Methods and devices for detecting the reduction of external radiation field in reactor core by primary circuit zinc injection.

Abstract

This invention provides a method and apparatus for detecting the reduction of the external radiation field of the reactor core by primary loop zinc injection. The detection method includes: before zinc injection, acquiring the dose rate data of the external radiation field of the reactor core at location i on the surface of the primary loop equipment, denoted as D. i,0 The unit is mSv / h; during the zinc injection process, zinc concentration samples were taken for analysis, and the cumulative zinc injection amount C at at least two time points was calculated based on the integral of the concentration over time. Zn The unit is µg / kg·month; in conjunction with the calculation of C Zn At the same time point, the dose rate data D after zinc injection was obtained. i The unit is mSv / h; based on D at at least two time points i,0 D i With C Zn Establish D i With C Zn The mapping relationship between them; using this mapping relationship, the corresponding dose rate D can be predicted based on the cumulative zinc addition at any subsequent time point. i The invention calculates the decrease in dose rate before and after zinc injection, using this decrease as the detection result of the reduction in the external radiation field of the reactor core caused by zinc injection. This invention solves the technical problem of the inability to quantify the reduction in the external radiation field of the reactor core caused by primary loop zinc injection.

Description

Technical Field

[0001] This invention relates to the field of nuclear power technology, and in particular to a method and apparatus for detecting the reduction of the external radiation field of the reactor core by zinc injection in the primary loop. Background Technology

[0002] The primary loop system of a pressurized water reactor nuclear power unit is subjected to high temperature, high pressure and strong radiation environment for a long time. Corrosion products of the primary loop structural materials migrate to the reactor core with the coolant. After being activated by neutrons, they form radioactive nuclides. These activation products are deposited on the surface of equipment outside the reactor core, resulting in a significant increase in the dose rate of the radiation field outside the reactor core, which poses a severe challenge to the radiation protection of maintenance personnel during major overhauls.

[0003] Zinc injection into the primary coolant circuit effectively reduces the dose rate of the external radiation field in the reactor core by replacing activated corrosion products in the metal oxide film with zinc ions. However, there is currently a lack of effective technical means to measure the specific extent to which zinc injection reduces the external radiation field. Therefore, there is an urgent need to establish a method that can quantify the degree to which zinc injection reduces the external radiation field. Summary of the Invention

[0004] This invention provides a method and apparatus for detecting the reduction of the external radiation field of the reactor core by primary circuit zinc injection, in order to solve the technical problem that the reduction of the external radiation field by primary circuit zinc injection cannot be quantified.

[0005] This invention provides a method for detecting the reduction of the external radiation field of the reactor core during primary loop zinc injection. The method includes: acquiring dose rate data of the external radiation field of at least one equipment surface area in the primary loop of a nuclear power plant before zinc injection, denoted as the pre-zinc injection dose rate data D. i,0 During the zinc injection process, the zinc concentration in the primary circuit was sampled and analyzed. Based on the integral of the zinc concentration over time, the cumulative zinc injection amount C corresponding to at least two different time points was calculated. Zn At the same time point as the calculation of the cumulative zinc loading data, the dose rate data of the external radiation field of the equipment surface area after zinc loading was acquired and denoted as the post-zinc loading dose rate data D. i Based on the obtained D at least two time points i,0 D i With C Zn Establish dose rate data after zinc injection D i With cumulative zinc addition C Zn The mapping relationship between them; using the mapping relationship, based on the cumulative zinc injection amount at any subsequent time point, the post-zinc injection dose rate data D at the corresponding time point is predicted. i The dose rate reduction before and after zinc injection was calculated, and the reduction rate was used as the detection result of the reduction in the external radiation field of the reactor core by zinc injection.

[0006] In one embodiment of the present invention, the mapping relationship is an exponentially decaying function relationship.

[0007] In one embodiment of the present invention, the mapping relationship is specifically as follows: .

[0008] In one embodiment of the present invention, based on the mapping relationship, the reduction in dose rate of the external radiation field after zinc injection is calculated as follows: (D i,0 -D i ) / D i,0 ×100%.

[0009] In one embodiment of the present invention, the primary loop includes a reactor pressure vessel, a primary loop main pipeline, a steam generator, a pressurizer, and a primary loop coolant pump; the equipment surface area includes at least one of the following: dose rate monitoring points at different heights and orientations on the outer wall of the reactor pressure vessel, the outer wall of the primary loop main pipeline, the outer shell of the steam generator, the outer shell of the pressurizer, and the outer shell of the primary loop coolant pump.

[0010] In one embodiment of the present invention, the pre-zinc injection dose rate data D i,0 and the dose rate data after zinc injection D i The data were obtained using a portable gamma spectrometer.

[0011] In one embodiment of the present invention, the cumulative zinc addition amount C Zn The zinc concentration in the primary circuit during zinc injection was obtained by continuous or intermittent sampling and analysis, and by integral calculation of the zinc concentration over time.

[0012] In one embodiment of the present invention, the detection method is used to predict the degree of reduction of the external radiation field of the reactor core before the implementation of zinc injection technology in the primary loop of a nuclear power plant, or to verify the degree of reduction of the external radiation field of the reactor core after implementation.

[0013] In one embodiment of the present invention, when acquiring the dose rate data of the external radiation field of the equipment surface area before zinc injection, at least three repeated measurement points are set for each equipment surface area, and the average value of the measured values ​​of each repeated measurement point is used as the radiation dose rate data of the equipment surface area.

[0014] The present invention also provides a detection device, the detection device comprising: The first acquisition module is used to acquire dose rate data of the external radiation field of at least one equipment surface area in the primary loop of the nuclear power plant before zinc injection, denoted as pre-zinc injection dose rate data D. i,0 ; The calculation module is used to sample and analyze the zinc concentration in the primary circuit during zinc injection, and calculate the cumulative zinc injection amount C at at least two different time points based on the integral of the zinc concentration over time. Zn ; The second acquisition module is used to acquire the dose rate data of the external radiation field of the equipment surface area after zinc injection at the same time point as the calculation of the cumulative zinc injection data, denoted as the post-zinc injection dose rate data D. i ; The quantity processing module is used to process D based on at least two time points. i,0 D i With C Zn Establish dose rate data after zinc injection D i With cumulative zinc addition C Zn The mapping relationship between them; The test result analysis module is used to analyze the cumulative zinc addition C at any subsequent time point using a mapping relationship. Zn Predict the dose rate data D after zinc injection at the corresponding time point. i The dose rate reduction before and after zinc injection was calculated, and the reduction rate was used as the detection result of the reduction in the external radiation field of the reactor core by zinc injection.

