JP7615003B2 - Neutron detector sensitivity calibration method - Google Patents

Description

An embodiment of the present invention relates to a method for calibrating the sensitivity of a neutron detector.

For example, ionization chamber type radiation detectors are often used as neutron detectors for start up range neutron monitors (SRNMs) or local power range monitors (LPRMs). In these neutron detectors, the material sensitive to neutrons to be measured is a fissile material such as uranium 235 ( ²³⁵ U) that undergoes nuclear fission by neutrons. Fission products (FPs) produced by nuclear fission by neutrons ionize gases such as Ar sealed in the ionization chamber. Neutrons are detected by measuring the current generated by this ionization. In order to measure the neutron flux level, it is necessary to measure the sensitivity of this detector to the neutron flux level.

Japanese Patent Application Publication No. 3-255396

As mentioned above, neutron detectors lose sensitivity to neutrons over time, so their sensitivity needs to be calibrated at regular intervals.

Regarding the calibration of neutron detectors for SRNM or LPRM, a method is known in which the output of the neutron detector is calibrated by estimating the reactor power from the heat balance of the plant. However, this method does not directly check the sensitivity of the neutron detector itself, and there is a problem that errors can become large in cases where there is a bias in the distribution of reactor power.

In addition, for the neutron detectors used in the start-up range neutron monitors, a method is known in which a neutron source such as Californium 252 ( ²⁵² Cf) is used for sensitivity calibration. The half-life of ²⁵² Cf is 265 years. For example, the radiation source strength decreases by 5% every 18.7 years. If the radiation source strength decreases, it is necessary to arrange for a new radiation source.

The problem that this invention aims to solve is to provide a method for calibrating the sensitivity of neutron detectors and radiation detectors that can calibrate themselves without relying on an external neutron source or heat balance calculations.

According to an embodiment, the method for calibrating the sensitivity of a neutron detector is characterized by comprising a preparation step including a step of measuring a first preparation output of the neutron detector in the zero power state of the reactor, a step of measuring a second preparation output of the neutron detector in the power state of the reactor, and a step of calculating a sensitivity coefficient from the first preparation output and the second preparation output, and a calibration step including a step of measuring a first calibration output of the neutron detector in the zero power state of the reactor, a step of measuring a second calibration output of the neutron detector in the power state of the reactor, and a step of calculating sensitivity from the first calibration output and the second calibration output .

1 is a block diagram showing a configuration of a neutron monitor according to a first embodiment. FIG. 1 is a vertical cross-sectional view showing a configuration of a neutron detector according to a first embodiment. 2 is a block diagram showing the configuration of a signal processing unit of the neutron monitor according to the first embodiment; FIG. 4 is a graph showing an example of an output of a first wave height discriminator of a signal processing unit of the neutron monitor according to the first embodiment. 5 is a graph showing an example of an output of a second wave height discriminator of a signal processing unit of the neutron monitor according to the first embodiment. 2 is a block diagram showing the configuration of a calculation device of the neutron monitor according to the first embodiment. FIG. 3 is a flow chart showing the procedure of a sensitivity calibration method for a neutron detector according to the first embodiment. FIG. FIG. 11 is a block diagram showing the configuration of a signal processing unit of a neutron monitor according to a second embodiment. FIG. 11 is a block diagram showing the configuration of a calculation device of a neutron monitor according to a second embodiment. 1 is a graph showing an example of a pulse height distribution of the output current of a nuclear fission counter. FIG. 11 is a block diagram showing the configuration of a calculation device of a neutron monitor according to a third embodiment.

Below, a neutron detector, a neutron monitor, and a method for calibrating the sensitivity of a neutron detector according to an embodiment of the present invention will be described with reference to the drawings. Here, identical or similar parts are given common reference numerals and duplicated explanations will be omitted.

