JP2001099981A - Reactor power measurement device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To accurately correct the influence of delayed γ-rays in an output signal from a γ-ray detector in a short time, and further, based on the corrected γ-ray detection signals, a neutron detector in a computer. To be able to calculate the calibration constant. Kind Code: A1 A gamma ray detector for measuring a calorific value of a metal due to a gamma ray generated in a nuclear reactor, and a data processing device for inputting an output signal output from the gamma ray detector.
2. a computer 14 for obtaining a reactor output based on a γ-ray detection signal output from the data processing device 12, wherein the data processing device also stores time-series data of the input output signal of the γ-ray detector. And a late γ-ray correction unit 121 for correcting the late γ-ray component, and a computer for obtaining the reactor output based on the γ-ray detection signal corrected for the late γ-ray component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor power measuring apparatus for measuring a reactor power by using a gamma ray detector for measuring a calorific value of a metal due to a gamma ray generated in a nuclear reactor. Of the output signals output from the γ-ray detector,
The present invention relates to a reactor power measuring device for measuring a reactor power by correcting a line component.

[0002]

2. Description of the Related Art As is well known, a neutron detector for measuring reactor power in a boiling water reactor is constituted by containing a fissile material in a cladding tube, and the fissile material absorbs neutrons. An output signal corresponding to the reactor power is obtained using the gas ionization effect at the time of fission.
However, since it is used in a reactor, the amount of fissile material decreases and the neutron detection sensitivity gradually changes, so it is necessary to calibrate the sensitivity.

Therefore, Japanese Patent Application Laid-Open Nos. Hei 6-289182 and Hei 9
-236687, and Proceedings of a Specialists' M
eeting on In Core Instrumentation and ReactorAsses
sment (1988, June), p271-p277 "Technology
and use of GammaThermometers, a gamma-ray detector is installed in a protective tube containing a neutron detector, and a neutron detector is installed based on the reactor power measured using the gamma-ray detector. The sensitivity was calibrated.

[0004] The above-mentioned γ-ray detector refers to a temperature measuring means such as a thermocouple or a resistance temperature detector which measures the temperature of a metal which is heated by energy (radiation irradiation) given by γ-rays and a small amount of neutrons in a reactor core. The γ-ray flux and the neutron flux are obtained from the detection result, and the furnace power is obtained by utilizing the fact that the γ-ray flux and the neutron flux are proportional to the reactor power. Also, Transactions of the American Nuclear Soc
Society, Vol. 75 (1996), p333-p334 "Applicat
ion of the Gamma Thermometer to BWR CoreMonitorin
As shown in “g”, since the sensitivity of the γ-ray detector changes with the operation of the plant, it is necessary to calibrate the γ-ray detector itself. Is supplied to the calibration heater, the calibration heater is heated to give heat to the gamma ray detector, and the calorific value of the calibration heater, the output voltage of the gamma ray detector at that time, the calorific value and the gamma ray detection The sensitivity is calibrated based on the calibration curve showing the relationship with the output voltage of the detector.The gamma ray detector is used not only for the calibration of neutron detectors but also for the measurement of the axial power distribution of the core. However, it is said that it is not suitable as a detector for a safety protection system of a nuclear reactor because of its poor response compared to a neutron detector.

[0005] Japanese Patent Application Laid-Open No. 9-236687 discloses that the output voltage of a gamma ray detector is input to a multiplexer processing unit installed in a reactor building, which is a site, converted into a digital signal, and then transmitted in a predetermined format. The signal is then transmitted by multiplex transmission to the signal processing unit in the middle operation, and the data is directly output from the signal processing unit to the computer.

[0006]

Γ generated in a nuclear reactor
The rays include prompt γ-rays generated by a fission reaction or a neutron capture reaction and delayed γ-rays generated by decay of fission products, etc. The delayed γ-rays contribute about 30%. Therefore,
It is necessary to correct the influence of the delayed γ-ray in a short time and to correct the sensitivity of the neutron detector using the corrected value. The calculation of the calibration constant required to correct the sensitivity of the neutron detector is performed by the above-described computer.

The delayed gamma rays are strongly affected by the output history and the like. Moreover, even if the reactor power becomes stable after the rise due to a plurality of nuclides having different decay constants, the output signal of the γ-ray detector changes over time. There are a plurality of delayed γ-ray decay constants ranging from short (eg, several seconds) to long (eg, several hundred hours or more). The effect of delayed γ-rays having decay constants on the order of minutes or more on the reactor power is large.After correcting the effects of these delayed γ-ray components, the calibration constant for correcting the sensitivity of the neutron detector is adjusted. It needs to be calculated. As described above, since delayed γ-rays are strongly affected by the output history, etc., it is necessary to monitor the history of delayed γ-ray components whose decay constants are on the order of minutes or more. For this purpose, it is necessary to be able to manage the history of the delayed γ-ray component in at least a short time, on the order of minutes.
In order to manage the history of the late γ-ray component on the order of minutes, an error will increase unless data can be sampled in about one tenth of the time. Therefore, the output signal from the γ-ray detector is sampled at least on the order of 0.1 minute, that is, on the order of seconds, and
The history of line components is managed. If this management is given to the computer, the following problem occurs.

The computer calculates a calibration constant of the neutron detector,
Since the main functions of calculating the furnace power distribution (three-dimensional power distribution and axial power distribution) and evaluating the thermal margin, the processing time is on the order of minutes. The number of γ-ray detectors is nine or more in the axial direction, and the number of strings is equal to the number of neutron detectors (eg, 50). Therefore, the number of output signal points of the γ-ray detector is, for example, 450 Also. When trying to manage the history of delayed γ-ray components for these signal points in addition to the above function, it becomes impossible to input the output signal from the γ-ray detector in the order of seconds, and the history of delayed γ-ray components An error occurs in the management, and as a result, a calibration constant required for correcting the sensitivity of the neutron detector cannot be correctly calculated.

