CN115938625A - In-reactor neutron monitoring method for first-time loading of nuclear reactor under strong gamma field - Google Patents

In-reactor neutron monitoring method for first-time loading of nuclear reactor under strong gamma field Download PDF

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CN115938625A
CN115938625A CN202211533741.7A CN202211533741A CN115938625A CN 115938625 A CN115938625 A CN 115938625A CN 202211533741 A CN202211533741 A CN 202211533741A CN 115938625 A CN115938625 A CN 115938625A
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boron
neutron
threshold voltage
discrimination threshold
coated
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何洋
程雄伟
罗良伟
何高魁
刘洋
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Liaoning Hongyanhe Nuclear Power Co Ltd
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Liaoning Hongyanhe Nuclear Power Co Ltd
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Abstract

The invention discloses an in-reactor neutron monitoring method used in the first loading process of a nuclear reactor under a strong gamma field, which comprises the following steps: respectively placing the boron-coated proportional counter tube assemblies at different positions in the reactor core; selecting a secondary neutron source assembly to be arranged in the reactor core at a position close to the boron-coated proportional counter tube assembly; performing neutron and gamma signal response test to obtain a response curve of the boron-coated proportional counter tube assembly, setting a lowest discrimination threshold voltage value according to the response curve of the boron-coated proportional counter tube assembly, gradually increasing the discrimination threshold voltage based on the lowest discrimination threshold voltage value, recording the counting rate of the boron-coated proportional counter tube assembly to obtain a discrimination threshold voltage-counting rate curve, and finally determining the final discrimination threshold voltage according to the discrimination threshold voltage-counting rate curve; and (4) carrying out the first loading of the nuclear reactor, and carrying out in-reactor neutron monitoring by the boron-coated proportional counter tube assembly according to the final discrimination threshold voltage.

