A method for inverting the time of metal foreign object entry into a nuclear power plant and irradiation experience

Abstract

The present application belongs to the technical field of nuclear reactor core state monitoring and safety evaluation, and discloses a kind of inversion method of nuclear power plant metal foreign matter into reactor time and irradiation experience, comprising the following steps: measuring analysis is carried out on the found metal foreign matter, and measurement data is obtained;The elements in the metal foreign matter are analyzed by different nuclide activation reaction channel, and analysis data is obtained;The parameter set required for solving is preset, including: the metal foreign matter in the core sequentially experiences two different orders of magnitude neutron fluence irradiation, and the preset parameter combination to be solved;Through traversing the preset parameter combination, combined with measurement data and analysis data, the activation equation set about multiple nuclides is established according to the activation reaction kinetics law and solved to determine the metal foreign matter into reactor time and irradiation experience.The present application can effectively utilize the multi-nuclide activation information, and the calculation conclusion is more reliable.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor core condition monitoring and safety assessment technology, and specifically relates to an inversion method for the time of entry of metallic foreign objects into the nuclear power plant and their irradiation experience. Background Technology

[0002] For metallic foreign objects, once they enter the reactor core and undergo power operation, they are activated by neutron irradiation within the core. Therefore, the activation activity of the foreign object can be used to estimate the time it entered the core. Current methods involve estimating the neutron fluence at the detected location of the foreign object during operation, assuming the foreign object remains constant at that location and the neutron fluence remains unchanged. Then, based on the material of the foreign object and the activity of a single nuclide after activation, the activation time is calculated, which is the time the foreign object entered the core. The main drawbacks are: 1. It heavily relies on neutron fluence data, while the neutron fluence at different locations within the core typically spans 4-5 orders of magnitude, from 1E+09n / (cm²). 2 .s) to 1E+14n / (cm 2 1. The neutron fluence at the location of the foreign object is inconsistent, making it difficult to accurately estimate the neutron fluence rate. 2. The foreign object may move through different locations within the reactor core, resulting in changes in the corresponding neutron fluence rate. 3. Only one activated nuclide can be selected for reactor entry time estimation; the activation information of other nuclides is not effectively utilized, and selecting multiple nuclides will yield different entry times. In summary, current methods for estimating reactor entry time cannot effectively utilize the activity data of each nuclide and heavily rely on neutron fluence rate data, resulting in high uncertainty in the assessment of reactor entry time. Summary of the Invention

[0003] To address the technical problems existing in the prior art, the purpose of this invention is to provide an inversion method for the time of entry of metallic foreign objects into a nuclear power plant and their irradiation experience.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for retrieving the time of introduction of metallic foreign objects into a nuclear power plant and their irradiation history includes the following steps: S1. Foreign object measurement and analysis: Measure and analyze the metallic foreign objects found in the reactor core to obtain measurement data of the metallic foreign objects; S2. Nuclide activation analysis: The elements in the metal foreign object are analyzed for activation reaction channels of different nuclides (referring to the main nuclear reaction channels where neutrons react with nuclides to generate radioactive products), and the analytical data of the metal foreign object are obtained. S3. A preset set of parameters required for solving the problem, including: the metal foreign object being irradiated by two different neutron fluence rates in the core, and a preset combination of parameters to be solved; the preset combination of parameters includes the intersection point parameter of the two different neutron fluence rates and the total number of power cycles experienced by the metal foreign object in the core. S4. By traversing the preset parameter combinations, combining the measurement data obtained in step S1 and the analysis data obtained in step S2, an activation equation set for multiple nuclides is established and solved according to the activation reaction kinetics law, so as to determine the stacking time and irradiation experience of the metal foreign object.

[0005] Furthermore, the measurement data in step S1 includes the mass, elemental composition, types of nuclides contained in the metallic foreign object, and the activity of the corresponding nuclides.

[0006] Furthermore, the elemental composition in step S1 is obtained by performing spectral measurements on the metallic foreign matter, and the elemental composition includes the element type and the mass fraction of each element in the metallic foreign matter.

[0007] Furthermore, the type of nuclide mentioned in step S1 is obtained by measuring the gamma spectrum of the metallic foreign object.

[0008] Further, the activity mentioned in step S1 is the activity measured by gamma spectrum of the metallic foreign object and corrected to the activity at the time of shutdown based on the time interval between the discovery time and the shutdown time.

[0009] Furthermore, the analytical data in step S2 includes the type of activated reaction channel, the neutron activation cross section corresponding to each activated reaction channel, and the natural abundance of the nuclide corresponding to each activated reaction channel.