[First embodiment]
In the following embodiments, ionization chamber type neutron detectors for startup range neutron monitors (SRNM) or local power monitors (LPRM) are collectively referred to as neutron detectors, and startup range neutron monitors (SRNM) or local power monitors (LPRM) using such neutron detectors are collectively referred to as neutron monitors. The following description will be given taking the case of an SRNM as an example, but the configuration of the neutron detector is similar for the case of an LPRM.

Figure 1 is a block diagram showing the configuration of a neutron monitor 60 according to the first embodiment.

The neutron monitor 60 has a neutron detector 10, a detector circuit 20 that applies a DC voltage to the neutron detector 10 and extracts a current signal, a preamplifier 30 that amplifies the current signal, a signal processing unit 40, and an arithmetic unit 50.

The detector circuit 20 has a DC power supply 21 that applies a DC voltage to the neutron detector 10, and an ammeter 22 that detects and outputs the current flowing through the neutron detector 10. The output of the ammeter 22 is weak, so it is taken out by a coaxial cable 24 and output to a preamplifier 30. A coaxial cable 18 is also used for the cable of the circuit including the ammeter 22 that is drawn from the neutron detector 10.

Figure 2 is a vertical cross-sectional view showing the configuration of the neutron detector 10 according to the first embodiment.

The neutron detector 10 has an anode 12, a cathode 13, a cathode material 14, and a housing 11 that contains these.

The housing 11 is a cylindrical container extending in the direction of the central axis, with both ends closed by closing portion 11b and closing portion 11c. A metal/ceramic portion 16 is provided on the outside of closing portion 11c of the housing 11. The metal/ceramic portion 16 is also one of the elements that make up the closed space. As a result, a sealed portion is formed within the housing 11. An internal gas 17 is sealed in the sealed portion within the housing 11.

The anode 12 is cylindrical and extends along the central axis of the housing 11. Both ends of the anode 12 are narrow, with one end 12a supported by an insulator 15a and the other end 12b supported by an insulator 15b. The insulators 15a and 15b are disposed in a sealed portion within the housing 11. Note that both ends of the anode 12 do not necessarily have to be narrow.

The cathode 13 is provided radially outward at a predetermined distance from the region of the anode 12, which is between the insulators 15a and 15b and has a uniform diameter. Specifically, the cathode 13 is attached circumferentially to the inner surface of the side portion 11a of the housing 11.

An internal conductor 18a is connected to the end 12b of the anode 12 that is supported by the insulator 15b. The internal conductor 18a penetrates the metal/ceramic part 16 by a sealing structure (not shown), such as a hermetic seal. A cylindrical external conductor 18b is attached to the outside of the metal/ceramic part 16 and is concentric with the internal conductor 18a, penetrating the end 12b. The internal conductor 18a and the external conductor 18b form a coaxial cable 18.

Next, the cathode side material 14 provided on the cathode 13 side will be described. The cathode side material 14 is provided so as to cover the radial inside of the cathode 13, i.e., the inner surface of the cathode 13. The cathode side material 14 has a sensitive material 14a and a radioactive isotope 14b. The cathode side material 14 may be present on the inner surface of the cathode 13, i.e., provided, for example, by being applied to the inner surface of the cathode 13 or by being vapor-deposited on the inner surface of the cathode 13. Alternatively, the cathode side material 14 may be impregnated into the inner surface of the cathode 13. Alternatively, the cathode side material 14 may be formed into a metal foil and attached to the inner surface of the cathode 13. The form may be selected according to the properties of the cathode side material 14 and the cathode 13.

The sensitive material 14a receives neutrons from outside the neutron detector 10 and generates a substance that ionizes the internal gas 17 through a nuclear reaction. As the sensitive material 14a, fissile nuclides such as uranium-235 ( ^235U ) and plutonium-239 ( ^239Pu ), or boron-10 ( ^10B ) can be used. In the case of a fissile nuclide, the substance that ionizes the internal gas 17 is a fission product (FP). In the case of ^10B , the substance that ionizes the internal gas 17 is an alpha particle.

