermometer into a value of γ-ray flux and converts the value of this γ-ray flux into the local average output of an adjacent fuel assembly. It has been disclosed.

In addition, the gamma ray in the reactor has a component that does not immediately respond to a change in output due to the effect of delayed gamma ray accompanying the decay of fission products, and a correction corresponding to the delayed gamma ray component is necessary. Are disclosed in JP-A-61-61095 and JP-B-5-48438.

[0004]

As described above, in the conventional reactor power measuring device using a gamma ray detector, when the measured gamma ray flux is converted into the local average power of the adjacent fuel assembly, the output change The correction for the delayed γ-ray component which does not immediately respond to the above is considered. On the other hand, the measured γ-rays include components originating from fuel rods inside the fuel assembly and components originating from structural materials outside the fuel assembly, and components originating from structural materials also account for a significant proportion of the total. The fact has not been pointed out so far. The amount of γ-rays generated from fuel rods is much larger than the amount generated from members other than fuel rods.However, since they reach the detector after passing through fuel with a high shielding effect, attenuation until detection Is big. On the other hand, γ-rays generated in regions other than the fuel rods, particularly in the detector assembly, are detected with little attenuation. For this reason, a fixed γ using a γ-ray thermometer installed in a typical boiling water reactor core
In the case of a line detector, about 70% of the measured γ-rays are generated from the fuel rods, and most of the remaining about 30% are generated by the detector assembly itself.

[0005] Therefore, first of all, if the contribution to the measured γ-rays from other than the fuel rods, especially the contribution from the detector assembly itself, is not considered, the apparent γ-rays generated from the fuel rods are about 30
%, Which may cause a large error in the output of the adjacent fuel assembly.

Second, the γ-ray generation mechanism is different between γ-rays generated from fuel rods and γ-rays generated from sources other than fuel rods.
Since the transportation process until the generated γ-rays reach the detector is different, there is a possibility that the accuracy of conversion to the output of the adjacent fuel assembly cannot be maintained by a method that treats both of them in a unified manner. In particular, the γ-rays generated from parts other than the fuel rods are only neutron capture γ-rays, and since most of the γ-rays are generated in the detector assembly, the transport process is substantially determined by the structure of the detector. Therefore, γ-rays from sources other than the fuel rod can be directly evaluated by using the neutron flux level near the detector, and this component can be evaluated separately from γ-rays generated from the fuel rod. This is extremely effective for maintaining accuracy. further,
The γ-rays generated from parts other than the fuel rods do not include a delayed γ-ray component that does not immediately respond to the output change generated in the fuel rods. Therefore, if the ratio of neutron capture γ-rays generated in the detector assembly other than the fuel rods is increased, the component that does not immediately respond to the output change can be reduced, and a measurement with a faster response can be performed.

An object of the present invention is to calculate a value of γ-ray at a detector position as a sum of γ-ray generated from a fuel rod and γ-ray generated from a portion other than the fuel rod. An object of the present invention is to provide a reactor power measuring apparatus having a function of converting an output signal of a γ-ray detector into an output of an adjacent fuel assembly with high accuracy by using a calculated value of the output.

[0008]

A first means for achieving the above object is a local power detector for measuring a power distribution from a neutron flux in a nuclear reactor, and a fixed type γ using a γ-ray thermometer. A plurality of detector assemblies including a X-ray detector are installed in a reactor, and a reactor power measuring device for obtaining a reactor power and a power distribution from measured values with a local power detector and a fixed γ-ray detector, Means for calculating a value at the detector position of γ-rays generated from the fuel rods of the adjacent fuel assembly, based on a parameter representing the state of the fuel assembly adjacent to the detector assembly,
Means for calculating a value at the detector position of γ-rays generated from members other than the fuel rods inside and outside the fuel assembly; and means for calculating the output of the adjacent fuel assembly, and the sum of the two calculated γ-ray values Calculate the value at the detector position with high accuracy by a simple method by calculating all the γ-rays, and measure the fixed γ-ray detector using this value and the calculated value of the output of the adjacent fuel assembly. It is to convert the value to the output of an adjacent fuel assembly.

The second means is that, in the first means, a value at a detector position of γ-rays generated from a portion other than the fuel rod is converted into a neutron flux level near a fixed γ-ray detector having a strong direct correlation. It is calculated as a function.

