System for evaluating lifetime of nuclear fuel fragments using radionuclides having long half-lives

Abstract

The present invention relates to a system for evaluating the lifetime of nuclear fuel fragments using radionuclides having long half-lives, and relates to technology whereby the lifetime of nuclear fuel fragments can be stably evaluated over a long period of time by utilizing radionuclides having long half-lives. According to the present invention, the system comprises: a radiation detection unit for detecting radiation in the nuclear fuel fragments; a data processing unit for calculating a change in total radioactivity on the basis of collected data; an elapsed time calculation unit that calculates the time elapsed since a leakage point by comparing an initial radioactivity value and a current radioactivity value of Am-241; and a lifetime evaluation unit that calculates the time remaining until the radioactivity of the nuclear fuel fragments reaches a safety threshold, and evaluates the total lifetime of the fragments by adding the elapsed time thereto. The system makes it possible to evaluate the elapsed time since the leakage point of the nuclear fuel fragments over a long period of time by using the radionuclides having long half-lives, and thus can be effectively utilized during long-term planned maintenance or decommissioning of nuclear power plants.

Description

Life assessment system for nuclear fuel fragment particles using long-half-life radionuclides

[0001] The present invention relates to a system for evaluating the lifespan of nuclear fuel fragment particles, and more specifically, to a technology capable of stably evaluating the lifespan by utilizing radionuclides having long half-lives.

[0002] Nuclear fuel fragments from nuclear power plants are released from the core into the reactor coolant system due to damage or micro-leakage of the fuel cladding.

[0003] Figure 1 shows the pathway of nuclear fission product release from nuclear fuel during normal operation of a nuclear power plant.

[0004] The nuclides constituting nuclear fuel fragments are primarily generated when nuclear fuel interacts with neutrons; beta- and gamma-emitting nuclides include Zr-95, Nb-95, Ru-103, Ru-106, Cs-134, Cs-137, Ce-141, and Ce-144, while pure beta-emitting nuclides include Sr-89, Sr-90, Y-90, Y-91, Pr-143, and Pr-144. In addition, there are transuranium elements such as Pu-239, Pu-241, Am-241, Cm-242, and Cm-244.

[0005] Figure 2 is an example of the ratio of Ce-141 / Ce-144 radionuclides according to the elapsed days after nuclear fuel fragment leakage.

[0006] According to NCRP Report No. 130, "Biological Effects and Exposure Limits for Hot Particles," the time at which nuclear fuel fragment particles leak from the core is calculated based on the ratio of Ce-141 to Ce-144. The reasons for selecting Cerium among the aforementioned nuclides are as follows: First, Cerium is insoluble, so its chemical behavior is similar to that of nuclear fuel fragment particles. Second, since the half-lives of Ce-141 and Ce-144 are 32.5 days and 284.9 days, respectively, the ratio of the nuclides decreases over time, making it easy to calculate the time of leakage. Third, Ce-141 and Ce-144 emit gamma rays, making them easier to detect compared to pure beta-emitting nuclides.

[0007] Therefore, if Ce-141 and Ce-144 are detected at a nuclear power plant, it indicates that nuclear fuel fragment particles have leaked from the fuel, and the time of leakage can be estimated based on the radioactivity ratio of the two nuclides.

[0008] When using the Ce-141 / Ce-144 ratio during long-term planned preventive maintenance or nuclear power plant decommissioning that lasts for more than one year, it is difficult to assess the timing of nuclear fuel fragment leakage because the half-life of Ce-141 is 32.5 days, causing the Ce-141 / Ce-144 ratio to approach 0.

[0009] In other words, nuclear fuel fragments are released into the coolant system during reactor operation due to cladding damage or micro-leakage. Conventionally, the timing of leakage was calculated using the radioactivity ratio of Ce-141 and Ce-144; however, there was a problem in that long-term evaluation was difficult due to the short half-life of Ce-141 (32.5 days). This makes it difficult to accurately assess the lifespan of nuclear fuel fragments in long-term situations, such as long-term planned preventive maintenance or nuclear power plant decommissioning.

[0010] [Prior Art Literature]

[0011] [Patent Literature]

[0012] (Patent Document 1) Republic of Korea Registered Patent 10-2498370 (February 6, 2023)

[0013] According to the present invention, the purpose is to provide a nuclear fuel fragment life evaluation system using long-half-life radionuclides that enables long-term evaluation of the elapsed time from the time of leakage of nuclear fuel fragment particles by utilizing long-half-life radionuclides.