[0010] Further, the candidate set of intersection location parameters in step S3 sequentially includes the intersection within the first power cycle after the metal foreign object enters the pile, within the second power cycle after the metal foreign object enters the pile, within the third power cycle after the metal foreign object enters the pile, and so on, until it is within the power cycle closest to when the metal foreign object was discovered. And / or, the candidate set of the total number of power cycle cycles parameter in step S3 includes 1, 2, 3, up to the total number of power cycle cycles from the first feed to the discovery of the metal foreign object.

[0011] Furthermore, the set of activation equations for multiple nuclides described in step S4 includes activation equations for at least three nuclides.

[0012] Furthermore, the plurality of nuclides in step S4 satisfy the following conditions: the half-life of each nuclide is not less than 20 days; and there is a half-life gradient among the plurality of nuclides.

[0013] Furthermore, the multiple nuclides mentioned in step S4 satisfy the following condition: the gamma spectrometer achieves a 90% accuracy rate in identifying radionuclides.

[0014] Furthermore, the plurality of nuclides in step S4 satisfy the following condition: the relative standard deviation of the activity measurement data corresponding to each nuclide is less than 5%.

[0015] Furthermore, in step S4, the activation equations of the at least three nuclides are rearranged into equations containing only the unknown t, and then solved.

[0016] Furthermore, the solution in step S4 includes substituting the number of days in each power cycle and the number of days in each overhaul cycle into the activation equation set.

[0017] Further, step S4 includes: S41. Select an intersection point in sequence as the preset position of the intersection point of the two different magnitudes of neutron fluence rates in the power cycle sequence; S42. Based on the irradiation time segment interval determined by the currently selected intersection position, and combining the measurement data obtained in step S1 and the analysis data obtained in step S2, establish a set of activation equations for multiple nuclides according to the activation reaction kinetic equation; wherein, different intersection positions result in different irradiation time segment intervals, and the corresponding activation equation set forms are also different. S43. Based on the currently established set of activation equations, select a total number of power cycle periods in sequence, solve the set of activation equations, and obtain the current solution; S44. Determine whether the current solution matches the historical data of the unit's operation: If the conditions are met, the total number of power cycle periods corresponding to the current solution and the current solution are determined as the entry time and irradiation experience of the metal foreign object, and the traversal is terminated. If it does not meet the requirements, return to step S43 and select the next total number of power cycle periods to continue solving; When no solution matching the historical data is found after traversing all power cycle periods, return to step S41, select the next intersection point, and repeat steps S42 to S44 until a solution matching the historical data is found or all intersection points have been traversed.

[0018] Furthermore, when the intersection point selected in step S41 is within the first power cycle after the metal foreign object is introduced into the stack, the activation equation for each nuclide is as follows: ; in: m: The number of power cycles that the metallic foreign object undergoes within the reactor core; A: The activity of a nuclide at the end of m power cycles, Bq; : Neutron fluence rate in stage 1, n / (cm) 2 .s); : Neutron fluence rate in stage 2, n / (cm) 2 .s); n: Activation reaction channel type, dimensionless; σ n : Neutron activation cross section corresponding to activation reaction channel n, cm 2 ; N pn : The number of target nuclei of nuclides generated in the activation reaction channel n, dimensionless; λ: decay constant of the nuclide, d -1 ; t: neutron irradiation time in stage 1, d; T1-T m : These represent the first to the mth power cycle periods from the discovery of the metallic foreign object to the first feed, in days; D1-D m : These are the first to mth overhaul cycles from the discovery of the metal foreign object to the first feed, excluding the overhaul cycle when the metal foreign object was discovered, in days; When the intersection point selected in step S41 is any other position, the expression of the activation equation is modified according to the power cycle period and overhaul period experienced by the neutron flux rate irradiation in the first stage and the power cycle period and overhaul period experienced by the neutron flux rate irradiation in the second stage.

[0019] Furthermore, the historical data consistent with unit operation mentioned in step S44 includes: the obtained two neutron flux rates being within the range of neutron flux rates during unit operation.

[0020] Furthermore, the historical data consistent with unit operation mentioned in step S4 includes: The two neutron fluence rates obtained are within the range of neutron fluence rates corresponding to the location where the metallic foreign object was found; And / or, the corresponding type of metal foreign object will appear during the maintenance activities of the overhaul cycle corresponding to the time when the obtained metal foreign object enters the pile.

[0021] The implementation of this invention has the following beneficial effects: The nuclear power plant metal foreign object insertion time and irradiation experience inversion method of this invention allows metal foreign objects to undergo neutron irradiation at different flux rates within the reactor core, without requiring preset neutron flux rates or corresponding irradiation times. The flux rate and corresponding irradiation time at each neutron stage can be obtained by solving the activation equation set. This invention can effectively utilize multi-nucleoside activation information, resulting in more reliable calculation conclusions. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the inversion method for the time of entry of metallic foreign objects into the nuclear power plant and their irradiation experience in some embodiments of the present invention.