Further, in the processing of the computer, the processing time for the input of the output signal from the γ-ray detector occupies most of the entire processing time, and the calculation of the calibration constant of the neutron detector, There is a possibility that the calculation of the power distribution (three-dimensional power distribution or axial power distribution) and the processing of the thermal margin evaluation may cause an error, or the processing time may be extended to hinder plant operation management.

The present invention has been made in view of the above points, and an object of the present invention is to firstly and accurately correct the influence of delayed γ-rays in an output signal from a γ-ray detector in a short time. Based on the corrected γ-ray detection signal, the calculation of the calibration constant of the neutron detector, the calculation of the reactor power distribution (three-dimensional power distribution and axial power distribution), and the evaluation of the thermal margin are performed with high accuracy by a computer. To provide a reactor power measuring device capable of performing the above.

[0011]

A feature of the present invention to achieve the above object is that a gamma ray detector for measuring the calorific value of metal due to gamma rays generated in a nuclear reactor, and a gamma ray output from the gamma ray detector. A data processing device for inputting an output signal, and a calculator for obtaining a reactor output based on a γ-ray detection signal output from the data processing device, wherein the data processing device inputs the output signal of the γ-ray detector. Means for correcting the delayed γ-ray component based on the time series data. In particular, the data processing device is configured to generate at least a delayed γ-ray component having a decay constant of a minute order to a time order among the delayed γ-ray components based on the time-series data of the input output signal of the γ-ray detector. Correct and calculate a component proportional to the furnace power level.

A method for accurately measuring the output signal output from a γ-ray detector in a short time by accurately correcting the influence of delayed γ-rays in the output signal from the γ-ray detector in a short time. Can be. Based on the γ-ray detection signal in which the delayed γ-ray component has been corrected, it becomes possible to calculate the calibration constant of the neutron detector with high accuracy and without time extension by a computer.

[0013]

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

FIG. 1 shows a reactor power measuring apparatus according to a preferred embodiment of the present invention. In FIG. 1, in a core 2 of a reactor pressure vessel 1, a plurality of detector assemblies are installed together with a plurality of fuel assemblies (not shown). The detector assembly includes a plurality of neutron flux detectors 5A to 5D (hereinafter, LPRM sensors 5A to 5D) for detecting a neutron flux in an output region inside each of a plurality of protection tubes 3 provided through the core 2.
5D) and a plurality of γ-ray detectors 4a to 4k.

The LPRM is a local power area monitor for detecting a local neutron flux in the core 2.
The PRM sensors 5A to 5D are provided along the axial direction of the core 2 as shown in the drawing. The LPRM signals, which are the neutron flux detection results of the LPRM sensors 5A to 5D installed in each of the plurality of protection tubes 3, pass through the penetration P1 provided in the storage container 15 via the signal cable 5S and are stored. The input is distributed to a plurality of transmission processing devices 6 installed inside the reactor building outside the vessel 15. In FIG. 1, a plurality of transmission processing devices 6 are shown in an overwritten manner. In the case of a plurality of other devices, overwriting is used.

The transmission processing device 6 individually inputs a plurality of LPRM signals to a filter 61. The filter 61 removes high-frequency electromagnetic noise contained in each of the input LPRM signals, and outputs the resultant signals. The transmission device 62 selectively takes in the LPRM signals output from the plurality of filters 61, A / D converts the taken LPRM signals into digital data in a predetermined format, and then transmits the LPRM signals to the transmission device 8 in the central control room. Multiplex transmission. Generally, the reactor building is separated from the main control room by about 150 to 200 [m], and since the LPRM signal has a large number of signal points, the LPRM signal is transmitted by multiplex transmission as in the present embodiment. Is cheaper. Further, since the LPRM signal is weak, in the present embodiment, by using digital transmission, switching noise occurs when the changeover switch 132 described later is switched or electric noise occurs due to current control of the calibration heater. Even in such a case, it is possible to prevent such noise from being superimposed on the LPRM signal, and the noise resistance is improved. Furthermore, the effect is further improved by using optical transmission.

The plurality of transmission devices 8 receive the LPRM signals transmitted from the transmission devices 62 of the plurality of transmission processing devices 6 and output the LPRM signals to the plurality of LPRM devices 10. The LPRM device 10 receives the input LPRM.
Apply the set gain to each signal.
The gain set in the LPRM device 10 will be described later. LPRM obtained in LPRM device 10
The signal is output to a plurality of devices such as an APRM (average output area monitor) device 11 and a computer 14. APRM device 11
Calculates an average of a plurality of input LPRM signals and outputs the average as an average furnace output. Further, the APRM device 11 compares the calculated average furnace power with a preset reference value, and outputs a scrum command for reducing the furnace power when the average furnace power exceeds the reference value. Multiple APRM devices 11
When a scrum command is output from any of the above, a control rod (not shown) is urgently inserted into the core 2 and the furnace output decreases. The γ-ray detectors 4a to 4k are, as shown in FIG.
More RM sensors are provided than the RM sensors 5A to 5D.
The PRM sensors 5 </ b> A to 5 </ b> D are provided along the axial direction of the core 2 with their positions in the radial direction shifted from each other. The reason why the number of γ-ray detectors installed is large is that LP
This is for improving the calibration accuracy of the RM sensors 5A to 5D and the measurement accuracy of the axial output distribution. In this embodiment, 1
Although one γ-ray detector 4a to 4k is provided, the LPRM
LP if the same number or more than the sensors 5A to 5D
Since it is possible to calibrate the RM sensors 5A to 5D,
For example, the number may be eight or nine. The radial arrangement in the protection tube 3 is such that the LPRM sensors 5A to 5D are arranged at the center, and the γ-ray detectors 4a to 4k are connected to the LPRM sensors 5A to 5K.
It is displaced from 5D. The reason for this arrangement is
Since the neutron flux detected by the LPRM sensors 5A to 5D is affected by the water gap, it is necessary to arrange the LPRM sensors 5A to 5D at the center of the protection tube 3 to make the distance from each fuel assembly uniform. Since the γ-rays detected by the γ-ray detectors 4a to 4k are not affected by the water gap, the same detection result can be obtained regardless of where the γ-ray detectors 4a to 4k are arranged in the protective tube 3. It is.