The third means is that by increasing the proportion of neutron capture γ-rays generated in the detector assembly, it is possible to more easily evaluate the γ-ray transport process and to reduce components that do not respond immediately to output changes. As described above, a substance that generates neutron-capturing γ-rays that is stronger than that of the detection section member is added near the detection section of the fixed γ-ray detector.

A fourth means is to install a fixed γ-ray detector inside a cylindrical γ-ray shielding member in order to increase the ratio of neutron capture γ-rays generated near the detector similarly to the third means. And
The purpose is to reduce the amount of detection by γ-rays from fuel rods.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of a reactor power measuring apparatus according to the present invention. As shown, a plurality of detector assemblies 3 are provided inside a reactor core 2 in a pressure vessel 1 of a nuclear reactor. Each of the detector assemblies 3 includes a plurality of local power detectors (hereinafter, referred to as LPRM sensors) 5 for detecting neutrons in a power region inside a protection tube provided through the core, and calibration of the LPRM sensors. A plurality of fixed γ-ray detectors 4, which serve both as a means and a second output detecting means, are inserted.

As shown by A, B, C and D, four LPRM sensors 5 are provided along the height direction of the core. Then, the output signal of the LPRM sensor is input to the LPRM processing unit 6 via a signal cable. LPRM
The processing unit 6 includes a filtering unit for suppressing a high-frequency signal and outputting a neutron flux signal, and a calibration unit for correcting the sensitivity deterioration of the LPRM sensor. L
The output signal of the PRM processing means 6 is output as a local output signal and is also output to an APRM (average output area monitor) 7 and a comparing means 13. APRM7 calculates the average power of the reactor using the output signal of the LPRM processing means,
Output as average furnace output. Further, APRM will calculate the average furnace power if it exceeds a preset reference value.
The scram signal for stopping the reactor by urgently inserting the control rod into the reactor is output.

On the other hand, the fixed type γ-ray detector has a
As shown by b, c,..., j, a larger number of LPRM sensors are provided. The reason why the number of fixed gamma ray detectors is increased in this way is to enhance the calibration accuracy of the LPRM sensor and the accuracy of measuring the power distribution in the height direction of the core. In the illustrated example, 11 fixed γ-ray detectors are provided.

As the fixed gamma ray detector, a gamma ray thermometer can be used. The γ-ray thermometer measures the power inside the reactor mainly by measuring the temperature of the metal that generates heat by γ-ray irradiation from the adjacent fuel assembly with a thermocouple, etc., and there is little sensitivity deterioration due to irradiation. In addition, it has features suitable for a fixed-type γ-ray detector because of its simple structure. For calibration of the γ-ray thermometer itself, an electric heater (not shown) arranged in parallel with the γ-ray thermometer is used. That is, the heating amount is evaluated based on the voltage and current applied to the electric heater and the resistance value of the electric heater, and the heating amount, the output voltage of the thermocouple, and a separately prepared calibration curve (heating value and thermocouple output) are used. The sensor sensitivity is determined based on the voltage relationship), and calibration is performed by correcting the thermocouple output signal by a method specifically described in, for example, JP-A-9-236686.

FIG. 1 shows a case where the LPRM sensor is at the same height as the fixed type γ-ray detector, and the LPRM sensors 5A, 5B, 5C and 5D are γ-ray thermometers 4c4e, 4c4e,
g, 4i. Therefore, these LPRM sensors 5A, 5B, 5C, 5D
Can be calibrated based on the outputs of the γ-ray thermometers 4c4e, 4g, and 4i, respectively.