The radioactive source isotope 14b is a radioactive isotope that emits alpha rays or beta rays as a substance that ionizes the internal gas 17 by natural decay. The requirement for the radioactive source isotope 14b is that it is an isotope whose half-life is sufficiently long for the service life of the nuclear power plant. Examples of isotopes that satisfy this requirement include radium-226 ( ^226Ra : half-life 1600 years), ^239Pu (half-life 2.4 x ¹⁰⁴ years), and uranium-234 ( ^234U : half-life 2.48 x ¹⁰⁵ years) as alpha ray sources.

In addition, when U ²³⁵ is used as the sensitive material, U ²³⁴ may be used as a conversion source to U ²³⁵ in order to mitigate the reduction of U ^235. Thus, conventionally, uranium isotopes have often been used as the cathode side material 14 of the neutron detector 10. That is, the conventional cathode side material is a uranium isotope as the sensitive material, and a radioactive source isotope such as that provided in this embodiment is not provided.

On the other hand, in this embodiment, a uranium isotope can be used as the cathode side material 14. In this case, U ²³⁴ , which is used as a conversion material to U ²³⁵ in the conventional example, can be used as the radioactive source isotope 14b in this embodiment. That is, ²³⁵ U can be used as the sensitive material 14a, and U ²³⁴ can be used as the radioactive source isotope 14b. As described above, U ²³⁴ is an alpha ray source, and its half-life is 2.48×10 ⁵ years. In the following, a case where ²³⁵ U is used as the sensitive material 14a and U ²³⁴ is used as the radioactive source isotope 14b will be described as an example.

Figure 3 is a block diagram showing the configuration of the signal processing unit 40 of the neutron monitor 60 according to the first embodiment.

The signal processing unit 40 receives the current signal amplified by the preamplifier 30 and outputs the processed signal to the computing device 50.

The signal processing unit 40 has a first wave height discriminator 41, a first counter 42, a second wave height discriminator 43, and a second counter 44.

Figure 4 is a graph showing an example of the output of the first pulse height discriminator 41 of the signal processing unit 40 of the neutron monitor 60 according to the first embodiment. The horizontal axis indicates time, and the vertical axis indicates pulse height value. The dashed area A indicates a group of current signals Is when neutrons are incident on the sensitive substance 14a. The dashed area B indicates a group of current signals Ir due to alpha rays from the radioisotope 14b.

The first pulse height discriminator 41 is provided to distinguish the current signal Is and the current signal Ir from electrical noise. Therefore, the first pulse height discriminator setting value Cth1, which is the discrimination level of the first pulse height discriminator 41, is set to a value higher than the noise level.

The first counter 42 receives and counts the current signal Is generated when neutrons are incident on the sensitive material 14a and the current signal Ir generated by alpha rays from the radioisotope 14b. That is, it outputs the sum of the count rate Cs (cps) of the group of current signals Is shown in the dashed area A and the count rate Cr (cps) of the group of current signals Ir shown in the dashed area B.

Figure 5 is a graph showing an example of the output of the second wave height discriminator 43 of the signal processing unit 40 of the neutron monitor 60 according to the first embodiment.

The second pulse height discriminator 43 is provided to distinguish the current signal Is when neutrons are incident on the sensitive substance 14a from the current signal Ir due to alpha rays from the radioisotope 14b. Therefore, the second pulse height discriminator setting value Cth2, which is the discrimination level of the second pulse height discriminator 43, is set to a value higher than the level of the group of current signals Ir shown in the dashed line area B and lower than the level of the group of current signals Is shown in the dashed line area A.

The second counter 44 receives the current signal generated when neutrons are incident on the sensitive material 14a and counts it. In other words, it outputs the counting rate Cs (cps) of the group of current signals Is shown in the dashed area A.

Figure 6 is a block diagram showing the configuration of the computing device 50 of the neutron monitor 60 according to the first embodiment.