FIG. 2 shows an example of the structure of the γ-ray detector. FIG.
FIG. 2A is a longitudinal sectional view of the γ-ray detector, and FIG. 2B is a transverse sectional view. As shown in the figure, the γ-ray detector is configured by inserting a γ-ray heating metal 42 (for example, SUS) into a cylindrical outer tube 41, and further includes a plurality of thermocouples 43 inside the γ-ray heating metal 42. A calibration heater 44 is provided. Further, the outer tube 41 and the γ-ray heating metal 42
A plurality of spaces are provided at arbitrary intervals in the axial direction, and the space is filled with an inert gas (e.g., argon gas) to reduce the thermal conductivity of the space and to provide heat insulation. A chamber 45 is formed.

In the γ-ray detector, the γ-ray heating metal 42
Is heated by irradiation with gamma rays and slight neutrons generated in the core. As shown in the figure, since the outer periphery of the γ-ray detector is cooled by circulation of the core cooling water, the γ-ray heat
Is substantially the same as the temperature of the core cooling water (actually, slightly higher than the cooling water temperature) even if heat is generated by radiation irradiation. On the other hand, since the γ-ray heat generating metal 42 inside the heat insulating chamber 45 is not cooled, the γ-ray heat generating metal 42 is in a high temperature state due to the heat generated by radiation irradiation. As shown in the drawing, a high temperature contact portion 43A and a cold temperature contact portion 43B of a thermocouple 43 are provided in an inner portion of the heat insulating chamber 45 and a portion where the heat insulating chamber 45 is not provided, respectively. Measure. The thermocouple 43 is a differential thermocouple, and outputs a temperature difference measured at the high-temperature contact portion 43A and the cold-temperature contact portion 43B as a measured voltage. This measured voltage becomes an output of the γ-ray detector, that is, a γ-ray detection signal.

As shown in FIG. 2B, the γ-ray heating metal 4
A thermocouple 43 is disposed inside the heater 2 so as to surround the calibration heater 44. In this example, since eight thermocouples 43 are provided, the number of γ-ray detectors is also eight. The calibration heater 44 is used when calibrating the sensitivity of the γ-ray detector. Calibration of the sensitivity of the γ-ray detector will be described later. Although the example of the structure of the γ-ray detector has been described above, the γ-ray detectors 4 a to 4 k of the present embodiment are basically the same as those in FIG. 2 except that the number of thermocouples is eleven. Structure.

The voltages measured by the thermocouples in the γ-ray detectors 4 a to 4 k are output from the respective γ-ray detectors 4 a to 4 k in the protection tube 3 as γ-ray detection signals.
Then, the signal passes through a penetration P2 provided in the containment vessel 15 via the signal cable 4S, is distributed to a plurality of transmission processing devices 7 installed in the reactor building outside the containment vessel 15, and is input. The transmission processing device 7 has the same configuration as the transmission processing device 6, and individually inputs the γ-ray detection signal 4S to a plurality of filters 71, and each filter 71 outputs a high-frequency electric signal included in the γ-ray detection signal 4S. Remove noise. The transmission device 72 selectively captures the γ-ray detection signal 4S from which the electrical noise has been removed by the filter 71, and A / D converts the captured γ-ray detection signal 4S into digital data of a predetermined format. Multiplex transmission is performed to the transmission device 9 in the central control room. In the present embodiment, the aforementioned L
Like the PRM signal, the γ-ray detection signal 4
It is inexpensive because it is configured to transmit S. Further, by using digital transmission, even if switching noise occurs when the changeover switch 132 described later is switched or electric noise occurs due to current control of the calibration heater, these noises are included in the γ-ray detection signal 4S. Can be prevented from being superimposed, and noise resistance is improved. Furthermore, the effect is further improved by using optical transmission.

The transmission device 9 receives the γ-ray detection signals transmitted from the transmission devices 75 of the plurality of transmission processing devices 7 and individually outputs the γ-ray detection signals to the plurality of data processing devices 12. . The data processing device 12 includes a delayed γ-ray correction unit 121, a signal processing unit 125, a data output switching unit 122
And a calibration constant calculation unit 123. Data processing device 1
In step 2, the input γ-ray detection signal is input to the delayed γ-ray correction unit 121, which performs a correction operation on the delayed γ-ray component and corrects the delayed γ-ray component, as described later. Is output to the signal processing unit 125. The signal processing unit 125 obtains the amount of heat generated by irradiation with radiation from the γ-ray detection signal using a conversion equation set in advance. This conversion formula is shown by Expression 1.

[0023]

(Equation 1)

In (Equation 1), W: amount of heat generated by radiation irradiation [w / g], U: output voltage of the thermocouple (γ-ray detection signal) [mV], S ₀ : sensitivity of the γ-ray detector [mV] / (W /
g)], α: temperature coefficient [1 / mV]. Here, α is a constant.

