An active detection method and system for nuclear fuel rods

Abstract

The present invention discloses an active detection method for nuclear fuel rods, including: obtaining the characteristic γ-ray counting curves before and after activation of the standard nuclear fuel rod pellets, and obtaining the characteristic γ-ray counting curves before and after activation of the nuclear fuel rod pellets to be tested; calculating the characteristic γ-ray counting curves before and after activation of the standard nuclear fuel rod pellets to obtain the final counting curve of the standard nuclear fuel rod, and calculating the characteristic γ-ray counting curves before and after activation of the nuclear fuel rod pellets to be tested to obtain the final counting curve of the nuclear fuel rod to be tested; calculating the pellet enrichment of the nuclear fuel rod to be tested, and determining whether the pellet enrichment of the nuclear fuel to be tested is qualified. The present invention also discloses an active detection system for nuclear fuel rods. The present invention can correct the pellet age of nuclear fuel rods, eliminate misjudgment caused by different pellet ages, extend the service life of <supgt;252< / supgt;Cf neutron sources or reduce the initial loading of <supgt;252< / supgt;Cf neutron sources, and reduce costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear engineering, and particularly relates to an active detection method and system for nuclear fuel rods. Background Art

[0002] A nuclear fuel rod is a unit for a reactor to release heat and is a core component of the reactor. When operating in a reactor, a nuclear fuel rod is in a strong neutron field, and is subject to the scouring of high-temperature, high-pressure, and high-flow-rate coolant, as well as the chemical action of fissile materials, complex mechanical loads, and steam corrosion. The working conditions are extremely harsh. When the manufacturing characteristics such as the enrichment of the inner pellets of a nuclear fuel rod are inconsistent with their designed values, it will cause the reactivity of the reactor core to deviate from the expectation, thereby increasing the control difficulty of the reactor and affecting the operation of the reactor. Therefore, after the nuclear fuel rod is assembled and before it is loaded into the fuel assembly, it is necessary to conduct a 100% enrichment inspection on all the pellets loaded inside.

[0003] Currently, an active detection device for nuclear fuel rods generally uses a 252 Cf neutron source with a mass of 0.3 - 1.2 mg to activate the nuclear fuel rod, and then uses 2 - 4 scintillation detectors with holes to detect the 235 γ-ray intensity emitted by the activation products of

[0004] Since 252 the half-life of 252 Cf is 2.7 years, the neutron yield of the equipment loaded with a 235 Cf neutron source with a mass of 1.2 mg will decrease and the activation ability will weaken after less than two half-lives (less than 5 years). At this time, the proportion of the γ-ray intensity spontaneously emitted by the inner pellet matrix of the nuclear fuel rod in the γ-ray intensity detected by the scintillation detector will increase and reach an identifiable level. However, the intensity of the γ-ray spontaneously emitted by pellets with the same enrichment is related to the time (pellet age) since the last chemical conversion of the pellets. As a result, the γ-ray intensity detected after activation of nuclear fuel rods loaded with pellets of the same enrichment but different ages will be inconsistent, thus causing the problem of misjudging a nuclear fuel rod with a qualified

[0005] When the neutron source decays to a mass less than 0.3 mg, a new 252 Cf neutron source needs to be loaded into the active detection device for nuclear fuel rods to avoid frequent misjudgments caused by different pellet ages. However, currently, 252C Cf neutron sources cannot be produced in China and need to be imported from Russia and the United States, which are expensive, resulting in high production costs for nuclear fuel rods. Summary of the Invention

[0006] In view of the above deficiencies in the prior art, the present invention provides a method and system for active detection of nuclear fuel rods, which can correct the pellet age of nuclear fuel rods, eliminate misjudgment caused by different pellet ages, and extend 252 the service life of the 252 Cf neutron source or reduce

[0007] the initial loading of the

[0008] Cf neutron source, thereby reducing costs.

[0009] Obtain the characteristic γ-ray counting curve before activation of the standard nuclear fuel rod pellets and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellets, and obtain the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellets to be measured and the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellets to be measured;

[0010] Calculate the characteristic γ-ray counting curve before activation of the standard nuclear fuel rod pellets and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellets to obtain the final counting curve of the standard nuclear fuel rod, and calculate the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellets to be measured and the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellets to be measured to obtain the final counting curve of the nuclear fuel rod to be measured;

[0011] Based on the final counting curve of the standard nuclear fuel rod and the final counting curve of the nuclear fuel rod to be measured, calculate the pellet abundance of the nuclear fuel rod to be measured, and determine whether the pellet abundance of the nuclear fuel to be measured is qualified.

[0012] Preferably, obtaining the characteristic γ-ray counting curve before activation of the standard nuclear fuel rod pellets and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellets specifically includes:

[0013] Collect the characteristic γ-ray characteristic information before activation of the standard nuclear fuel rod pellets detected by a single detector respectively to obtain a plurality of first counting curves;

[0014] Collect the characteristic γ-ray characteristic information after activation of the standard nuclear fuel rod pellets detected by a single detector respectively to obtain a plurality of second counting curves;

[0015] Shift and accumulate the plurality of first counting curves to obtain the characteristic γ-ray counting curve before activation of the standard nuclear fuel rod pellets;

[0016] Shift and accumulate the plurality of second counting curves to obtain the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellets.

[0017] Preferably, obtain the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the nuclear fuel pellet to be measured, specifically including:

[0018] Collect the characteristic γ-ray characteristic information of the nuclear fuel pellet to be measured before activation detected by a single detector respectively to obtain multiple third counting curves;

[0019] Collect the characteristic γ-ray characteristic information of the nuclear fuel pellet to be measured after activation detected by a single detector respectively to obtain multiple fourth counting curves;

[0020] Shift and accumulate the multiple third counting curves to obtain the characteristic γ-ray counting curve before activation of the nuclear fuel pellet to be measured;

[0021] Shift and accumulate the multiple fourth counting curves to obtain the characteristic γ-ray counting curve after activation of the nuclear fuel pellet to be measured.

[0022] Preferably, calculate the final counting curve of the standard nuclear fuel rod based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the standard nuclear fuel pellet, and calculate the final counting curve of the nuclear fuel rod to be measured based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the nuclear fuel pellet to be measured, specifically including:

[0023] Calculate the age correction coefficient based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the standard nuclear fuel pellet, or based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the nuclear fuel pellet to be measured;

[0024] Calculate the final counting curve of the standard nuclear fuel rod and the final counting curve of the nuclear fuel rod to be measured based on the age correction coefficient.

[0025] Preferably, calculate the age correction coefficient based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the standard nuclear fuel pellet, or based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the nuclear fuel pellet to be measured, specifically including:

[0026] Determine the corresponding head and tail of the standard / test nuclear fuel rod on the characteristic γ-ray counting curves before and after activation of the standard / test nuclear fuel rod pellet, and set the point corresponding to the head of the standard / test nuclear fuel rod on the characteristic γ-ray counting curve before activation of the standard / test nuclear fuel rod pellet as the starting point of the characteristic γ-ray counting curve before activation of the standard / test nuclear fuel rod pellet and set the point corresponding to the head of the standard / test nuclear fuel rod on the characteristic γ-ray counting curve after activation of the standard / test nuclear fuel rod pellet as the starting point of the characteristic γ-ray counting curve after activation of the standard / test nuclear fuel rod pellet;

[0027] Based on the count values at any two time points on the characteristic γ-ray counting curves before and after activation of the standard / test nuclear fuel rod pellet at the same position of the same standard / test nuclear fuel rod, calculate the age correction coefficient, and the calculation formula is as follows:

[0028] F=(C A1 -C A2 ) / (C B1 -C B2 )

[0029] In the formula, F is the age correction coefficient, C A1 is the count value at the first time point on the characteristic γ-ray counting curve after activation of the standard / test nuclear fuel rod pellet, C A2 is the count value at the second time on the characteristic γ-ray counting curve after activation of the standard / test nuclear fuel rod pellet, C B1 is the count value at the first time point on the characteristic γ-ray counting curve before activation of the standard / test nuclear fuel rod pellet, C B2 is the count value at the second time point on the characteristic γ-ray counting curve before activation of the standard / test nuclear fuel rod pellet.