Description

In-reactor neutron monitoring method for first-time loading of nuclear reactor under strong gamma field
Technical Field
The invention relates to the technical field of nuclear power, in particular to in-reactor neutron monitoring of the first-time loading of a nuclear reactor under a strong gamma field.
Background
In the process of loading and starting of reactorIn the process, in order to ensure critical safety, the whole process should be under effective supervision of the neutron detector. To overcome the detection blind zone, nuclear power plants generally use two neutron sources: primary neutron source ( 252 Cf) and two groups of secondary neutron sources (Sb-Be) for nuclear reactor startup neutron monitoring. Wherein a primary neutron source is used in the first charge, which does not emit gamma rays per se, and is therefore generally used 3 The He proportional counter tube is used as an in-pile neutron monitoring device for first charging; and the secondary neutron source is activated in the first cycle for the charging start of the subsequent cycle reactor. Practice has shown that it is feasible to use a secondary neutron source activated in advance for the first charging of a nuclear reactor, which can be accomplished to some extent without the primary neutron source being available. However, the secondary neutron source has gamma background, an in-pile monitoring method is needed to eliminate gamma background interference under the condition, and activated secondary neutron source charging can be used in the first cycle of certain experimental pile projects, so that similar problems exist at the moment.
Disclosure of Invention
The invention aims to provide a method for monitoring in-core neutrons of a nuclear reactor during first-time loading under a strong gamma field, which is used for monitoring in-core neutrons of the nuclear reactor during first-time loading under the strong gamma field and eliminating gamma ray interference.
In order to achieve the above object, an embodiment of the present invention provides a method for monitoring in-core neutrons during first-time charging of a nuclear reactor under a strong gamma field, the method including:
respectively placing one or more boron-coated proportional counter tube assemblies at different positions in a reactor core;
selecting a secondary neutron source assembly to be arranged in the position, close to any boron-coated proportional counting tube assembly, in the reactor core;
performing neutron and gamma signal response test to obtain a response curve of any one boron-coated proportional counter tube assembly, setting the lowest discrimination threshold voltage value of any one boron-coated proportional counter tube assembly according to the response curve of any one boron-coated proportional counter tube assembly, gradually increasing the discrimination threshold voltage based on the lowest discrimination threshold voltage value, recording the count rate of the boron-coated proportional counter tube assembly to obtain a discrimination threshold voltage-count rate curve, and finally determining the final discrimination threshold voltage according to the discrimination threshold voltage-count rate curve;
and carrying out nuclear reactor first charging, and carrying out in-reactor neutron monitoring on the one or more boron-coated proportional counter tube assemblies according to the final discrimination threshold voltage.
Preferably, the secondary neutron source assembly adopts an Sb-Be neutron source.
Preferably, the first boron-coated proportional counter tube assembly, the second boron-coated proportional counter tube assembly and the third boron-coated proportional counter tube assembly comprise boron-coated proportional counter tubes, preamplifiers, main amplifiers, discriminators and scalers, the boron-coated proportional counter tubes are used for detecting neutron and gamma signals and sending the detected neutron and gamma signals to the preamplifiers; the preamplifier is used for carrying out primary amplification on the received neutron and gamma signals and then sending the signals to the main amplifier, and the main amplifier is used for carrying out secondary amplification on the received neutron and gamma signals and then sending the signals to the discriminator; the discriminator is used for filtering gamma signals in the received neutrons and gamma signals according to a set discrimination threshold voltage to obtain neutron signals; the scaler is used for reading and displaying the neutron signal output by the discriminator.
The embodiment of the invention has the following beneficial effects:
the embodiment of the invention utilizes the boron-coated proportional counter tube assembly to realize in-core neutron monitoring of the first charging of the nuclear reactor under a strong gamma field, and the method can reasonably set the discrimination threshold voltage of the boron-coated proportional counter tube assembly and effectively eliminate the gamma signal detected by the boron-coated proportional counter tube, thereby further ensuring that the first charging of the nuclear reactor can be still finished under the condition that a primary neutron source is unavailable.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is within the scope of the present invention for those skilled in the art to obtain other drawings based on the drawings without inventive exercise.
FIG. 1 is a flow chart of a method for monitoring in-core neutrons during a first loading process of a nuclear reactor in a strong gamma field according to an embodiment of the present invention;
FIG. 2 is an exemplary illustration of an in-core detector placement and response test for an in-core neutron monitoring method during initial loading of a nuclear reactor in an embodiment of the present invention under a high gamma field;
FIG. 3 is a view showing an in-core neutron monitoring device (C) during the first charging of a nuclear reactor in the prior art 3 He proportional counter tube);
FIG. 4 is an example of detector signals for an in-core neutron monitoring method during the first loading of a nuclear reactor in a high gamma field in an embodiment of the present invention;
fig. 5 is a discrimination threshold-count rate curve of a method for monitoring in-core neutrons during a first loading process of a nuclear reactor under a strong gamma field according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.
Referring to fig. 1, an embodiment of the present invention provides a method for monitoring in-core neutrons during a first nuclear reactor loading under a strong gamma field, including the following steps:
s1, respectively placing one or more boron-coated proportional counter tube assemblies at different positions in a reactor core;
specifically, as shown in FIG. 2, 3 boron-coated proportional counter tube assemblies may be included; three boron-coated proportional counter tube assemblies are respectively arranged at the positions B05, B11 and P11 in the reactor core shown in FIG. 2;
s2, selecting a secondary neutron source assembly to be arranged at a position close to any boron-coated proportional counter tube assembly in the reactor core;
specifically, a secondary neutron source assembly inserted into a new fuel assembly is placed in the in-core D05 position shown in fig. 2;
s3, performing neutron and gamma signal response test to obtain a response curve of any one boron-coated proportional counting tube assembly, setting the lowest discrimination threshold voltage value of any one boron-coated proportional counting tube assembly according to the response curve of any one boron-coated proportional counting tube assembly, gradually increasing the discrimination threshold voltage based on the lowest discrimination threshold voltage value, recording the counting rate of the boron-coated proportional counting tube assembly to obtain a discrimination threshold voltage-counting rate curve, and finally determining the final discrimination threshold voltage according to the discrimination threshold voltage-counting rate curve;