The calculation device 50 receives the output from the signal processing unit 40, calculates the sensitivity of the neutron detector 10, and outputs it. The calculation device 50 has an input unit 51, a memory unit 52, a calculation unit 53, and an output unit 54. The calculation device 50 is, for example, a computer system. Alternatively, it may be a collection of individual devices each having a function.

The input unit 51 accepts information relating to the neutron detector 10 from the outside. Examples of main information relating to the neutron detector 10 include the main dimensions including the gap dimension between the anode 12 and the cathode 13, the weights of the sensitive material 14a and the radioactive source isotope 14b in the cathode side material 14, the nuclide of the internal gas 17, specifications such as gas pressure, and nuclear constants relating to the sensitive material 14a, the radioactive source isotope 14b, the internal gas 17, etc. The input unit 51 also accepts other external inputs as necessary.

The memory unit 52 includes a detector information memory unit 52a that stores and stores information about the neutron detector 10 received by the input unit 51, a first count memory unit 52b that stores the sum of the count rate Cr and the count rate Cs obtained by the signal processing unit 40, a second count memory unit 52c that stores the count rate Cs (cps) obtained by the signal processing unit 40, a calculation result memory unit 52d that stores the calculation results of the calculation unit 53, and a sensitivity coefficient memory unit 52f.

The calculation unit 53 has an existence ratio calculation unit 53a, a sensitivity coefficient calculation unit 53b, and a sensitivity calculation unit 53c.

The abundance ratio calculation unit 53a calculates the number of atoms Nn of the sensitive substance 14a and the number of atoms Nr of the radioactive source isotope 14b from the weights of the sensitive substance 14a and the radioactive source isotope 14b stored in the detector information storage unit 52a, and further divides Nn by Nr to calculate the ratio NNR.

The sensitivity coefficient calculation unit 53b calculates the sensitivity coefficient SCF based on the data stored in the detector information storage unit 52a and the sensitivity coefficient storage unit 52f. The process of calculating the sensitivity coefficient SCF is shown below.

First, the nuclear reaction cross section of the nuclear reaction caused by neutrons in the sensitive material 14a is σn (σf in the case of nuclear fission), and the decay constant of the radiation source isotope 14b caused by the radiation of interest, such as alpha rays, is λr.

The number of counts Cr ₀ (cps) from the radioactive source isotope 14b in the case of zero output (Φn=0) is obtained using the following formula (1).
Cr ₀ =λr・Nr・Er・Fr (1)
where Er is the ionization efficiency of the gas product of the nuclear reaction, and Fr is the efficiency of the detector.

The sensitivity Cn ₀ (cps/nv) at a given power (neutron flux level Φn) is obtained using the following equation (2).
Cn ₀ = (σn・Nn・Φn・En・Fn)/Φn
=σn・Nn・En・Fn...(2)
where En is the efficiency of ionization of the gas by radiation, and Fn is the efficiency of the detector.

The sensitivity coefficient SCF is obtained from the equations (1) and (2) using the following equation (3).
SCF=Cn ₀ /Cr ₀
=(σn・Nn・En・Fn)/(λr・Nr・Er・Fr)
= (σn・En・Fn)/(λr・Er・Fr)・(Nn/Nr)
=A・NNR...(3)
Where:
A=(σn・Nn・En・Fn)/(λr・Nr・Er・Fr)
where A is a constant depending on the nuclear constant, the efficiency of the detector, etc.
Moreover, NNR is the calculation result in the existence ratio calculation unit 53a stored in the calculation result storage unit 52d.

The sensitivity coefficient SCF calculated by the sensitivity coefficient calculation unit 53b is stored in the sensitivity coefficient storage unit 52f.

