A method and system for measuring basic characteristic parameters of high temperature gas cooled reactor primary circuit radioactive dust

Abstract

The application discloses a kind of high temperature gas cooled reactor primary circuit radioactive dust basic characteristic parameter measurement method and system. Dust sample is obtained by short-time sampling of sampling filter or long-time sampling of dust filter;Obtain solid and liquid phase part by ultrasonic oscillation and solid-liquid separation;Solid part is weighed, γ nuclide measurement, particle size measurement, specific surface area measurement, morphology observation and component analysis are carried out, and β nuclide activity of Sr such as catalytic oxidation combustion and liquid scintillation counting measurement 3 H、 14 C、 90 Sr is measured;Liquid phase part is measured by γ nuclide, element content analysis and β nuclide;Finally, according to the measurement results and gas flow information, determine dust concentration, nuclide type and specific activity, particle size distribution and specific surface area and other parameters.The application fills the gap of high temperature gas cooled reactor radioactive dust systematic measurement technology, and provides key data support for radiation protection and accident source term evaluation.

Description

Technical Field

[0001] This invention relates to a method and system for measuring the basic characteristic parameters of radioactive dust in the primary loop of a high-temperature gas-cooled reactor, belonging to the field of nuclear power safety and radiation protection technology. Background Technology

[0002] As of the end of April 2026, there were over 400 commercially operating reactors worldwide, providing approximately 9% of global electricity generation. High-temperature gas-cooled reactors (HTGRs) are the first stage of the internationally recognized fourth-generation advanced reactor—the ultra-high-temperature gas-cooled reactor (UHTGR). Their inherent safety, high thermal conversion efficiency, and core outlet temperature provide them with broad development prospects in nuclear power generation, hydrogen production, and seawater desalination. China, the United States, Russia, France, Japan, and other countries are actively engaged in the research and development of HTGRs.

[0003] The Institute of Nuclear and New Energy Technology (INFUT) at Tsinghua University is my country's leading research and development unit for high-temperature gas-cooled reactor (HTGR) technology. In 2000, it successfully built China's first modular pebble bed 10MW HTGR experimental reactor (HTR-10) and formulated my country's development roadmap for HTGR technology: HTR-10 experimental reactor → HTGR demonstration project (HTR-PM) → 600MW HTGR (HTR-PM600) commercial promotion. Based on the HTR-10, the Shandong Rongcheng Shidaowan HTR-PM entered commercial operation in December 2023, becoming the world's first pebble bed modular HTGR reactor with fourth-generation nuclear power technology characteristics. The larger-scale HTR-PM600 is currently under construction.

[0004] For pebble bed high-temperature gas-cooled reactors, radioactive dust is one of the most significant safety concerns. In 2009, German nuclear scientist R. Moormann pointed out that primary coolant dust can carry radionuclides, contaminating piping and equipment, and causing difficulties in reactor maintenance and decommissioning; in the event of a primary coolant depressurization accident, radioactive dust resuspension will be a major accident source. Dust primarily originates from friction and wear of spherical fuel elements in the reactor core and fuel loading / unloading system, and can also originate from corrosion and wear of piping and equipment materials. Dust provides a new pathway parallel to coolant transport for primary coolant fission and activation products. Therefore, research on radioactive dust is a crucial issue related to the safety of pebble bed high-temperature reactors.

[0005] Currently, there are few studies on direct measurement of radioactive dust on reactors, with most data coming from early experimental results on German AVRs. In 1990, CBDecken and U. Wawrzik provided information on primary loop radioactive dust measurements during 20 years of AVR operation, including dust concentration in the coolant (average concentration of 5 μg / m³). 3STP), particle size distribution, and typical nuclides carried by the dust. In 1990, H. Gottaut and K. Krüger estimated the total dust generation over the AVR's lifetime to be 50-60 kg, with specific activities of Co-60 and Cs-137 on the dust of 2.0 × 10⁻⁶. 5 -8.0×10 6 and 2.0×10 6 -9.6×10 7 Bq / g. In 2008, J. Fachinger et al. measured the specific activities and distributions of Cs-137, Co-60, and Eu-154 on dust inside AVR pipes, finding both loose and tightly bound dust on the pipe walls. Radioactive dust poses significant challenges to the maintenance and decommissioning of AVR reactors. In 2011, W. Humrickhouse, a researcher at INL National Laboratory in the United States, summarized the dust problem in high-temperature gas-cooled reactors, pointing out that in-depth research on dust issues is a prerequisite for conducting any meaningful safety analysis of next-generation ultra-high-temperature gas-cooled reactor nuclear energy systems.

[0006] However, the measurement of basic characteristic parameters of radioactive dust from high-temperature gas-cooled reactors (HTGRs) remains severely lacking both domestically and internationally, with a shortage of scientific and systematic measurement techniques and methods. On the one hand, existing technologies lack a systematic measurement procedure capable of simultaneously acquiring multiple basic characteristic parameters such as radioactive dust concentration, particle size distribution, typical nuclide types, and specific activity. On the other hand, there is a lack of dedicated sampling devices and supporting radiochemical analysis methods for radioactive dust under the special environment (high temperature, high pressure, and strong radioactivity) of the HTGR primary loop. These deficiencies make it difficult to accurately grasp the source term information of radioactive dust in the HTGR primary loop, thus hindering the scientific and rational assessment of radiation dose and the implementation of effective radiation protection. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for measuring the basic characteristic parameters of primary loop radioactive dust in a high-temperature gas-cooled reactor. Addressing the technological gap in the existing technology regarding the lack of scientific and systematic means for measuring the basic characteristic parameters of primary loop radioactive dust in a high-temperature gas-cooled reactor, this invention provides a measurement method and experimental procedure that can comprehensively and accurately obtain key source term information such as the concentration, particle size distribution, typical nuclide types and their specific activities, particle morphology, and composition of primary loop radioactive dust.