[0023] Figure 2 This is a schematic diagram of the activation process of a metallic foreign object in a nuclear power plant in some embodiments of the present invention, where d is the time interval between the discovery time of the metallic foreign object and the shutdown time of the current overhaul. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0025] Unless otherwise specified, all reagents used in the examples are commercially available.

[0026] like Figure 1 As shown, in some embodiments, the method for retrieving the time of introduction of metallic foreign objects into a nuclear power plant and their irradiation experience includes the following steps: S1. Foreign Object Measurement and Analysis: Measure and analyze the metallic foreign objects found in the reactor core to obtain measurement data.

[0027] Specifically, the measurement data includes the mass of the metallic foreign object, its elemental composition, the types of nuclides it contains, and the activity of the corresponding nuclides.

[0028] Specifically, the elemental composition is obtained through spectral measurements of the metallic foreign material, including the element types and the mass fraction of each element in the metallic foreign material. The nuclide types are obtained through gamma-ray spectral measurements of the metallic foreign material. The activity is the activity obtained through gamma-ray spectral measurements of the metallic foreign material, corrected to the shutdown time based on the time interval between discovery and shutdown.

[0029] S2. Nuclide Activation Analysis: Analyze the activation reaction pathways (the main nuclear reaction pathways through which neutrons react with nuclides to generate radioactive products) of elements in metallic foreign objects to obtain analytical data of the metallic foreign objects.

[0030] Specifically, based on the elemental composition determined in step S1, the activation reaction pathways of different nuclides in each element are analyzed.

[0031] Specifically, the analysis data includes the type of activated reaction channels, the neutron activation cross section corresponding to each activated reaction channel, and the natural abundance of the nuclides corresponding to each activated reaction channel.

[0032] S3. The preset parameter set required for the solution includes: the metal foreign object being irradiated by two different neutron fluence rates in the core, and the preset parameter combination to be solved; the preset parameter combination includes the intersection position parameter of the two different neutron fluence rates and the total number of power cycles experienced by the metal foreign object in the core.

[0033] Specifically, the candidate set of intersection point location parameters sequentially includes the intersection point within the first power cycle after the metal foreign object enters the stack, the second power cycle after the metal foreign object enters the stack, the third power cycle after the metal foreign object enters the stack, and so on, until it is within the power cycle closest to when the metal foreign object was detected. In the solution of step S4, the locations of the intersection points are preset sequentially in the order listed above.

[0034] Specifically, the candidate set for the total number of power cycle periods includes 1, 2, 3, up to the total number of power cycle periods from the first feed to the discovery of a metallic foreign object. In the solution of step S4, the total number of power cycle periods is preset sequentially in the order listed above.

[0035] S4. By traversing the preset parameter combinations, combining the measurement data obtained in step S1 and the analysis data obtained in step S2, an activation equation set for multiple nuclides is established and solved according to the activation reaction kinetics to determine the stacking time and irradiation experience of the metallic foreign object. Specifically, step S4 includes: S41. Select an intersection point in sequence as the preset position of the intersection point of the two different magnitudes of neutron fluence rates in the power cycle period sequence.

[0036] S42. Based on the irradiation time interval determined by the currently selected intersection position, and combining the measurement data obtained in step S1 and the analysis data obtained in step S2, establish a set of activation equations for multiple nuclides according to the activation reaction kinetic equation; wherein, different intersection positions result in different irradiation time intervals, and the corresponding activation equations will also have different forms.

[0037] Specifically, the activation equation set for multiple nuclides includes activation equations for at least three nuclides: at least three nuclides are selected from the nuclide types determined in step S1, and activation equations for the selected nuclides are established based on the analysis results obtained in step S2 and the mass and activity of the nuclides obtained in step S1.

[0038] Specifically, the selected nuclides meet the following criteria: a half-life of not less than 20 days; and a half-life gradient between multiple nuclides. Furthermore, the nuclide identification accuracy corresponding to the selected nuclide is greater than 90%, and the relative standard deviation of the activity measurement data is less than 5%. Understandably, in the selection of nuclides, those with a measured nuclide identification accuracy greater than 90% and a relative standard deviation of the identified nuclide activity data less than 5% meet the confidence requirements for the data and can be selected. Generally speaking, confidence is directly proportional to the measured activity; a higher measured activity generally indicates higher confidence and more reliable data. Therefore, nuclides with higher measured activity values ​​can be selected from the range of nuclides tested.