[0030] Preferably, based on the age correction coefficient, obtain the final counting curve of the standard nuclear fuel rod and the final counting curve of the test nuclear fuel rod, specifically including:

[0031] Subtract the product of the count value at the same position of the standard / test nuclear fuel rod on the characteristic γ-ray counting curve before activation of the standard / test nuclear fuel rod pellet and the age correction coefficient from the count value at each position of the standard / test nuclear fuel rod on the characteristic γ-ray counting curve after activation of the standard / test nuclear fuel rod pellet, to obtain the final count value of the counting curve at each position on the standard / test nuclear fuel rod, where the calculation formula for the final count value of the counting curve is:

[0032] C F =C AA-F×C BA

[0033] wherein, C F is the final count value of the counting curve, C AA is the count value on the characteristic γ-ray counting curve after activation of the standard / test nuclear fuel rod pellet, C BA is the count value on the characteristic γ-ray counting curve before activation of the standard / test nuclear fuel rod pellet, and F is the age correction coefficient;

[0034] Based on the final count values of the counting curves at various positions of the standard / test nuclear fuel rod, the final counting curve of the standard nuclear fuel rod and the final counting curve of the test nuclear fuel rod are obtained respectively.

[0035] Preferably, based on the final counting curve of the standard nuclear fuel rod and the final counting curve of the test nuclear fuel rod, the pellet enrichment of the test nuclear fuel rod is calculated, which specifically includes:

[0036] Fitting the pellet enrichment values at different positions of the standard nuclear fuel rod with the final counting curve of the standard nuclear fuel rod to obtain the abundance-count relationship equation of the standard nuclear fuel rod;

[0037] Substituting each count value on the final counting curve of the test nuclear fuel rod into the abundance-count relationship equation of the standard nuclear fuel rod to obtain the abundance curve of the test nuclear fuel rod;

[0038] Based on the abundance curve of the test nuclear fuel rod, the pellet enrichment at different positions of the test nuclear fuel rod is obtained;

[0039] Comparing the pellet enrichment at different positions of the test nuclear fuel rod with the nuclear fuel rod detection technical indicators, and judging whether the pellet enrichment of the test fuel rod is qualified according to the comparison result.

[0040] According to another aspect of the present invention, a nuclear fuel rod active detection system is provided, including a neutron activation unit, a detection unit, and a data acquisition and processing unit, wherein:

[0041] The neutron activation unit is used to perform neutron activation on the nuclear fuel rod pellet;

[0042] The detection unit includes a first detector unit (8) and a second detector unit (3). The first detector unit is arranged at the inlet end of the neutron activation unit and is connected to the data acquisition and processing unit. It is used to detect the γ-ray characteristic information of the nuclear fuel rod pellet before activation, obtain a first signal, and transmit the first signal to the data acquisition and processing unit. The second detector unit is arranged at the outlet end of the neutron activation unit and is connected to the data acquisition and processing unit. It is used to detect the γ-ray characteristic information of the nuclear fuel rod pellet after activation, obtain a second signal, and transmit the second signal to the data acquisition and processing unit;

[0043] The data acquisition and processing unit is used to receive the first signal and the second signal, and determine the characteristic γ-ray counting curve of the nuclear fuel rod pellet before activation and the characteristic γ-ray counting curve of the nuclear fuel rod pellet after activation according to the first signal and the second signal. Moreover, it calculates the characteristic γ-ray counting curve of the nuclear fuel rod pellet before activation and the characteristic γ-ray counting curve of the nuclear fuel rod pellet after activation to obtain the final counting curve of the nuclear fuel rod, and calculates the pellet enrichment of the nuclear fuel rod based on the final counting curve, and judges whether the pellet enrichment of the nuclear fuel rod is qualified.

[0044] Preferably, the data acquisition and processing unit includes an acquisition module and a calculation module. The acquisition module includes a first pulse amplitude analyzer, a first data acquisition card, a second pulse amplitude analyzer, and a second data acquisition card, where:

[0045] The first pulse amplitude analyzer is connected to the first detector unit and is used to convert the first signal into a first square wave signal;

[0046] The first data acquisition card is respectively connected to the first pulse amplitude analyzer and the calculation module, and is used to acquire the first square wave signal converted in the first pulse amplitude analyzer, obtain the characteristic γ-ray counting curve of the nuclear fuel rod pellet before activation, and transmit the characteristic γ-ray counting curve of the nuclear fuel rod pellet before activation to the calculation module;

[0047] The second pulse amplitude analyzer is connected to the second detector unit and is used to convert the second signal into a second square wave signal;

[0048] The second data acquisition card is respectively connected to the second pulse amplitude analyzer and the calculation module, and is used to acquire the second square wave signal converted in the second pulse amplitude analyzer, obtain the characteristic γ-ray counting curve of the nuclear fuel rod pellet after activation, and transmit the characteristic γ-ray counting curve of the nuclear fuel rod pellet after activation to the calculation module;

[0049] The calculation module is preset with the technical index data of the nuclear fuel rod detection, which is used to calculate the characteristic γ-ray counting curve before the activation of the nuclear fuel rod pellet and the characteristic γ-ray counting curve after the activation of the nuclear fuel rod pellet, so as to obtain the final counting curve of the nuclear fuel rod, and calculate the pellet enrichment of the nuclear fuel rod based on the final counting curve, and compare the pellet enrichment of the nuclear fuel rod with the nuclear fuel rod detection technical index, and judge whether the pellet enrichment of the nuclear fuel rod is qualified according to the comparison result.

[0050] Preferably, the acquisition module further includes a first amplifier and a second amplifier, wherein:

[0051] The first amplifier is respectively connected to the first detector unit and the first pulse amplitude analyzer, and is used to amplify the first signal detected by the first detector unit and transmit it to the first pulse amplitude analyzer, and the first pulse amplitude analyzer then converts the amplified first signal into the first square wave signal;

[0052] The second amplifier is respectively connected to the second detector unit and the second pulse amplitude analyzer, and is used to amplify the second signal detected by the second detector unit and transmit it to the second pulse amplitude analyzer, and the second pulse amplitude analyzer then converts the amplified second signal into the second square wave signal.

[0053] Preferably, both the first pulse amplitude analyzer and the second pulse amplitude analyzer are one of a comparator, a single-channel pulse amplitude analyzer, and a multi-channel pulse amplitude analyzer. Among them, when the first pulse amplitude analyzer is a single-channel pulse amplitude analyzer, the lower threshold of the single-channel pulse amplitude analyzer is the signal generated by 250 keV γ-rays, and the upper threshold of the single-channel pulse amplitude analyzer is the signal generated by 1.1 MeV γ-rays;

[0054] When the second pulse amplitude analyzer is a single-channel pulse amplitude analyzer, the lower threshold of the single-channel pulse amplitude analyzer is the signal corresponding to the maximum noise of the second detector unit, and the upper threshold of the single-channel pulse amplitude analyzer is the signal generated by 2.5 MeV γ-rays;

[0055] The γ-ray energy range that the multi-channel pulse amplitude analyzer can receive is greater than 2.5 MeV.

[0056] Preferably, the first detector unit includes a plurality of first detectors, the second detector unit includes a plurality of second detectors, and both the first detector and the second detector include a scintillation crystal, a photoelectric conversion device, a preamplifier, and a housing, wherein:

[0057] The scintillation crystal and the photoelectric conversion device are both disposed within the outer shell. Through holes are provided on both the scintillation crystal and the outer shell, and the through holes are used for the nuclear fuel rod to pass through. The scintillation crystal is configured to emit an optical signal after absorbing γ rays emitted by the nuclear fuel rod pellets when the nuclear fuel rod passes through the through hole, and the photoelectric conversion device is configured to convert the optical signal emitted by the scintillation crystal into an electrical signal and output it;

[0058] The preamplifier is connected to the photoelectric conversion device and is configured to receive the electrical signal and amplify it to obtain the first signal / the second signal.

[0059] Preferably, the number of the first detectors is two or more, and each of the first detectors is arranged in a straight line at the inlet end of the neutron activation unit. Each of the first detectors is respectively configured to detect the γ ray characteristic information of the nuclear fuel rod pellets before activation, and the first signal includes the γ ray characteristic information of the nuclear fuel rod pellets before activation respectively detected by each of the first detectors;

[0060] The number of the second detectors is two or more, and each of the second detectors is arranged in a straight line at the outlet end of the neutron activation unit. Each of the second detectors is respectively configured to detect the γ ray characteristic information of the nuclear fuel rod pellets after activation, and the second signal includes the γ ray characteristic information of the nuclear fuel rod pellets after activation respectively detected by each of the second detectors.