[0008] The method for measuring basic characteristic parameters of radioactive dust in a high-temperature gas-cooled reactor provided by this invention includes the following steps: S1. Obtain radioactive dust samples from the primary loop of the high-temperature gas-cooled reactor. S2. Separate the radioactive dust sample to obtain the dust to be tested; S3. Perform multiple parameter measurements on the dust to be tested. The multiple parameter measurements include mass measurement of the dust to be tested to obtain mass information, measurement of radioactive nuclides on the dust to be tested to obtain radioactive nuclide information, particle size measurement of the dust to be tested to obtain particle size distribution information, and specific surface area measurement of the dust to be tested to obtain specific surface area information. S4. Based on the quality information, the radionuclide information, the particle size distribution information, the specific surface area information, and the gas flow rate information when acquiring the radioactive dust sample, determine the radioactive dust source term information of the primary loop of the high-temperature gas-cooled reactor. The radioactive dust source term information includes at least one of dust concentration, typical nuclide type, typical nuclide specific activity, particle size distribution, and specific surface area.

[0009] Preferably, step S1 specifically includes the following steps: Short-term sampling is performed using a sampling filter in a primary radioactive dust measurement loop to obtain radioactive dust samples with an accumulation period of days, weeks, or months; or... By replacing the dust filter in the helium purification system and conducting long-term sampling, radioactive dust samples with an accumulation period of up to one year were obtained.

[0010] Preferably, the short-time sampling includes the following steps: The sampling filter is installed in the primary loop of the radioactive dust measurement circuit and isolated from the purification column of the helium purification system; the primary loop of the radioactive dust measurement circuit is evacuated; the primary loop of the radioactive dust measurement circuit is connected to the purification column, and the helium flow rate is adjusted using an electric regulating valve to collect dust, and the flow rate, temperature, and pressure parameters are recorded; after collection, the primary loop of the radioactive dust measurement circuit is isolated again, the pressure is released, and the sampling filter is removed; the filter element is immersed in the solution, and the dust particles are separated from the filter material by ultrasonic separation; the separated solution is allowed to stand, and solid-liquid separation is performed to obtain a solid dust portion and a liquid phase portion; Preferably, the long-term sampling includes the following steps: When the reactor is shut down or the system is modified, the dust filter in the helium purification system is removed, and the shell of the dust filter is cut to expose the filter column inside. The filter column is taken out and placed in a solution for ultrasonic vibration treatment to separate the radioactive dust on the filter column. After the separation is allowed to stand, solid-liquid separation is performed to obtain the solid dust part and the liquid phase part.

[0011] Preferably, the solution is a 2% HNO3 solution, and the conditions for ultrasonic oscillation treatment are: oscillation power 400W, oscillation time 2 hours, and oscillation times 2; the time for the solution after static separation is 1 week.

[0012] Preferably, in step S3, the mass, particle size, and specific surface area are measured according to the following steps: The solid dust is dried and weighed using a precision electronic balance to obtain the dust mass information. Take a portion of the solid dust and place it in a liquid medium for ultrasonic oscillation to disperse it; take the dispersed liquid sample and use a laser particle size analyzer, optical microscope or scanning electron microscope to measure and statistically analyze the particle size distribution information. The gas adsorption method is used to measure the specific surface area of ​​the solid dust using a specific surface area analyzer to obtain the specific surface area information of the dust to be tested.

[0013] Preferably, in step S3, radionuclide measurement is performed in two branches: solid-phase measurement and liquid-phase measurement. The solid phase measurement branch includes the following steps: The solid dust fraction was measured using a high-purity germanium gamma spectrometer to obtain the type and activity of gamma radionuclides on the solid dust; the gamma radionuclides included at least one selected from the group consisting of: 124 I, 131 I, 137 Cs、 140 Ba、 140 La、 152 Eu、 181 Hf, 51 Cr 54 Mn, 59 Fe、 57 Co、 58 Co、 60 Co、 75 Se、 203 Hg; The liquid phase measurement branch includes the following steps: The liquid phase is measured using a high-purity germanium gamma spectrometer to obtain the types and activities of gamma radionuclides in the liquid phase; the elemental content in the liquid phase is measured using an inductively coupled plasma spectrometer or an inductively coupled plasma mass spectrometer.

[0014] Furthermore, the solid-phase measurement branch also includes the following steps: A portion of the solid dust was accurately weighed using a precision balance and placed in a sample combustion device for catalytic oxidation combustion, converting graphite into CO2 and H2O. The gases produced during combustion were absorbed using an alkaline solution to prepare a liquid sample. The β-radioactive nuclide activity of the liquid sample was measured using a liquid scintillation counter, and the total carbon content in the liquid sample was determined using acid-base titration to obtain... 3 H and 14 C activity; The solid residue after combustion was dissolved using a strong acid and prepared into a liquid sample; the α / β radionuclide activity of the liquid sample was measured using a liquid scintillation counter. Furthermore, the liquid phase measurement branch also includes the following steps: Take an appropriate amount of liquid sample and mix it directly with the scintillation fluid. Use a liquid scintillation counter to measure the activity of α / β radionuclides in the sample.

[0015] The method of the present invention further includes at least one of the following steps: The particle morphology of the dust to be tested was observed, and the particle morphology of the dust to be tested was characterized by scanning electron microscopy. The dust to be tested was subjected to compositional analysis, and the composition of the dust to be tested was qualitatively analyzed using an energy dispersive spectroscopy (EDS) instrument.

