Neutron poison detection method and device based on D-D neutron source

Abstract

The invention discloses a neutron poison detection method and device based on a D-D neutron source. A neutron poison detection method based on a D-D neutron source comprises the steps that D-D fast neutrons are moderated into thermal neutrons through a neutron moderator, a sample channel is arranged in the neutron moderator, a thermal neutron detector and a neutron stability monitor are arranged, 10B neutrons penetrating through a sample are detected, the relation between the neutron transmissivity and the 10B content is established, and the content of the 10B neutrons is determined according to the relation between the neutron transmissivity and the 10B content. And calculating to obtain the neutron poison content and the spatial distribution uniformity. According to the method, at least five samples with different B mass fractions are arranged, and the mass fraction of B in the samples is 0.2%-10%. The method provided by the invention is a non-destructive nondestructive detection technology, and does not cause damage to the pellet or the sample. The detection method is high in detection efficiency and high in detection result accuracy, and neutron poison with the mass percent smaller than or equal to 0.5 wt% can be detected.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear fuel detection, and in particular, relates to a neutron poison detection method and device based on a DD neutron source. Background Art

[0002] With the development of nuclear power and nuclear power technology, higher requirements are put forward for the operating life and safety of fuel elements. The doping content and spatial distribution uniformity of neutron poisons in fuel elements directly affect the efficiency and safety of the reactor. It is very important to strictly control the uniform distribution of poisons in nuclear fuel elements. At present, the main methods for detecting the content and uniformity of neutron poisons in fuel elements are quantitative metallography, X-ray fluorescence spectroscopy, thermal ionization mass spectrometry, etc. These methods are all destructive analysis methods, and the detection process is complicated and the detection speed is slow, which cannot meet the requirements of nuclear fuel element production. Therefore, the present invention proposes a neutron poison detection method and device based on a DD neutron source, which is used for non-destructive detection of the content and uniformity of neutron poisons in fuel elements. Summary of the invention

[0003] The purpose of the present invention is to provide a neutron poisoning detection method and device based on a DD neutron source, aiming to solve the problem of detecting the neutron poisoning content and spatial distribution uniformity of fuel elements, establish a method for detecting the neutron poisoning content and spatial distribution uniformity of fuel elements based on a DD neutron source, provide a reliable detection method for online rapid detection of neutron poisoning in nuclear fuel pellets, and ensure the manufacturing quality of fuel elements and the safety of reactor operation.

[0004] The present invention provides a neutron poisoning detection method based on a DD neutron source, wherein DD fast neutrons are slowed down into thermal neutrons by a neutron moderator, wherein a channel for a sample is provided in the neutron moderator, and a thermal neutron detector and a neutron stability monitor are provided to detect the neutron poisoning through the sample. 10 B's neutrons are detected to establish the neutron transmittance and 10 B content, and calculate the neutron poison content and spatial distribution uniformity. 10 B content refers to the mass fraction of B in the poison sample.

[0005] Optionally, the present invention provides at least 5 samples with different mass fractions of B, and the mass fraction of B in the samples is 0.2%-10%.

[0006] Optionally, the normalized count rate is obtained by comparing the neutron count of the thermal neutron detector with the neutron count of the neutron stability monitor, and the neutron transmittance is obtained by comparing the normalized count rate of the sample with the normalized count rate of a blank.

[0007] Optionally, the neutron source is a compact DD neutron source that produces neutrons with an energy of 2.45 MeV.

[0008] Optionally, the material of the neutron moderator is polyethylene.

[0009] Optionally, a neutron absorber is arranged on the outside of the neutron moderator, and the material is boron-containing polyethylene.

[0010] Optionally, after moderation, the average neutron flux in the neutron moderator is greater than 10 5 n / (cm 2 ·s), wherein the amount of thermal neutrons accounts for no less than 75% of the total neutron fluence.

[0011] Optionally, the thermal neutron detector is a He-3 neutron detector, and the neutron stability monitor is a liquid scintillator detector.

[0012] The present invention also provides a neutron poisoning detection device based on a DD neutron source, which includes any device involved in the above-mentioned neutron poisoning detection method based on a DD neutron source, the channel for the sample is provided in the neutron moderator, and the thermal neutron detector and the neutron stability monitor are provided.