[0061] Preferably, the detection efficiency of the scintillation crystal for γ rays of 1.1 MeV is ≥ 75%, and the thickness of the scintillation crystal is 1 - 2.5 times the height of the nuclear fuel rod pellets in the length direction of the nuclear fuel rod.

[0062] Preferably, the photoelectric conversion device is a photomultiplier tube or a silicon photomultiplier device.

[0063] Preferably, the material of the scintillation crystal is one of bismuth germanate (BGO), cesium iodide (CsI), sodium iodide (NaI), and cadmium zinc telluride (CZT).

[0064] Preferably, the first detectors and the second detectors both further include a first shielding body. The first shielding body is disposed outside the outer shell and is configured to shield γ rays with an energy lower than 1.1 MeV. An opening is provided on the first shielding body, and the position of the opening is concentric with the through hole on the scintillation crystal.

[0065] Preferably, the neutron activation unit includes a neutron source and a neutron shielding body. The neutron source is disposed within the neutron shielding body, and an activation channel is provided on the neutron shielding body. The position of the activation channel is concentric with the through holes of the scintillation crystals in the first detector unit and the second detector unit.

[0066] Preferably, the number of the activation channels is multiple, and the number of the detection units is multiple sets equal to the number of the activation channels. The multiple sets of detection units are arranged in parallel. The first detector unit and the second detector unit in each set of detection units are respectively arranged at the inlet end and the outlet end of the same activation channel.

[0067] Second shielding bodies are respectively arranged between the first detector units of two adjacent sets of detection units and between the second detector units of two adjacent sets of detection units. The second shielding bodies are used for shielding the mutual interference of gamma rays between the activation channels.

[0068] The active detection method and system for nuclear fuel rods of the present invention can, compared with the prior art, correct the pellet age of the nuclear fuel rods, eliminate the misjudgment caused by different pellet ages, and extend 252 the service life of the Cf neutron source (more than 3 years) or reduce 252 the initial loading amount of the Cf neutron source (reduced to 1 / 4 of the original), thereby reducing the cost. Description of the Drawings

[0069] Figure 1 It is a schematic structural diagram of the active detection system for nuclear fuel rods in an embodiment of the present invention;

[0070] Figure 2 It is a schematic structural diagram of a data acquisition and processing unit in an embodiment of the present invention;

[0071] Figure 3 It is another schematic structural diagram of a data acquisition and processing unit in an embodiment of the present invention;

[0072] Figure 4 It is a schematic structural diagram of the first detector / second detector in an embodiment of the present invention.

[0073] In the figure: 1-neutron source; 2-neutron shielding body; 3-second detector unit; 4-acquisition module; 5-calculation module; 61-loading rack; 62-unloading rack; 71-loading transmission mechanism; 72-unloading transmission mechanism; 8-first detector unit; 9-second data acquisition card; 10-first amplifier; 11-first pulse amplitude analyzer; 12-first data acquisition card; 13-scintillation crystal; 14-housing; 15-shielding body; 16-second amplifier; 17-second pulse amplitude analyzer. Detailed Embodiments

[0074] To enable those skilled in the art to better understand the technical solution of the present invention, the following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0075] In the description of the present invention, it should be noted that the terms such as "upper" indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of description and simplification, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0076] In the description of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0077] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "connection", "setting", "installation", "fixing", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0078] Embodiment 1

[0079] This embodiment discloses an active detection method for nuclear fuel rods, including:

[0080] Obtaining the characteristic γ-ray count curve before activation of the standard nuclear fuel rod pellet and the characteristic γ-ray count curve after activation of the standard nuclear fuel rod pellet;

[0081] Obtaining the characteristic γ-ray count curve before activation of the nuclear fuel rod pellet to be tested and the characteristic γ-ray count curve after activation of the nuclear fuel rod pellet to be tested;

[0082] Calculating the characteristic γ-ray count curve before activation of the standard nuclear fuel rod pellet and the characteristic γ-ray count curve after activation of the standard nuclear fuel rod pellet to obtain the final count curve of the standard nuclear fuel rod;

[0083] Calculate the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the nuclear fuel pellet to be measured, and obtain the final counting curve of the nuclear fuel rod to be measured;

[0084] Based on the final counting curve of the standard nuclear fuel rod and the final counting curve of the nuclear fuel rod to be measured, calculate the pellet enrichment of the nuclear fuel rod to be measured, and determine whether the pellet enrichment of the nuclear fuel to be measured is qualified.

[0085] In some embodiments, obtaining the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellet specifically includes:

[0086] Use a number of detectors (the first detector) to detect the standard nuclear fuel rod before activation, and respectively collect the characteristic γ-ray characteristic information of the standard nuclear fuel rod pellet before activation detected by each single detector to obtain the initial characteristic γ-ray counting curve of the standard nuclear fuel rod pellet before activation (denoted as the first counting curve), and shift and accumulate multiple first counting curves to obtain the characteristic γ-ray counting curve of the standard nuclear fuel rod pellet before activation;

[0087] Similarly, use a number of detectors (the second detector) to detect the standard nuclear fuel rod after activation, and respectively collect the characteristic γ-ray characteristic information of the standard nuclear fuel rod pellet after activation detected by each single detector to obtain multiple initial characteristic γ-ray counting curves of the standard nuclear fuel rod pellet after activation (denoted as the second counting curve), and shift and accumulate multiple second counting curves to obtain the characteristic γ-ray counting curve of the standard nuclear fuel rod pellet after activation.

[0088] In some embodiments, obtaining the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the nuclear fuel pellet to be measured specifically includes:

[0089] Use a number of detectors (the first detector) to detect the nuclear fuel rod to be measured before activation, and respectively collect the characteristic γ-ray characteristic information of the nuclear fuel rod pellet to be measured before activation detected by each single detector to obtain multiple initial characteristic γ-ray counting curves of the nuclear fuel rod pellet to be measured before activation (denoted as the third counting curve), and shift and accumulate multiple third counting curves to obtain the characteristic γ-ray counting curve of the nuclear fuel rod pellet to be measured before activation;

[0090] Similarly, several detectors (second detectors) are used to detect the activated nuclear fuel rod to be tested, and the characteristic γ-ray characteristic information after activation of the fuel rod core to be tested detected by each individual detector is collected respectively, obtaining multiple initial characteristic γ-ray counting curves after activation of the fuel rod core to be tested (denoted as the fourth counting curves), and the multiple fourth counting curves are shifted and accumulated to obtain the characteristic γ-ray counting curve after activation of the fuel rod core to be tested.

[0091] In some embodiments, the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod core are calculated to obtain the final counting curve of the standard nuclear fuel rod, and the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the nuclear fuel rod core to be tested are calculated to obtain the final counting curve of the nuclear fuel rod to be tested, specifically including:

[0092] Based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod core, or based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the nuclear fuel rod core to be tested, an age correction coefficient is calculated;

[0093] Based on the age correction coefficient, the final counting curve of the standard nuclear fuel rod and the final counting curve of the nuclear fuel rod to be tested are calculated.

[0094] In some embodiments, based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod core, or based on the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the nuclear fuel rod core to be tested, an age correction coefficient is calculated, specifically including:

[0095] On the characteristic γ-ray counting curve before activation and the characteristic γ-ray counting curve after activation of the standard / to-be-tested nuclear fuel rod core, the head end and the tail end of the corresponding standard / to-be-tested nuclear fuel rod are determined respectively, and the point corresponding to the head end of the standard / to-be-tested nuclear fuel rod on the characteristic γ-ray counting curve before activation of the standard / to-be-tested nuclear fuel rod core is set as the starting point of the characteristic γ-ray counting curve before activation of the standard / to-be-tested nuclear fuel rod core and the point corresponding to the head end of the standard / to-be-tested nuclear fuel rod on the characteristic γ-ray counting curve after activation of the standard / to-be-tested nuclear fuel rod core is set as the starting point of the characteristic γ-ray counting curve after activation of the standard / to-be-tested nuclear fuel rod core;

[0096] Based on the count values at any two time points on the characteristic γ-ray count curves before and after the activation of the standard / sample nuclear fuel rod pellets at the same position of the same standard / sample nuclear fuel rod, the age correction coefficient is calculated, and the calculation formula is as follows:

[0097] F = (C A1 - C A2 ) / (C B1 - C B2 )

[0098] In the formula, F is the age correction coefficient, C A1 is the count value at the first time point on the characteristic γ-ray count curve after the activation of the standard / sample nuclear fuel rod pellets, C A2 is the count value at the second time point on the characteristic γ-ray count curve after the activation of the standard / sample nuclear fuel rod pellets, C B1 is the count value at the first time point on the characteristic γ-ray count curve before the activation of the standard / sample nuclear fuel rod pellets, C B2 is the count value at the second time point on the characteristic γ-ray count curve before the activation of the standard / sample nuclear fuel rod pellets.