[0016] The present invention further provides a measurement system for basic characteristic parameters of radioactive dust in a high-temperature gas-cooled reactor, comprising: A sampling unit is used to obtain radioactive dust samples in the primary loop of a high-temperature gas-cooled reactor. The sampling unit includes a sampling filter connected in parallel with a dust filter in a helium purification system or a dust filter installed in a helium purification system. The sample processing unit is used to separate the radioactive dust sample to obtain the dust to be tested. The separation process includes ultrasonic oscillation processing and solid-liquid separation processing to obtain a solid dust part and a liquid phase part. The measurement unit is used to measure multiple parameters of the dust to be tested. The measurement unit includes a gamma spectrometer for measuring gamma radionuclides, a laser particle size analyzer for measuring particle size, a precision electronic balance for measuring mass, a specific surface area analyzer for measuring specific surface area, an inductively coupled plasma spectrometer or an inductively coupled plasma mass spectrometer for measuring elemental content, and a liquid scintillation counter for measuring α / β radionuclides. The data processing unit is used to determine the radioactive dust source term information of the primary loop of the high-temperature gas-cooled reactor based on the measurement results of the measurement unit and the gas flow information of the sampling unit. The radioactive dust source term information includes at least one of dust concentration, nuclide type and specific activity, particle size distribution and specific surface area.

[0017] The sampling filter includes one or more filter elements with different filtration precisions, the filtration precisions including at least one selected from 1μm, 3μm, 5μm, 10μm, 20μm, 50μm and 80μm; the dust filter includes a filter column with a filtration precision of 5μm; the filtration precision in this invention refers to a filtration efficiency of 98% for particles of the corresponding size.

[0018] Preferably, the filter element or filter column is made of sintered stainless steel powder or sintered stainless steel fiber.

[0019] The measurement unit also includes at least one of the following: a scanning electron microscope for observing particle morphology, an energy dispersive spectrometer for component analysis, and a portable radiation meter for measuring sample gamma dose rate.

[0020] The present invention has the following beneficial technical effects: This invention proposes a complete technical solution for radioactive dust in the primary loop of high-temperature gas-cooled reactors, encompassing sampling, separation, measurement, and parameter determination. Through a complementary design of online sampling loops and offline dust filter disassembly, comprehensive acquisition of dust source term information is achieved across different time scales, from short-term (days / weeks / months) to long-term (years).

[0021] This invention employs a dual-branch measurement design combining solid and liquid phases, comprehensively utilizing multiple analytical techniques such as gamma spectrometer, liquid scintillation counter, laser particle size analyzer, BET surface area analyzer, and ICP / ICP-MS. This allows for the simultaneous acquisition of comprehensive information on dust concentration, gamma / β nuclide types and specific activities, particle size distribution, specific surface area, elemental content, and particle morphology and composition. In particular, by combining catalytic oxidation combustion with liquid scintillation counting, it achieves accurate measurement of radioactive graphite dust. 3 H, 14 C 90 Accurate determination of pure β-nuclides such as Sr.

[0022] The technical solution of this invention has been verified on the 10MW high-temperature gas-cooled experimental reactor (HTR-10) and has been applied to the world's first pebble bed modular high-temperature gas-cooled reactor demonstration project (HTR-PM), demonstrating its industrial applicability. The basic characteristic parameters of radioactive dust obtained by this invention can be directly used for radiation dose evaluation and radiation protection measure formulation under normal operating conditions of high-temperature gas-cooled reactors. It also provides key experimental data for the assessment of radioactive dust resuspension source terms under accident conditions (such as loss of cooling and depressurization accidents), which is of great practical significance for ensuring the safe operation and decommissioning of high-temperature gas-cooled reactors. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method for measuring the basic characteristic parameters of radioactive dust in a high-temperature gas-cooled reactor according to the present invention. Detailed Implementation

[0024] The present invention will now be clearly and completely described in conjunction with the technical solutions in the embodiments thereof. Obviously, the described embodiments are merely a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Figure 1 The flowchart of the measurement method of the present invention includes the following steps: Step 1: Collect primary loop radioactive dust samples using a sampling filter or dust filter; Step 2: Measurement of gamma dose rate on the outer surface of the filter; Step 3: Separation and acquisition of radioactive dust samples from the filter (dust separation by oscillation on the filter element / filter column); Step 4: Dust mass measurement (precision electronic balance); Step 5: Gamma radionuclide measurement (sampling filters can obtain both long-lived and short-lived nuclides; dust filters mainly obtain long-lived nuclides), using a high-purity germanium gamma spectrometer; Step 6: Dust particle size measurement (using an optical microscope or laser particle size analyzer) Step 7: Measure the specific surface area of ​​dust particles; Step 8: Observation of radioactive dust particle morphology (using scanning electron microscopy); Step 9: Radioactive dust composition analysis (using energy dispersive spectroscopy). Step 10: Liquid sample preparation (using a sample combustion device / oxygen bomb for pure β-nucleoside measurement). Step 11: Measurement of β-radioactive nuclides (using a liquid scintillation counter); Step 12: Determination of primary loop radioactive dust source term information (obtain dust concentration, specific activity of typical nuclides, particle size distribution, etc.).

[0026] Example 1: Short-time sampling and measurement of primary-loop radioactive dust based on sampling filters This embodiment uses the 10MW high-temperature gas-cooled experimental reactor (HTR-10) as a platform. Through the sampling filter in the primary loop radioactive dust measurement loop, a short-term accumulated primary loop radioactive dust sample is obtained, and basic characteristic parameters are measured.

[0027] 1. Structure and setup of sampling filters The sampling filter is installed in the sampling loop in parallel with the normal purification line of the helium purification system. A certain flow rate of helium gas from the primary loop (e.g., approximately 10% of the total primary loop flow rate) is diverted from the dust filter into the sampling loop, and the sampling flow rate is regulated by an electrically operated regulating valve. The sampling filter contains filter elements with different filtration accuracies, exemplarily selected from at least one or more of 1μm, 3μm, 5μm, 10μm, 20μm, 50μm, and 80μm. The filter elements are made of sintered stainless steel powder or sintered stainless steel fibers.