[0039] For example, taking 316 stainless steel as an example, after being activated by neutrons, the nuclides Co60, Co58 and Cr51 generated have high activities, and the half-lives of these three nuclides are 5.271 years, 70.86 days and 27.7 days, respectively, showing a relatively obvious half-life gradient. Therefore, these three nuclides can be selected for analysis.

[0040] Specifically, when the intersection point selected in step S41 is within the first power cycle after the metal foreign object is introduced into the stack, the activation equation for each nuclide is as follows: ; in: m: The number of power cycles that the metallic foreign object undergoes within the reactor core; A: The activity of a nuclide at the end of m power cycles, Bq; : Neutron fluence rate in stage 1, n / (cm) 2 .s); : Neutron fluence rate in stage 2, n / (cm) 2 .s); n: Activation reaction channel type, dimensionless; σ n : Neutron activation cross section corresponding to activation reaction channel n, cm 2 ; N pn : The number of target nuclei of nuclides generated in the activation reaction channel n, dimensionless; λ: decay constant of the nuclide, d -1 ; t: neutron irradiation time in stage 1, d; T1-T m : These represent the first to the mth power cycle periods from the discovery of the metallic foreign object to the first feed, in days; D1-D m: These are the first to mth overhaul cycles from the discovery of the metal foreign object to the first feed, excluding the overhaul cycle when the metal foreign object was discovered, in days; When the intersection point selected in step S41 is any other position, the expression of the activation equation is modified according to the power cycle period and overhaul period experienced by the neutron flux rate irradiation in the first stage and the power cycle period and overhaul period experienced by the neutron flux rate irradiation in the second stage.

[0041] For example, when the intersection point selected in step S41 is within the second power cycle after the metal foreign object is introduced into the pile, the activation equation expression for each nuclide is as follows: .

[0042] Specifically, the activation equations for multiple nuclides are simplified into equations containing only the unknown variable t, and then solved. Taking the intersection point occurring within the first power cycle after the introduction of a metallic foreign object into the reactor, and establishing three activation equations for three nuclides as an example: like Figure 2 As shown, after the foreign object undergoes neutron flux irradiation in stages 1 and 2, the radioactivity of activated nuclide i to the end of the cycle is given by formulas (1) and (2), respectively: (1); (2); in: A i1 : The activity of nuclide i generated by neutron irradiation in stage 1 at the end of the cycle, Bq; A i2 : The activity of nuclide i generated by neutron irradiation in stage 2 at the end of the cycle, Bq; : Neutron fluence rate in stage 1, n / (cm) 2 .s); : Neutron fluence rate in stage 2, n / (cm) 2 .s); n: Activation reaction channel type, dimensionless; σ in : Neutron activation cross section corresponding to activation reaction channel n, cm 2 ; N pin : The number of target nuclei atoms that generate nuclide i in the activation reaction channel n, dimensionless; λ i The decay constant of nuclide i, d -1 ; t: neutron irradiation time in stage 1, d; T1-T m: These represent the first to the mth power cycle periods from the discovery of the metallic foreign object to the first feed, in days; D1-D m : These are the first to the mth overhaul cycles from the discovery of the metal foreign object to the first feed, excluding the overhaul cycle when the metal foreign object is discovered. The unit is days.

[0043] Formula (1) + Formula (2) is the nuclide activity of nuclide i at the end of the cycle after m power cycles, which can be simplified to Formula (3): (3); make: ; ; ; Then formula (3) becomes: (4); Similarly, the activities of nuclides j and k at the end of m power cycles can also be summarized as follows: (5); (6); Where A2, B2, and C2 correspond to nuclide j, and A3, B3, and C3 correspond to nuclide k. Combining equations (4) to (6), we obtain: (7); (8); (9); Formula (9) contains only the unknown t, and the root can be searched and solved by the bisection method.

[0044] S43. Based on the currently established activation equations, sequentially select a total number of power cycle periods to solve the activation equations and obtain the current solution.

[0045] Specifically, the solution involves substituting the number of days in each power cycle and the number of days in each overhaul cycle into the activation equations. Nuclear power units typically operate for one fuel cycle after each fuel loading, followed by a refueling overhaul. Each power cycle lasts approximately 1-2 years, and each refueling overhaul lasts approximately 30-130 days. Foreign objects generally enter the reactor core during refueling shutdowns. To ensure the safe and stable operation of the unit, nuclear power plants conduct core foreign object inspections after each refueling overhaul.