[0099] In some embodiments, based on the age correction coefficient, the final count curve of the standard nuclear fuel rod and the final count curve of the sample nuclear fuel rod are obtained, specifically including:

[0100] Subtract the product of the count value at the same position of the standard / sample nuclear fuel rod on the characteristic γ-ray count curve before the activation of the standard / sample nuclear fuel rod pellets and the age correction coefficient from the count value at each position of the standard / sample nuclear fuel rod on the characteristic γ-ray count curve after the activation of the standard / sample nuclear fuel rod pellets, to obtain the final count value of the count curve at each position on the standard / sample nuclear fuel rod. Among them, the calculation formula of the final count value of the count curve is:

[0101] C F = C AA - F × C BA

[0102] In the formula, C F is the final count value of the count curve, C AA is the count value on the characteristic γ-ray count curve after the activation of the standard / sample nuclear fuel rod pellets, C BA is the count value on the characteristic γ-ray count curve before the activation of the standard / sample nuclear fuel rod pellets, and F is the age correction coefficient;

[0103] Based on the final count values of the counting curves at various positions of the standard / test nuclear fuel rod, the final count curve of the standard nuclear fuel rod and the final count curve of the test nuclear fuel rod are respectively obtained.

[0104] In some embodiments, based on the final count curve of the standard nuclear fuel rod and the final count curve of the test nuclear fuel rod, calculating the pellet enrichment of the test nuclear fuel rod specifically includes:

[0105] Fitting the pellet enrichment values at different positions of the standard nuclear fuel rod with the final count curve of the standard nuclear fuel rod to obtain the abundance-count relationship equation of the standard nuclear fuel rod;

[0106] Substitute each count value on the final count curve of the test nuclear fuel rod into the abundance-count relationship equation of the standard nuclear fuel rod to obtain the abundance curve of the test nuclear fuel rod;

[0107] Based on the abundance curve of the test nuclear fuel rod, obtain the pellet enrichment at different positions of the test nuclear fuel rod;

[0108] Compare the pellet enrichment at different positions of the test nuclear fuel rod with the technical indicators of nuclear fuel rod detection, and judge whether the pellet enrichment of the test fuel rod is qualified according to the comparison result.

[0109] The active detection method of the nuclear fuel rod in this embodiment can correct the pellet age of the nuclear fuel rod, eliminate misjudgment caused by different pellet ages, and extend 252 the service life of the 252 Cf neutron source or reduce

[0110] Embodiment 2

[0111] As Figure 1 shown, this embodiment discloses an active detection system for nuclear fuel rods, which is used for the active detection method of nuclear fuel rods described in Embodiment 1, and includes a neutron activation unit, a detection unit, and a data acquisition and processing unit, wherein:

[0112] The neutron activation unit is used to perform neutron activation on the nuclear fuel rod pellets;

[0113] The detection unit includes a first detector unit 8 and a second detector unit 3. The first detector unit 8 is arranged at the inlet end of the neutron activation unit and is connected to the data acquisition and processing unit, and is used to detect the γ-ray characteristic information before the activation of the nuclear fuel rod pellets, obtain a first signal, and transmit the first signal to the data acquisition and processing unit. The second detector unit 3 is arranged at the outlet end of the neutron activation unit and is connected to the data acquisition and processing unit, and is used to detect the γ-ray characteristic information after the activation of the nuclear fuel rod pellets, obtain a second signal, and transmit the second signal to the data acquisition and processing unit;

[0114] A data acquisition and processing unit, configured to receive a first signal and a second signal, determine a characteristic γ-ray counting curve before activation of nuclear fuel rod pellets and a characteristic γ-ray counting curve after activation of the nuclear fuel rod pellets according to the first signal and the second signal, calculate the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellets and the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellets to obtain a final counting curve of the nuclear fuel rod, calculate the pellet enrichment of the nuclear fuel rod based on the final counting curve, and determine whether the pellet enrichment of the nuclear fuel rod is qualified.

[0115] In some embodiments, the data acquisition and processing unit includes an acquisition module 4 and a calculation module 5. The acquisition module 4 includes a first pulse amplitude analyzer 11, a first data acquisition card 12, a second pulse amplitude analyzer 17, and a second data acquisition card 9.

[0116] Specifically, the first pulse amplitude analyzer 11 is connected to the first detector unit 8 and is configured to convert the first signal into a first square wave signal.

[0117] The first data acquisition card 12 is respectively connected to the first pulse amplitude analyzer 11 and the calculation module 5, and is configured to acquire the first square wave signal converted in the first pulse amplitude analyzer 11 to obtain a characteristic γ-ray counting curve before activation of the nuclear fuel rod pellets, and transmit the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellets to the calculation module 5.

[0118] The second pulse amplitude analyzer 17 is connected to the second detector unit 3 and is configured to convert the second signal into a second square wave signal.

[0119] The second data acquisition card 9 is respectively connected to the second pulse amplitude analyzer 17, the second detector unit 3, and the calculation module 5, and is configured to acquire the first square wave signal converted in the second pulse amplitude analyzer 17 to obtain a characteristic γ-ray counting curve after activation of the nuclear fuel rod pellets, and transmit the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellets to the calculation module 5.

[0120] The calculation module 5 is preset with the nuclear fuel rod detection technical index data, and is configured to calculate the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellets and the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellets to obtain a final counting curve of the nuclear fuel rod, calculate the pellet enrichment of the nuclear fuel rod based on the final counting curve, and compare the pellet enrichment of the nuclear fuel rod with the nuclear fuel rod detection technical index, and determine whether the pellet enrichment of the nuclear fuel rod is qualified according to the comparison result.

[0121] In this embodiment, the single-point acquisition time of the first data acquisition card 12 and the second data acquisition card 9 is uniformly on the order of 10 ms.

[0122] In some embodiments, the acquisition module 4 further includes a first amplifier 10 and a second amplifier 16.

[0123] Specifically, the first amplifier 10 is respectively connected to the first detector unit 8 and the first pulse amplitude analyzer 11, and is configured to amplify the first signal detected by the first detector unit 8 and transmit it to the first pulse amplitude analyzer 11. The first pulse amplitude analyzer 11 then converts the electrical pulses with a specific amplitude in the amplified first signal into the first square wave signal. By providing the first amplifier 10, the matching degree between the amplitude of the first signal and the first pulse amplitude analyzer 11 can be improved.

[0124] The second amplifier 16 is respectively connected to the second detector unit 3 and the second pulse amplitude analyzer 17, and is configured to amplify the second signal detected by the second detector unit 3 and transmit it to the second pulse amplitude analyzer 17. The second pulse amplitude analyzer 17 then converts the electrical pulses with a specific amplitude in the amplified second signal into the second square wave signal. By providing the second amplifier 16, the matching degree between the amplitude of the second signal and the second pulse amplitude analyzer 17 can be improved.

[0125] In some embodiments, both the first pulse amplitude analyzer 11 and the second pulse amplitude analyzer 17 are one of a comparator, a single-channel pulse amplitude analyzer, and a multi-channel pulse amplitude analyzer.

[0126] Specifically, when the first pulse amplitude analyzer is a single-channel pulse amplitude analyzer, the lower threshold of the single-channel pulse amplitude analyzer is the pulse signal generated by 250 keV γ-rays, and the upper threshold of the single-channel pulse amplitude analyzer is the pulse signal generated by 1.1 MeV γ-rays. When the second pulse amplitude analyzer is a single-channel pulse amplitude analyzer, the lower threshold of the single-channel pulse amplitude analyzer is the pulse signal corresponding to the maximum noise of the second detector in the second detector unit 3, and the upper threshold of the single-channel pulse amplitude analyzer is the pulse signal generated by 2.5 MeV γ-rays. The energy range of γ-rays that the multi-channel pulse amplitude analyzer can receive is greater than 2.5 MeV.