[0028] The sampling circuit is equipped with electrically operated isolation valves (one at the inlet and one at the outlet), an electrically operated regulating valve, a temperature transmitter, a pressure transmitter, and a mass flow meter to control and record the flow rate, temperature, and pressure parameters of helium gas flowing through the sampling filter. The sampling circuit is also connected to a helium-assisted vacuum subsystem for vacuuming and depressurization operations before and after sampling.

[0029] The dust filter is located in the helium purification system. Its housing is made of stainless steel of a certain thickness (for example, the dust filter housing of HTR-10 is 8mm thick). Inside, there is a filter column with a fixed filtration accuracy (for example, 5μm). The filter column is made of sintered stainless steel metal powder or sintered stainless steel metal fiber.

[0030] 2. Acquisition of radioactive dust samples Before sampling, install the sampling filter into the primary radioactive dust sampling circuit. Isolate the sampling circuit from the normal purification section of the helium purification system using an electrically operated isolation valve, creating a closed circuit. Connect the helium-assisted vacuum subsystem and evacuate the entire sampling circuit to a vacuum level better than 10 Pa before closing the isolation valve.

[0031] Adjust the electric regulating valve to a smaller opening (e.g., about 5%), and open the electric isolation valve separating the helium purification system's normal purification column inlet and outlet, allowing helium from the primary loop to slowly enter the sampling loop. Then, gradually adjust the opening of the electric regulating valve until the helium flow rate in the sampling loop reaches the set value of 15 Nm³. 3 / h, begin collecting radioactive dust carried in the primary loop helium gas. During sampling, continuously record flow rate, temperature, and pressure parameters, and calculate the cumulative volume of helium gas passing through the sampling filter (converted to standard conditions) as 2911.2 Nm³. 3 .

[0032] The sampling and collection cycle is determined based on actual operating conditions, and can be exemplarily 4 weeks, but can also be adjusted to 5 days or 2 weeks depending on the actual sampling and collection situation. After the collection cycle is completed, close the electric isolation valves separating the sampling circuit from the normal purification column inlet and outlet of the helium purification system to isolate the sampling circuit from the normal purification column of the helium purification system. Connect the helium auxiliary vacuum subsystem to release the high-pressure helium gas in the sampling circuit to atmospheric pressure before isolation. Remove the entire sampling filter and transport it to the radiochemistry laboratory using a lead-shielded container for subsequent measurement and analysis.

[0033] 3. Measurement of gamma dose rate on the outer surface of the filter In the radiochemistry laboratory, a portable gamma dose rate meter was first used to measure the gamma dose rate of approximately 0.3 μSv / h on the outer surface of the sampling filter (about 1 cm from the surface) to determine the overall gamma radioactivity level of the sampling filter, in order to confirm whether a sufficient amount of radioactive dust sample had been collected, and to take corresponding radiation protection measures for different radioactivity levels.

[0034] 4. Separation of radioactive dust samples Open the sampling filter housing, remove the filter elements of each filtration precision, and label each filter element.

[0035] The labeled filter elements were immersed in beakers containing anhydrous ethanol solution and then subjected to ultrasonic oscillation in an ultrasonic oscillator. The ultrasonic oscillation caused the graphite dust adhering to the filter elements to be fully detached and transferred to the ethanol solution, forming a suspension containing radioactive graphite dust.

[0036] The ethanol suspension containing dust was allowed to stand at room temperature (e.g., for 24 hours) to allow larger dust particles to settle. The supernatant and the sediment were collected and stored separately for subsequent measurements and analyses.

[0037] 5. Dust mass measurement The ethanol suspension containing the remaining dust was transferred to a pre-weighed aluminum weighing dish and placed in a constant temperature drying oven to evaporate to constant weight. Then, the mass of dust obtained on the 80 μm filter element was weighed using a precision electronic balance, which was 0.0162 g (graphite dust on the filter element with smaller particle sizes can be ignored).

[0038] 6. Measurement of gamma radionuclides First, the high-purity germanium gamma spectrometer was calibrated for energy and efficiency. Energy calibration was performed using a standard radioactive source, and efficiency calibration was performed using a standard source with the same geometry as the sample under test. Energy-channel address curves and efficiency-energy curves were obtained.

[0039] Containers containing radioactive dust were placed at the measurement positions of a high-purity germanium gamma spectrometer, and appropriate measurement times were set to acquire gamma spectra. Characteristic peaks in the gamma spectra were identified using spectral analysis software to determine the types of radionuclides. 124 I, 131 I, 137 Cs、 140 Ba、 140 La、 152 Eu、 181 Hf, 51 Cr 54 Mn, 59 Fe、 57 Co、 58 Co、 60 Co、 75 Se、 203 Hg et al. calculated the activity of each nuclide by using the net area of ​​characteristic peaks, measurement time, detection efficiency, and nuclide branching ratio.

[0040] In one embodiment of the invention, the gamma radionuclides detected in the HTR-10 sampling filter sample include fission products (such as...124 I, 131 I, 137 Cs、 140 Ba、 140 La、 152 Eu、 181 Hf) and activated products (such as Hf) and activation products (such as Hf) 51 Cr 54 Mn, 59 Fe、 57 Co、 58 Co、 60 Co、 75 Se、 203 Hg) and other nuclides were detected, including both short-lived and long-lived nuclides. It should be noted that the above-mentioned nuclide types are only exemplary and may vary in actual measurements due to different reactor operating conditions and sample accumulation time. The scope of protection of this invention is not limited to the detection of specific nuclides.

[0041] 7. Particle size distribution measurement Take a small amount (e.g., about 0.5 mL) of the ethanol suspension containing radioactive dust and add it to a glass slide. After the ethanol evaporates, observe it under an optical microscope. At different magnifications (e.g., 200x, 500x, and 1000x), randomly select multiple fields of view to photograph and measure the particle size of the particles in the field of view. Use image analysis software to label the equivalent diameter of each particle, perform statistical analysis, and plot a particle size distribution histogram and cumulative distribution curve to determine the particle size distribution range and characteristic particle size values ​​of the dust. It was found that particles with diameters between 5 μm and 10 μm are dominant.