[0013] Optionally, the thermal neutron detector is disposed above the moderator and the sample.

[0014] The present invention is a non-destructive non-destructive testing technology and will not cause damage to the core block or the sample.

[0015] The detection method of the present invention has high detection efficiency and high detection result accuracy, and can detect neutron poisoning with a mass percentage of ≤0.5wt%. The relative detection accuracy of the mass percentage of neutron poisoning is ≤5%, which can meet the needs of batch detection on production lines and has good application prospects.

[0016] The detection device of the present invention is aimed at 10 B is a special detection device designed for the absorption characteristics of thermal neutrons. It creatively detects samples with different poison contents and has high detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the structure of the detection device of Example 3, wherein 1 is a thermal neutron detector, 2 is a sample, 3 is a neutron moderator, 4 is a DD neutron source, and 5 is a shield.

[0018] Figure 2 Schematic diagram of the moderator and absorber structure of Example 3, 6 is the detector channel, 7 is the sample channel, 8 is the boron-containing polyethylene absorber, and 9 is the neutron source channel. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but cannot be understood as limiting the present invention.

[0020] A neutron poisoning detection method based on a DD neutron source, wherein DD fast neutrons are slowed down into thermal neutrons by a neutron moderator, and the average neutron flux in the transmission channel of the neutron moderator is greater than 10 5 n / (cm 2 ·s), where the number of thermal neutrons accounts for no less than 75% of the total neutron injection. A channel for the sample is provided in the neutron moderator, and a He-3 neutron detector and a liquid scintillator detector are provided to detect the neutrons passing through the sample. 10 Neutrons from B are detected. Neutron poison 10 B has a large absorption cross section for thermal neutrons. Under the condition of a certain neutron source intensity, the intensity of transmitted thermal neutrons is similar to that of the poison rod. 10 The content of B shows a specific corresponding relationship. The normalized count rate is obtained by comparing the neutron count of the thermal neutron detector with the neutron count of the neutron stability monitor, and the neutron transmittance is obtained by comparing the normalized count rate of the sample with the normalized count rate of the blank. 10 B content, and calculate the neutron poison content and spatial distribution uniformity.

[0021] The He-3 neutron detector detects neutrons using the nuclear reaction method. When neutrons enter the sensitive volume of the detector, they will react with the 3 He reacts as follows: .

[0022] Transmitting thermal neutrons into the sensitive area, 3 He interacts with each other to produce p and t particles, and neutron detection is achieved by collecting the signals formed by the p and t particles in a gas-type counter tube.

[0023] The present invention sets at least 5 samples with different mass fractions of B, and can also set more than 5 samples. Less than 5 samples will lead to inaccurate fitting results. The size and size of each sample are the same, and the mass fraction of B in the sample is 0.2%-10%.

[0024] The DD fast neutron source is a compact DD neutron source that produces neutrons with an energy of 2.45 MeV.

[0025] Example 1 In this embodiment, a fuel poison pellet of Φ10.2 mm×33 mm is used as the detection object, and 6 B4C—Zr-2 samples with different B mass fractions are set. The B mass fractions of the pellet samples are shown in Table 1.

[0026] The neutron poisoning detection method based on DD neutron source slows down DD fast neutrons into thermal neutrons through neutron moderators. The average neutron flux in the transmission channel of the neutron moderator is 9.98×10 5 n / (cm 2 ·s), of which the number of thermal neutrons accounts for 88% of the total neutron flux. Set up He-3 neutron detectors and liquid scintillator detectors to detect the neutrons that pass through the sample. 10 B's neutrons are detected. 10 B abundance is the natural abundance, and the test results are shown in Table 1.

[0027] Table 1

[0028] The normalized count rate is obtained by comparing the neutron count of the thermal neutron detector with the neutron count of the neutron stability monitor, and the neutron transmittance is obtained by comparing the normalized count rate of the sample with the normalized count rate of the blank. 10 Relationship between B content: y=0.81+0.182e -x / 1.24 , where y is the neutron transmittance and x is the neutron poison 10 B content (%).

[0029] Substituting x=0.5 into the relationship, the neutron transmittance of the sample with a mass fraction of 0.5% B is 0.932. The neutron transmittance of the poison pellet with a mass fraction of 0.5% B is 0.933 through experimental testing. Substituting y=0.933 into the relationship, the neutron poison content of the test sample is 0.486%, with a relative error of less than 5%.