The output signals of the fixed γ-ray detectors 4 installed in the detector assemblies 3 in units of 11 are converted into the outputs of the adjacent fuel assemblies in the following procedure. First, the output signal of the γ-ray detector is input to the filter 8 and sent to the output conversion device 9 after noise is removed. On the other hand, in the adjacent aggregate output calculating means 10, each fixed γ
Parameters indicating the state of the fuel adjacent to the line detector 4, such as parameters such as the average burnup of the fuel assembly and the void fraction in the fuel assembly channel box, are taken in. Calculate the output of the fuel assembly. Further, the fuel rod γ-ray calculation means 11 fetches a parameter representing the state of the adjacent fuel, similarly to the adjacent assembly output calculation means 10, and is generated from the fuel rods of the adjacent assembly by a built-in evaluation method and detected by a detector. The measured γ-ray is calculated. Furthermore, the structural material γ
The line calculating means 12 calculates a γ-ray generated from a member other than the fuel rods inside and outside the adjacent assembly including the detector assembly and measured by the detector based on a parameter representing the state of the adjacent fuel by an evaluation method incorporated in advance. calculate. The adjacent fuel assembly output calculated by the adjacent assembly output calculating means 10, the fuel rod γ-ray calculating means 11, and the structural material γ-ray calculating means 12, and γ
The value of the line is sent to the output conversion device 9. Output conversion device 9
First, the fuel rod γ-ray calculating means 11 and the structural material γ
As the sum of the calculated value of the γ-ray from the fuel rod and the calculated value of the γ-ray from the members other than the fuel rod output from the line calculating means 12, the calculated value of all the γ-rays at each detector position is obtained. next,
By calculating the ratio between the calculated value of the output of the adjacent fuel assembly and the calculated value of all the γ-rays, a coefficient for converting the measured value of the γ-ray to the output of the adjacent fuel assembly is used for each fixed γ-ray detection. Determined for each vessel 4. By multiplying this coefficient by the measurement value of the corresponding γ-ray detector, the output of the adjacent fuel assembly is obtained. Also, γ
The measurement value of the line is obtained by converting the output signal of the γ-ray detector that has passed through the filter 8 into the measurement value of the γ-ray based on a built-in relational expression.

The power (local power) of the adjacent fuel assembly obtained in this manner can be used as it is as a measurement result of the local power in the reactor, but it is separately required to measure the reactor power and the power distribution. It can also be used for calibration of the installed LPRM5. That is, as shown in FIG. 1, the local output outputted from the output conversion device 9 and the LPRM
On the basis of the output signal from the processing means 6 and in the comparing means 13 according to a predetermined calculation method,
LPRM sensor 5 in the same string in the furnace
And the signal for the fixed γ-ray detector 4 having the same height is compared to calculate a calibration constant of the LPRM sensor. The calculated calibration constant is automatically or manually input to the LPRM processing means 6 to calibrate the gain for the LPRM sensor signal.

FIG. 2 shows an embodiment corresponding to the second means for solving the problem. In the second means, in the structural material γ-ray calculating means 12, the neutron flux level near the fixed γ-ray detector, which has a strong direct correlation with the value of the γ-ray generated from other than the fuel rod at the detector position, Calculate as a function. It is also possible to use a method of calculating the neutron flux level used here from the parameter indicating the state of the adjacent fuel assembly used in the first embodiment, but in the example of FIG. In the neutron flux calculating device 14 near the detector, the obtained local output signal is
It is converted to an absolute neutron flux level with a unit of 3 / sec.
The structural material γ-ray calculating means 12 has a built-in relational expression for calculating a value at the detector position of γ-rays generated from parts other than the fuel rod from the absolute neutron flux level. As the simplest relational expression, a relational expression in which the value of a γ-ray generated at a position other than the fuel rod at the detector position is considered to be proportional to the absolute neutron flux level Φ can be considered.

FIG. 3 is a horizontal sectional view showing an embodiment of a fixed γ-ray detector using a γ-ray thermometer, which corresponds to the third means for solving the problem. The third means is that a γ-ray transport process can be more easily evaluated, and neutron capture γ-rays generated in the detector assembly 3 having no component not responding to an output change can be detected by a detector of a fixed γ-ray detector. It was increased by adding a substance that generates strong neutron capture γ-rays in the vicinity. In the embodiment shown in FIG. 3, a fixed γ-ray detector 4 using a γ-ray thermometer is provided inside the detector assembly 3.
And the local output detector 5, and the fixed γ-ray detector 4
Stainless steel tube 15, thermocouple 16, heat insulating rare gas region 17, and neutron capture γ-ray generator 18
It consists of. A high temperature contact 16a of a thermocouple is installed in a region where the stainless steel tube 15 for γ-ray heating is insulated by the rare gas region 17 and becomes high temperature, and a low temperature contact 16b is installed in a region where there is no rare gas region and the temperature is relatively low. Thus, the calorific value of the γ-ray is measured from the temperature difference between the two contacts. In this embodiment, the members for detecting these γ-rays are neutron capture γ.
The complete coverage with the ray generator 18 increases the neutron capture gamma rays generated by the detector assembly. As the substance used for the neutron capture γ-ray generation unit 18, a substance such as hafnium having a high neutron capture γ-ray intensity and having a small decrease in neutron capture ability even when used for a long period of time can be considered.