[0127] In some embodiments, the first amplifier 10, the first pulse amplitude analyzer 11, and the first data acquisition card 12 can be discrete devices, or can be a first integrated device having exactly the same functions as the first amplifier 10, the first pulse amplitude analyzer 11, and the first data acquisition card 12. The first integrated device can directly complete the acquisition and conversion of the first detector unit signal (the first signal).

[0128] The second amplifier 16, the second pulse amplitude analyzer 17, and the second data acquisition card 9 can be discrete devices (such as Figure 2(as shown), it can also be a second integrated device with exactly the same functions as the second amplifier 16, the second pulse amplitude analyzer 17, and the second data acquisition card 9. The second integrated device can directly complete the acquisition and conversion of the signals (second signals) of the second detector unit.

[0129] It should be noted that, as Figure 1 , Figure 3 shown, in this embodiment, the second amplifier 16 and the second pulse amplitude analyzer 17 in this embodiment can also be integrated with the second detector unit 3 into one body and integrated onto the second detector unit 3.

[0130] In some embodiments, the first detector unit 8 includes a plurality of first detectors, and the second detector unit 3 includes a plurality of second detectors. Both the first detector and the second detector include a scintillation crystal 13, a photoelectric conversion device, a preamplifier, and a housing 14.

[0131] Specifically, both the scintillation crystal 13 and the photoelectric conversion device are arranged inside the housing 14. Through holes are provided on both the scintillation crystal 13 and the housing 14 for the nuclear fuel rod to pass through. The scintillation crystal 13 is used to emit a light signal after absorbing the γ-rays emitted by the nuclear fuel rod pellets when the nuclear fuel rod passes through the through hole. The photoelectric conversion device is used to convert the light signal emitted by the scintillation crystal into an electrical signal (electrical pulse signal) and output it. The preamplifier is connected to the photoelectric conversion device and is used to receive the electrical signal output by the photoelectric conversion device and amplify it to obtain the first signal / the second signal.

[0132] In this embodiment, the number of the first detectors is more than two. Each of the first detectors is arranged in a straight line at the inlet end of the neutron activation unit. Each of the first detectors is respectively used to detect the γ-ray characteristic information of the nuclear fuel rod pellets before activation. The first signal includes the γ-ray characteristic information of the nuclear fuel rod pellets before activation respectively detected by each of the first detectors.

[0133] The number of the second detectors is more than two. Each of the second detectors is arranged in a straight line at the outlet end of the neutron activation unit. Each of the second detectors is respectively used to detect the γ-ray characteristic information of the nuclear fuel rod pellets after activation. The second signal includes the γ-ray characteristic information of the nuclear fuel rod pellets after activation respectively detected by each of the second detectors.

[0134] Moreover, in this embodiment, a third shielding body can also be provided between two adjacent first detectors and between two adjacent second detectors. The third shielding body can be specifically made of tungsten or lead, preferably made of tungsten, for shielding γ-rays to avoid mutual interference.

[0135] In this embodiment, the scintillation crystal 13 and the outer shell 14 are preferably opened by means of central drilling, that is, the through hole is located at the center of the scintillation crystal 13 and the outer shell 14, so as to improve the spatial detection efficiency of γ-rays of the nuclear fuel rod matrix (pellets).

[0136] In some embodiments, the detection efficiency of the scintillation crystal 13 for γ-rays of 1.1 MeV should be ≥75%.

[0137] Specifically, the material type of the scintillation crystal 13 can be bismuth germanate (BGO), cesium iodide (CsI), sodium iodide (NaI), cadmium zinc telluride (CZT), etc. The thickness of the scintillation crystal 13 along the length direction of the nuclear fuel rod is selected according to the height of the cylindrical pellets to be measured in the nuclear fuel rod. In this embodiment, the thickness of the scintillation crystal 13 is preferably 1-2.5 times the height of the nuclear fuel rod pellets in the length direction of the nuclear fuel rod.

[0138] In this embodiment, the photoelectric conversion device is a photomultiplier tube or a silicon photomultiplier device.

[0139] In some embodiments, both the first detector and the second detector further include a first shielding body 15.

[0140] Specifically, the first shielding body 15 is sleeved outside the outer shell 14 and is used to shield γ-rays with an energy lower than 1.1 MeV, so as to shield the influence of the outside world (including other parts of the nuclear fuel rod) on the structures inside the outer shell 14 (that is, the scintillation crystal 13 and the photoelectric converter) during operation. An opening is provided on the first shielding body 15, and the position of the opening is concentric with the through hole on the scintillation crystal 13 (that is, directly opposite to the position of the through hole) for the nuclear fuel rod to pass through.

[0141] In this embodiment, the shielding effect requirement of the first shielding body 15 for γ-rays with an energy lower than 1.1 MeV is to shield more than 98% of the γ-rays. The first shielding body 15 can be specifically made of tungsten or lead, and is preferably made of tungsten.

[0142] In some embodiments, the neutron activation unit includes a neutron source 1 and a neutron shielding body 2.

[0143] Specifically, the neutron source 1 is arranged inside the neutron shielding body 2, and an activation channel is provided on the neutron shielding body 2. The position of the activation channel is concentric with the through hole of the scintillation crystal 13 in the first detector unit 8 and the second detector unit 3 (that is, directly opposite to the position of the through hole), so that the nuclear fuel rod can pass through the through hole of the scintillation crystal 13 in the first detector unit 8 and enter the activation channel for neutron activation, and then pass through the through hole of the scintillation crystal 13 in the second detector unit 3 after neutron activation.

[0144] In some embodiments, the number of activation channels can be one or multiple. The number of detection units is one set or multiple sets equal to the number of activation channels, and is specifically selected according to the requirements of the production line for performance such as equipment detection speed and detection accuracy.

[0145] In this embodiment, the number of activation channels is preferably multiple (for example, two as shown in Figure 1 ), and the number of detection units is preferably multiple sets. The multiple sets of detection units are arranged in parallel. The first detector unit 8 and the second detector unit 3 in each set of detection units are respectively arranged at the inlet end and the outlet end of the same activation channel. Second shielding bodies are respectively arranged between the first detector units 8 of adjacent two sets of detection units and between the second detector units 3 of adjacent two sets of detection units. The second shielding body is used to shield the mutual interference of γ-rays between the activation channels. The material of the second shielding body can be tungsten or lead, and tungsten is preferred.

[0146] In this embodiment, the number of acquisition modules 4 is the same as the number of detection units, so that the number of acquisition channels of the acquisition module matches the number of detection channels in the detection unit, thereby improving the acquisition and conversion efficiency of the first signal and the second signal.

[0147] In some embodiments, the system further includes a loading device and an unloading device.

[0148] Specifically, the loading device is arranged at the inlet end of the first detector 8. It includes a loading rack 61 and a loading transmission mechanism 71. The loading rack 61, the loading transmission mechanism 71, and the first detector unit 8 are arranged in a straight line, and the loading transmission mechanism 71 is between the loading rack 61 and the first detector unit 8. The loading rack 61 is used to place the nuclear fuel rods to be tested. The loading transmission mechanism 71 is used to feed the nuclear fuel rods placed on the loading rack 61 into and through the through hole of the scintillation crystal 13 in the first detector unit 8 and into the activation channel in the neutron activation unit for neutron activation, and to send the nuclear fuel assembly after neutron activation to the second detector unit 3 to detect the γ-ray characteristic information of the activated nuclear fuel pellet.

[0149] The unloading device is arranged at the outlet end of the second detector 3. It includes an unloading rack 62 and an unloading transmission mechanism 72. The second detector unit 3, the unloading transmission mechanism 72, and the unloading rack 62 are arranged in a straight line, and the unloading transmission mechanism 72 is between the unloading rack 62 and the second detector unit 3. The unloading transmission mechanism 72 is used to receive the nuclear fuel rods detected by the second detector unit 3 and transport them out to the unloading rack 62 for unloading.