[0015] The beneficial effects of this invention are as follows: First, by establishing a mapping relationship between the dose rate data after zinc injection and the cumulative zinc injection amount, the reduction in dose rate before and after zinc injection can be calculated, achieving quantitative detection of the degree to which zinc injection reduces the radiation field outside the reactor core, thus solving the technical problem that this degree cannot be quantified in the prior art. Second, by using the dose rate data before zinc injection as its own benchmark, this invention eliminates background differences between different units and different monitoring locations, making the detection results comparable. Third, by establishing a mapping relationship between the radiation dose rate and the decay of the radiation dose rate over zinc injection time using the cumulative zinc injection amount, the radiation dose rate and the reduction amount at any future time point can be predicted, providing data support for optimizing zinc injection strategies and planning radiation protection measures. In addition, this mapping relationship can identify the saturation point of zinc injection benefits, avoiding resource waste caused by excessive zinc injection. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0017] In the attached diagram: Figure 1 This is a schematic flowchart of a detection method for reducing the intensity of external radiation field in a reactor core by primary loop zinc injection, as provided in an embodiment of this application. Figure 2 This application provides an embodiment of an optional schematic diagram illustrating the trend and fitting results of the normalized dose rate ratio as a function of the cumulative zinc injection amount in the detection method for reducing the degree of external radiation field of the reactor core by primary loop zinc injection. Detailed Implementation

[0018] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0019] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the shape, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0020] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0021] The application scenarios and technical background of the embodiments of this application are described in detail below. The detection method and detection device provided in this application are mainly applied to pressurized water reactor nuclear power units that adopt primary loop zinc injection technology. The primary loop system (i.e., reactor coolant system) of a pressurized water reactor nuclear power plant is one of the safety barriers of the nuclear power plant. It mainly consists of the reactor pressure vessel, steam generator, primary loop coolant pump, pressurizer, and primary loop main pipeline connecting these devices. During the power operation of the nuclear power plant, the primary loop system is filled with a high-temperature (average temperature 310°C), high-pressure (approximately 15.5 MPa) coolant containing boric acid and lithium hydroxide.

[0022] Under such harsh operating conditions, trace corrosion inevitably occurs in the primary circuit structural materials (such as the nickel-based alloys used in the steam generator heat transfer tubes and the stainless steel used in the main pipelines). The corroded metallic elements (such as Fe, Ni, and Co) are released into the coolant in ionic or particulate form and circulate with the coolant through the reactor core's active zone. Under the strong neutron flux irradiation of the reactor core, these metallic elements undergo neutron capture reactions, transforming into radioactive activated corrosion products, among which the most harmful are… 60 Co (from impurity elements in structural materials) 59 It is activated from Co, has a half-life of 5.27 years, and releases high energy of 1.17 MeV and 1.33 MeV. (rays) and 58 Co (a major element in structural materials) 58 Ni Jing ( , It is formed by a reaction, has a half-life of 70.86 days, and releases 0.81 MeV. (Radiation). These radioactive cobalt nuclides migrate with the coolant and redeposit on the equipment surfaces outside the reactor core, integrating into the spinel oxide film, resulting in a continuous increase in radiation dose rates in areas such as the primary loop main pipes and the steam generator water chambers. This not only increases the daily radiation dose to operating personnel but also places enormous radiation protection pressure on equipment maintenance, valve upkeep, and chemical cleaning work during major overhauls.

[0023] To control the growth of the external radiation field of the reactor core and mitigate primary side stress corrosion cracking of nickel-based alloys, zinc injection (zinc injection) technology for the primary coolant is widely used internationally. The physicochemical mechanism of zinc injection technology lies in the presence of zinc ions (Zn...). 2+ In spinel ions, tetrahedral site occupancy energy is extremely high, significantly higher than that of cobalt ions (Co). 2+ ) and nickel ions (Ni 2+ When a trace amount of zinc (usually zinc acetate) is injected into the primary coolant, the zinc ions displace radioactive cobalt nuclides and nickel and iron ions from the oxide film lattice on the equipment surface, forming zinc spinel (such as zinc chromate ZnCr2O4 or zinc ferrite ZnFe2O4), which is thermodynamically more stable and has lower solubility. The displaced radioactive cobalt nuclides enter the coolant and are subsequently removed by the purification and desalination system (RCV), thereby reducing the dose rate of the radiation field outside the reactor core.

[0024] However, in practical engineering, how to quantitatively assess and predict the effect of zinc injection technology on reducing the radiation field outside the reactor core has remained an unresolved problem. First, the initial radioactive source term accumulation levels differ among different nuclear power units, and significant differences exist in the geometry, water flow shear force, and material surface conditions of different equipment within the same unit (such as the primary side of the steam generator, primary loop main piping, pressurizer, etc.), leading to orders-of-magnitude deviations in the initial radiation background. Directly comparing absolute dose rates cannot accurately and objectively evaluate the actual contribution of zinc injection. Second, the primary loop water chemistry system is a highly complex dynamic equilibrium system. The injection, consumption, adsorption, and loss of zinc ions are influenced by a complex interplay of factors such as temperature, boron and lithium concentration, and discharge flow rate. Traditional models based on macroscopic mass balance suffer from excessive unknown parameters and extremely high computational uncertainty, rendering them impractical in engineering. Furthermore, the primary loop coolant contains extremely high-energy... 16 The background radiation of nitrogen makes it difficult for online measurement equipment to accurately obtain the true dose rate of nuclides attached to the surface of the equipment.