FIG. 4 is a horizontal sectional view showing an embodiment of a fixed γ-ray detector using a γ-ray thermometer, corresponding to a fourth means for solving the problem. In the fourth means, by installing a fixed γ-ray detector inside the cylindrical γ-ray shielding member, by shielding γ-rays generated from the fuel rod,
This is to relatively increase the detection ratio of γ-rays from the detector assembly 3. In the embodiment occupied in FIG. 4, the gamma ray shielding member 19 made of lead is lined with the protective tube of the detector assembly.

[0023]

According to the present invention, γ-rays generated from parts other than the fuel rods among the γ-rays at the detector position can be explicitly handled, and the output signal of the γ-ray detector can be obtained with high accuracy by a simple method. Can be converted to the output of the adjacent fuel assembly. Also, by increasing the γ-rays generated from other than the fuel rods, particularly the γ-rays generated by the detector assembly itself, by reducing the delayed γ-ray components that do not respond to the output change among the γ-rays measured by the detector, Fast response output measurement can be realized.

[Brief description of the drawings]

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

FIG. 2 is a system configuration diagram of a second embodiment using a neutron flux near a detector.

FIG. 3 is a diagram illustrating an embodiment of a fixed γ-ray detector including a neutron capture γ-ray generation unit.

FIG. 4 is a diagram showing an embodiment of a fixed type γ-ray detector provided with a γ-ray shielding member.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Reactor core, 3 ... Detector assembly, 4 ... Fixed gamma ray detector, 5 ... Local power detector, 6 ...
LPRM processing means, 7: APRM (average output area monitor), 8: filter, 9: output conversion device, 10: adjacent assembly output calculation means, 11: fuel rod γ-ray calculation means, 12 ...
Structural material γ-ray calculating means, 13: Calibration means, 14: Neutron flux calculating device near detector, 15: Stainless steel tube for γ-ray heating, 16: Thermocouple, 17: Rare gas area for heat insulation,
18: neutron capture γ-ray generator, 19: γ-ray shielding member.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Kunihara Kurihara, Inventor 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within the Power & Electricity Development Division, Hitachi, Ltd. (72) Keiichiro Shibata, Inventor Keiichiro Shibata 7-2-1, Machi-cho, Hitachi, Ltd. Electricity & Electricity Development Division (72) Inventor Koichi Maki 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture, Hitachi Ltd. Electricity & Electricity Development Division (72 ) Inventor Makoto Hasegawa 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref.Hitachi, Ltd. Power and Electricity Development Division (72) Inventor Setsuo Arita 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. F-term (Reference) in Hitachi, Ltd. Electric Power & Electronics Development Division 2G075 AA03 BA03 CA08 DA01 FA11 FA19 FB02 FB05 FB07 GA21

Claims (4)

[Claims] 1. A plurality of detector assemblies including a local power detector for measuring a power distribution from a neutron flux in a reactor and a fixed γ-ray detector using a γ-ray thermometer are installed in the reactor. And
In a reactor power measuring device that obtains a reactor power and a power distribution from measured values of a local power detector and a fixed γ-ray detector, an adjacent power is measured based on a parameter representing a state of a fuel assembly adjacent to the detector assembly. Means for calculating a value at the detector position of γ-rays generated from the fuel rods of the fuel assembly, and means for calculating a value at the detector position of γ-rays generated from members other than the fuel rods inside and outside the fuel assembly, A means for calculating the output of the adjacent fuel assembly, and a fixed expression using a value at the detector position of all γ-rays calculated as a sum of the two calculated values of γ-rays and a calculated value of the output of the adjacent fuel assembly. a power conversion device for converting an output signal of the γ-ray detector into an output of an adjacent fuel assembly. 2. The apparatus according to claim 1, further comprising means for calculating a value at a detector position of γ-rays generated from parts other than the fuel rod as a function of a neutron flux level near the fixed γ-ray detector. Reactor power measurement device. 3. The reactor power measuring apparatus according to claim 1, wherein a substance that generates neutron capture γ-rays stronger than the detection unit member is added near the detection unit of the fixed γ-ray detector. 4. The reactor power measuring apparatus according to claim 1, wherein a fixed γ-ray detector is installed inside the cylindrical γ-ray shielding member.