The sensitivity calculation unit 53c calculates the neutron detection sensitivity of the neutron detector 10 based on the sensitivity coefficient SCF. The sensitivity calculation unit 53c first calculates a counting rate Cr by subtracting the value stored in the second counting memory unit 52c from the value obtained when the neutron detector 10 is calibrated and stored in the first counting memory unit 52b. Next, the sensitivity calculation unit 53c calculates the sensitivity SC during the calibration using the counting rate Cr (cps) obtained when the neutron detector 10 is calibrated and the sensitivity coefficient SCF stored in the sensitivity coefficient memory unit 52f, using the following formula (4).
SC=SCF・Cr...(4)

Figure 7 is a flow diagram showing the procedure of the method for calibrating the sensitivity of a neutron detector according to the first embodiment. The method for calibrating the sensitivity of a neutron detector includes a calibration preparation step S10 in which the sensitivity coefficient SCF is calculated in advance, stored, and memorized, followed by a calibration step S20 in which calibration is performed when calibration is required.

In the calibration preparation step S10, first, the output of the neutron detector 10 in the zero power state of the reactor is measured (step S11). Specifically, the input unit 51 receives the first count value, which is stored in the first count memory unit 52b. At this stage, the amount of neutrons flowing from the outside into the neutron detector 10 can be almost ignored. Therefore, in the neutron detector 10, the count number Cr ₀ (cps) of the pulse current caused by the ionization of the internal gas 17 by radiation such as alpha rays from the radioactive isotope 14b of the neutron detector 10 itself is measured.

Next, the output of the neutron detector 10 in the power state of the reactor is measured (step S12). Specifically, the input unit 51 receives the value of the second count, which is stored in the second count memory unit 52c. That is, the sensitivity _Cn0 (cps/nv) due to the ionization of the internal gas 17 by the product of the nuclear reaction between the sensitive material 14a and neutrons is obtained.

Next, the sensitivity coefficient SCF is calculated (step S13). Specifically, the sensitivity coefficient calculation unit 53b calculates the sensitivity coefficient SCF by dividing the sensitivity _Cn0 (cps/nv) obtained in step S12 by the count number _Cr0 (cps) obtained in step S11. The calculated sensitivity coefficient SCF is stored in the sensitivity coefficient storage unit 52f.

Next, in the calibration step S20, the output of the neutron detector 10 is measured when the reactor is in a zero-power state (step S21). The specific content is the same as in step S11, and the number of counts Cr (cps) of the pulse current caused by the ionization of the internal gas 17 by radiation such as alpha rays from the radioactive source isotope 14b is measured.

Next, the output of the neutron detector 10 in the power state of the reactor is measured (step S22). The specific content is the same as in step S11, and the sensitivity Cn (cps/nv) due to the ionization of the internal gas 17 by the products of the nuclear reaction between the sensitive material 14a and neutrons is obtained.

Next, the sensitivity calculation unit 53c calculates the neutron detection sensitivity of the neutron detector 10 (step S23). That is, the sensitivity calculation unit 53c first calculates the counting rate Cr by subtracting the value stored in the second counting memory unit 52c from the value obtained when the neutron detector 10 is calibrated and stored in the first counting memory unit 52b. Next, the sensitivity calculation unit 53c calculates the sensitivity SC using the counting rate Cr (cps) obtained at the time of the calibration and the sensitivity coefficient SCF stored in the sensitivity coefficient memory unit 52f.

As described above, the neutron detector 10, neutron monitor 60, and neutron detector sensitivity calibration method of this embodiment make it possible to calibrate the sensitivity of the neutron detector 10 using radiation from the radioactive source isotope 14b built into the neutron detector 10.
Second Embodiment

The second embodiment is a variation of the first embodiment. Below, only the differences from the first embodiment will be described. In other respects, the present embodiment is similar to the first embodiment.

Figure 8 is a block diagram showing the configuration of the signal processing unit 40a of the neutron monitor 60 according to the second embodiment.