[0025] To overcome the aforementioned technical deficiencies, this application provides a method for detecting the reduction of the external radiation field of the reactor core by primary-loop zinc injection. This method introduces the "cumulative zinc injection amount" as a standardized independent variable and "normalizes" the radiation dose rate at each monitoring location, eliminating differences in initial background and geometric structure. It constructs an exponential decay response model that conforms to the ion replacement kinetics of spinel oxide films, achieving standardized, high-precision quantitative detection and prediction of the dose reduction effect of zinc injection.

[0026] The core method flow of the embodiments of this application will be described in detail below with reference to the accompanying drawings. Figure 1 As shown in the embodiment of this application, a method for detecting the reduction of the external radiation field of the reactor core by primary circuit zinc injection is provided. This method is applied to a system for detecting and evaluating the effect of primary circuit zinc injection and specifically includes the following steps: Step S1: Before zinc injection, acquire the dose rate data of the external radiation field at location i on the surface of at least one piece of equipment in the primary loop of the nuclear power plant, and record it as the pre-zinc injection dose rate data. ,0 .

[0027] In this embodiment, to establish an accurate initial radiation background benchmark, during the reactor shutdown overhaul before the implementation of the primary loop zinc injection technology, a portable gamma spectrometer is used to conduct radiation dose rate surveys on multiple equipment surface areas of the primary loop. The primary loop equipment includes steam generators, main pumps, pipes, valves, etc. The corresponding equipment surface areas can be one or more of the following: the surface of the primary side water chamber of the steam generator, the surface of the transition section of the main pipe, the surface of the main pump casing, and the surface of the pressurizer ripple tube. Due to the complex geometry of the primary loop equipment surfaces and the potential spatial inhomogeneity of activated corrosion product deposition, to improve data representativeness, in this embodiment, at least three repeated measurement points are set for each equipment surface area location i when acquiring radiation dose rate data for each equipment surface area. During measurement, the detector of the portable gamma spectrometer is placed close to the surface of the measurement point for sufficient counting accumulation time to reduce statistical fluctuation errors. Subsequently, the arithmetic mean of the measurements from the at least three repeated measurement points is calculated, and this average is used as the representative radiation dose rate data for equipment surface area location i, denoted as the pre-zinc injection dose rate data D. i,0 (Unit: μSv / h). By averaging measurements from multiple points, random errors caused by localized radioactive "hot spots" or minor deviations in detector placement can be effectively eliminated, ensuring the accuracy and reliability of the initial background data.

[0028] Of course, if the above effects are not considered, it is also possible to obtain only one measurement point at location i on the surface of each device, and use the radiation dose at that measurement point as the final radiation dose rate.

[0029] It should be noted that in this step, it is possible to obtain the dose rate data of the external radiation field of the reactor core for only one of the above-mentioned equipment surface areas, or to obtain the dose rate data of the external radiation field of the reactor core for several or all of the equipment surface areas.

[0030] Step S2: During the zinc injection process, sample and analyze the zinc concentration in the primary circuit, and calculate the cumulative zinc injection amount at at least two different time points based on the integral of the zinc concentration over time. Zn .

[0031] During the operation of the nuclear power unit and the zinc injection process, the zinc concentration in the primary coolant is periodically sampled and analyzed. Sampling can be performed using a continuous online chemical analyzer, or intermittent manual sampling can be used for precise determination via inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectrometry. The zinc concentration values ​​obtained from each analysis and the corresponding sampling time are recorded to establish a data series of zinc concentration changes over time. Because the zinc concentration in the primary coolant fluctuates transiently due to various factors such as water replenishment, drainage and purification, boric acid concentration adjustment, and dynamic adsorption on material surfaces, directly using instantaneous concentrations or simple arithmetic averages cannot accurately reflect the cumulative contact and total reaction between zinc ions and the primary coolant surface. Therefore, in this embodiment, a "cumulative zinc addition amount" C is introduced. Zn (Unit: μg / kg) The physical index (month) is calculated using the following formula:

[0032] in,[ ]( () represents the zinc concentration in the primary coolant at time τ, in units of... g / kg; t0 represents the start time of zinc injection; t represents the evaluation deadline. In actual data processing, this integration process can be achieved by numerically integrating discrete zinc concentration monitoring data (e.g., using the trapezoidal rule or Simpson's rule). By calculating the cumulative zinc injection amount at at least two different time points (usually corresponding to different operating cycles or overhaul nodes), the total cumulative zinc ion exposure received by the primary loop system at different stages can be obtained.

[0033] Furthermore, during operation cycles lasting several months, zinc concentration data gaps are inevitable due to periodic calibration of chemical analysis instruments, online instrument malfunctions, or manual sampling intervals. To prevent data gaps from causing interruptions in integral calculations or introducing step errors, if missing zinc concentration [Zn](τ) ​​data is detected within a certain time period, linear interpolation is automatically used to fill in the missing data. Specifically, assuming measured zinc concentrations [Zn](t1) and [Zn](t2) are available at times t1 and t2, but data is missing at time τ, the interpolation calculation is as follows:

[0034] By using this linear interpolation method to fill in the missing data, the continuity and smoothness of the integral curve are ensured.

[0035] To obtain a high-precision, continuous zinc concentration curve, this embodiment uses periodic manual sampling and analysis data (such as inductively coupled plasma mass spectrometry, ICP-MS) as a reference value to periodically calibrate the online chemical instrument, ensuring that the measurement is free of systematic bias. Simultaneously, high-frequency zinc concentration data is acquired in real time through the online chemical instrument to provide continuous trend tracking. To eliminate random noise in the online data, a Kalman filter algorithm is introduced into the continuous trend tracking to denoise the acquired zinc concentration data, generating a smooth zinc concentration change curve [Zn](τ) ​​over time.

[0036] Step S3: At the same time point as calculating the cumulative zinc addition data, acquire the dose rate data of the external radiation field of the equipment surface region i after zinc injection, and record it as the dose rate data after zinc injection D. i .