[0042] 8. Measurement of β-radioactive nuclides Accurately weigh 0.1 g of the graphite dust sample using a precision electronic balance and place it in the crucible of the sample combustion apparatus. Fill the oxygen bomb with pure oxygen and ignite the sample until it is completely burned. After combustion, the carbon in the graphite is converted into CO2, and the hydrogen is converted into H2O. The gas produced by combustion is passed through a gas delivery tube into an absorption bottle containing 10 ml of a 4 mol / L NaOH solution. The CO2 and H2O are absorbed by the NaOH solution, thus... 14 C and 3 H is captured in the absorption liquid and a liquid sample is prepared for β-radioactivity measurement.

[0043] The total carbon content in the obtained liquid sample was determined using acid-base titration, which was then used to calculate... 14 Specific activity of C.

[0044] Take 1 mL of the above liquid sample, add 10 mL of OPTIPHASE 'HISAFE' 3 scintillation solution, mix thoroughly, and then place in a liquid scintillation counter for measurement. Set the measurement time to 20 min, acquire the liquid scintillation spectrum, and use spectral analysis software to distinguish the components. 3 H and 14 The counting contribution of C is determined. 3 H and 14 The activity of C.

[0045] 9. Measurement of primary loop radioactive dust source term information Based on the above measurement results, the basic characteristic parameters of primary loop radioactive dust were calculated: (1) Radioactive dust concentration: 5.57 μg / m³ was calculated by dividing the total mass of dust collected by each filter element by the cumulative volume of helium gas passing through the sampling filter during the sampling period (converted to standard conditions). 3 (STP).

[0046] (2) Particle size distribution: The particle diameter distribution is determined by statistical analysis results from optical microscope or laser particle size analyzer: the main proportion of particles with diameters between 5 μm and 10 μm.

[0047] (3) Types of nuclides: The following nuclides were determined by the spectral measurements obtained from a high-purity germanium gamma spectrometer and a liquid scintillation counter: 124 I, 131 I, 137 Cs、 140 Ba、 140 La、 152 Eu、 181 Hf, 51 Cr 54 Mn, 59 Fe、 57 Co、 58 Co、 60 Co、 75 Se.

[0048] Example 2: Long-term cumulative sampling and measurement of primary-loop radioactive dust based on a dust filter This embodiment uses the 10MW high-temperature gas-cooled experimental reactor (HTR-10) as a platform. By replacing the dust filter in the helium purification system, a long-term accumulated primary loop radioactive dust sample is obtained, and basic characteristic parameters are measured.

[0049] 1. Structure and Installation of Dust Filters The dust filter is installed in the normal purification column of the HTR-10 helium purification system. Helium gas from the primary loop is drawn from the reactor cold end, cooled and depressurized, and then enters the purification column, first flowing through the dust filter. The dust filter housing is made of stainless steel (e.g., the HTR-10 dust filter housing is 8mm thick), and is cylindrical. Inside, multiple filter columns (e.g., 4) are arranged vertically. The filtration accuracy of the filter columns is, for example, 5μm, and the material is sintered stainless steel powder or sintered stainless steel fiber.

[0050] 2. Acquisition of radioactive dust samples During reactor shutdown overhauls or system upgrades, the dust filters should be completely replaced. Before operation, ensure that the dust filters are isolated from the helium system and purge any residual helium inside with an inert gas (such as nitrogen) to ensure safety.

[0051] Use a circular pipe cutter to make a circumferential cut to the housing below the lower partition of the dust filter. After removing the lower end cap, use an electric straight grinder and angle grinder to separate the filter column outlet pipe from the nuts fixed to the lower partition. Before processing the outlet pipe, seal the outlet pipe opening with a lint-free cloth to prevent metal fragments generated during grinding from entering the cylinder from the outlet pipe. After removing all the nuts on the lower partition, confirm that the upper section of the filter column is no longer secured. Use the circular pipe cutter again to make a circumferential cut from the appropriate position above the lower partition. After cutting, the dust filter cylinder is opened, and each filter column is removed in sequence and numbered A, B, C, and D.

[0052] 3. Measurement of γ-dose rate on the outer surface of the filter column A portable gamma dose rate meter was used to measure the gamma dose rate on the outer surface of the filter column (about 1 cm from the surface), which was approximately 0.18 μSv / h. This was used to determine the overall gamma radioactivity level of the dust filter, to confirm whether a sufficient amount of radioactive dust sample had been collected, and to take appropriate radiation protection measures for different radioactivity levels.

[0053] 4. Separation of radioactive dust samples Since the graphite dust adhering to the filter column is difficult to remove by tapping and vibration, the filter column is placed in a suitable solution (e.g., 2% HNO3 solution) and treated with ultrasonic vibration in evenly divided sections (upper, middle, and lower) to remove the dust. The ultrasonic vibration conditions are: power 400W, time 2h, and number of cycles 2.

[0054] After collecting the extract containing radioactive dust, allow it to stand for about a week to allow the solid radioactive dust to settle naturally and separate from the extract. Use a peristaltic pump to slowly extract the supernatant and transfer it to another container for storage, to be used for subsequent measurements. The lower sediment is washed with deionized water during centrifugation, repeated several times. Finally, place the beaker containing the radioactive dust in an oven and dry it to constant weight to obtain a dry radioactive graphite dust sample.

[0055] The dust filter's actual cumulative operating time from installation to removal was 225 full-power days. The total helium flow through the dust filter during this time was 3.17 × 10⁻⁶ days. 5 Nm 3 .