[0030] Example 2 In this example, four B4C-Zr-2 poison cores with a designed B mass fraction content of 0.5% were used for testing to obtain the spatial distribution uniformity of the neutron poison content in the sample. The size of the sample was Φ10.2 mm×33 mm.

[0031] The neutron transmittance of the sample obtained by the test is shown in Table 2. The neutron transmittance established by Example 1 is 10 The mass fraction of sample B is obtained in relation to the content of B as shown in Table 2, which reflects the spatial distribution uniformity of the mass fraction of B. It can be concluded from Table 2 that this method can obtain the spatial distribution of the poison content of the entire poison sample in the axial direction.

[0032] Table 2

[0033] Example 3 A neutron poisoning detection device based on a DD neutron source, such as Figure 1 As shown, the neutron moderator 3 is placed above the DD neutron source 4. A channel for the sample 2 is provided in the neutron moderator 3, and a thermal neutron detector 1 and a neutron stability monitor are provided. The thermal neutron detector 1 is provided above the sample 2. The thermal neutron detector is a He-3 neutron detector with a diameter of 21 mm. The detection efficiency of the He-3 neutron detector for 0.0253 eV thermal neutrons is about 90%. The material of the neutron moderator 3 is polyethylene with a thickness of 110 mm. The structure of the neutron moderator and the absorber is shown in FIG. Figure 2 As shown, it is mainly composed of a boron-containing polyethylene absorber 8 and a neutron moderator 3. The boron-containing polyethylene absorber 8 is 50 mm thick and mainly plays the role of absorbing and shielding neutrons. The moderator is reserved with a detector channel 6, a sample channel 7 and a neutron source channel 9. The diameter of the sample channel 7 is not less than Φ24 mm, and can accommodate poison core blocks and poison rod samples with a diameter of less than Φ24 mm.

[0034] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A neutron poisoning detection method based on a DD neutron source, characterized in that: The DD fast neutrons are moderated into thermal neutrons by a neutron moderator, wherein a channel for the sample is provided in the neutron moderator, and a thermal neutron detector and a neutron stability monitor are provided to monitor the neutrons passing through the sample. 10 B's neutrons are detected to establish the neutron transmittance and 10 B content, and calculate the neutron poison content and spatial distribution uniformity.

2. The neutron poisoning detection method based on DD neutron source according to claim 1, characterized in that: At least 5 samples with different B contents are provided, and the mass fraction of B in the samples is 0.2%-10%.

3. The neutron poisoning detection method based on DD neutron source according to claim 1, characterized in that: The normalized count rate is obtained by comparing the neutron count of the thermal neutron detector with the neutron count of the neutron stability monitor, and the neutron transmittance is obtained by comparing the normalized count rate of the sample with the normalized count rate of a blank.

4. The neutron poisoning detection method based on DD neutron source according to claim 1, characterized in that: The neutron source is a compact DD neutron source, which produces neutrons with an energy of 2.45 MeV.

5. The neutron poisoning detection method based on DD neutron source according to claim 1, characterized in that: The material of the neutron moderator is polyethylene.

6. The neutron poisoning detection method based on DD neutron source according to claim 1, characterized in that: A neutron absorber is arranged outside the neutron moderator, and the material is boron-containing polyethylene.

7. The neutron poisoning detection method based on DD neutron source according to claim 1, characterized in that: After moderation, the average neutron flux in the neutron moderator is greater than 10 5 n / (cm 2 ·s), wherein the amount of thermal neutrons accounts for no less than 75% of the total neutron fluence.

8. The neutron poisoning detection method based on DD neutron source according to claim 1, characterized in that: The thermal neutron detector is a He-3 neutron detector, and the neutron stability monitor is a liquid scintillator detector.

9. A neutron poisoning detection device based on a DD neutron source, characterized in that: It comprises the device involved in the neutron poisoning detection method based on DD neutron source as described in any one of claims 1-8, the channel for the sample is arranged in the neutron moderator, and the thermal neutron detector and the neutron stability monitor are arranged.

10. The neutron poisoning detection device based on DD neutron source according to claim 9, characterized in that: The thermal neutron detector is arranged above the moderator and the sample.

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