[0037] During the overhaul following zinc injection, at the same time points as when calculating the cumulative zinc injection data, radiation dose rate surveys were performed on the same equipment surface area and the same repeated measurement points identified in step S1 using the same portable gamma spectrometer. Similarly, measurements were taken at least three repeated measurement points for each equipment surface area location i, and their arithmetic mean was calculated as the value of that location i at a specific cumulative zinc injection amount C. Zn Dose rate data D i The unit is μSv / h. Since the measurement was carried out during a reactor shutdown overhaul, the short half-life nuclides in the coolant (such as nitrogen-16) had completely decayed. The dose rate measured at this time can truly reflect the radiation level of long-term activated corrosion products (such as cobalt-60 and cobalt-58) deposited on the inner side of the tube wall, eliminating the interference of high background noise during power operation.

[0038] Step S4: Based on the obtained D at least two time points i,0 Di With C Zn Establish dose rate data after zinc injection D i With cumulative zinc addition C Zn The mapping relationship between them.

[0039] D. Pre-zinc injection dose rate data was obtained. i,0 Cumulative zinc addition C at different time points Zn And the corresponding zinc injection dose rate data D i Next, these data were normalized. Specifically, the normalized dose rate ratios at different time points for each monitoring location were calculated. This ratio is a dimensionless physical quantity representing the residual proportion of the radiation field dose rate after zinc injection relative to the initial background. Through normalization, systematic errors caused by differences in initial radiation levels and equipment geometry between different units and different circuit locations were successfully eliminated.

[0040] Next, based on the cumulative zinc addition amount C Zn The normalized dose rate ratio is the independent variable. Using C as the dependent variable, a mapping relationship is established between them. In this embodiment, this mapping relationship is specifically defined as an exponentially decaying function relationship. This definition is supported by a strong physicochemical mechanism. In the high-temperature and high-pressure water chemical environment of the primary loop, the replacement of activated corrosion products in the metal oxide film on the surface of the primary loop equipment by zinc ions is a typical kinetic replacement process. With the cumulative zinc addition C... Zn As zinc ions increase, the active sites are gradually occupied, and the release and replacement rates of activated corrosion products exhibit an exponentially decreasing trend. Therefore, using an exponentially decreasing functional relationship can most realistically and accurately describe this physicochemical reaction law.

[0041] Specifically, the mathematical expression for this mapping relationship can be represented as: .

[0042] Right now: Where a, b, and c are fitting coefficients. a is the coefficient of the exponential decay term, b is the decay rate constant, and c is the asymptote height (representing the limit of residual radiation that can be reduced after long-term zinc injection). Since when C... Z When = 0, the normalized dose rate ratio It must be strictly equal to 1 (i.e., the initial state before zinc injection), therefore the fitting coefficients satisfy the constraint condition: a+c=1.

[0043] In this embodiment, by performing nonlinear least squares fitting on measured normalized dose rate data of a large number of nuclear power units at different overhaul cycles and the corresponding cumulative zinc addition, the specific mathematical expression of the mapping relationship was determined as follows: .

[0044] In this formula, coefficient 0.7 represents the maximum proportion of releasable activated corrosion products that zinc injection technology can replace and reduce under specific water quality and material conditions in the first loop (i.e., the maximum dose reduction potential is 70%); coefficient 0.3 represents the limit of residual radiation field energy reduction after long-term zinc injection (i.e., the asymptote height is 30%); and the constant 246 in the denominator is the decay rate constant (unit: μg / kg). The formula (month) determines how quickly the dose rate decreases with increasing cumulative zinc dosage. This formula exhibits extremely high fitting accuracy and physical consistency.

[0045] Step S5: Using this mapping relationship, predict the post-zinc injection dose rate data D at any subsequent time point based on the cumulative zinc injection amount at any subsequent time point. i The dose rate reduction before and after zinc injection was calculated, and this reduction was used as the detection result of the reduction in the external radiation field of the reactor core by zinc injection.

[0046] After establishing the above mapping relationship model, this method can be used to predict the degree of reduction of the external radiation field of the reactor core before the implementation of zinc injection technology in the primary loop of nuclear power plants, or to verify the degree of reduction of the external radiation field of the reactor core after implementation.

[0047] When used for forecasting, nuclear power plant planners can calculate the corresponding expected cumulative zinc injection amount C based on the preset future zinc injection operation time and the planned controlled zinc concentration in the primary loop. Zn The expected cumulative zinc addition amount and the initial radiation dose rate D at a certain monitoring location are used to calculate this. i,0 Substituting into the above formula, the predicted dose rate D of the external radiation field at that location at a specific future time point can be calculated. i .

[0048] Subsequently, the relative reduction η of the dose rate of the external radiation field after zinc injection was calculated using the following formula: η= ×100%.

[0049] The reduction magnitude η is used as a quantitative prediction of the reduction in the external radiation field of the reactor core due to zinc injection. This provides valuable quantitative data support for nuclear power plants to assess the economic feasibility of zinc injection technology and compare the costs and effects of other dose reduction measures.

[0050] When used for verification, nuclear power plant operators will use the actual zinc addition amount C accumulated during actual operation. Zn The actual dose rate data measured during the overhaul was substituted into the model to calculate the actual dose reduction η, in order to verify whether the zinc injection technology achieved the expected dose reduction effect and to provide performance indicators for subsequent operation.

[0051] In one embodiment of the present invention, the mapping relationship is specifically defined as an exponentially decaying function relationship.

[0052] This limitation is supported by a robust physicochemical mechanism. In the high-temperature, high-pressure aqueous chemical environment of the primary loop, the replacement of activated corrosion products (such as cobalt-60 and cobalt-58) in the metal oxide film on the surface of primary loop equipment by zinc ions is a typical kinetic replacement process. With the cumulative addition of zinc C... Zn As the zinc content increases, the active sites are gradually occupied by zinc ions, and the release and replacement rates of activated corrosion products exhibit an exponentially decreasing trend. Therefore, using an exponentially decreasing functional relationship can most realistically and accurately describe this physicochemical reaction law. In the normalization and curve fitting steps, the cumulative zinc addition C is used as the criterion. Zn The normalized dose rate ratio is the independent variable. Using a nonlinear fit with the dependent variable, the resulting exponential decay curve perfectly matches the measured data points. This exponential decay model not only accurately fits historical monitoring data but also scientifically predicts the future effects of zinc injection dose reduction. Through this model, nuclear power plants can clearly predict the theoretical limit to which the external radiation field of the reactor core can be reduced when a specific cumulative zinc injection amount is reached. This provides extremely accurate quantitative data support for radiation protection planning, avoiding the non-physical divergence problems that occur in extreme extrapolation of linear or polynomial models, and ensuring the scientific and physical rationality of the evaluation results.