[0150] The working process of the active detection system for nuclear fuel rods in this embodiment is described in detail below, specifically as follows:

[0151] Detection process: Place a standard nuclear fuel rod (i.e., a nuclear fuel rod with a known enrichment) on the loading rack 61. Use the loading transmission mechanism 71 to sequentially and uniformly pass the standard nuclear fuel rod through the first detector unit 8, the neutron activation unit, and the second detector unit 3. Then, use the unloading transmission mechanism 72 to transfer the standard nuclear fuel rod that has passed through the second detector unit 3 to the unloading rack 62. During this period, each first detector in the first detector unit 8 respectively detects the first signal of the standard nuclear fuel rod, and each second detector in the second detector unit 3 respectively detects the second signal of the standard nuclear fuel rod.

[0152] Similarly, place a nuclear fuel rod to be measured (i.e., a nuclear fuel rod with an unknown enrichment) on the loading rack 61. Use the loading transmission mechanism 71 to sequentially and uniformly pass the nuclear fuel rod to be measured through the first detector unit 8, the neutron activation unit, and the second detector unit. Then, use the unloading transmission mechanism 72 to transfer the nuclear fuel rod to be measured that has passed through the second detector unit 3 to the unloading rack 62. During this period, each first detector in the first detector unit 8 respectively detects the first signal of the nuclear fuel rod to be measured, and each second detector in the second detector unit 3 respectively detects the second signal of the nuclear fuel rod to be measured.

[0153] Data acquisition process: The first signal of the standard nuclear fuel rod detected by each first detector is amplified by the first amplifier 10 and then transmitted to the first pulse amplitude analyzer 11 to be converted into the first square wave signal of the standard nuclear fuel rod. The first data acquisition card 12 acquires these first square wave signals of the standard nuclear fuel rod, obtains multiple initial characteristic γ-ray counting curves (i.e., the first counting curves) of the standard nuclear fuel rod pellets before activation, and transmits these first counting curves to the calculation module 5;

[0154] The second signal of the standard nuclear fuel rod detected by each second detector is amplified by the second amplifier 16 and then transmitted to the second pulse amplitude analyzer 17 to be converted into the second square wave signal of the standard nuclear fuel rod. The second data acquisition card 9 acquires these second square wave signals of the standard nuclear fuel rod, obtains multiple initial characteristic γ-ray counting curves (i.e., the second counting curves) of the standard nuclear fuel rod pellets after activation, and transmits these second counting curves to the calculation module 5.

[0155] Similarly, the first signal of the nuclear fuel rod to be measured detected by each first detector is amplified by the first amplifier 10 and then transmitted to the first pulse amplitude analyzer 11 to be converted into the first square wave signal of the nuclear fuel rod to be measured. The first data acquisition card 12 acquires these first square wave signals of the nuclear fuel rod to be measured, obtains multiple initial characteristic γ-ray counting curves (i.e., the third counting curves) of the nuclear fuel rod pellets before activation, and transmits these third counting curves to the calculation module 5;

[0156] The second signals of the nuclear fuel rods to be measured detected by each second detector are amplified by the second amplifier 16 and then transmitted to the second pulse amplitude analyzer 17 to be converted into the second square wave signals of the nuclear fuel rods to be measured. The second data acquisition card 9 collects these second square wave signals of the nuclear fuel rods to be measured, obtains multiple initial characteristic γ-ray counting curves (i.e., the fourth counting curves) after the activation of the pellets of the nuclear fuel rods to be measured, and transmits these fourth counting curves to the calculation module 5.

[0157] Data processing process: First, the calculation module 5 respectively performs shift accumulation on the received first counting curves to obtain the characteristic γ-ray counting curves of the standard nuclear fuel rod pellets before activation; performs shift accumulation on the received second counting curves to obtain the characteristic γ-ray counting curves of the standard nuclear fuel rod pellets after activation; performs shift accumulation on the received third counting curves to obtain the characteristic γ-ray counting curves of the nuclear fuel rod pellets to be measured before activation; performs shift accumulation on the received fourth counting curves to obtain the characteristic γ-ray counting curves of the nuclear fuel rod pellets to be measured after activation.

[0158] Then, the calculation module 5 calculates the age correction coefficient based on the characteristic γ-ray counting curves of the standard nuclear fuel rod pellets before activation and the characteristic γ-ray counting curves of the standard nuclear fuel rod pellets after activation, or based on the characteristic γ-ray counting curves of the nuclear fuel rod pellets to be measured before activation and the characteristic γ-ray counting curves of the nuclear fuel rod pellets to be measured after activation. Specifically:

[0159] On the characteristic γ-ray counting curves of the standard / nuclear fuel rod pellets before activation and the characteristic γ-ray counting curves of the standard / nuclear fuel rod pellets after activation, the head and tail of the corresponding standard / nuclear fuel rod are respectively determined, and the point corresponding to the head of the standard / nuclear fuel rod on the characteristic γ-ray counting curve of the standard / nuclear fuel rod pellets before activation is set as the starting point of the characteristic γ-ray counting curve of the standard / nuclear fuel rod pellets before activation, and the point corresponding to the head of the standard / nuclear fuel rod on the characteristic γ-ray counting curve of the standard / nuclear fuel rod pellets after activation is set as the starting point of the characteristic γ-ray counting curve of the standard / nuclear fuel rod pellets after activation. Based on the count values at any two time points on the characteristic γ-ray counting curve of the standard / nuclear fuel rod pellets before activation and the characteristic γ-ray counting curve of the standard / nuclear fuel rod pellets after activation at the same position of the same standard / nuclear fuel rod, the age correction coefficient is calculated. The calculation formula is as follows:

[0160] F = (C A1 - C A2 ) / (C B1 - C B2 )

[0161] In the formula, F is the age correction coefficient, CA1 is the count value at the first time point on the characteristic γ-ray count curve after activation of the standard / test nuclear fuel rod pellet, C A2 is the count value at the second time point on the characteristic γ-ray count curve after activation of the standard / test nuclear fuel rod pellet, C B1 is the count value at the first time point on the characteristic γ-ray count curve before activation of the standard / test nuclear fuel rod pellet, C B2 is the count value at the second time point on the characteristic γ-ray count curve before activation of the standard / test nuclear fuel rod pellet.

[0162] Then, the calculation module 5 calculates the final count curve of the standard nuclear fuel rod and the final count curve of the test nuclear fuel rod based on the age correction coefficient, specifically including:

[0163] Subtract the product of the count value at the same position on the standard / test nuclear fuel rod before activation of the standard / test nuclear fuel rod pellet and the age correction coefficient from the count value at each position on the characteristic γ-ray count curve after activation of the standard / test nuclear fuel rod pellet, to obtain the final count value of the count curve at each position on the standard / test nuclear fuel rod. Among them, the calculation formula for the final count value of the count curve is:

[0164] C F = C AA − F × C BA

[0165] In the formula, C F is the final count value of the count curve, C AA is the count value on the characteristic γ-ray count curve after activation of the standard / test nuclear fuel rod pellet, C BA is the count value on the characteristic γ-ray count curve before activation of the standard / test nuclear fuel rod pellet, and F is the age correction coefficient;

[0166] Based on the final count values of the count curves at each position of the standard / test nuclear fuel rod, the final count curve of the standard nuclear fuel rod and the final count curve of the test nuclear fuel rod are respectively obtained.

[0167] Finally, the calculation module 5 calculates the pellet enrichment of the test nuclear fuel rod based on the final count curve of the standard nuclear fuel rod and the final count curve of the test nuclear fuel rod, specifically including:

[0168] Based on the pellet enrichment values at different positions of the standard nuclear fuel rod and the final count curve of the standard nuclear fuel rod, a relationship equation between enrichment and count of the standard nuclear fuel rod is obtained by fitting;

[0169] Substitute each count value on the final count curve of the nuclear fuel rod to be measured into the abundance-count relationship equation of the standard nuclear fuel rod to obtain the abundance curve of the nuclear fuel rod to be measured.

[0170] Based on the abundance curve of the nuclear fuel rod to be measured, obtain the pellet abundances at different positions of the nuclear fuel rod to be measured.

[0171] Compare the pellet abundances at different positions of the nuclear fuel rod to be measured with the nuclear fuel rod detection technical indicators, and judge whether the pellet abundances of the nuclear fuel rod to be measured are qualified according to the comparison results.