[0014] A life evaluation system for nuclear fuel fragment particles using long-half-life radionuclides according to the present invention comprises: a radiation detection unit (100) that detects radioactivity data of Am-241 and Pu-241 within the nuclear fuel fragment particles in real time; a data processing unit (200) that calculates the total change in radioactivity by calculating the decrease in radioactivity of Am-241 and the increase in Am-241 due to the decay of Pu-241 based on the data collected through the radiation detection unit; an elapsed time calculation unit (300) that calculates the elapsed time from the time of leakage by comparing the initial radioactivity value of Am-241 with the current radioactivity value; and a life evaluation unit (400) that calculates the remaining time until the radioactivity of the nuclear fuel fragment particles reaches a safety threshold and evaluates the total life of the fragment particles by summing the elapsed time.

[0015] The lifespan evaluation unit visually displays the results of the elapsed time calculation unit and provides information to the user.

[0016] The radiation detection unit (100) includes a gamma ray detector capable of detecting 59 keV gamma rays of Am-241 with high sensitivity.

[0017] The data processing unit (200) calculates the decrease in radioactivity of Am-241 based on the detected data, the decrease in radioactivity due to the natural decay of Am-241, and the increase in radioactivity of Am-241 based on the increase in radioactivity according to the rate at which Pu-241 decays and is converted into Am-241, thereby calculating the total change in radioactivity of Am-241.

[0018] The elapsed time calculation unit (300) uses the total radioactivity change of Am-241 and the half-lives of Pu-241 and Am-241 to compare the initial radioactivity values ​​of Am-241 and Pu-241 measured at the time of leakage with the currently measured radioactivity values ​​of Am-241, and tracks the amount of Am-241 that has decreased over time and the amount of Am-241 generated by the decay of Pu-241, thereby calculating the elapsed time from the time of leakage to the present in reverse.

[0019] Meanwhile, in a method using a life assessment system for nuclear fuel fragment particles utilizing long-half-life radionuclides, (a) the life assessment system for nuclear fuel fragment particles collects radioactivity data of Am-241 and Pu-241 using a radiation detector that measures Am-241 radioactivity within the nuclear fuel fragment particles; (b) based on the collected data, the life assessment system for nuclear fuel fragment particles calculates the decrease in radioactivity of Am-241 due to the natural decay of Am-241 and calculates the increase in radioactivity of Am-241 due to the increase in radioactivity according to the rate at which Pu-241 decays and converts into Am-241, thereby calculating the total change in radioactivity of Am-241; and (c) using the total change in radioactivity of Am-241 and the half-lives of Pu-241 and Am-241, the life assessment system for nuclear fuel fragment particles calculates the initial radioactivity values ​​of Am-241 and Pu-241 measured at the time of leakage and the currently measured radioactivity value of Am-241. (d) the nuclear fuel fragment particle life evaluation system calculates the remaining time until the radioactivity of the nuclear fuel fragment particle reaches a safety threshold, and evaluates the total life of the fragment particle by summing the elapsed time from the time of leakage to the present using these values, and (d) the nuclear fuel fragment particle life evaluation system calculates the remaining time until the radioactivity of the nuclear fuel fragment particle reaches a safety threshold, and evaluates the total life of the fragment particle by summing the elapsed time from step (c).

[0020] This invention enables long-term evaluation of the elapsed time since the leakage of nuclear fuel fragment particles by utilizing long-half-life radionuclides, thereby allowing for efficient use during long-term planned preventive maintenance or decommissioning of nuclear power plants. It overcomes the shortcomings of existing evaluation methods based on the Ce-141 / Ce-144 ratio and provides longer evaluation periods and greater accuracy through the use of an Am-241 / Pu-241-based radioactivity ratio.

[0021] Figure 1 shows the pathway of nuclear fission product release from nuclear fuel during normal operation of a nuclear power plant.

[0022] Figure 2 is an example of the ratio of Ce-141 / Ce-144 radionuclides according to the elapsed days after nuclear fuel fragment leakage.

[0023] FIG. 3 is a configuration diagram of a nuclear fuel fragment life evaluation system using long-half-life radionuclides according to one embodiment of the present invention.

[0024] Figure 4 shows the elapsed time 144 Ce / 241 This represents the radioactivity ratio of Am.

[0025] FIG. 5 is a flowchart illustrating a method using a nuclear fuel fragment particle life evaluation system using long-half-life radionuclides according to one embodiment of the present invention.

[0026] The present invention is a life assessment system for nuclear fuel fragment particles using long-half-life radionuclides for calculating the elapsed time during long-term planned preventive maintenance or nuclear power plant decommissioning.