[0053] In one embodiment of the present invention, the mapping relationship is specifically as follows: .

[0054] This mapping is based on the following theory: Zinc injection stabilizes the oxide film in the reactor coolant system, reducing the incorporation of radioactive cobalt on the oxide film surface. The measured primary loop dose rate is expected to decrease according to the natural decay rate of the radioactive isotopes. If zinc replaces the radionuclides on the oxide film surface, the measured dose rate will decrease faster than the natural decay rate of the radionuclides. Assuming Co-60 is the primary contributor to the shutdown dose rate, the calculated decay constant should be comparable to the natural decay constant of Co-60.

[0055] This formula was determined by performing nonlinear least-squares fitting on measured normalized dose rate data points from a large number of nuclear power units at different overhaul cycles and the corresponding cumulative zinc additions. Figure 2 In the diagram, the horizontal axis represents the cumulative zinc addition C. Zn The vertical axis represents the normalized dose rate ratio. Measured normalized dose rate data points ( Figure 2 (As shown in the blue box in the middle) Figure 2 The data exhibits a clear exponential decay trend. By fitting these data points, an exponential decay fitting curve was obtained (e.g., Figure 2(As shown by the red line in the middle). The coefficients in this formula have specific physical meanings. Coefficient 0.7 represents the maximum proportion of releaseable activated corrosion products that zinc injection technology can replace and reduce under specific water quality and material conditions in the first loop (i.e., the maximum dose reduction potential is 70%); coefficient 0.3 represents the limit of residual radiation field energy reduction after long-term zinc injection (i.e., the asymptote height, corresponding to...). Figure 2 The asymptote in the formula tends to flatten out (5); the constant 246 in the denominator is the decay rate constant, which determines how quickly the dose rate decreases with increasing cumulative zinc dosage. When the cumulative zinc dosage C... Zn When C = 0, the normalized dose rate ratio calculated by the formula is 1.0, which perfectly matches the initial state without zinc injection. With the cumulative zinc injection amount C... Zn As the amount of zinc added increases, the normalized dose-rate ratio decreases rapidly along the exponential decay fitting curve 4. Zn More than 1000 μg / kg A month later, the data points entered the asymptote and tended to level off in region 5, indicating that the zinc injection dosage reduction effect had reached saturation. This formula provides nuclear power plants with a highly accurate quantitative calculation basis, which can directly guide on-site water chemistry control.

[0056] In one embodiment of the present invention, based on the mapping relationship, the reduction in dose rate of the external radiation field after zinc injection is calculated as follows: (D i,0 -D i ) / D i,0 ×100%.

[0057] In the step of calculating the dose rate reduction, this formula converts the absolute dose rate change into a dimensionless relative reduction η. In actual nuclear power plant operation, the absolute dose rate values ​​of different units, and even different monitoring locations within the same unit, may differ by several times or even tens of times. If the difference in absolute dose rate (D) is directly used... i,0 D i Using a single method to evaluate zinc injection effectiveness can lead to inconsistent evaluation criteria due to significant differences in initial background. For example, the absolute dose rate decrease in high-radiation areas is obviously much greater than in low-radiation areas, but this does not necessarily mean that zinc injection replacement efficiency is higher in high-radiation areas. By introducing a formula for the relative reduction magnitude η, the absolute change is divided by the initial value D. i,0 Normalization completely eliminates the influence of initial background intensity, accurately reflecting the percentage benefit of zinc injection technology in replacing activated corrosion products. This allows nuclear power plant managers to intuitively assess the actual contribution of zinc injection technology on different equipment surfaces and to use this reduction as a unified performance indicator to compare the cost and effectiveness of other measures to reduce the external radiation field of the reactor core (such as chemical decontamination and electrochemical passivation), providing standardized and scientific data support for radiation protection decisions at nuclear power plants.

[0058] In one embodiment of the present invention, the primary loop includes at least a reactor pressure vessel, a main pipeline, a steam generator, a pressurizer, and a primary loop coolant pump. The surface area of ​​the equipment includes at least one of the following: dose rate monitoring points at different heights and orientations on the outer wall of the reactor pressure vessel, the outer wall of the primary loop main pipeline, the outer shell of the steam generator, the outer shell of the pressurizer, and the outer shell of the primary loop coolant pump.

[0059] The primary loop system is the core area for the generation, transport, and deposition of radioactive materials in a nuclear power plant. During reactor operation, structural materials (such as Alloy 600 and stainless steel) corrode, releasing metal ions. These ions are activated by neutrons as they flow through the reactor core with the coolant, forming radioactive nuclides (such as Cobalt-60 and Cobalt-58). These radionuclides subsequently deposit on the surfaces of various primary loop equipment, causing an increase in the dose rate of the radiation field outside the reactor core. The heat transfer tubes of the steam generator have a very large surface area, making them a primary site for the deposition of activated corrosion products. Main pipelines, steam generators, pressurizers, and coolant pumps are also prone to localized deposition and enrichment of corrosion products due to fluid shear forces and changes in their geometry. Therefore, limiting the surface area to be monitored to these critical devices ensures accurate acquisition of pre-zinc injection dose rate data. i,0 and the dose rate data after zinc injection D i This approach is highly representative and targeted. By conducting long-term, systematic radiation dose rate monitoring of the surface areas of these critical equipment, a comprehensive understanding of the suppression effect of zinc injection technology on the radiation field of the entire primary loop system can be achieved. This not only helps assess the actual benefits of implementing zinc injection technology on specific equipment, but also provides refined and localized dose distribution data for equipment maintenance and radiation protection planning during nuclear power plant overhauls, ensuring the radiation safety of maintenance personnel.