The signal processing unit 125 further calculates the LP corresponding to the LPRM signal from the heat generation amount W obtained by (Equation 1).
An RM equivalent signal is calculated. The signal processing unit 125 determines
An LPRM equivalent signal is output to the data output switching unit 122, and a γ-ray detection signal is output to the calibration constant calculation unit 123.
The data output switching unit 122 includes a power control device 134 described later.
The switch performs an opening / closing operation in response to an instruction from the computer. When the switch is closed, the input LPRM-equivalent signal is output to the computer 14, and when the switch is open, the LPRM-equivalent signal is not output. Calibration constant calculating unit 123 is for updating the sensitivity S ₀ in the conversion formula is set to the signal processing section 125 (the number 1), described later updates the sensitivity S ₀ by a calibration constant calculating unit 123 I do. Note that the calibration constant calculation unit 123 outputs information related to the calibration of the sensitivity to the display unit 124 to display the information.

As shown in FIG. 1, in this embodiment, the LPR
M sensors 5A, 5B, 5C, 5D and γ-ray detector 4c,
4e, 4g, 4i are the same height (axial position)
Are located in Accordingly, the LPRM sensors 5A, 5A
The sensitivities of B, 5C and 5D are determined by the γ-ray detectors 4c, 4e and 4
Calibration can be performed based on the detection results by g and 4i, respectively, and the computer 14 calculates a calibration constant for calibrating the LPRM sensor. The computer 14 compares the level ratio between the corresponding signals (for example, the signal obtained by the LPRM sensor 5A and the signal obtained by the γ-ray detector 4c) among the input LPRM signal and the LPRM equivalent signal for each LPRM sensor. And outputs it as a calibration constant to a printer (not shown).

The printer prints out the input calibration constant for each LPRM sensor, and the operator corrects the gain of the LPRM device 10 using the result, whereby
Calibration of the sensitivity of the LPRM sensors 5A to 5D is performed. In addition,
In this embodiment, the operator operates the LPRM device 1 via the printer.
Although the gain of 0 is corrected, the calibration may be automatically corrected by directly inputting the calibration constant to the LPRM device 10 without going through a printer.

The computer 14 has LPRM sensors 5A to 5D.
In addition to the calculation of the calibration constants for calibrating, the calculation of the furnace power distribution such as the three-dimensional power distribution and the axial power distribution and the evaluation of the thermal margin are performed. The three-dimensional power distribution and axial power distribution are calculated by first performing a three-dimensional core simulation based on core state data (thermal balance data, core flow, etc.) to obtain the flow distribution and void distribution, and then calculating the power distribution. The calculation is repeated, and finally the γ-ray detectors 4a to 4k
The output distribution is determined so as to match the detection result of.

The gamma rays generated in a nuclear reactor include prompt gamma rays generated by fission reactions and neutron capture reactions, and delayed gamma rays generated by the decay of fission products and the like. Strongly affected by output history and the like. Moreover, even if the reactor power becomes stable after the rise due to a plurality of nuclides having different decay constants, the output signal of the γ-ray detector changes over time.
There are a plurality of delayed γ-ray decay constants ranging from short (eg, several seconds) to long (eg, several hundred hours or more). The effect of delayed γ-rays having decay constants on the order of minutes or more on the reactor power is large.After correcting the effects of these delayed γ-ray components, the calibration constant for correcting the sensitivity of the neutron detector is adjusted. It needs to be calculated. As described above, since delayed γ-rays are strongly affected by the output history, etc., it is necessary to monitor the history of delayed γ-ray components whose decay constants are on the order of minutes or more. For this purpose, it is necessary to be able to manage the history of the delayed γ-ray component in at least a short time, on the order of minutes. In order to manage the history of the late γ-ray component on the order of minutes, an error will increase unless data can be sampled in about one tenth of the time. Therefore, the output signal from the γ-ray detector is sampled at least on the order of 0.1 minutes, that is, on the order of seconds, and the history of the late γ-ray component is managed. Since the computer 14 has the main functions of calculating the calibration constants of the LPRM sensors 5A to 5D, calculating the furnace power distribution (three-dimensional power distribution and axial power distribution), and evaluating the thermal margin, the processing time is on the order of minutes. become. In addition, since 9 or more γ-ray detectors are installed in the axial direction and the number of strings is the same as the number of LPRM sensors (for example, 50),
The number of output signal points of the γ-ray detector reaches, for example, 450 points.
When trying to manage the history of delayed γ-ray components for these signal points in addition to the above function, it becomes impossible to input the output signal from the γ-ray detector in the order of seconds, and the history of delayed γ-ray components An error occurs in the management, and as a result, a calibration constant required for correcting the sensitivity of the neutron detector cannot be correctly calculated.

Further, in the processing of the computer 14, the processing time for the input of the output signal from the γ-ray detector occupies most of the entire processing time, and the calculation of the calibration constant of the LPRM sensor, the There is a possibility that the calculation of the power distribution (three-dimensional power distribution or axial power distribution) and the processing of the thermal margin evaluation may cause an error, or the processing time may be extended to hinder plant operation management. For this,
The delayed γ-ray component is corrected based on the time series data of the output signal of the γ-ray detector input in the data processing device 12 for inputting the output signal output from the γ-ray detector.

This makes it possible to accurately correct the effect of delayed γ-rays in the output signal from the γ-ray detector in a short time, and to measure the output signal output from the γ-ray detector in a short time. It can be performed with high accuracy. Based on the γ-ray detection signal in which the delayed γ-ray component is corrected, it becomes possible to calculate the calibration constant of the LPRM sensor with high accuracy and without time extension by a computer.