[0027] Previously, the Ce-141 / Ce-144 ratio was used, but in this embodiment, Am-241 (half-life 432.6 years) is used instead of Ce-141, which has a short half-life, to calculate the elapsed time for nuclear fuel fragment particles to leak from the core.

[0028] A life evaluation system for nuclear fuel fragment particles using long-half-life radionuclides according to one embodiment of the present invention will be described with reference to the attached drawings.

[0029] FIG. 3 is a configuration diagram of a nuclear fuel fragment life evaluation system using long-half-life radionuclides according to one embodiment of the present invention.

[0030] As illustrated in FIG. 3, a lifespan evaluation system (10) for nuclear fuel fragment particles using long-half-life radionuclides includes a radiation detection unit (100), a data processing unit (200), an elapsed time calculation unit (300), and a lifespan evaluation unit (400).

[0031] The radiation detection unit (100) detects radioactivity data of Am-241 and Pu-241 in nuclear fuel fragment particles in real time.

[0032] This radiation detector (100) detects 59 keV gamma rays of Am-241 and radiation of Pu-241 in real time.

[0033] For reference, the radiation detector (100) according to the present embodiment includes a high-performance semiconductor detector (e.g., high-purity germanium detector, HPGe) or a scintillation detector to detect gamma rays with high sensitivity. This detector has an energy resolution capable of distinguishing between 59 keV gamma rays from Am-241 and radiation of various energies emitted from Pu-241.

[0034] The detected radiation is converted into an electrical signal inside the detector, and this signal is processed through an electronic amplifier. The converted signal is analyzed into an energy spectrum through a digital signal processor, which distinguishes and quantifies the 59 keV gamma rays of Am-241 and the radiation of Pu-241.

[0035] The radiation detection unit (100) uses a high-speed ADC (Analog-to-Digital Converter) to process the signal in real time and transmits the digitized data to the data processing unit (200). This enables the continuous generation of radiation data to be analyzed and stored in real time.

[0036] In addition, the radiation detector uses a radiation shielding device to minimize interference from external background radiation. The shielding device is made of high-density materials such as lead or tungsten and suppresses noise in the detection signal to increase the signal-to-noise ratio (SNR). In addition, a low-temperature operating environment (e.g., liquid nitrogen cooling) is sometimes utilized to reduce electronic noise.

[0037] This radiation detection unit includes a multichannel analyzer (MCA) capable of simultaneously analyzing radiation across multiple energy ranges. This enables the simultaneous real-time detection and separation of radioactivity data for Am-241 and Pu-241 for individual analysis.

[0038] The data processing unit (200) calculates the total change in radioactivity by calculating the decrease in radioactivity of Am-241 and the increase in Am-241 due to the decay of Pu-241 based on the data collected through the radiation detection unit.

[0039] The total radioactivity of Am-241 after nuclear fuel fragment leakage can be calculated using the following formula.

[0040] [Equation 1]

[0041]

[0042] is the decrease in radioactivity of Am-241 at elapsed time (t) after nuclear fuel fragment particle leakage, is the increase in radioactivity of Am-241 due to Pu-241 decay at elapsed time (t) after nuclear fuel fragment particle leakage, The radioactivity of Am-241 at the time of nuclear fuel fragment leakage, is the radioactivity of Pu-241 at the time of nuclear fuel fragment leakage, The half-life of Am-241 (432.6 years), is the half-life of Pu-241 (14.33 years).

[0043] The operation of this data processing unit (200) is described as follows.

[0044] Regarding the amount of radioactivity reduction of Am-241, Am-241 decreases in radioactivity as it naturally decays over time. The data processing unit (200) calculates this amount of reduction using the following formula.

[0045]

[0046] is the decrease in radioactivity of Am-241 at elapsed time t, and is the initial radioactivity value of Am-241, is the decay constant of Am-241 am.

[0047] Regarding the calculation of the increase in Am-241 due to the decay of Pu-241, Pu-241 decays over time and converts into Am-241, which causes an increase in the radioactivity of Am-241. The increase is calculated using the following formula.

[0048]

[0049] is the radioactivity of Am-241 increased due to Pu-241 decay at elapsed time t, is the initial radioactivity value of Pu-241, is the decay constant of Pu-241 am.

[0050] The total change in radioactivity is calculated as the sum of the decrease in Am-241 and the increase generated by the decay of Pu-241.