The signal processing unit 40a in this embodiment has a pulse-height distribution acquisition unit 45. The pulse-height distribution acquisition unit 45 is, for example, a pulse-height analyzer, and acquires the pulse-height distribution of the current pulse signal output from the preamplifier 30. The current pulse signal of interest may be the entire current pulse generated, or may be a current pulse signal at a predetermined sampling interval. The pulse-height distribution acquisition unit 45 outputs the pulse-height distribution as a digital value. It is preferable that the channel number of the pulse-height distribution, i.e., the standard of the energy level, corresponds to or is the same as the standard of the channel number of the pulse-height distribution data stored in the pulse-height distribution database 52h described later.

Figure 9 is a block diagram showing the configuration of the computing device 50a of the neutron monitor 60 according to the second embodiment.

In the calculation device 50a, the memory unit 52 includes a wave height data memory unit 52g and a wave height distribution database 52h, and the calculation unit 53 further includes a wave height distribution evaluation unit 53d.

The wave height data storage unit 52g stores the output from the wave height distribution acquisition unit 45 of the signal processing unit 40a. The wave height data storage unit 52g stores wave height distribution data for a predetermined time width and updates it sequentially. The predetermined time width may be, for example, the time width (500 seconds in FIG. 10) for the wave height distribution data stored in the wave height distribution database 52h described later.

The wave height distribution database 52h stores wave height distribution data under normal conditions.

Fig. 10 is a graph showing an example of pulse height distribution of the output current of a nuclear fission counter. The horizontal axis is pulse height (channel number), and the vertical axis is count rate, which is counts every 10 minutes in this example. The applied voltage and the temperature of the internal gas are parameters. The example of Fig. 10 shows a case where the distance d between the electrodes is 1 mm, the pressure of the internal gas is 4 atm (4 x 0.101325 MPa), and the neutron flux φn is 550 (n/ ^cm2 sec).

The pulse-height distribution database 52h stores pulse-height distribution data under normal conditions for the distance d between the electrodes in the neutron detector 10 and the voltage applied by the DC power supply 21. The distance d between the electrodes is the distance between the surface of the anode 12 and the inner surface of the cathode 13. The database also has functions for interpolating and extrapolating the values of parameters, with the pressure of the internal gas 17 and the voltage V applied by the DC power supply 21 as parameters. The data stored in the pulse-height distribution database 52h may be data obtained by detailed calculations, or may be data measured under normal conditions.

The pulse-height distribution evaluation unit 53d of the calculation unit 53 reads out the reference pulse-height distribution corresponding to the above-mentioned parameter conditions for the neutron detector 10 from the pulse-height distribution database 52h. The pulse-height distribution evaluation unit 53d further compares the pulse-height distribution of the target current pulse stored in the pulse-height data storage unit 52g with the reference pulse-height distribution.

For example, the comparison involves calculating the ratio between the counts of the target wave-height distribution and the counts of the reference wave-height distribution for each corresponding channel number, and determining that an abnormality has occurred if the variance or standard deviation of the distribution of the ratios for each channel exceeds a predetermined value.

In the above explanation, data was collected and evaluated in the form of wave height distribution, but this is not limited to the above. Since wave height distribution also corresponds to a waveform, data may be collected and evaluated in the form of, for example, the change in wave height over time, i.e., the waveform itself. In this case, the reference database will also be stored in the form of a waveform.

According to Paschen's law, the discharge inception voltage depends on the product of the internal gas pressure and the distance between the electrodes for each type of internal gas. Therefore, if this condition is met, the discharge will continue stably and will show normal pulse height distribution and waveform. Conversely, if this condition is not met, the pulse height distribution and waveform will deviate from the normal distribution, and it can be determined that at least one of the internal gas pressure, the distance d between the electrodes, and the applied voltage V is abnormal. If the applied voltage V is normal, it can be determined that the neutron detector 10 itself is not in a normal state.

As described above, according to this embodiment, it is possible to determine whether the neutron detector 10 is in a normal state.

[Third embodiment]
The third embodiment is a modification of the first embodiment. Only the differences from the first embodiment will be described below. The present embodiment is otherwise similar to the first embodiment.