[0172] The active detection system for nuclear fuel rods in this embodiment, compared with the prior art, can correct the pellet age of the nuclear fuel rod, eliminate misjudgment caused by different pellet ages, and extend 252 the service life of the Cf neutron source (more than 3 years) or reduce 252 the initial loading of the Cf neutron source (reduced to 1 / 4 of the original), thereby reducing costs.

[0173] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present invention. However, the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims

1. An active detection method for nuclear fuel rods, including: Obtaining the characteristic γ-ray counting curve before activation of the standard nuclear fuel rod pellet and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellet, Obtaining the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellet to be measured and the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellet to be measured; Calculating the characteristic γ-ray counting curve before activation of the standard nuclear fuel rod pellet and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellet to obtain the final counting curve of the standard nuclear fuel rod, Calculating the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellet to be measured and the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellet to be measured to obtain the final counting curve of the nuclear fuel rod to be measured, Specifically including, first, calculating an age correction coefficient based on the characteristic γ-ray counting curve before activation of the standard nuclear fuel rod pellet and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellet, or based on the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellet to be measured and the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellet to be measured, and then calculating the final counting curve of the standard nuclear fuel rod and the final counting curve of the nuclear fuel rod to be measured based on the age correction coefficient; Calculating the pellet enrichment of the nuclear fuel rod to be measured based on the final counting curve of the standard nuclear fuel rod and the final counting curve of the nuclear fuel rod to be measured, and determining whether the pellet enrichment of the nuclear fuel to be measured is qualified.

2. The active detection method for nuclear fuel rods according to claim 1, characterized in that Obtaining the characteristic γ-ray counting curve before activation of the standard nuclear fuel rod pellet and the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellet specifically includes: Respectively collecting the characteristic γ-ray characteristic information before activation of the standard nuclear fuel rod pellet detected by a single detector to obtain multiple first counting curves, Respectively collecting the characteristic γ-ray characteristic information after activation of the standard nuclear fuel rod pellet detected by a single detector to obtain multiple second counting curves; Performing shift accumulation on the multiple first counting curves to obtain the characteristic γ-ray counting curve before activation of the standard nuclear fuel rod pellet, Performing shift accumulation on the multiple second counting curves to obtain the characteristic γ-ray counting curve after activation of the standard nuclear fuel rod pellet; Obtaining the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellet to be measured and the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellet to be measured specifically includes: Respectively collecting the characteristic γ-ray characteristic information before activation of the nuclear fuel rod pellet to be measured detected by a single detector to obtain multiple third counting curves, Respectively collecting the characteristic γ-ray characteristic information after activation of the nuclear fuel rod pellet to be measured detected by a single detector to obtain multiple fourth counting curves; Performing shift accumulation on the multiple third counting curves to obtain the characteristic γ-ray counting curve before activation of the nuclear fuel rod pellet to be measured, Performing shift accumulation on the multiple fourth counting curves to obtain the characteristic γ-ray counting curve after activation of the nuclear fuel rod pellet to be measured.

3. The active detection method for nuclear fuel rods according to claim 2, characterized in that Based on the characteristic γ-ray counting curves of the standard nuclear fuel rod pellets before activation and after activation, or based on the characteristic γ-ray counting curves of the nuclear fuel rod pellets to be measured before activation and after activation, the age correction coefficient is calculated, specifically including: On the characteristic γ-ray counting curves of the standard / to-be-measured nuclear fuel rod pellets before activation and after activation, determine the corresponding head and tail ends of the standard / to-be-measured nuclear fuel rods respectively, and set the point corresponding to the head end of the standard / to-be-measured nuclear fuel rod on the characteristic γ-ray counting curve of the standard / to-be-measured nuclear fuel rod pellets before activation as the starting point of the characteristic γ-ray counting curve of the standard / to-be-measured nuclear fuel rod pellets before activation, and set the point corresponding to the head end of the standard / to-be-measured nuclear fuel rod on the characteristic γ-ray counting curve of the standard / to-be-measured nuclear fuel rod pellets after activation as the starting point of the characteristic γ-ray counting curve of the standard / to-be-measured nuclear fuel rod pellets after activation. Based on the count values at any two time points on the characteristic γ-ray counting curves of the standard / to-be-measured nuclear fuel rod pellets before activation and after activation at the same position of the same standard / to-be-measured nuclear fuel rod, the age correction coefficient is calculated, and the calculation formula is as follows: F=(C A1 -C A2 ) / (C B1 -C B2 ) where F is the age correction coefficient, C A1 is the count value at the first time point on the characteristic γ-ray count curve after activation of the standard / test nuclear fuel rod pellet, C A2 is the count value at the second time on the characteristic γ-ray count curve after activation of the standard / test nuclear fuel rod pellet, C B1 is the count value at the first time point on the characteristic γ-ray count curve before activation of the standard / test nuclear fuel rod pellet, C B2 is the count value at the second time point on the characteristic γ-ray count curve before activation of the standard / test nuclear fuel rod pellet.

4. The active detection method for nuclear fuel rods according to claim 3, characterized in that Based on the age correction coefficient, the final counting curves of the standard nuclear fuel rod and the nuclear fuel rod to be measured are obtained, specifically including: Subtract the product of the count value at the same position of the standard / to-be-measured nuclear fuel rod on the characteristic γ-ray counting curve of the standard / to-be-measured nuclear fuel rod pellets before activation and the age correction coefficient from the count value at each position of the standard / to-be-measured nuclear fuel rod on the characteristic γ-ray counting curve of the standard / to-be-measured nuclear fuel rod pellets after activation, to obtain the final count values of the counting curves at each position on the standard / to-be-measured nuclear fuel rod, where the calculation formula for the final count values of the counting curves is: C F = C AA - F × C BA Wherein, C F is the final count value of the counting curve, C AA is the count value on the characteristic γ-ray counting curve after activation of the standard / test nuclear fuel pellet, C BA is the count value on the characteristic γ-ray counting curve before activation of the standard / test nuclear fuel pellet, and F is the age correction coefficient; Based on the final count values of the counting curves at each position of the standard / to-be-measured nuclear fuel rod, the final counting curves of the standard nuclear fuel rod and the nuclear fuel rod to be measured are obtained respectively.

5. The active detection method for nuclear fuel rods according to claim 4, characterized in that Based on the final counting curves of the standard nuclear fuel rod and the nuclear fuel rod to be measured, the pellet enrichment of the nuclear fuel rod to be measured is calculated, specifically including: Based on the pellet enrichment values at different positions of the standard nuclear fuel rod and the final counting curve of the standard nuclear fuel rod, perform fitting to obtain the abundance-count relationship equation of the standard nuclear fuel rod; Substitute each count value on the final counting curve of the nuclear fuel rod to be measured into the abundance-count relationship equation of the standard nuclear fuel rod to obtain the enrichment curve of the nuclear fuel rod to be measured; Based on the enrichment curve of the nuclear fuel rod to be measured, obtain the pellet enrichment at different positions of the nuclear fuel rod to be measured. Compare the pellet enrichments at different positions of the nuclear fuel rod to be tested with the technical indicators of the nuclear fuel rod detection, and judge whether the pellet enrichment of the fuel rod to be tested is qualified according to the comparison result.