[0051]

[0052]

[0053] For example, initial data initial Am-241 radioactivity value , initial Pu-241 radioactivity value , if we let the elapsed time (t=10 years),

[0054] The calculation of the radiation reduction amount of Am-241 is

[0055]

[0056]

[0057] am.

[0058] The calculation of the increase in Am-241 due to Pu-241 decay is

[0059]

[0060]

[0061] by,

[0062] am.

[0063] The total change in radioactivity is calculated as follows.

[0064]

[0065]

[0066] The data processing unit (200) calculates the total change in radioactivity by calculating the decrease in radioactivity of Am-241 (natural decay) and the increase in Am-241 generated due to the decay of Pu-241 based on data collected from the radiation detection unit. In the operation example, the total radioactivity value is calculated to be 100.34 Bq, which is slightly higher than the initial Am-241 radioactivity value, showing that additional Am-241 was generated due to the decay of Pu-241. These calculations are performed in real time within the system and are used for calculating elapsed time and evaluating lifespan.

[0067] The elapsed time calculation unit (300) calculates the elapsed time from the time of leakage by comparing the initial radioactivity value of Am-241 with the current radioactivity value.

[0068] The change in radioactivity of Am-241 is determined by two factors (the decrease due to the natural decay of Am-241 and the increase in Am-241 generated by the decay of Pu-241). Therefore, the calculation of the elapsed time is based on the initial value of Am-241 ( ) and current value( It is based on the change of ), and time t is calculated by analyzing the change trend of Am-241 alone.

[0069] Pu-241 is a radionuclide that influences the increase in Am-241 as it decays into Am-241, but it is not a direct comparison subject when calculating elapsed time. The initial radioactivity value of Pu-241 ( ) and decay constants are used as auxiliary variables in the calculation of Am-241 radioactivity changes. For example, Am-241 increase ( The initial value of Pu-241 is required as an input value to calculate ). Since the calculation of elapsed time is based on the change in radioactivity of Am-241, the actual comparison targets are the initial value and the current value of Am-241.

[0070] The formula for calculating the elapsed time is as follows.

[0071]

[0072] is the current radioactivity value of Am-241, is the initial radioactivity value of Am-241, is the initial radioactivity value of Pu-241, is the decay constant of Am-241, is the decay constant of Pu-241. In this formula, the elapsed time t is and It is calculated based on, and the value of Pu-241 is used only in the calculation of the increase amount of Am-241.

[0073] The process of calculating the elapsed time is explained in detail as follows.

[0074] is the amount of decrease due to the natural decay of Am-241.

[0075] is the increase in Am-241 generated by the decay of Pu-241.

[0076] Since these two terms are intertwined in the form of an exponential function with respect to t, in order to find t Group them into common terms and organize.

[0077]

[0078] Compare the value of with the coefficients of each exponential function and Separate.

[0079]

[0080] The t-value is calculated using a numerical approach (e.g., Newton-Raphson method, bisection method).

[0081] First, convert it into an equation form,

[0082]

[0083] Initial value Set (e.g., =0) and, by repeatedly calculating Find the value of t for which = 0. That is, approximate the value of t using numerical calculation methods, and computer programs (Python, MATLAB) can be used to implement this.

[0084] Meanwhile, if the contribution of Am-241 generated by the decay of Pu-241 is very small or negligible, the following equation can be used to estimate the elapsed time based on the radioactivity decay term of Am-241 in a simplified case.

[0085]

[0086] Here, and ≡ and ≡ are the current and initial radioactivity values ​​of Am-241, respectively.

[0087] The lifespan evaluation unit (400) evaluates the lifespan of nuclear fuel fragment particles based on data calculated by the elapsed time calculation unit (300).

[0088] This lifespan evaluation unit (400) calculates the remaining time until the radioactivity of the nuclear fuel fragment particles reaches a safe threshold, and evaluates the total lifespan of the fragment particles by summing the elapsed time.

[0089] For reference, long-half-life radionuclides refer to radioactive materials with a half-life of more than one year in which radioactivity gradually decreases over time, and in this invention, Am-241 and Pu-241 fall into this category. The safety threshold is a reference value at which radioactivity is considered to be at a safe level, and is set in compliance with international radiation protection regulations.

[0090] These safety thresholds (A 목표 It is established in compliance with the International Atomic Energy Agency (IAEA) radiation protection standards and the domestic Nuclear Safety Commission's permissible concentration regulations (recommended standards of international organizations such as the IAEA, ICRP, and UNSCEAR), and is stored in a predefined database within the system. For example, the annual radiation exposure limit for the general public is set to 1 millisievert (mSv), and the permissible amount of radioactive emission is calculated based on this.