Next, the correction of the late γ-ray component in the late γ-ray correction unit 121 will be described. FIG. 3 shows an output signal of the γ-ray detector when the furnace power is increased stepwise. The reactor power when the stepwise increase at time t _1,
The output signal of the γ-ray detector is ideally at level L at time t _1.
It only has to reach 4 and then be constant. However, late γ
This is not the case due to the effects of the line components. The output signal of the gamma ray detector rises instantaneously from level L1 to L2 in proportion to the furnace power. This is the prompt gamma ray component. Then, L
It takes a long time to rise from 2 to L4. This portion is the delayed gamma ray component.

It is assumed that the output signal of the γ-ray detector is input by the delayed γ-ray correction unit 121 at time t ₂ . At this time, obtaining the final settling level L4 of the output signal of the γ-ray detector is the correction of the delayed γ-ray. There are two types of correction methods. First, to calculate the final settling level L4 using time-series data input up to time t _2. Another method is to obtain a L2 level by subtracting a delayed γ-ray component from an output signal of a γ-ray detector using time-series data input up to time t ₂ , and obtain an L2 level, and obtain a L2 level based on the L2 level. To calculate the L4 level. Here, the former method will be described below.

An embodiment of a method for correcting delayed gamma rays will be described.

The fixed gamma ray detector 4 is for measuring the power distribution in the furnace, and ideally an output signal proportional to the output of the adjacent fuel assembly is obtained. However, as described above, even if the output level becomes constant mainly due to the influence of decay γ-rays of fission products, the output of the γ-ray detector does not always become constant. Moreover, since this change depends on the power history at each point in the furnace, it is necessary to remove this effect and convert it to a signal proportional to the power. It should be noted here that this signal does not necessarily have to be proportional to the absolute value of the output, but only that the relative relationship between the outputs at each point in the furnace be maintained. This is because the output of the entire core is normalized to a value obtained by a plant heat balance calculation or the like.

In general, the change in gamma ray energy generated from fission products after the output level becomes constant is approximately expressed by the following equation (2).

[0037]

(Equation 2)

Can be expressed as follows. Here, i is the nuclide, ε is the γ-ray emission energy per decay, F is the fission rate, γ is the fission yield, λ is the decay constant, and t is the time when the output level is constant. Elapsed time from (for example, at the start of measurement), N _{0, i} is the density of nuclide i at the base time. Here, since there are many fission nuclides, it is convenient to handle fission products in several groups having almost the same decay constant. For example, in order to represent the time variation of the decay heat of a nuclear reactor, it is recommended that the decay heat be divided into sets of nuclides having a decay constant of 33. In this case, i in Equation 1 may be considered as a set of nuclides (i = 1 to 33).

The effect of the output history appears as a difference in the composition of nuclides having different decay constants at each point, that is, a difference in the nuclide densities contained in the second term on the right side of Equation 1. As can be seen from this equation, after a sufficiently long time, this contribution can be ignored, and the γ-ray energy becomes proportional to fission.

FIG. 4 shows the average value and the variance of the γ-ray energy in several cases in which the same output level was obtained at t = 0 through different output histories. As shown in the figure, immediately after the output is settled, the influence of the output history is large, but after 10 hours or more, the variance due to it becomes small. Thus, a measurement value more than 10 hours ahead can be predicted and if it is proportional to the output, it can be used as an output measurement without the effect of output history. FIG. 5 shows a procedure for correcting delayed gamma rays according to an embodiment of the present invention. This figure shows an example in which the furnace power setting is confirmed based on the APRM average furnace power signal, and a time-series data acquisition start signal is generated. The reactor power is set by confirming that the reactor period calculated from the average power signal of the APRM has maintained a value equal to or greater than a predetermined value for a certain period of time (for example, 5 minutes). Generate a start signal. Upon receiving this signal, the data processing device starts acquiring time-series data. The asymptote determination device uses Equation 3 based on Equation 2

[0041]

(Equation 3)

This is applied to the function form of That is, the coefficients A and B in the above equation are determined from the time-series data. However, N in Equation 3 does not necessarily have to be the number of fission product sets 33 described above. The half-life of 33 sets ranges from very short (eg, 10 ⁻⁵ h) to very long (eg, 10 ⁻⁵ h).
Up to ¹⁰ h). Those with very short half-lives immediately follow their output level, while those with very long half-life change little in the time of measurement. Assuming that the measurement is performed within a few minutes to about one hour after the furnace power is settled, only the group having a half life of several minutes to several tens of hours contributes to the change of the γ-ray measurement value during this period. Therefore, the fitting accuracy is improved when the set of decay constants used in Equation 3 is selected based on the time at which the settling is determined, that is, the elapsed time from the time at which the time-series data acquisition start signal is issued.

7 sets with half life 0.1h-100h
Using (N = 7), 50% output to 80% and 100%
%, The change in γ-ray energy when the output is increased to 1% is measured for 1 hour from 1 hour after the output is settled, and is applied to Equation 3 to estimate the γ-ray energy after 10 hours when the influence of the output history described above is reduced. Table 1 shows the results.

[0044]

[Table 1]

The γ-ray energy prediction error after 10 hours in this embodiment was 1% or less. Further, as shown in the results, the predicted value of the γ-ray energy after 10 hours matches the output level with an accuracy of 1%, and it can be seen that the output measurement without the influence of the output history can be performed by this method. . This means that the measurement of γ-ray energy after waiting for 10 hours can be achieved in 1 hour by using the present invention.