[0046] Specifically, solving the equations involves presupposing that the metallic foreign object has undergone one power cycle, two power cycles, and then, respectively, until it enters the reactor core during the initial refueling (corresponding to a total of 1 and 2 power cycles, up to the total number of power cycles from the initial refueling to the discovery of the metallic foreign object). After the foreign object is detected and activated (if a metallic foreign object is found in the core but not activated, it can be assumed that it entered the core during the overhaul without experiencing neutron irradiation during the unit's power operation), we can first presuppose that the foreign object has undergone one power cycle (i.e., irradiated by power operation for one power cycle). Combining the measured activity data, the neutron activation cross section corresponding to the activated reaction channel, and the operating time, we solve the equations. If there is no solution, it can be assumed that the foreign object has undergone more than one power cycle. Then, we presuppose that it has undergone two power cycles and continue solving the equations until there is a solution and the solution satisfies the objective conditions.

[0047] S44. Determine if the current solution matches the historical data of the unit's operation: If the conditions are met, the total number of power cycle periods corresponding to the current solution and the current solution are determined as the time of entry of the metallic foreign object into the pile and the irradiation experience, and the traversal is terminated. If it does not meet the requirements, return to step S43 and select the next total number of power cycle periods to continue solving; When no solution matching the historical data is found after traversing all power cycle periods, return to step S41, select the next intersection point, and repeat steps S42 to S44 until a solution matching the historical data is found or all intersection points have been traversed.

[0048] Among them, the historical data that conforms to the unit's operation includes: the two neutron flux rates obtained are within the range of neutron flux rates during the unit's operation.

[0049] In some embodiments, under various preset conditions, there may be cases where the two neutron flux rates obtained from the solution are within the range of the neutron flux rates during unit operation. In such cases, the historical data consistent with unit operation includes: the two obtained neutron flux rates being within the neutron flux rate range corresponding to the location where the metallic foreign object was discovered; and the occurrence of the corresponding type of metallic foreign object during maintenance activities in the overhaul cycle corresponding to the time the metallic foreign object entered the reactor. This determines a unique solution.

[0050] For example, theoretically, there might be cases where a solution exists after one power cycle and another after two power cycles. In such cases, the location of the foreign object within the core should be considered, along with the neutron fluence rate during power operation. The solution set that best matches the neutron fluence rate corresponding to that location should be prioritized. Simultaneously, the compatibility between the type of foreign object and the overhaul maintenance activities should be considered. For instance, if the foreign object is a certain type of metal gasket that was only used near the core during a specific overhaul but not in other overhauls, then the overhaul that used that gasket can be considered more suitable under the objective conditions.

[0051] Example 1 During a major overhaul of a nuclear power plant, a metallic foreign object was found at the location of the lower grid plate of the reactor core.

[0052] S1. Measure and analyze the discovered metallic foreign objects to obtain their mass, elemental composition, types of nuclides they contain, and the activity of the corresponding nuclides.

[0053] Analysis and comparison confirmed that the metallic foreign object was an M5 gasket, made of 316 stainless steel, with a mass of 0.51g. The elemental composition of the M5 gasket is shown in Table 1, and the radionuclide activities measured by gamma spectroscopy are shown in Table 2. The foreign object was discovered 13 days after reactor shutdown. The activities of each nuclide were corrected to those at the time of shutdown, and the corrected activities are shown in Table 3.

[0054] Table 1: Elemental composition (mass percentage) of 316 stainless steel for M5 gaskets as measured by spectroscopic measurements Table 2: Activity of each nuclide obtained from gamma spectroscopy measurements Table 3: Activity of each nuclide corrected to shutdown S2. Based on the elemental composition determined in step S1, analyze the activation reaction pathways of different nuclides in each element.

[0055] Based on the elemental composition in Table 1, we looked up the elemental abundance and activation reaction pathways, and compiled them into Table 4.

[0056] Table 4: Analysis of the radionuclide activation reaction pathway of 316 stainless steel material for M5 gaskets Note: In Table 4, the neutron cross section marked (thermal) represents the thermal neutron reaction cross section, while the unmarked section represents the fast neutron reaction cross section.

[0057] S3. Preset the set of parameters required for the solution, including: the metallic foreign object undergoes irradiation by two different magnitudes of neutron flux rate in the core.

[0058] S4. The intersection of the two neutron flux rates is pre-set to be within the first power cycle after the metal foreign object is introduced into the reactor. Three nuclides are selected from the nuclide types determined in step S1, including Co58, Co60 and Cr51. Based on the results of the analysis in step S2 and the mass and activity of the nuclides obtained in step S1, activation equations for the three nuclides are established. The activation equations for the nuclides are shown in the above activation equation expressions. The activation equations for the three nuclides are rearranged into equations containing only the unknown t, as shown in the above formula (9).