[0091] The threshold is calculated through a radiation dose assessment model that estimates the impact of a given radioactivity concentration on humans or the environment. The dose assessment model calculates the radiation dose (Sv) generated at a specific radioactivity concentration (Bq),

[0092] For example, dose = radioactivity concentration × dose conversion factor. By inversely calculating the allowable dose standard (e.g., 1 mSv / year), the allowable radioactivity concentration (A 목표 derives ).

[0093] The Life Assessment Department [determines] the radioactivity of nuclear fuel fragment particles at a safe threshold (A 목표 The remaining time until reaching ) is calculated using the following formula.

[0094]

[0095] t 잔여 is remaining lifespan, A 목표 is the safety threshold at which radioactivity meets safety standards, is the currently measured radioactivity value of Am-241, is the half-life of Am-241.

[0096] Total lifespan is calculated by summing the remaining lifespan and the elapsed time (t) to determine the total lifespan of the fragment particles. 총 = t + t 잔여 , where t is the elapsed time up to now.

[0097] The life evaluation unit of the nuclear fuel fragment particle life evaluation system using long-half-life radionuclides according to this embodiment predicts long-term radioactive behavior by simulating the decay processes of Am-241 and Pu-241 and changes in the Ce-144 / Am-241 ratio.

[0098] The lifespan evaluation unit according to the present embodiment Predict the reduction amount of Am-241 through, and The increase in Am-241 generated by the decay of Pu-241 is calculated through this, and through this, the total radioactivity value of Am-241 It is predicted to be.

[0099] In the elapsed time analysis based on the Ce-144 / Am-241 ratio, the radioactivity ratio of Ce-144 to Am-241 changes linearly with elapsed time, and this ratio is expressed by the following equation.

[0100] [Equation 2]

[0101]

[0102] ε is the ratio of the radioactivity of Ce-144 and Am-241 at elapsed time t. It represents the trend of relative change over time by comparing the radioactivity concentrations of the two nuclides. is the radioactivity value of Ce-144 at elapsed time t. It decreases over time due to the natural decay of Ce-144. ε is the radioactivity value of Am-241 at elapsed time t. It changes to reflect both the increase due to the natural decay of Am-241 and the increase due to the decay of Pu-241. This ratio By tracking changes in radioactivity over time, changes in radioactivity are analyzed, and long-term decay patterns are predicted.

[0103] Here, the radioactivity of Ce-144 decreases according to its half-life (284.9 days), which is calculated by the following formula.

[0104] [Equation 3]

[0105]

[0106] θ is the radioactivity value of Ce-144 at elapsed time t. It decreases exponentially according to the decay characteristics of Ce-144. is the radioactivity value of Ce-144 at the initial time point (t=0). It represents the radioactivity of Ce-144 measured at the time of leakage. is the decay constant of Ce-144. The half-life of Ce-144 It is determined according to and has the following relationship.

[0107] Here, It is 284.9 days.

[0108] Equation (2) represents the ratio of the radioactivity of Ce-144 and Am-241, which changes linearly with time t. Equation (3) is an exponential function representing the decrease in radioactivity of Ce-144, which calculates the value over time based on the initial radioactivity value and the decay constant. By combining Equation (2) and Equation (3), the change in radioactivity of Ce-144 and Am-241 at time t can be tracked, thereby allowing for the prediction of the long-term trend of radioactivity change and the calculation of the elapsed time.

[0109] The lifetime evaluation unit according to the present embodiment extends the decay equations of Am-241, Pu-241, and Ce-144 along the time axis to simulate how radioactivity concentration changes over the long term. Based on the half-life and initial concentration of each nuclide, it calculates radioactivity values ​​at specific times (e.g., after 10, 50, or 100 years). Using this data, it predicts the time at which radioactivity reaches a safe threshold.

[0110] In addition, the Lifespan Assessment Department analyzes the impact of radioactivity on the environment by utilizing calculated radioactivity data. By modeling radioactivity concentrations and ecosystem exposure levels, it can assess long-term radiation effects and safety.

[0111] Furthermore, the Lifetime Assessment Department visualizes predicted radioactivity behavior data in the form of graphs and charts. It displays trends in radioactivity changes over time in graphs to allow for intuitive verification. This enables the evaluation of radioactivity concentration and safety at specific points in time. In other words, the Lifetime Assessment Department simulates the long-term behavior of radioactivity based on the decay equations of Am-241 and Pu-241 and changes in the Ce-144 / Am-241 ratio, thereby allowing for the long-term prediction and management of the radioactivity safety of nuclear fuel fragment particles.