Next, another embodiment of a method for correcting the effect of delayed gamma rays based on an operation pattern as shown in FIG. 6 will be described. This embodiment is an example in which time-series data is applied with a simpler function (the number of sets of decay constants 1 to 2) as compared with the above-described embodiment, and further, the accuracy is improved by a correction coefficient derived analytically. . FIG. 6 shows the rated output (100
%), The output is reduced by ΔP (50%), increased in ΔT time, and output set when the output is settled (t = 0). In the figure, t _o , t _i , and t _n indicate measurement value sample times.

In the reactor core, there are prompt γ-rays associated with the fission reaction, delayed γ-rays associated with the decay of the generated fission products (FP nuclides), γ-rays associated with the neutron absorption reaction, and the like. . When the output is changed from 50% to 100% of the rated output (output increase), the relative time change of the total γ-ray intensity (elapsed time after 100% output increase) is calculated by general-purpose radionuclide production / decay calculation. FIG. 7 shows an analysis example calculated using the code ORIGEN2 or the like. These changes over time
It is caused by the effect of delayed gamma rays, and greatly changes depending on the operating state of the reactor and the output change pattern.Therefore, it is important that a correction method that can appropriately cope with these actual machine conditions is important. . Therefore, in the present invention, a physical model that makes full use of the actual measured value of the total γ-ray intensity is employed as described below.

In the present invention, the time change of the total γ-ray intensity due to the effect of the delayed γ-ray when the output is changed during the steady operation of the nuclear reactor is determined by the following equation, which depends on the elapsed time (t) after the power rise. Is displayed by Equation 4.

[0049]

G _T (t) = α · G ₀ · f (t) where G ₀ is a quantity representing the total γ-ray intensity at t = 0 after the output rise, and f (t) is: This is a quantity representing a relative change over time. α is a correction factor for correcting the total γ-ray intensity at t = 0 to a value at the time of steady operation, and is obtained by a numerical simulation by a method described later.

Hereinafter, a method of specifically calculating Equation 4 using the actually measured values will be described.

The physical phenomena described by the time-dependent function f (t) are exponentially released from a large number of fission products (FP nuclides) generated by fission with their own decay constants. This is the result of integrating the time change of the emitted γ-ray. Accordingly, in the present invention, f (t) is displayed by a function formula using one or two or more exponential functions having two or three or more parameters (exponential function exponent and component ratio). Note that the number of exponential functions (which is closely related to the number of measurement points as described below) should be set in consideration of required accuracy, measurement time, and the like. It can be said that as the number increases, the reliability of the correction value increases. The simplest example of f (t) is f
This is a function of the form (t) = A + Bexp (−λt). In the case of the present embodiment, the decay constant λ is also an object to be applied, unlike the aforementioned equation (3).

Next, during operation of the measurement system using the fixed type γ-ray detector according to the present invention, at three or four or more points (t _o ,... T _i , t _n ) after the output rises. The measured value of the measured total γ-ray intensity is taken in, and the function G defined above is taken.
Three or four or more parameters (G ₀ ) included in this function so that the value of ₀ · f (t) matches the actually measured value.
Is obtained by an analytical method or a method using a fitting equation, thereby obtaining a correction function (G ₀ · f).
(t)) is determined.

The correction function (G ₀ determined in this manner)
The analysis accuracy of (f (t)) is high within the range of the actual measurement time (assuming 1 to 3 hours after the output rise) because only numerical calculation errors or fitting calculation errors are expected. Actually, the results of numerical simulations simulating various operating conditions of the reactor show that the results agree with the results of the rigorous calculation with very good accuracy (within 0.5% difference).
That has been confirmed.

In the above examination, the measurement time by the γ-ray detector is assumed to be within a relatively short range of 1 to 3 hours after the output rise, but this is due to the local output for measuring the thermal neutron flux. This is because operational requirements for the measurement system, such as the need to reflect the measurement results of the γ-ray detector at an early stage in the calibration of the detector, etc., were considered. On the other hand, as can be seen from FIG. 8, which shows the time change of the delayed gamma ray intensity emitted in one nuclear fission, about 80% is emitted after 10 hours and about 90% is emitted after 100 hours. It is determined that there is no practical problem if an elapsed time of 10 hours or more is used as an elapsed time when the intensity of the delayed γ-ray almost reaches a steady state.

The correction function G ₀ · f (t) defined above is defined as 1
When applied as a correction value after a long time of about 00 hours, if the parameters are recalculated using measured values after a long time, the same accuracy can be obtained in principle. . However, due to the restrictions on the actual operation of the measurement system described above, such measured values are not expected to be obtained, and some countermeasures are required.

In this embodiment, as shown on the left side of Equation 4, a correction factor α is introduced to correct this effect.

The basic idea in determining the correction factor α is that, as described above, the effect of the long half-life component of the delayed γ-ray cannot be determined using an actually measured value. In consideration of the above, the nuclear property analysis technology, which has reached a high technical level in terms of nuclear data and analysis techniques through long-term research and development in the past, will be used to make corrections.

In the present embodiment, the correction factor α is defined by the following equation (5).

[0059]

Α = {G (t ₁₀₀ ) / G (t ₀ )} | (a) Here, G (t) is an analysis value of the total γ-ray intensity at the elapsed time t after the output rise ( t ₀ is the first measurement time, t
₁₀₀ is 100 hours after the passage), the symbol <<>> | (a) indicates the various operating states of the core (initial loading core / equilibrium core, initial / middle / end stages of operation cycle, burnup, power level, etc.) and output patterns ( This means that a large number of analysis results on the power increase rate, the output change width, the furnace shutdown period, etc.) are averaged as a function of the parameter a. Here, the parameter a is an amount representing the rate of change of the total γ-ray intensity, and a value at the beginning of the measurement is used.