6. An active detection system for nuclear fuel rods, characterized in that, it includes a neutron activation unit, a detection unit, and a data acquisition and processing unit, the neutron activation unit is used to perform neutron activation on the nuclear fuel rod pellets; the detection unit includes a first detector unit (8) and a second detector unit (3), the first detector unit is arranged at the inlet end of the neutron activation unit and is connected to the data acquisition and processing unit, and is used to detect the γ-ray characteristic information before the activation of the nuclear fuel rod pellets, obtain a first signal, and transmit the first signal to the data acquisition and processing unit, the second detector unit is arranged at the outlet end of the neutron activation unit and is connected to the data acquisition and processing unit, and is used to detect the γ-ray characteristic information after the activation of the nuclear fuel rod pellets, obtain a second signal, and transmit the second signal to the data acquisition and processing unit; the data acquisition and processing unit is used to receive the first signal and the second signal, and determine the characteristic γ-ray counting curve before the activation of the nuclear fuel rod pellets and the characteristic γ-ray counting curve after the activation of the nuclear fuel rod pellets according to the first signal and the second signal. Specifically, it includes determining the characteristic γ-ray counting curve before the activation of the standard nuclear fuel rod pellets according to the first signal of the detected standard nuclear fuel rod, determining the characteristic γ-ray counting curve after the activation of the standard nuclear fuel rod pellets according to the second signal of the detected standard nuclear fuel rod, determining the characteristic γ-ray counting curve before the activation of the nuclear fuel rod pellets to be tested according to the first signal of the detected nuclear fuel rod to be tested, determining the characteristic γ-ray counting curve after the activation of the nuclear fuel rod pellets to be tested according to the second signal of the detected nuclear fuel rod to be tested, and, calculating the characteristic γ-ray counting curve before the activation of the nuclear fuel rod pellets and the characteristic γ-ray counting curve after the activation of the nuclear fuel rod pellets to obtain the final counting curve of the nuclear fuel rod. Specifically, first, calculate the age correction coefficient based on the characteristic γ-ray counting curve before the activation of the standard nuclear fuel rod pellets and the characteristic γ-ray counting curve after the activation of the standard nuclear fuel rod pellets, or based on the characteristic γ-ray counting curve before the activation of the nuclear fuel rod pellets to be tested and the characteristic γ-ray counting curve after the activation of the nuclear fuel rod pellets to be tested. Then, calculate the final counting curve of the standard nuclear fuel rod and the final counting curve of the nuclear fuel rod to be tested based on the age correction coefficient, and, calculate the pellet enrichment of the nuclear fuel rod based on the final counting curve and judge whether the pellet enrichment of the nuclear fuel rod is qualified.

7. The active detection system for nuclear fuel rods according to claim 6, characterized in that, the data acquisition and processing unit includes an acquisition module (4) and a calculation module (5), and the acquisition module includes a first pulse height analyzer (11), a first data acquisition card (12), a second pulse height analyzer (17), and a second data acquisition card (9). The first pulse amplitude analyzer is connected to the first detector unit and is configured to convert the first signal into a first square wave signal; The first data acquisition card is respectively connected to the first pulse amplitude analyzer and the calculation module, and is configured to collect the first square wave signal converted in the first pulse amplitude analyzer, obtain the characteristic γ-ray count curve before the activation of the nuclear fuel rod pellet, and transmit the characteristic γ-ray count curve before the activation of the nuclear fuel rod pellet to the calculation module; The second pulse amplitude analyzer is connected to the second detector unit and is configured to convert the second signal into a second square wave signal; The second data acquisition card is respectively connected to the second pulse amplitude analyzer and the calculation module, and is configured to collect the second square wave signal converted in the second pulse amplitude analyzer, obtain the characteristic γ-ray count curve after the activation of the nuclear fuel rod pellet, and transmit the characteristic γ-ray count curve after the activation of the nuclear fuel rod pellet to the calculation module; The nuclear fuel rod detection technical index data is preset in the calculation module, and is configured to calculate the characteristic γ-ray count curve before the activation of the nuclear fuel rod pellet and the characteristic γ-ray count curve after the activation of the nuclear fuel rod pellet to obtain the final count curve of the nuclear fuel rod, and calculate the pellet enrichment of the nuclear fuel rod based on the final count curve, and compare the pellet enrichment of the nuclear fuel rod with the nuclear fuel rod detection technical index, and judge whether the pellet enrichment of the nuclear fuel rod is qualified according to the comparison result.

8. The active detection system for nuclear fuel rods according to claim 7, wherein, The acquisition module further includes a first amplifier (10) and a second amplifier (16), The first amplifier is respectively connected to the first detector unit and the first pulse amplitude analyzer, and is configured to amplify the first signal detected by the first detector unit and transmit it to the first pulse amplitude analyzer, and the first pulse amplitude analyzer then converts the amplified first signal into the first square wave signal; The second amplifier is respectively connected to the second detector unit and the second pulse amplitude analyzer, and is configured to amplify the second signal detected by the second detector unit and transmit it to the second pulse amplitude analyzer, and the second pulse amplitude analyzer then converts the amplified second signal into the second square wave signal.

9. The active detection system for nuclear fuel rods according to claim 7, wherein, The first pulse amplitude analyzer (11) and the second pulse amplitude analyzer (17) are one of a comparator, a single-channel pulse amplitude analyzer, and a multi-channel pulse amplitude analyzer, wherein, when the first pulse amplitude analyzer is a single-channel pulse amplitude analyzer, the lower threshold of the single-channel pulse amplitude analyzer is the signal generated by 250 keV γ-rays, and the upper threshold of the single-channel pulse amplitude analyzer is the signal generated by 1.1 MeV γ-rays, When the second pulse amplitude analyzer is a single-channel pulse amplitude analyzer, the lower threshold of the single-channel pulse amplitude analyzer is the signal corresponding to the maximum noise of the second detector unit, and the upper threshold of the single-channel pulse amplitude analyzer is the signal generated by 2.5 MeV γ-rays. The γ-ray energy range that the multi-channel pulse amplitude analyzer can receive is greater than 2.5 MeV.

10. The active detection system for nuclear fuel rods according to claim 6, characterized in that the first detector unit includes a plurality of first detectors, the second detector unit includes a plurality of second detectors, and both the first detector and the second detector include a scintillation crystal (13), a photoelectric conversion device, a preamplifier, and a housing (14). Both the scintillation crystal and the photoelectric conversion device are arranged inside the housing. Through holes are provided on both the scintillation crystal and the housing, and the through holes are used for the nuclear fuel rod to pass through. The scintillation crystal is used to emit a light signal after absorbing the γ-rays emitted by the nuclear fuel rod pellets when the nuclear fuel rod passes through the through hole. The photoelectric conversion device is used to convert the light signal emitted by the scintillation crystal into an electrical signal and output it. The preamplifier is connected to the photoelectric conversion device and is used to receive the electrical signal and amplify it to obtain the first signal / the second signal.

11. The active detection system for nuclear fuel rods according to claim 10, characterized in that the number of the first detectors is more than two, and each of the first detectors is arranged in a straight line at the inlet end of the neutron activation unit. Each of the first detectors is respectively used to detect the γ-ray characteristic information before the activation of the nuclear fuel rod pellets, and the first signal includes the γ-ray characteristic information before the activation of the nuclear fuel rod pellets respectively detected by each of the first detectors. The number of the second detectors is more than two, and each of the second detectors is arranged in a straight line at the outlet end of the neutron activation unit. Each of the second detectors is respectively used to detect the γ-ray characteristic information after the activation of the nuclear fuel rod pellets, and the second signal includes the γ-ray characteristic information after the activation of the nuclear fuel rod pellets respectively detected by each of the second detectors.

12. The active detection system for nuclear fuel rods according to claim 11, characterized in that the detection efficiency of the scintillation crystal for 1.1 MeV γ-rays is ≥ 75%, and the thickness of the scintillation crystal is 1 - 2.5 times the height of the nuclear fuel rod pellets in the length direction of the nuclear fuel rod. The photoelectric conversion device is a photomultiplier tube or a silicon photomultiplier device.

13. The active detection system for nuclear fuel rods according to claim 12, characterized in that the material of the scintillation crystal is one of bismuth germanate (BGO), cesium iodide (CsI), sodium iodide (NaI), and cadmium zinc telluride (CZT).

14. The active detection system for nuclear fuel rods according to claim 12, characterized in that both the first detector and the second detector further include a first shielding body (15). The first shielding body is arranged outside the housing and is used to shield γ-rays with an energy lower than 1.1 MeV. An opening is provided on the first shielding body, and the position of the opening is concentric with the through hole on the scintillation crystal.

15. The active detection system for nuclear fuel rods according to claim 14, characterized in that, the neutron activation unit includes a neutron source (1) and a neutron shield (2), the neutron source is arranged inside the neutron shield, and an activation channel is provided on the neutron shield. The position of the activation channel is concentrically arranged with the through holes of the scintillation crystals in the first detector unit and the second detector unit.

16. The active detection system for nuclear fuel rods according to claim 15, characterized in that, the number of the activation channels is multiple, and the number of the detection units is multiple sets same as the number of the activation channels, the multiple sets of detection units are arranged in parallel. The first detector unit and the second detector unit in each set of detection units are respectively arranged at the inlet end and the outlet end of the same activation channel; second shields are respectively arranged between the first detector units and between the second detector units in two adjacent sets of detection units, and the second shields are used to shield the mutual interference of γ rays between the activation channels.

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