[0112] This analyzes how the lifespan of fragment particles can vary depending on environmental factors (temperature, radiation exposure, etc.).

[0113] In addition, calculated remaining lifespan, total lifespan, and radioactivity change data are visualized in the form of graphs, charts, etc., and provided to user terminals; reports are automatically generated to document the lifespan assessment results and enable their utilization in nuclear power plant decommissioning or management operations.

[0114] For reference, in this embodiment, the initial radioactivity concentration calculation uses the ORIGEN 2.1 code to calculate the initial radioactivity concentration of Fuel-Type Hot Particles (FTHP), which takes into account reactor operating parameters such as fuel burn rate, effective power days (EFPD), and uranium enrichment. Through this, the initial concentration of major radionuclides is quantitatively predicted.

[0115] Here, regarding the initial radioactivity values ​​of Am-241 and Pu-241, calculations considering reactor operating conditions and fuel characteristics are required to accurately determine the initial radioactivity values. To this end, combustion simulation codes such as ORIGEN can be used to calculate the initial radioactivity concentration.

[0116] For example, if the ORIGEN code is used to calculate the initial radioactivity concentration of nuclear fuel and the fuel burn rate is set to 40 GWd / tU, the uranium enrichment to 4.5%, and the cooling time to 5 years, the initial radioactivity value of Pu-241 is calculated to be 500 Bq / g, and the initial radioactivity value of Am-241 is calculated to be 100 Bq / g. These values ​​are used as initial input data for the life assessment system.

[0117] In addition, this embodiment includes the following three-step procedure for evaluating the internal exposure dose from FTHP inhalation. It includes calculating the initial radioactivity concentration at the time of leakage, calculating the elapsed time using the Ce-141 / Ce-144 ratio, and calculating the Committed Effective Dose (CED) using dose factors according to ICRP 119.

[0118] Here, the life evaluation system for nuclear fuel fragment particles using long-half-life radionuclides according to the present embodiment calculates changes in radioactivity and elapsed time, but the life evaluation unit (400) can evaluate the internal exposure dose (effective dose) based on this. The application range of the system can be expanded by calculating the internal exposure dose using dose coefficients proposed by the ICRP (International Commission on Radiological Protection).

[0119] The dose factor of Am-241 is 4.3E-5 Sv / Bq, and the dose factor of Pu-241 is 2.5E-6 Sv / Bq. For example, if the accumulated radioactivity of Am-241 over 10 years is 200 Bq and the radioactivity of Pu-241 is 50 Bq, the total effective dose is calculated as follows.

[0120] Total effective dose =

[0121]

[0122] This result can be used to assess risk by comparing it with radiation safety standards.

[0123] In addition, the nuclear fuel fragment life evaluation system using long-half-life radionuclides in this embodiment can improve the accuracy of long-term analysis by using the Ce-144 / Am-241 ratio instead of the existing Ce-141 / Ce-144 ratio, and improve the performance of FastScan by introducing an Artificial Neural Network (ANN) for low-energy gamma ray measurement, thereby enhancing the accuracy of low-energy gamma ray analysis.

[0124] The present invention evaluates lifetimes based on radioactivity data of Am-241 and Pu-241, but the accuracy of long-term analysis can be improved by utilizing the Ce-144 / Am-241 ratio. The half-life of Ce-144 is 284.9 days, allowing for a more precise analysis of long-term behavior through changes in the ratio with Am-241. If the Ce-144 / Am-241 ratio is observed to start at 10 at the time of initial leakage and decrease to 1 after 5 years, this reflects the rate of radioactivity decline and decay pattern. Based on this data, the long-term radioactivity behavior of fragment particles and the elapsed time of leakage can be calculated more precisely.

[0125] The life evaluation system for nuclear fuel fragment particles using long-half-life radionuclides according to the present embodiment detects 59 keV gamma rays of Am-241 and radioactivity of Pu-241. By utilizing an Artificial Neural Network (ANN), the detection accuracy of low-energy gamma rays can be increased and the speed of data analysis can be improved. Accordingly, by introducing an ANN algorithm into the data processing unit (200), the gamma ray detection signal and noise of Am-241 can be separated, and accurate radioactivity values ​​can be provided in real time. For example, in the conventional method, the detection error rate was 5%, but by utilizing an ANN, this can be reduced to 2% or less.