specifically, two types of detectors are listed, which have the following reaction equations for neutrons with boron-10 and helium-3:
Figure BDA0003976779780000041
n+ 3 He→ 1 H+ 3 H+765keV
the two types of detectors work on a similar principle, i.e. thermal neutrons and target nuclei: ( 10 B or 3 He) reaction to generate charged particles with certain energy, the charged particles ionize the working gas, the generated ion pairs generate pulse signals under the action of high voltage, and the pulse signals are processed to obtain the counting rate of neutrons; neutron and neutron 10 The reaction energy of the reaction of B is about 2.8Mev, which is greater than that of the reaction with B 3 He reaction energy of 0.756Mev, and corresponding ionization pulse signal amplitude greater than 3 He counts the pulse amplitude in the tube; the gamma rays entering the detector can also ionize the working gas, the amplitude of the generated pulse is small, the gamma signals can be filtered by a method of properly setting a discrimination threshold, and only neutron signals with high amplitude are reserved; however, under a strong gamma field, the gamma pulse can be stacked and superposed to form a high pulse, and further generates interference with the neutron pulse; because the amplitude of a neutron pulse signal in the boron-coated proportional counting tube is larger, the gamma accumulation pulse discrimination capability is stronger; among the common neutron detectors, the boron-coated proportional counter tube has the strongest gamma interference resistance, and BF 3 The number of the counting tubes is proportional to the number of the counting tubes, 3 he proportional counter tube worst;
therefore, in the embodiment, the proportional counter tube made of boron-containing material is selected for in-reactor neutron detection, and compared with the proportional counter tube coated with boron, the neutron signal amplitude ratio BF of the proportional counter tube coated with boron is larger 3 The proportional counter tube is small and cannot detect the full energy peak, but the signal amplitude is still in proportion to 3 The He proportional counter tube is large, the gamma interference resistance is high, and the performance is stable, so that the method eliminates the strong gamma ray interference in the first loading process of the nuclear reactor by using the boron-coated proportional counter tube.
Further, in this embodiment, an oscilloscope is used to record a response curve of the DET-B boron-coated proportional counter, and detected neutron and gamma signals are divided into two paths, one path enters the oscilloscope, and the other path enters the discriminator; a more pronounced difference between the background signal and the neutron signal can be seen in fig. 4 compared to fig. 3; setting a lowest discrimination threshold voltage value according to a background signal amplitude value displayed in a response curve, taking fig. 4 as an example, the lowest discrimination threshold voltage value is about 2.8V, and fig. 4 shows a front signal of a main amplifier, and the amplitude value of the front signal of the main amplifier and the amplitude value of a rear signal of the main amplifier are in a 10-fold relationship in the embodiment; on the basis of the lowest value of the discrimination threshold voltage, reading the counting rate of the detector in a period of time through a scaler, then gradually increasing the discrimination threshold voltage and reading the corresponding counting rate, and drawing a discrimination threshold voltage-counting rate curve, as shown in fig. 5; according to a response curve of the boron-coated proportional counter tube assembly recorded by an oscilloscope and a discrimination threshold voltage-counting rate curve, requirements of signal-to-noise ratio and lowest counting rate are comprehensively considered to determine the discrimination threshold voltage, the discrimination threshold voltage is finally selected to be 3V, gamma signals are filtered, and only neutron signals with higher amplitude are left.
Further, placing secondary neutron source components inserted into the new fuel components at positions D11 and M11 in the reactor core shown in FIG. 2, repeating the operation of the step S3, comparing whether the characteristics of the 3 boron-coated proportional counter tube components have obvious differences according to the response test result, and if the characteristics of the 3 boron-coated proportional counter tube components have no obvious differences, setting corresponding discrimination threshold voltages for the 3 boron-coated proportional counter tube components, namely selecting the discrimination threshold voltage to be 3V; it should be noted that, because there is a certain difference in the manufacturing process of different boron-coated proportional counter tube assemblies, the difference of the characteristics of 3 boron-coated proportional counter tube assemblies is normal as long as it is within a reasonable range, and then the first charging operation is completed according to the specified charging steps; if the difference of the characteristics of the 3 boron-coated proportional counter tube assemblies is too large, the boron-coated proportional counter tube assemblies are abnormal, the situation that the three boron-coated proportional counter tube assemblies possibly have faults or inaccurate detection results is indicated, the boron-coated proportional counter tube assemblies need to be replaced, and the steps are repeated;
and S4, carrying out nuclear reactor first charging, and carrying out in-reactor neutron monitoring on the one or more boron-coated proportional counter tube assemblies according to the final discrimination threshold voltage.
Preferably, the secondary neutron source assembly employs an Sb-Be neutron source.
Specifically, in order to enable the detector to obtain the lowest neutron counting rate to achieve the purpose of in-pile monitoring, an additional neutron source is required to reach certain intensity; therefore, in the embodiment, the Sb-Be neutron source is used as a neutron source for charge monitoring, and the charge can meet the requirement of the detector for the lowest counting rate within 5 half-lives (about 300 days) after the saturated source stops irradiation. Because the neutron and gamma signal intensities are different under different signal source intensities, the signal discrimination test before charging is beneficial to obtaining the optimal thermal neutron sensitivity.
Preferably, the first boron-coated proportional counter tube assembly, the second boron-coated proportional counter tube assembly and the third boron-coated proportional counter tube assembly comprise boron-coated proportional counter tubes, preamplifiers, main amplifiers, discriminators and scalers, the boron-coated proportional counter tubes are used for detecting neutron and gamma signals and sending the detected neutron and gamma signals to the preamplifiers; the preamplifier is used for carrying out primary amplification on the received neutron and gamma signals and then sending the signals to the main amplifier, and the main amplifier is used for carrying out secondary amplification on the received neutron and gamma signals and then sending the signals to the discriminator; the discriminator is used for filtering gamma signals in the received neutrons and gamma signals according to a set discrimination threshold voltage to obtain neutron signals; the scaler is used for reading and displaying the neutron signal output by the discriminator.
The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention, and it is therefore to be understood that the invention is not limited by the scope of the appended claims.