According to the simulation results using the ORIGEN2 code and the like, the value of the correction factor α for the initial / middle / end stages of the operating cycle of the equilibrium core of the BWR is 1.01 to
It varies almost linearly with the value of a in the range of 1.02 (variation: ± 〜0.005). Therefore, it is understood that the contribution of the correction factor α is not so large, and these data may be arranged in the form of a table or the like, and may be used in actual correction calculation according to Equation 3.

From the above analysis result, the delayed γ-ray correction unit 121
Is corrected based on the time-series data of the input output signal of the γ-ray detector, by correcting at least the delayed γ-ray component having a decay constant from the order of minutes to the order of time from among the delayed γ-ray components. It is possible to improve the correction accuracy of the emitted γ-ray component.

By the way, the sensitivity S ₀ of the γ-ray detector changes with the operation of the plant. This is caused by the fact that hydrogen contained in the γ-ray heating metal (SUS) of the γ-ray detector enters the heat-insulating chamber due to the heat generated by the radiation irradiation, and changes the heat-insulating characteristics of the heat-insulating chamber.
Since the change in the sensitivity S ₀ is large especially during the output rising process at the time of starting the plant and for a certain period thereafter, it is necessary to frequently perform the sensitivity calibration for correcting the sensitivity S ₀ at the time of starting the plant and for a certain period thereafter. is there. Meanwhile, while the plant output constant operation is carried out, the change in the sensitivity S ₀ is small, there is no need to perform calibration of the sensitivity S ₀ frequently. Further, when the load following operation is performed due to the relationship between the power demand and the like, the output changes, the calorific value of the γ-ray heating metal changes, and the sensitivity S ₀ also changes. Calibration must be performed frequently.

Next, the gamma ray detectors 4a to 4a according to the present embodiment will be described.
The calibration of the sensitivity of 4k will be outlined.

First, a calibration command is input to a plurality of heater control devices 13 by an operator. Note that the heater control device 1
Numeral 3 is provided in a central control room outside the reactor building, and includes a filter 131, a changeover switch 132, and a power supply device 13 respectively.
3 and a power supply control device 134.

In the heater control device 13, the calibration command is input to the power control device 134, and the power control device 134 to which the calibration command is input outputs a current command of a preset pattern to the power device 133. At the same time, the power supply control device 134
And outputs a calibration constant calculation command to the calibration constant calculation unit 123. In this embodiment, the power supply control unit 134 controls the power supply 133 by supplying a current command to the power supply 133. However, the control may be performed by supplying a voltage command or both a current command and a voltage command.

FIG. 9A shows a current command pattern set in the power supply control device 134. As shown in FIG. 9A, the current command output from the power control device 134 is the first current command.
After ramping up to the set value I1, it becomes constant at the first set value I1 for a while. The power supply device 133 ramps the output current to the first set value I1 in response to the input current command, and then keeps the output current constant at the first set value I1.

The current output from the power supply 133 is supplied to one of the filters 131 via the changeover switch 132.
Are entered. The filter 131 to which the current is input is
The current noise is removed, and the current is supplied to the calibration heaters provided in the γ-ray detectors 4a to 4n in the protection tube 3 via the signal cable 4H. As described above, by flowing the output current of the power supply device 133 to the calibration heater during plant operation,
The calibration heater is heated. FIG. 9B shows a time change of a calorific value of the calibration heater. As shown in the figure,
The calorific value of the calibration heater rises like a ramp with a slight response delay to the current flowing through the calibration heater,
It will be constant. Since the calorific value of the calibration heater is increased like a ramp as described above, thermal stress in the calibration heater can be reduced. In the γ-ray detectors 4a to 4k,
When the calorific value of the calibration heater is added to the calorific value due to the radiation irradiation, a voltage (γ-ray detection signal) increased by that amount is output. This voltage rise and the calorific value of the calibration heater (determined by heater resistance and heater current) and (Equation 1)
, The new sensitivity S is calculated by the calibration constant calculation unit 123.
₀ can be calculated.

The γ-ray detection signal at the time of calibrating the sensitivity of the γ-ray detector is output from the transmission processing device 7 to the data processing device 12 via the transmission device 9. Therefore, the late γ-ray correction unit 1
To 21, a detector output signal whose output has increased due to heater heating for calibration of the γ-ray detector is input. If the delayed γ-ray component is corrected using the increased signal as it is, erroneous correction will be performed. For this reason, when the output stop command from the power supply control device 134 is input and the heater heating is being heated for the γ-ray detector calibration, the correction of the delayed γ-ray component is interrupted. further,
During the interruption period, the delayed γ-ray correction unit 121 converts the input data into the signal processing device 12 so as not to hinder the calculation processing in the calibration constant calculation unit 123.
5 is output. After the calibration of the γ-ray detector is completed, the correction of the delayed γ-ray component is performed again.
Since the gamma-ray detector calibration is performed when the output is stable in about a minute and the output is stable, an error that causes a problem in the correction calculation of the delayed gamma-ray component even if the data for 10 minutes is missing. It does not cause it. The data output switching unit 122
Since the output stop command is also input from the power supply control device 134, the switch of the data output switching unit 122 is opened, and the LPRM equivalent signal output from the signal processing unit 125 is output from the data output switching unit 122. There is no.
Therefore, it is possible to prevent the LPRM sensor from being erroneously calibrated based on data different from the plant data or calculating the power distribution of the core during the calibration of the sensitivity of the γ-ray detector.

In this embodiment, the detection signal of the γ-ray detector is input to the data processing device via the transmission device. However, the detection signal need not be transmitted via the transmission device.