[0126] In this embodiment, the life assessment system for nuclear fuel fragment particles using long-half-life radionuclides can make more accurate long-term predictions by performing simulations based on changes in the Ce-144 / Am-241 ratio and changes in the total radioactivity of Am-241. For example, when the life assessment unit (400) predicts radioactivity 50 years later based on changes in the Ce-144 / Am-241 ratio, it is shown that the radioactivity of Am-241 has decreased to 20% of the initial value and Ce-144 has completely decayed. Through this, the time at which radioactivity reaches a safe threshold can be calculated and utilized in radiation management planning.

[0127] Hereinafter, a detailed description will be provided of a nuclear fuel fragment particle life evaluation system using a long-half-life radionuclide according to one embodiment of the present invention.

[0128] The configuration and overall operating principle of the nuclear fuel fragment life evaluation system using long-half-life radionuclides according to the present embodiment are described as follows.

[0129] The reason Am-241 was selected instead of Ce-141 to calculate the elapsed time of nuclear fuel fragmentation leakage from the core is as follows.

[0130] Its half-life is 432.6 years, which is considerably longer than that of Ce-141. Since Americium is insoluble, its chemical behavior is similar to that of nuclear fuel fragments, just like Cerium. It is easy to detect because it emits 59 keV gamma rays.

[0131] If nuclear fuel fragments leak, the radioactivity of Am-241 increases because the Pu-241 within the fragments decays and converts into Am-241.

[0132] In other words, since the half-life of Pu-241 is 14.33 years, which is shorter than the half-life of Am-241 (432.6 years), the amount produced by the decay of Pu-241 is greater than the amount of Am-241 radioactivity that decreases over time, so the total radioactivity of Am-241 increases.

[0133] The total radioactivity of Am-241 after nuclear fuel fragment leakage can be calculated using the following formula.

[0134] [Equation 1]

[0135]

[0136] is the decrease in radioactivity of Am-241 at elapsed time (t) after nuclear fuel fragment particle leakage, is the increase in radioactivity of Am-241 due to Pu-241 decay at elapsed time (t) after nuclear fuel fragment particle leakage, The radioactivity of Am-241 at the time of nuclear fuel fragment leakage, is the radioactivity of Pu-241 at the time of nuclear fuel fragment leakage, The half-life of Am-241 (432.6 years), is the half-life of Pu-241 (14.33 years).

[0137] Figure 4 shows the elapsed time 144 Ce / 241 This represents the radioactivity ratio of Am.

[0138] According to Figure 4, it can be seen that the ratio of the radioactivity of Ce-144 and Am-241 calculated by Equation (1) decreases over time.

[0139] The results of linear regression using the natural logarithm to determine the relationship between the Ce-144 / Am-241 radioactivity ratio and elapsed time are shown in Table 1 below.

[0140] Classification ln( 141 Ce / 144 Ce)ln( 144 Ce / 241 Am) Linear regression function slope (λ) -6.85 -0.9923 Half-life of radioactivity rate (years) 0.1012 0.6985 Correlation coefficient 10.9973

[0141] In the above, the half-life t of the radioactivity rate ½ It can be calculated as =ln2 / λ.

[0142] It can be seen that the half-life of the Ce-144 / Am-241 radioactivity ratio is calculated to be 0.6985 years, which is about 7 times longer than the half-life of the Ce-141 / Ce0144 radioactivity ratio of 0.1012 years.

[0143] In addition, the linear regression correlation coefficient for the radioactivity ratio of Ce-144 / Am-241 was calculated to be 0.9973, which is close to 1. Therefore, when using the method of this embodiment, the lifetime of nuclear fuel fragment particles can be evaluated for a longer period than when using the Ce-141 / Ce-144 radioactivity ratio.

[0144] FIG. 5 is a flowchart illustrating a method using a nuclear fuel fragment particle life evaluation system using long-half-life radionuclides according to one embodiment of the present invention.

[0145] In a method using a system (hereinafter referred to as the system) for evaluating the elapsed time from the time of leakage of nuclear fuel fragment particles released from a nuclear power plant using the americium-241 (Am-241) radionuclide having a long half-life, the system collects radioactivity data of Am-241 and Pu-241 using a radiation detector that measures Am-241 radioactivity within the nuclear fuel fragment particles (a).

[0146] Next, based on the collected data, the system calculates the decrease in radioactivity of Am-241 due to the natural decay of Am-241 and the increase in radioactivity of Am-241 due to the increase in radioactivity according to the rate at which Pu-241 decays and is converted into Am-241, thereby calculating the total change in radioactivity of Am-241 (b).