[0056] 5. Dust mass measurement The total mass of dried graphite dust obtained from each filter column was measured to be 804.04 mg using a precision electronic balance. Based on the cumulative operating time of the dust filter, the dust concentration in the first loop can be estimated to be 2.53 μg / m³. 3 (STP).

[0057] 6. Measurement of gamma radionuclides Following the same method as in Example 1, the high-purity germanium gamma spectrometer was first calibrated for energy and efficiency. Then, a sample container containing graphite dust was placed in the spectrometer for measurement, obtaining the corresponding results. Next, a sample container containing 10 ml of shaken supernatant was placed in the spectrometer for measurement, obtaining the corresponding results. Integrating the two sets of results yielded the types of radionuclides on the graphite dust and their specific activities (decay corrected to the time of filter removal). 60 Co (1.20×10) 5 Bq / g), 137 Cs (1.34×10 3 Bq / g), 152 Eu-152 (8.6×10 2 Bq / g).

[0058] Because dust filters are sampled over a long period (on an annual basis), the radioactive dust on them is predominantly composed of long-lived nuclides. In one embodiment of the present invention, the gamma radionuclides measured in the HTR-10 dust filter sample include long-lived nuclides, such as... 137 Cs、 60 Co、 152 Eu et al. Short-lived nuclides are generally difficult to detect because they decay during long-term accumulation. This underscores the necessity of complementarity between short-term sampling using a sampling filter and long-term sampling using a dust filter—the former provides information on short-lived nuclides, while the latter provides information on the total amount accumulated over long periods.

[0059] 7. Measurement of basic characteristic parameters of dust samples (1) Particle size distribution measurement A small amount of dry graphite dust was immersed in anhydrous ethanol and ultrasonically vibrated for 2 minutes to disperse it evenly. A drop of the suspension was placed on a glass slide, and after the ethanol evaporated, it was observed under SEM. Multiple fields of view were randomly selected at different magnifications, and the particles in each field of view were photographed and their size measured. The particle size distribution was statistically analyzed using image analysis software, and a cumulative distribution curve was plotted to determine the particle size distribution range and characteristic particle size values ​​of the dust: most particles were smaller than 5 μm, and dust particles smaller than 2 μm accounted for 50%.

[0060] (2) Analysis of dust morphology and composition A small amount of dry graphite dust was taken and fixed on the scanning electron microscope (SEM) stage. The particle morphology was observed under the SEM, revealing irregular shapes with some fine fragments adhering to larger particles, as well as some dust structures composed of agglomerated large numbers of sheet-like structures. Simultaneously, energy dispersive spectroscopy (EDS) was used for qualitative or semi-quantitative analysis of the dust's elemental composition, revealing the presence of elements such as O (11.34%), Fe (3.69%), Cr (3.13%), and Ni (0.35%) in addition to C (80.62%).

[0061] 8. Measurement of β-radioactive nuclides Take 0.5 mL of the supernatant and add 10 mL of OPTIPHASE 'HISAFE' 3 scintillation solution. Place the solution in a liquid scintillation counter and measure for 10 min to determine the concentration of ions. 3 H activity was (1.27±0.04)×10 7 Bq / g (decay correction to filter removal time).

[0062] Take another 10 mg of dry graphite dust, burn it in an oxygen bomb according to the method in Example 1, and prepare a liquid sample after the gas is absorbed by NaOH solution. Measure the liquid sample using a liquid scintillation counter. 3 H-3 and 14 C-14 activity.

[0063] 9. Measurement of primary loop radioactive dust source term information Based on the above measurement results and the accumulated helium flow rate of the dust filter, the basic characteristic parameters of the primary loop radioactive dust are calculated: (1) Total mass and annual production of radioactive dust: The total mass of dust collected on each filter column is calculated by dividing the total mass of dust collected by each filter column by the cumulative operating time. The total mass is 804.04 g.

[0064] (2) Radioactive dust concentration (long-term average): Calculated by dividing the total mass of dust by the cumulative total volume of helium gas passing through the dust filter (converted to standard conditions). The long-term average dust concentration is 2.53 μg / m³.3 (STP).

[0065] (3) Specific activity of typical long-lived nuclides: calculated by dividing the activity of each long-lived nuclide by the corresponding dust mass. 137 Cs、 60 Co、 152 The specific activities of nuclides such as Eu are 1.20 × 10⁻⁶. 5 1.34×10 3 8.6×10 2 Bq / g.

[0066] (4) Particle size distribution: determined by statistical analysis results of optical microscope or laser particle size analyzer: most particles are smaller than 5 μm, and dust particles smaller than 2 μm account for 50%.

[0067] Example 3: Composition and Working Process of the Measurement System This embodiment provides an overall description of the structure and workflow of the measurement system of the present invention.

[0068] 1. Composition of the measurement system The basic characteristic parameter measurement system for radioactive dust in the primary loop of a high-temperature gas-cooled reactor of this invention mainly includes: (1) Sampling circuit: A pipeline connected in parallel with the normal purification line of the helium purification system. The pipeline is equipped with an inlet electric isolation valve, a sampling filter, a mass flow meter, a temperature transmitter, a pressure transmitter, an electric regulating valve, and an outlet electric isolation valve in series. The sampling circuit is also connected to the helium auxiliary vacuum pumping subsystem through a valve.

[0069] (2) Sampling filter: It is installed in the sampling circuit and can be equipped with filter elements of different filtration precision. The filter element material is sintered stainless steel metal powder or sintered stainless steel metal fiber.

[0070] (3) Dust filter: It is installed in the purification column of the helium purification system, located at the inlet end of the purification column. It contains a filter column with a fixed filtration accuracy. The filter column is made of sintered stainless steel metal powder or sintered stainless steel metal fiber, and the shell is made of stainless steel.

[0071] (4) Portable gamma dose rate meter: used to measure the gamma dose rate on the outer surface of the filter.

[0072] (5) Ultrasonic oscillator: used to separate graphite dust on filter elements or filter columns into the solution.