[0059] First, it is assumed that the metal foreign object has undergone one power cycle in the core (i.e., the total number of power cycles is 1), then m in formula (9) is 1. The power cycle closest to the discovery of the metal foreign object is T1 = 526 days. In the activation calculation, the fast neutron flux rate and the thermal neutron flux rate are taken to be the same value (if the fast neutron flux rate and the thermal neutron flux rate are different, the ratio of the fast neutron flux rate and the thermal neutron flux rate can be estimated according to the location of the foreign object in the core, and then the fast neutron flux rate or the thermal neutron flux rate can be used uniformly). Based on the mass of the metal foreign object of 0.51g, combined with the data in Tables 3 and 4, the data of A1 (corresponding to Co58 nuclide), A2 (corresponding to Co60 nuclide) and A3 (corresponding to Cr51 nuclide) are calculated. The results are: A1 = 4.31E+11, A2 = 6.08E+11, A3 = 3.7E+10.

[0060] The specific calculation process for A1, A2, and A3 is as follows: (1) A1 (Co58 nuclide): According to A1= ,in: A i =1.78E+07 Bq, from Table 3, corrected to the activity at shutdown; The activation reaction pathways involve (Ni58, Co58) and (Co59, Co58), σ in They are 0.111×10 -24 cm 2 0.0004×10 -24 cm 2 From Table 4; The activation reaction channel (Ni58, Co58) generates the target nucleus Co58 with the number of Ni58 atoms N. pi1 Foreign matter mass × mass fraction × natural abundance / average mass number × Avogadro's constant = 0.51g × 10.44% × 68.08% / 58.69g / mol × 6.02 × 10 23 mol -1 =3.72×10 20 ; The number of Co59 atoms (N) in the target nucleus of the activated reaction channel (Co59, Co58) that produces nuclide Co58. pi2 Foreign matter mass × mass fraction × natural abundance / average mass number × Avogadro's constant = 0.51g × 0.02% × 100% / 58.93g / mol × 6.02 × 10 23 mol -1 =1.04×10 18 ; have: A1 = 1.78E + 0.7 / (0.111 × 10⁻⁷) -24 ×3.72×10 20 +0.0004×10 -24 ×1.04×10 18 =4.31E+11.

[0061] (2) A2 (Co60 nuclide): A j =2.39E+07 Bq, from Table 3, corrected to the activity at shutdown; The activation reaction pathways involve (Ni60, Co60), (Cu63, Co60), and (Co59, Co60), σ jn They are 0.002×10 -24 cm 2 0.0006×10 -24 cm 2 and 37.45×10 -24 cm 2 From Table 4; The activation reaction channel (Ni60, Co60) generates the target nucleus Co60 with the number of Ni60 atoms N. pj1 Foreign matter mass × mass fraction × natural abundance / average mass number × Avogadro's constant = 0.51g × 10.44% × 26.22% / 58.69g / mol × 6.02 × 10 23 mol -1 =1.43×10 20 ; The number of Cu63 atoms (N) in the target nucleus for the activation reaction channel (Cu63, Co60) to generate the nuclide Co60. pj2 Foreign matter mass × mass fraction × natural abundance / average mass number × Avogadro's constant = 0.51g × 0.24% × 69.15% / 63.55g / mol × 6.02 × 10 23 mol -1 =8.02×10 18 ; The number of Co59 atoms (N) in the target nucleus for the activation reaction pathway (Co59, Co60) to generate nuclide Co60.pj3 Foreign matter mass × mass fraction × natural abundance / average mass number × Avogadro's constant = 0.51g × 0.02% × 100% / 58.93g / mol × 6.02 × 10 23 mol -1 =1.04×10 18 ; have: A2 = 2.39E + 0.7 / (0.002 × 10) -24 ×1.43×10 20 +0.0006×10 -24 ×8.02×10 18 +37.45×10 -24 ×1.04×10 18 =6.08E+11.

[0062] (3) A3 (Cr51 nuclide): A k =2.49E+07 Bq, from Table 3, corrected to the activity at shutdown; The activation reaction pathways involve (Fe54, Cr51) and (Cr50, Cr51), σ kn They are 0.0006×10 -24 cm 2 15.9×10 -24 cm 2 From Table 4; The number of Fe54 atoms in the target nucleus N for the activation reaction channel (Fe54, Cr51) to generate nuclide Cr51 pk1 Foreign matter mass × mass fraction × natural abundance / average mass number × Avogadro's constant = 0.51g × 69.28% × 5.85% / 55.85g / mol × 6.02 × 10 23 mol -1 =2.23×10 20 ; The number of Cr50 atoms (N) in the target nucleus for the activation reaction pathway (Cr50, Cr51) to generate nuclide Cr51 pk2 Foreign matter mass × mass fraction × natural abundance / average mass number × Avogadro's constant = 0.51g × 16.48% × 4.35% / 52.00g / mol × 6.02 × 10 23 mol -1 =4.23×10 19 ; have: A3 = 2.49E + 0.7 / (0.0006 × 10) -24 ×2.23×10 20 +15.9×10-24 ×2.23×10 20 =3.70E+10.