[0060] In one embodiment of the present invention, the pre-zinc injection dose rate data D i,0 and the dose rate data after zinc injection D i The data were obtained using a portable gamma spectrometer.

[0061] During nuclear power plant outages and major overhauls, the radiation field on the surface of primary loop equipment is mainly contributed by gamma rays generated from the decay of radioactive nuclides (such as cobalt-60, manganese-54, and cobalt-58) deposited on the inner walls of pipes. Using a portable gamma spectrometer for surveys offers significant technical advantages over traditional total gamma dose rate meters. The portable gamma spectrometer can not only measure the total dose rate but also identify the characteristic peaks of different radioactive nuclides through energy spectrum analysis, thereby quantitatively analyzing the contribution ratio of each nuclide to the total dose rate. In the steps of collecting radiation data before and after zinc injection, radiation protection personnel carry a portable gamma spectrometer and closely measure the designated equipment surface areas. Since the primary loop system is shut down during the overhaul, the short-half-life nuclides in the coolant have decayed completely. At this time, the dose rate data measured by the portable gamma spectrometer can accurately reflect the radiation level of long-term activated corrosion products deposited on the inner walls, eliminating interference from high background noise and transient nuclides during power operation. This ensures that the data source for the input normalization and curve fitting steps has extremely high authenticity and reliability, laying a solid data foundation for the subsequent construction of a high-precision exponential decay model.

[0062] In one embodiment of the present invention, the cumulative zinc addition amount C Zn The zinc concentration in the primary circuit during zinc injection was obtained by continuous or intermittent sampling and analysis, and by integral calculation of the zinc concentration over time.

[0063] In primary loop water chemistry control, zinc is injected into the coolant in trace dissolved states (typically a few micrograms per kilogram). Due to variations in operating conditions, fluctuations in the discharge flow of the purification system, and differences in absorption on material surfaces, the zinc concentration in the primary loop coolant will exhibit transient fluctuations during operation. Using only the instantaneous zinc concentration at a specific moment or a simple arithmetic mean as an evaluation index cannot accurately reflect the total long-term cumulative contact between the primary loop system and zinc ions. Therefore, in calculating the cumulative zinc addition, continuous or intermittent sampling and analysis of the zinc concentration is performed to obtain a curve of zinc concentration change over time, and the cumulative zinc addition C is calculated using a time integral formula. Zn This integration process perfectly transforms dynamically fluctuating concentrations into cumulative physical indicators, accurately quantifying the total cumulative replacement of the oxide film on the surface of primary circuit equipment by zinc ions. Using the cumulative zinc addition amount as an independent variable in the normalization and curve fitting steps ensures that the resulting exponential decay model has extremely high physical consistency, eliminating fitting bias caused by transient concentration fluctuations and greatly improving the scientific rigor and accuracy of the evaluation method.

[0064] In one embodiment of the present invention, the detection method is used to predict the degree of reduction of the external radiation field of the reactor core before the implementation of zinc injection technology in the primary loop of a nuclear power plant, or to verify the degree of reduction of the external radiation field of the reactor core after implementation.

[0065] This limitation endows this method with a dual core function, covering the entire lifecycle of zinc injection technology application. Before implementing zinc injection technology, nuclear power plants need to assess its economic feasibility and radiation protection benefits. By using the exponential decay response model established by this method, and inputting a preset zinc injection time or primary loop zinc concentration, the expected cumulative zinc injection amount is calculated, thereby predicting the reduction in radiation dose rate on the surfaces of various equipment during future overhauls. This provides nuclear power plants with valuable quantitative data for comparing the costs and effects of other dose reduction measures, aiding in decision-making. After implementing zinc injection technology, nuclear power plants need to verify the actual effectiveness of the technology and provide performance indicators for subsequent operation. By collecting the cumulative zinc injection amount during actual operation and the measured dose rate data during reactor shutdown overhauls, this method is used to calculate the actual reduction, verifying whether it has met the design targets. This not only assesses the actual benefits of the implemented zinc injection technology but also identifies the saturation point of zinc injection benefits through feedback from the fitted curve, guiding nuclear power plants to optimize subsequent zinc injection strategies, avoiding economic waste and negative material effects caused by over-zinc injection, and achieving refined, closed-loop water chemistry control.

[0066] In one embodiment of the present invention, at least one equipment surface area in the primary loop includes at least one of the following: dose rate monitoring points at different heights and orientations on the outer wall of the reactor pressure vessel, the outer wall of the primary loop main pipeline, the outer casing of the steam generator, the outer casing of the pressurizer, and the outer casing of the primary loop coolant pump. When acquiring the dose rate data of the external radiation field at equipment surface area location i before zinc injection, at least three repeated measurement points are set for each equipment surface area location i, and the average value of the measurements at each repeated measurement point is taken as the radiation dose rate data for that equipment surface area.

[0067] Due to the complex geometry and non-uniform fluid flow on the surface of primary loop equipment, the deposition of activated corrosion products often exhibits spatial inhomogeneity. If only a single measurement point is selected on each equipment surface, it is highly susceptible to local deposition anomalies or measurement alignment deviations, leading to significant random errors in the acquired dose rate data. To overcome this deficiency, this method sets at least three repeated measurement points for each of the aforementioned key equipment surface regions at location i in both the pre-zinc injection and post-zinc injection radiation data collection steps. By performing multi-point measurements at these three repeated points and using the arithmetic mean of the measured values ​​as the representative radiation dose rate data for that equipment surface, this multi-point sampling and averaging preprocessing method effectively eliminates random errors caused by local deposition inhomogeneity and minor detector placement deviations. This significantly improves the spatial representativeness and measurement accuracy of the input data, ensuring the accuracy and stability of the exponential decay model constructed in the subsequent normalization and curve fitting steps.

[0068] To enable those skilled in the art to more intuitively understand the detection method for reducing the degree of external radiation field of the reactor core by primary loop zinc injection provided in this application, a detailed comparative demonstration is provided below through specific embodiments, comparative examples, and experimental data.