[0073] (6) Precision electronic balance: used to weigh dust.

[0074] (7) Optical microscope or laser particle size analyzer: used to measure the particle size distribution of dust.

[0075] (8) High-purity germanium gamma spectrometer: used to measure the type and activity of gamma radionuclides.

[0076] (9) Sample combustion device (oxygen bomb): used to burn graphite dust to prepare liquid samples for β radioactivity measurement.

[0077] (10) Liquid scintillation counter: used for measuring 3 H, 14 The activity of pure β-radioactive nuclides such as C.

[0078] (11) Scanning electron microscope and energy dispersive spectrometer: used to observe the morphology and particle size of dust particles and analyze elemental composition.

[0079] 2. Sampling process The sampling process for the sampling loop is as follows: (1) Close the inlet electric isolation valve and the outlet electric isolation valve to isolate the sampling circuit from the helium purification system.

[0080] (2) Open the valve connected to the helium-assisted vacuum subsystem and evacuate the entire sampling circuit to a vacuum level better than 10 Pa.

[0081] (3) Close the vacuum valve to maintain the vacuum state of the sampling circuit.

[0082] (4) Adjust the electric regulating valve to a smaller opening and open the inlet electric isolation valve to allow the primary loop helium to slowly enter the sampling loop.

[0083] (5) Gradually adjust the opening of the electric regulating valve to make the helium flow rate in the sampling circuit reach the set value.

[0084] (6) Continuously run and record the readings of the mass flow meter, temperature transmitter and pressure transmitter, and accumulate the volume of helium passing through the sampling filter.

[0085] (7) After the sampling cycle is completed, close the inlet electric isolation valve and the outlet electric isolation valve.

[0086] (8) Open the valve connected to the helium-assisted vacuum subsystem to release the high-pressure helium in the sampling circuit to atmospheric pressure.

[0087] (9) Remove the sampling filter and send it to the radiochemistry laboratory.

[0088] The dust filter sampling process is as follows: (1) During reactor shutdown overhaul or system modification, confirm that the dust filter has been isolated from the helium purification system and replaced by inert gas purging.

[0089] (2) Use a circular pipe cutter to cut the housing circumferentially at the appropriate position below the dust filter lower partition.

[0090] (3) Remove the lower end cap, use power tools to separate the filter column outlet pipe from the nut on the lower partition, and seal the outlet pipe opening with a lint-free cloth.

[0091] (4) After removing the nuts, confirm that each filter column is no longer fixed.

[0092] (5) Use a circular pipe cutter to cut the housing around the bottom from the appropriate position above the lower partition.

[0093] (6) Open the cylinder, take out each filter column and number it.

[0094] 3. Sample Analysis Procedure The sample analysis procedure in the radiochemistry laboratory is as follows: (1) First, use a portable gamma dose rate meter to measure the gamma dose rate on the outer surface of the filter.

[0095] (2) Remove each filter element from the sampling filter or remove the filter column from the dust filter and label it; or perform ultrasonic vibration on the filter element or filter column in the solution to separate and collect the dust.

[0096] (3) Weigh the dust using a precision electronic balance.

[0097] (4) Take some dust samples and measure them with a high-purity germanium gamma spectrometer to determine the types and activities of gamma nuclides.

[0098] (5) Take a portion of the dust sample for particle size distribution measurement (optical microscope or laser particle size analyzer).

[0099] (6) Take a portion of the dust sample and measure the particle specific surface area.

[0100] (7) Take some dust samples for morphology and composition measurement (scanning electron microscope and energy dispersive spectroscopy).

[0101] (8) A portion of the dust sample was burned in an oxygen bomb, and after absorption by NaOH solution, a liquid sample was prepared. Liquid scintillation counting was performed to determine the composition of the sample. 3 H and 14 C activity.

[0102] (9) Take some dust samples for scanning electron microscopy and energy dispersive spectroscopy analysis.

[0103] (10) Take a sample of liquid and measure it with a high-purity germanium gamma spectrometer to determine the gamma nuclide type and activity.

[0104] (9) Take samples of liquid and use a liquid scintillation analyzer to measure the β / α nuclide type and activity.

[0105] (10) Based on all the measurement data, calculate the basic characteristic parameters such as radioactive dust concentration, specific activity of typical nuclides, and particle size distribution.

[0106] The specific embodiments of the present invention are not limited to those described in the above embodiments. Those skilled in the art can make various modifications and variations without departing from the spirit of the present invention, and such modifications and variations should all fall within the protection scope of the present invention.

Claims

1. A method for measuring basic characteristic parameters of radioactive dust in a high-temperature gas-cooled reactor, comprising the following steps: S1. Obtain radioactive dust samples from the primary loop of the high-temperature gas-cooled reactor. S2. Separate the radioactive dust sample to obtain the dust to be tested; S3. Perform multiple parameter measurements on the dust to be tested. The multiple parameter measurements include mass measurement of the dust to be tested to obtain mass information, measurement of radioactive nuclides on the dust to be tested to obtain radioactive nuclide information, particle size measurement of the dust to be tested to obtain particle size distribution information, and specific surface area measurement of the dust to be tested to obtain specific surface area information. S4. Based on the quality information, the radionuclide information, the particle size distribution information, the specific surface area information, and the gas flow rate information when acquiring the radioactive dust sample, determine the radioactive dust source term information of the primary loop of the high-temperature gas-cooled reactor. The radioactive dust source term information includes at least one of dust concentration, typical nuclide type, typical nuclide specific activity, particle size distribution, and specific surface area.

2. The method according to claim 1, characterized in that: Step S1 specifically includes the following steps: Short-term sampling is performed using a sampling filter in a primary radioactive dust measurement loop to obtain radioactive dust samples with an accumulation period of days, weeks, or months; or... By replacing the dust filter in the helium purification system and conducting long-term sampling, radioactive dust samples with an accumulation period of up to one year were obtained.