[0063] The bisection method is used to find the root of the unknown t in formula (9). The calculation process is shown in Table 5.

[0064] Table 5: Root-finding calculation process using the bisection method (X is the right-hand side of the equation (9)) Substituting t=223d into formulas (7) and (8), we can obtain the following results: =3.28E+10 n / (cm 2 .s), =8.74E+12 n / (cm 2 From the above data, it can be concluded that the metallic foreign object first underwent approximately 223 days within the reactor core, with a neutron fluence rate of 8.74E+12 n / (cm²). 2 The neutrons were irradiated with .s and, in the later stages of the cycle, the neutron flux was 3.28E+10 n / (cm²). 2 Neutron irradiation (.s).

[0065] The two neutron fluence rates obtained in this embodiment are 8.74E+12 n / (cm²). 2 .s) and 3.28E+10 n / (cm 2 Within the neutron flux range of the unit's operation, and given that the location of the discovered metallic foreign object was very close to the outer perimeter of the lower grid plate in the reactor core, the two neutron flux rates obtained in this embodiment (8.74E+12 n / (cm)) were within the range of the unit's operating neutron flux. 2 .s) and 3.28E+10 n / (cm 2 The .s)) is also within the neutron flux range corresponding to this location. Furthermore, an M5 shim was used during the maintenance activities of the previous overhaul cycle. Therefore, the solution corresponding to one power cycle in which the metallic foreign object experienced within the core is the desired one, i.e., the time of the metallic foreign object's entry into the core is the overhaul cycle preceding the one in which the metallic foreign object was discovered. The irradiation experience of the metallic foreign object is as follows: the metallic foreign object first experienced approximately 223 days in the core with a neutron flux rate of 8.74E+12 n / (cm²). 2 The neutrons were irradiated with .s and, in the later stages of the cycle, the neutron flux was 3.28E+10 n / (cm²). 2 Neutron irradiation (.s).

[0066] Furthermore, based on the actual operating conditions of the unit (T1=526d, D1=78.43d, T2=595d, D2=130d, T3=526d), two power cycle periods and three power cycle periods are preset. Among them, it is preset that the metal foreign object has experienced two power cycle periods in the core, so m in formula (9) is 2. Then the data of the two power cycle periods and one overhaul period closest to the discovery of the metal foreign object are used (T1= Substituting 526d, D1=78.43d, T2=595d) into the equation system to solve; assuming the metal foreign object has undergone 3 power cycles in the core, then m in formula (9) is 3. Substituting the data of the 3 power cycles closest to the discovery of the metal foreign object and 2 overhaul cycles (T1=526d, D1=78.43d, T2=595d, D2=130d, T3=526d) into the equation system to solve; neither of the two assumptions has a solution.

[0067] Therefore, the solution obtained under the first preset condition that conforms to the unit's historical data is the time of entry of the metal foreign object into the reactor and the irradiation experience in this embodiment. This method can effectively invert the time of entry of the metal foreign object into the reactor and the irradiation experience in a nuclear power plant.

[0068] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for retrieving the time of introduction of metallic foreign objects into a nuclear power plant and their irradiation history, characterized in that, Includes the following steps: S1. Foreign object measurement and analysis: Measure and analyze the metallic foreign objects found in the reactor core to obtain measurement data of the metallic foreign objects; S2. Nuclide activation analysis: Analyze the activation reaction pathways of different nuclides in the metal foreign object to obtain analytical data of the metal foreign object; S3. A preset set of parameters required for solving the problem, including: the metal foreign object being irradiated by two different neutron fluence rates in the core, and a preset combination of parameters to be solved; the preset combination of parameters includes the intersection point parameter of the two different neutron fluence rates and the total number of power cycles experienced by the metal foreign object in the core. S4. By traversing the preset parameter combinations, combining the measurement data obtained in step S1 and the analysis data obtained in step S2, an activation equation set for multiple nuclides is established and solved according to the activation reaction kinetics law, so as to determine the stacking time and irradiation experience of the metal foreign object.

2. The inversion method for determining the time of entry of metallic foreign objects into the nuclear power plant and their irradiation experience according to claim 1, characterized in that: The measurement data in step S1 includes the mass, elemental composition, types of nuclides contained in the metallic foreign object, and the activity of the corresponding nuclides.

3. The inversion method for determining the time of entry of metallic foreign objects into the nuclear power plant and their irradiation experience according to claim 1, characterized in that: The analytical data in step S2 includes the type of activated reaction channel, the neutron activation cross section corresponding to each activated reaction channel, and the natural abundance of the nuclide corresponding to each activated reaction channel.