[0069] In this embodiment, the primary loop system of a large pressurized water reactor nuclear power unit (CPR1000, rated power 1000MWe) is used as the application object. The heat transfer tubes of the steam generator of this unit are made of nickel-based 600 alloy material. Before the implementation of the primary loop zinc injection technology, the unit had run multiple fuel cycles, and a large amount of activation corrosion products (mainly cobalt-60 and cobalt-58) had been deposited on the surface of the equipment outside the core, resulting in a high radiation dose rate during the overhaul.

[0070] To evaluate the dose reduction effect of zinc injection technology, radiation data collection was conducted before zinc injection during the unit's 10th major outage. Radiation protection personnel used a portable high-purity germanium (HPGe) gamma spectrometer to conduct radiation dose rate measurements on three key equipment surfaces: the primary side water chamber of the steam generator in the primary loop, the cold section of the main piping, and the pressurizer ripple tube. To eliminate spatial non-uniformity errors, three repeated measurement points were set for each equipment surface area, with an interval of approximately 10 cm between the measurement points. The measurement time for each point was set to 300 seconds to ensure that the statistical error was within 1%.

[0071] The dose rates measured at three repeated measurement points on the surface of the primary side water chamber of the steam generator were 125.4 μSv / h, 128.6 μSv / h, and 124.0 μSv / h, respectively. Their arithmetic mean was calculated to obtain the initial dose rate data D before zinc injection in this area. i,0 =126.0 μSv / h. The dose rates measured at three repeated measurement points on the surface of the cold section of the main pipe were 45.2 μSv / h, 46.8 μSv / h, and 44.5 μSv / h, respectively. The arithmetic mean was calculated to obtain the initial dose rate data D before zinc injection in this area. 2,0 =45.5 μSv / h. The dose rates measured at three repeated measurement points on the surface of the voltage regulator's oscillating tube were 88.5 μSv / h, 91.2 μSv / h, and 87.9 μSv / h, respectively. Their arithmetic mean was calculated to obtain the initial dose rate data D before zinc injection in this area. 3,0 =89.2μSv / h.

[0072] During the subsequent 11th fuel cycle, the nuclear power plant began implementing zinc addition technology for the primary coolant. Zinc addition was performed using a zinc acetate solution, continuously injected into the primary coolant via a chemical volumetric system (CVCS). During operation, chemists sampled and analyzed the zinc concentration in the primary coolant daily, maintaining it at a level of 5%. Within the range of 10 μg / kg. Based on the daily measured zinc concentration data, a computer program is used to perform time integration calculations to accumulate the zinc dosage in real time.

[0073] Before the 11th reactor shutdown overhaul (approximately 12 months of operation), the cumulative zinc addition data C corresponding to that time point was calculated. Zn,1 =120μg / kg Month. During the 11th reactor shutdown overhaul, the same portable high-purity germanium gamma spectrometer was used to conduct post-zinc injection radiation dose rate surveys at the same measurement points. The average dose rate measured on the surface of the primary side water chamber of the steam generator dropped to 91.2 μSv / h, recorded as the post-zinc injection dose rate data D. 1,1 The average dose rate on the surface of the cold section of the main pipeline decreased to 32.9 μSv / h, which is recorded as the dose rate data after zinc injection, D. 2,1 The average dose rate on the surface of the voltage regulator's fluctuating tube decreased to 64.6 μSv / h, recorded as the dose rate data D after zinc injection. 3,1 .

[0074] Zinc addition continued during the 12th fuel cycle. Prior to the 12th reactor outage (approximately 24 months of cumulative operation), the cumulative zinc addition amount C at that time point was calculated. Zn,2 =240μg / kg Month. During the 12th reactor shutdown overhaul, radiation dose rate monitoring was conducted again. The average dose rate measured on the surface of the primary side water chamber of the steam generator dropped to 68.4 μSv / h, recorded as the dose rate data after zinc injection, D. 1,2 The average dose rate on the surface of the cold section of the main pipeline decreased to 24.7 μSv / h, which is recorded as the dose rate data after zinc injection, D. 2,2 The average dose rate on the surface of the voltage regulator's fluctuating tube decreased to 48.4 μSv / h, recorded as the dose rate data D after zinc injection. 3,2 .

[0075] After acquiring the data at the two aforementioned time points, the data processing module normalized the data. For the surface of the primary side water chamber of the steam generator, the normalized dose rate ratios at the two time points were calculated as follows:

[0076]

[0077] For the cold section surface of the main pipeline, the normalized dose rate ratios at the two time points were calculated as follows:

[0078]

[0079] For the voltage regulator's ripple tube surface, the normalized dose rate ratios at the two time points were calculated as follows:

[0080]

[0081] Surprisingly, the calculation results show that although the absolute dose rate values ​​of the three equipment surface regions differ greatly (the dose rate on the primary side water chamber surface of the steam generator is nearly three times that on the cold section surface of the main pipeline), after normalization, the normalized dose rate ratios of the three regions under the same cumulative zinc addition are almost identical (at 120 μg / kg). The value is approximately 0.724 in the month, and in 240... g / kg The value is approximately 0.543 (monthly). This result irrefutably proves that normalization can completely eliminate systematic errors caused by equipment geometry and initial radiation background, revealing the essential physicochemical law of primary-loop zinc injection reducing the radiation field.

[0082] The data processing module uses the nonlinear least squares method to calculate the cumulative zinc addition C. Zn Using the normalized dose rate ratio Y as the dependent variable, a fitting was performed. Under the constraint a+c=1, the fitting coefficients were found to be: a=0.7, b=1 / 246, c=0.3. Thus, an exponential decay response model for the primary circuit zinc injection dose reduction of this unit was successfully established.

[0083] Using this model, the detection results analysis module predicts the future dose reduction effect. If the plan is to achieve a cumulative zinc addition of C at the end of the 13th fuel cycle... Zn,3 =500 μg / kg Substituting this value into the model, the predicted normalized dose rate ratio for the surface of the primary side water chamber of the steam generator is calculated as follows:

[0084] The corresponding dose rate prediction value is: μSv / h The calculated relative reduction is: η= ×100%=60.8% During the 13th reactor shutdown overhaul, radiation protection personnel conducted on-site measurements. The actual average dose rate measured on the surface of the primary side water chamber of the steam generator was 49.1 μSv / h, with a relative error of only 0.6% compared to the predicted value of 49.4 μSv / h. This greatly confirms that the detection and prediction method established in this application has extremely high accuracy and engineering practical value.