3. The method according to claim 2, characterized in that: The short-time sampling includes the following steps: The sampling filter is installed in the primary loop of the radioactive dust measurement circuit and isolated from the purification column of the helium purification system; the primary loop of the radioactive dust measurement circuit is evacuated; the primary loop of the radioactive dust measurement circuit is connected to the purification column, and the helium flow rate is adjusted using an electric regulating valve to collect dust, and the flow rate, temperature, and pressure parameters are recorded; after collection, the primary loop of the radioactive dust measurement circuit is isolated again, the pressure is released, and the sampling filter is removed; the filter element is immersed in the solution, and the dust particles are separated from the filter material by ultrasonic separation; the separated solution is allowed to stand, and solid-liquid separation is performed to obtain a solid dust portion and a liquid phase portion; The long-term sampling includes the following steps: When the reactor is shut down or the system is modified, the dust filter in the helium purification system is removed, and the shell of the dust filter is cut to expose the filter column inside. The filter column is taken out and placed in a solution for ultrasonic vibration treatment to separate the radioactive dust on the filter column. After the separation is allowed to stand, solid-liquid separation is performed to obtain the solid dust part and the liquid phase part.

4. The method according to any one of claims 1-3, characterized in that: In step S3, the mass, particle size, and specific surface area are measured according to the following steps: The solid dust is dried and weighed using a precision electronic balance to obtain the dust mass information. Take a portion of the solid dust and place it in a liquid medium for ultrasonic oscillation to disperse it; take the dispersed liquid sample and use a laser particle size analyzer, optical microscope or scanning electron microscope to measure and statistically analyze the particle size distribution information. The gas adsorption method is used to measure the specific surface area of ​​the solid dust using a specific surface area analyzer to obtain the specific surface area information of the dust to be tested.

5. The method according to any one of claims 1-4, characterized in that: In step S3, radionuclide measurements are performed according to two branches: solid-phase measurement and liquid-phase measurement. The solid phase measurement branch includes the following steps: The solid dust fraction was measured using a high-purity germanium gamma spectrometer to obtain the type and activity of gamma radionuclides on the solid dust; the gamma radionuclides included at least one selected from the group consisting of: 124 I, 131 I, 137 Cs、 140 Ba、 140 La、 152 Eu、 181 Hf, 51 Cr 54 Mn, 59 Fe、 57 Co、 58 Co、 60 Co、 75 Se、 203 Hg; The liquid phase measurement branch includes the following steps: The liquid phase is measured using a high-purity germanium gamma spectrometer to obtain the types and activities of gamma radionuclides in the liquid phase; the elemental content in the liquid phase is measured using an inductively coupled plasma spectrometer or an inductively coupled plasma mass spectrometer.

6. The method according to claim 5, characterized in that: The solid-phase measurement branch also includes the following steps: A portion of the solid dust was accurately weighed using a precision balance and placed in a sample combustion device for catalytic oxidation combustion, converting graphite into CO2 and H2O. The gases produced during combustion were absorbed using an alkaline solution to prepare a liquid sample. The β-radioactive nuclide activity of the liquid sample was measured using a liquid scintillation counter, and the total carbon content in the liquid sample was determined using acid-base titration to obtain... 3 H and 14 C activity; The solid residue after combustion was dissolved using a strong acid and prepared into a liquid sample; the α / β radionuclide activity of the liquid sample was measured using a liquid scintillation counter. The liquid phase measurement branch also includes the following steps: Take an appropriate amount of liquid sample and mix it directly with the scintillation fluid. Use a liquid scintillation counter to measure the activity of α / β radionuclides in the mixture.

7. The method according to any one of claims 1-6, characterized in that: The method further includes at least one of the following steps: The particle morphology of the dust to be tested was observed, and the particle morphology of the dust to be tested was characterized by scanning electron microscopy. The dust to be tested was subjected to compositional analysis, and the composition of the dust to be tested was qualitatively analyzed using an energy dispersive spectroscopy (EDS) instrument.

8. A measurement system for basic characteristic parameters of radioactive dust in a high-temperature gas-cooled reactor, comprising: A sampling unit is used to obtain radioactive dust samples in the primary loop of a high-temperature gas-cooled reactor. The sampling unit includes a sampling filter connected in parallel with a dust filter in a helium purification system or a dust filter installed in a helium purification system. The sample processing unit is used to separate the radioactive dust sample to obtain the dust to be tested. The separation process includes ultrasonic oscillation processing and solid-liquid separation processing to obtain a solid dust part and a liquid phase part. The measurement unit is used to measure multiple parameters of the dust to be tested. The measurement unit includes a gamma spectrometer for measuring gamma radionuclides, a laser particle size analyzer for measuring particle size, a precision electronic balance for measuring mass, a specific surface area analyzer for measuring specific surface area, an inductively coupled plasma spectrometer or an inductively coupled plasma mass spectrometer for measuring elemental content, and a liquid scintillation counter for measuring α / β radionuclides. The data processing unit is used to determine the radioactive dust source term information of the primary loop of the high-temperature gas-cooled reactor based on the measurement results of the measurement unit and the gas flow information of the sampling unit. The radioactive dust source term information includes at least one of dust concentration, nuclide type and specific activity, particle size distribution and specific surface area.

9. The measurement system according to claim 8, characterized in that: The sampling filter includes one or more filter elements with different filtration precisions, the filtration precisions including at least one selected from 1μm, 3μm, 5μm, 10μm, 20μm, 50μm and 80μm; the dust filter includes a filter column with a filtration precision of 5μm.

10. The measurement system according to claim 9, characterized in that: The measurement unit also includes at least one of the following: a scanning electron microscope for observing particle morphology, an energy dispersive spectrometer for component analysis, and a portable radiation meter for measuring the sample gamma dose rate.

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