Figure 11 is a block diagram showing the configuration of a calculation device 50b of a neutron monitor 60 according to the third embodiment. The calculation device 50b in this embodiment further includes a radioactivity ratio calculation unit 53f.

The radioactivity ratio calculation unit 53f calculates the ratio RR between the radioactivity Rn of the sensitive substance 14a and the radioactivity Rr of the radioactive source isotope 14b.

As described in the first embodiment, the sensitivity coefficient calculation unit 53b calculates the sensitivity coefficient SCF from the equations (1) and (2) as shown in the following equation (3).
SCF=Cn ₀ /Cr ₀
=(σn・Nn・En・Fn)/(λr・Nr・Er・Fr)
= (σn・En・Fn)/(λr・Er・Fr)・(Nn/Nr)
...(3)

Here, equation (3) can be rewritten as follows:
SCF=(Rn/Rr)・(Nn/Nr)=RR・NNR...(5)
Here, NNR is the abundance ratio of the sensitive substance 14a to the radioisotope 14b calculated by the abundance ratio calculation unit 53a.

The sensitivity coefficient SCF calculated by the sensitivity coefficient calculation unit 53b is stored in the sensitivity coefficient storage unit 52f.

The sensitivity calculation unit 53c calculates the neutron detection sensitivity of the neutron detector 10 based on the sensitivity coefficient SCF. As in the first embodiment, the sensitivity calculation unit 53c first calculates a counting rate Cr by subtracting the value stored in the second counting memory unit 52c from the value obtained when the neutron detector 10 is calibrated and stored in the first counting memory unit 52b. Next, the sensitivity calculation unit 53c calculates the sensitivity SC during the calibration using the counting rate Cr (cps) obtained when the neutron detector 10 is calibrated and the sensitivity coefficient SCF stored in the sensitivity coefficient memory unit 52f, using the following formula (6).
SC=SCF・Cr...(6)

As described above, in this embodiment, the sensitivity SC can be calculated from the abundance ratio NNR calculated by the abundance ratio calculation unit 53a and the radioactivity ratio RR calculated by the radioactivity ratio calculation unit 53f.

The above-described embodiment makes it possible to provide a sensitivity calibration method for neutron detectors and radiation detectors that can calibrate themselves without relying on an external neutron source or heat balance calculations.

Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. In addition, the features of each of the second and third embodiments may be combined. These new embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents as set forth in the claims.

10...Neutron detector, 11...Housing, 11a...Side, 12...Anode, 12a, 12b...End, 13...Cathode, 14...Cathode side material, 14a...Sensitive material, 14b...Radiation source isotope, 15a, 15b...Insulator, 16...Metal/ceramic part, 17...Internal gas, 18...Coaxial cable, 18a...Internal conductor, 18b...Outer conductor, 20...Detector circuit, 21...DC power supply, 22...Ammeter, 23...Coaxial cable, 24...Grounding part, 30...Front A positional amplifier, 40...signal processing unit, 41...first wave height discriminator, 42...first counter, 43...second wave height discriminator, 44...second counter, 50...arithmetic unit, 51...input unit, 52...storage unit, 52a...detector information storage unit, 52b...first counting memory unit, 52c...second counting memory unit, 53...arithmetic unit, 53a...sensitivity coefficient calculation unit, 53b...abundance ratio calculation unit, 53c...radioactivity ratio calculation unit, 53d...sensitivity calculation unit, 54...output unit, 60...neutron monitor

Claims (1)

measuring a first warm-up output of the neutron detector at a zero power state of the nuclear reactor;
measuring a second output of the neutron detector during preparation at a power state of the reactor;
calculating a sensitivity coefficient from the preparation-time first output and the preparation-time second output;
A preparation step comprising:
measuring a first output during calibration of the neutron detector at a zero power state of the reactor;
measuring a second output during calibration of the neutron detector at a power state of the reactor;
calculating a sensitivity from the first proofread output and the second proofread output;
a review step having
A method for calibrating the sensitivity of a neutron detector, comprising:

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