[0085] This application also provides a detection device for detecting the reduction of the external radiation field of the reactor core by primary circuit zinc injection, used to perform the aforementioned detection method for the reduction of the external radiation field of the reactor core by primary circuit zinc injection. The detection device includes: The first acquisition module is used to acquire dose rate data of the external radiation field of at least one equipment surface area in the primary loop of the nuclear power plant before zinc injection, denoted as pre-zinc injection dose rate data D. i,0 ; The calculation module is used to sample and analyze the zinc concentration in the primary circuit during zinc injection, and calculate the cumulative zinc injection amount C at at least two different time points based on the integral of the zinc concentration over time. Zn ; The second acquisition module is used to acquire, at the same time point as calculating the cumulative zinc addition data, the dose rate data of the external radiation field of the equipment surface area after zinc injection, denoted as the post-zinc injection dose rate data D. i ; The data processing module is used to process data based on at least two time points of D. i,0 D i With C Zn Establish dose rate data after zinc injection D i With cumulative zinc addition C Zn The mapping relationship between them; The test result analysis module is used to utilize the mapping relationship to determine the cumulative zinc addition C at any subsequent time point. Zn Predict the dose rate data D after zinc injection at the corresponding time point. i The dose rate reduction before and after zinc injection was calculated, and the reduction was used as the detection result of the reduction in the external radiation field of the reactor core by zinc injection.

[0086] The specific working mechanisms and data interaction flow of each module in the detection device correspond one-to-one with the steps in the aforementioned method embodiments, and will not be repeated here.

[0087] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for detecting the reduction of the external radiation field of a reactor core due to primary loop zinc injection, characterized in that, The detection method includes: Prior to zinc injection, dose rate data of the external radiation field of at least one equipment surface area in the primary loop of the nuclear power plant was acquired and denoted as the pre-zinc injection dose rate data D. i,0 ; During the zinc injection process, the zinc concentration in the primary circuit was sampled and analyzed. Based on the integral of the zinc concentration over time, the cumulative zinc injection amount C corresponding to at least two different time points was calculated. Zn ; At the same time point as when calculating the cumulative zinc loading data, the dose rate data of the external radiation field of the equipment surface area after zinc loading was acquired and denoted as the post-zinc loading dose rate data D. i ; Based on the D obtained at least two time points i,0 D i With C Zn Establish dose rate data after zinc injection D i With cumulative zinc addition C Zn The mapping relationship between them; Using the aforementioned mapping relationship, the post-zinc injection dose rate data D at any subsequent time point can be predicted based on the cumulative zinc injection amount at any subsequent time point. i The dose rate reduction before and after zinc injection was calculated, and the reduction was used as the detection result of the reduction in the external radiation field of the reactor core by zinc injection.

2. The detection method according to claim 1, characterized in that, The mapping relationship is an exponentially decaying function relationship.

3. The detection method according to claim 2, characterized in that, The mapping relationship is specifically as follows: 。 4. The detection method according to claim 1, characterized in that, Based on the mapping relationship, the reduction in dose rate of the external radiation field after zinc injection is calculated as follows: (D) i,0 -D i ) / D i,0 ×100%.

5. The method according to claim 1, characterized in that, The primary loop includes a reactor pressure vessel, a primary loop main pipeline, a steam generator, a pressurizer, and a primary loop coolant pump; the equipment surface area includes at least one of the following: dose rate monitoring points at different heights and orientations on the outer wall of the reactor pressure vessel, the outer wall of the primary loop main pipeline, the outer casing of the steam generator, the outer casing of the pressurizer, and the outer casing of the primary loop coolant pump.

6. The method according to claim 1, characterized in that, The zinc injection pre-injection dose rate data D i,0 and the dose rate data after zinc injection D i The data were obtained using a portable gamma spectrometer.

7. The method according to claim 1, characterized in that, The cumulative zinc addition C Zn The zinc concentration in the primary circuit during zinc injection was obtained by continuous or intermittent sampling and analysis, and by integral calculation of the zinc concentration over time.

8. The method according to claim 1, characterized in that, The detection method is used to predict the degree of reduction in the external radiation field of the reactor core before the implementation of zinc injection technology in the primary loop of a nuclear power plant, or to verify the degree of reduction in the external radiation field of the reactor core after implementation.

9. The method according to claim 1, characterized in that, When acquiring the dose rate data of the external radiation field of the equipment surface area before zinc injection, at least three repeated measurement points are set for each equipment surface area, and the average value of the measured values ​​of each repeated measurement point is used as the radiation dose rate data of the equipment surface area.

10. A detection device, characterized in that, The detection device includes: The first acquisition module is used to acquire dose rate data of the external radiation field of at least one equipment surface area in the primary loop of the nuclear power plant before zinc injection, denoted as pre-zinc injection dose rate data D. i,0 ; The calculation module is used to sample and analyze the zinc concentration in the primary circuit during zinc injection, and calculate the cumulative zinc injection amount C at at least two different time points based on the integral of the zinc concentration over time. Zn ; The second acquisition module is used to acquire, at the same time point as calculating the cumulative zinc addition data, the dose rate data of the external radiation field of the equipment surface area after zinc injection, denoted as the post-zinc injection dose rate data D. i ; The quantity processing module is used to process D based on at least two time points. i,0 D i With C Zn Establish dose rate data after zinc injection D i With cumulative zinc addition C Zn The mapping relationship between them; The test result analysis module is used to utilize the mapping relationship to determine the cumulative zinc addition C at any subsequent time point. Zn Predict the dose rate data D after zinc injection at the corresponding time point. i The dose rate reduction before and after zinc injection was calculated, and the reduction was used as the detection result of the reduction in the external radiation field of the reactor core by zinc injection.

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