[0147] Next, the system compares the initial radioactivity values ​​of Am-241 and Pu-241 measured at the time of leakage with the current radioactivity values ​​of Am-241 measured at the time of leakage using the total radioactivity change of Am-241 and the half-lives of Pu-241 and Am-241, tracks the amount of Am-241 that has decreased over time and the amount of Am-241 generated by the decay of Pu-241, and calculates the elapsed time from the time of leakage to the present using these values ​​(c).

[0148] The system calculates the remaining time until the radioactivity of the nuclear fuel fragment particles reaches a safety threshold, and evaluates the total lifetime of the fragment particles by summing the elapsed time in step (c) above (d).

[0149] Through this invention, it is possible to evaluate the elapsed time from the time of nuclear fuel fragment particle leakage by using the Ce-144 / Am-241 radioactivity ratio instead of the Ce-141 / Ce-144 radioactivity ratio during long-term planned preventive maintenance or nuclear power plant decommissioning.

Claims

1. A radiation detector (100) that detects radioactivity data of Am-241 and Pu-241 in nuclear fuel fragment particles in real time, A data processing unit (200) that calculates the total change in radioactivity by calculating the decrease in radioactivity of Am-241 and the increase in Am-241 due to the decay of Pu-241 based on the data collected through the radiation detection unit above, An elapsed time calculation unit (300) that calculates the elapsed time from the time of leakage by comparing the initial radioactivity value and the current radioactivity value of Am-241, and A life evaluation system for nuclear fuel fragment particles using long-half-life radionuclides, comprising a life evaluation unit (400) that calculates the remaining time until the radioactivity of the nuclear fuel fragment particles reaches a safety threshold and evaluates the total life of the fragment particles by summing the elapsed time.

2. In Paragraph 1, A life evaluation system for nuclear fuel fragment particles using long-half-life radionuclides, characterized in that the life evaluation unit visually displays the results of the elapsed time calculation unit and provides information to the user.

3. In Paragraph 1, A system for evaluating the lifespan of nuclear fuel fragment particles using long-half-life radionuclides, characterized in that the radiation detection unit (100) includes a gamma ray detector capable of detecting 59 keV gamma rays of Am-241 with high sensitivity.

4. In Paragraph 1, The above data processing unit (200) is A system for evaluating the lifespan of nuclear fuel fragment particles using long-half-life radionuclides, characterized by calculating the decrease in radioactivity of Am-241 based on the detected data above, calculating the decrease in radioactivity due to the natural decay of Am-241, and calculating the increase in radioactivity of Am-241 based on the increase in radioactivity according to the rate at which Pu-241 decays and converts into Am-241, thereby calculating the total change in radioactivity of Am-241.

5. In Paragraph 1, The above elapsed time calculation unit (300) is Using the total radioactivity change of Am-241 and the half-lives of Pu-241 and Am-241, the initial radioactivity values ​​of Am-241 and Pu-241 measured at the time of leakage and the currently measured radioactivity value of Am-241 are compared, and A system for evaluating the lifespan of nuclear fuel fragment particles using long-half-life radionuclides, characterized by tracking the amount of Am-241 that has decreased over time and the amount of Am-241 generated by the decay of Pu-241, and calculating the elapsed time from the time of leakage to the present in reverse.

6. A method for using a nuclear fuel fragment life assessment system using long-half-life radionuclides, (a) The above-mentioned nuclear fuel fragment life assessment system collects radioactivity data of Am-241 and Pu-241 using a radiation detector that measures Am-241 radioactivity within the nuclear fuel fragment, and (b) Based on the collected data, the above-mentioned nuclear fuel fragment life assessment system calculates the decrease in radioactivity of Am-241 due to the natural decay of Am-241, and calculates the increase in radioactivity of Am-241 due to the increase in radioactivity according to the rate at which Pu-241 decays and converts into Am-241, thereby calculating the total change in radioactivity of Am-241, and (c) The above-mentioned nuclear fuel fragment life assessment system uses the total radioactivity change of Am-241 and the half-lives of Pu-241 and Am-241 to compare the initial radioactivity values ​​of Am-241 and Pu-241 measured at the time of leakage with the currently measured radioactivity value of Am-241, tracks the amount of Am-241 that has decreased over time and the amount of Am-241 generated by the decay of Pu-241, and calculates the elapsed time from the time of leakage to the present in reverse using these values, and (d) A method using a nuclear fuel fragment life evaluation system using a long-half-life radionuclide, characterized in that the nuclear fuel fragment life evaluation system calculates the remaining time until the radioactivity of the nuclear fuel fragment reaches a safe threshold, and evaluates the total life of the fragment by summing the elapsed time of step (c).

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