Claims (3)

1. A method for in-core neutron monitoring of a first fill of a nuclear reactor in a high gamma field, the method comprising:
respectively placing one or more boron-coated proportional counter tube assemblies at different positions in a reactor core;
selecting a secondary neutron source assembly to be arranged in the position, close to any boron-coated proportional counter tube assembly, in the reactor core;
performing neutron and gamma signal response test to obtain a response curve of any one boron-coated proportional counting tube assembly, setting the lowest discrimination threshold voltage value of any one boron-coated proportional counting tube assembly according to the response curve of any one boron-coated proportional counting tube assembly, gradually increasing the discrimination threshold voltage based on the lowest discrimination threshold voltage value, recording the counting rate of the boron-coated proportional counting tube assembly to obtain a discrimination threshold voltage-counting rate curve, and finally determining the final discrimination threshold voltage according to the discrimination threshold voltage-counting rate curve;
and carrying out nuclear reactor first charging, and carrying out in-reactor neutron monitoring on the one or more boron-coated proportional counter tube assemblies according to the final discrimination threshold voltage.
2. The method for monitoring in-core neutrons of a nuclear reactor in initial loading under a strong gamma field as claimed in claim 1, wherein said secondary neutron source assembly employs a Sb-Be neutron source.
3. The method of monitoring in-core neutrons during a first nuclear reactor charge under a high gamma field of claim 1 wherein the first, second and third boron-coated proportional counter tube assemblies each include a boron-coated proportional counter tube, a preamplifier, a main amplifier, a discriminator and a scaler, the boron-coated proportional counter tube is configured to detect neutron and gamma signals and to transmit the detected neutron and gamma signals to the preamplifier; the preamplifier is used for carrying out primary amplification on the received neutron and gamma signals and then sending the signals to the main amplifier, and the main amplifier is used for carrying out secondary amplification on the received neutron and gamma signals and then sending the signals to the discriminator; the discriminator is used for filtering gamma signals in the received neutrons and gamma signals according to a set discrimination threshold voltage to obtain neutron signals; the scaler is used for reading and displaying the neutron signal output by the discriminator.
CN202211533741.7A 2022-12-02 2022-12-02 In-reactor neutron monitoring method for first-time loading of nuclear reactor under strong gamma field Pending CN115938625A (en)

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