[0070]

According to the present invention, the output signal from the γ-ray detector can be measured by accurately correcting the effect of delayed γ-rays in the output signal from the γ-ray detector in a short time. Can be performed accurately in a short time. Based on the γ-ray detection signal in which the delayed γ-ray component has been corrected, it becomes possible to calculate the calibration constant of the neutron detector with high accuracy and without time extension by a computer. Furthermore, when calibrating the γ-ray detector itself, the correction of the effects of delayed γ-rays was interrupted,
Since the calibration is restarted after the completion of the calibration, the calibration of the γ-ray detector itself is not affected by the output signal of the γ-ray detector which rises due to the heating of the heater, and high correction accuracy can be secured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a reactor power measuring apparatus according to a preferred embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a γ-ray detector.

FIG. 3 is a diagram showing an output signal of a γ-ray detector when the furnace output is stepwise increased.

FIG. 4 is a diagram showing an average γ-ray energy change and a dispersion state in cases with different output histories.

FIG. 5 is a diagram showing a flow of a procedure for correcting a delayed γ-ray.

FIG. 6 is a diagram showing an operation output pattern.

FIG. 7 is a diagram showing a state of a temporal change of the total γ-ray intensity (after 50% → 100% output increase).

FIG. 8 is a diagram showing a state of delayed gamma ray intensity change (U-235 thermal neutron fission).

9A is a diagram showing a pattern of a current command set in the power supply control device 134 in FIG. 1, and FIG.
FIG. 4 is a diagram showing a change over time in a calorific value of a calibration heater.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Reactor core, 3 ... Protection tube, 4a-4
k: γ-ray detector, 5A-5D: LPRM sensor, 6, 7
... Transmission processing device, 8, 9 ... Transmission device, 10 ... LPRM device, 11 ... APRM device, 12 ... Data processing device, 13
... heater control device, 14 ... computer, 15 ... containment vessel, 1
7: current detector, 121: delayed gamma ray correction unit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiromi Maruyama 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Power & Electric Development Laboratory, Hitachi, Ltd. (72) Inventor Kazuhiko Ishii Omika, Hitachi City, Ibaraki Prefecture 5-2-1, Machi, Omika Works, Hitachi, Ltd. (72) Inventor Ken Nozaki 3-1-1, Sakaimachi, Hitachi, Ibaraki F-term, Hitachi Works, Hitachi Works 2G075 AA03 BA03 CA08 DA01 FA11 FB02 FB05 FB07 FC04 GA15 GA21

Claims (7)

[Claims] 1. A gamma ray detector for measuring a calorific value of a metal due to a gamma ray generated in a nuclear reactor, a data processing device for inputting an output signal output from the gamma ray detector, A computer for calculating the reactor power based on the output γ-ray detection signal, wherein the data processing device corrects the delayed γ-ray component based on the input time-series data of the output signal of the γ-ray detector. A reactor power measuring device, characterized in that: 2. A gamma ray detector for measuring a calorific value of a metal due to gamma rays generated in a nuclear reactor, a data processing device for inputting an output signal output from the gamma ray detector, and a data processing device. A computer for obtaining a reactor power based on the output γ-ray detection signal, wherein the data processing device has a component proportional to the reactor power level based on the input time-series data of the output signal of the γ-ray detector. A nuclear reactor power measurement device characterized by calculating: 3. A gamma ray detector for measuring a calorific value of a metal due to a gamma ray generated in a reactor, a data processing device for inputting an output signal output from the gamma ray detector, and an output from the data processing device. A computer for obtaining a reactor output based on the γ-ray detection signal, a heater for applying heat to the γ-ray detector, a power supply device for supplying power to the heater to generate heat, and applying heat by the heater Calibrating means for calibrating the sensitivity of the γ-ray detector based on the output signal of the γ-ray detector at the time of the input, and the data processing device is based on time-series data of the output signal of the γ-ray detector that is input. Means for correcting the delayed γ-ray component, and while the heater is generating heat for calibration of the sensitivity of the γ-ray detector, the correction of the delayed γ-ray component is interrupted. Furnace power measurement device. 4. A gamma ray detector for measuring a calorific value of metal due to gamma rays generated in a nuclear reactor, a data processing device for inputting an output signal output from the gamma ray detector, and an output from the data processing device A computer for obtaining a reactor output based on the γ-ray detection signal, a heater for applying heat to the γ-ray detector, a power supply device for supplying power to the heater to generate heat, and applying heat by the heater Calibrating means for calibrating the sensitivity of the γ-ray detector based on the output signal of the γ-ray detector at the time when the data processing device receives the time-series data of the input output signal of the γ-ray detector. Means for calculating a component proportional to the reactor power level, and while the sensitivity of the γ-ray detector is being calibrated, the calculation of the component proportional to the reactor power level is interrupted. . 5. The data processing device according to claim 1, wherein at least one of the delayed gamma ray components has a delayed gamma having a decay constant in the order of minutes to time on the basis of the input time-series data of the output signal of the gamma ray detector. 2. A line component is corrected.
Alternatively, the reactor power measuring device according to claim 3. 6. The reactor power measurement according to claim 1, wherein the data processing device inputs the output signal of the γ-ray detector at a sampling cycle of at least a minute order or less. apparatus. 7. A neutron flux detector for detecting a neutron flux generated in the reactor, and means for obtaining a reactor output by multiplying an output signal output from the neutron flux detector by a preset gain. Wherein the computer calculates a calibration constant for correcting the gain based on the drift-corrected output signal output from the γ-ray detector output from the transmission processing device. A reactor power measuring device according to any one of claims 1 to 6.