4. The inversion method for determining the time of entry of metallic foreign objects into the nuclear power plant and their irradiation experience according to claim 1, characterized in that: The candidate set of intersection location parameters in step S3 includes the intersection within the first power cycle after the metal foreign object enters the pile, within the second power cycle after the metal foreign object enters the pile, within the third power cycle after the metal foreign object enters the pile, and so on, until it is within the power cycle closest to when the metal foreign object was discovered. And / or, the candidate set of the total number of power cycle cycles parameter in step S3 includes 1, 2, 3, up to the total number of power cycle cycles from the first feed to the discovery of the metal foreign object.

5. The inversion method for determining the time of introduction of metallic foreign objects into a nuclear power plant and their irradiation history according to claim 1, characterized in that, The plurality of nuclides in step S4 satisfy the following conditions: the half-life of each nuclide is not less than 20 days; and there is a half-life gradient among the plurality of nuclides.

6. The inversion method for determining the time of introduction of metallic foreign objects into a nuclear power plant and their irradiation history according to claim 1, characterized in that: The solution in step S4 includes substituting the number of days in each power cycle and the number of days in each overhaul cycle into the activation equation set.

7. The inversion method for determining the time of introduction of metallic foreign objects into a nuclear power plant and their irradiation history according to claim 4, characterized in that, Step S4 includes: S41. Select an intersection point in sequence as the preset position of the intersection point of the two different magnitudes of neutron fluence rates in the power cycle sequence; S42. Based on the irradiation time segment interval determined by the currently selected intersection position, and combining the measurement data obtained in step S1 and the analysis data obtained in step S2, establish a set of activation equations for multiple nuclides according to the activation reaction kinetic equation; wherein, different intersection positions result in different irradiation time segment intervals, and the corresponding activation equation set forms are also different. S43. Based on the currently established set of activation equations, select a total number of power cycle periods in sequence, solve the set of activation equations, and obtain the current solution; S44. Determine whether the current solution matches the historical data of the unit's operation: If the conditions are met, the total number of power cycle periods corresponding to the current solution and the current solution are determined as the entry time and irradiation experience of the metal foreign object, and the traversal is terminated. If it does not meet the requirements, return to step S43 and select the next total number of power cycle periods to continue solving; When no solution matching the historical data is found after traversing all power cycle periods, return to step S41, select the next intersection point, and repeat steps S42 to S44 until a solution matching the historical data is found or all intersection points have been traversed.

8. The inversion method for determining the time of introduction of metallic foreign objects into a nuclear power plant and their irradiation history according to claim 7, characterized in that, When the intersection point selected in step S41 is within the first power cycle after the metal foreign object is introduced into the stack, the expression for the activation equation of each nuclide is as follows: ； in: m: The number of power cycles that the metallic foreign object undergoes within the reactor core; A: The activity of a nuclide at the end of m power cycles, Bq; : Neutron fluence rate in stage 1, n / (cm) 2 .s); : Neutron fluence rate in stage 2, n / (cm) 2 .s); n: Activation reaction channel type, dimensionless; σ n : Neutron activation cross section corresponding to activation reaction channel n, cm 2 ; N pn : The number of target nuclei of nuclides generated in the activation reaction channel n, dimensionless; λ: decay constant of the nuclide, d -1 ; t: neutron irradiation time in stage 1, d; T1-T m : These represent the first to the mth power cycle periods from the discovery of the metallic foreign object to the first feed, in days; D1-D m : These are the first to mth overhaul cycles from the discovery of the metal foreign object to the first feed, excluding the overhaul cycle when the metal foreign object was discovered, in days; When the intersection point selected in step S41 is any other position, the expression of the activation equation is modified according to the power cycle period and overhaul period experienced by the neutron flux rate irradiation in the first stage and the power cycle period and overhaul period experienced by the neutron flux rate irradiation in the second stage.

9. The inversion method for determining the time of introduction of metallic foreign objects into a nuclear power plant and their irradiation history according to claim 7, characterized in that, The historical data that conforms to the unit's operation in step S44 includes: the two neutron flux rates obtained are within the range of neutron flux rates during unit operation.

10. The inversion method for determining the time of introduction of metallic foreign objects into a nuclear power plant and their irradiation history according to claim 7 or 9, characterized in that, The historical data consistent with unit operation mentioned in step S44 includes: The two neutron fluence rates obtained are within the range of neutron fluence rates corresponding to the location where the metallic foreign object was found; And / or, the corresponding type of metal foreign object will appear during the maintenance activities of the overhaul cycle corresponding to the time when the obtained metal foreign object enters the pile.

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