Method and system for online monitoring of gas-liquid two-phase flow for radioisotope separation systems

Abstract

The application discloses a method and system for on-line monitoring of gas-liquid two-phase flow of a radioactive separation system, and belongs to the technical field of fluid detection. The method comprises the following steps: a reference source emitting two different energy gamma rays is arranged outside a clean section of a pipeline to be detected, a reference source detector is arranged on the opposite side of the pipeline, the two energy transmittances after the reference source rays penetrate the pipeline, fluid and deposits are measured, and a transmission attenuation pair is obtained; based on the transmission attenuation pair and a pre-acquired clean pipeline transmittance benchmark, the mass thickness of the deposits in the pipeline is obtained by inversion; a main detector and a narrow field-of-view collimator thereof are arranged; and the application can realize real-time and high-precision on-line monitoring of the radioactivity concentration of fluid under the working condition of gas-liquid two-phase flow of the radioactive separation system, synchronously obtains the deposit adhesion state parameters, and provides reliable data support for system process control, pipeline cleaning control and compliance judgment of radioactive waste discharge.

Description

Technical Field

[0001] This invention relates to the field of fluid detection technology, and more specifically, to a method and system for online monitoring of gas-liquid two-phase flow in a radioactive separation system. Background Technology

[0002] During the operation of a radioactive separation system, the fluid medium often presents a gas-liquid two-phase flow state. For example, in radioactive labeling synthesis, chromatographic column elution, or waste discharge, in order to ensure the safe and stable operation of the system and to ensure product quality, it is necessary to monitor the concentration of radioactivity in the fluid in real time and accurately online. Existing online monitoring technologies mostly use non-contact radioactive detectors, such as gamma detectors or scintillator detectors, which are installed on the outside of the pipeline. The radioactivity of the fluid is estimated by measuring the gamma or beta rays emitted when the fluid flows through the detector's field of view.

[0003] In practical applications, the above monitoring methods face a significant problem: interference from radioactive deposits on the inner wall of the pipe. Due to the adhesive properties of radioactive substances or other matrices carried in the fluid, such as salts, organic matter, and proteins, or due to the decrease in solubility caused by temperature and pressure changes during fluid flow in the pipe, radioactive nuclides can easily form a deposit layer on the inner wall of the pipe. Under gas-liquid two-phase flow conditions, the fluid state is more complex. Fluctuations at the gas-liquid interface, changes in flow velocity, and the generation and collapse of bubbles can all exacerbate the precipitation and adhesion of solutes on the pipe wall.

[0004] This deposit layer possesses the same radioactive characteristics as the flowing fluid, namely the same nuclides and similar energy spectra. However, it is a static deposit. When the online monitoring system measures, the radiation signal received by the detector actually comes from two parts: one part is the dynamic radiation from the normally flowing gas-liquid two-phase fluid in the center of the pipe, and the other part is the static radiation from the deposit layer on the pipe wall. Existing signal processing technology has difficulty effectively distinguishing these two parts of radiation from the mixed energy spectrum signal. Due to the presence of the deposit layer, the radioactivity reading displayed by the monitoring system will be consistently higher, and this deviation is cumulative and uncertain. The thicker the deposit layer, the more radioactivity accumulates, and the more serious the interference with the measurement results. This interference not only prevents operators from obtaining the true concentration of radioactivity in the fluid, affecting process control, such as judging separation efficiency and determining the timing of product collection, but may also cause misjudgments in system cleaning verification, radioactive waste emission monitoring, etc., leading to false positives or incorrect emission calculations, thus causing unnecessary compliance issues. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide an online monitoring method and system for gas-liquid two-phase flow in a radioactive separation system. This method enables real-time, high-precision online monitoring of the radioactive concentration of the fluid under gas-liquid two-phase flow conditions in the radioactive separation system, while simultaneously acquiring sediment adhesion parameters. This provides reliable data support for system process control, pipeline cleaning management, and compliance assessment of radioactive waste discharge.

[0006] To solve the above problems, the present invention adopts the following technical solution:

[0007] The first aspect is a method for online monitoring of gas-liquid two-phase flow in a radioactive separation system, including:

[0008] A reference source emitting two different energies of gamma rays is set outside the clean section of the pipe to be tested, and a reference source detector is set on the opposite side of the pipe. The transmittance of the two energies of the reference source rays after passing through the pipe, fluid and sediment is measured to obtain the transmission attenuation pair.

[0009] Based on the transmission attenuation pairs and the pre-obtained clean pipe transmittance benchmark, the mass thickness of the deposits inside the pipe is obtained by inversion.

[0010] By setting up a main detector and its narrow field-of-view collimator, the detection field of the main detector is limited to the pipe axis area, and the main count rate is measured.

[0011] The main count rate is compensated by using the mass thickness of the sediment and the attenuation coefficient of the radionuclide to be tested in the sediment, and the compensated count rate is obtained.

[0012] Zero-deposit calibration is performed at predetermined time intervals to update the clean pipe transmittance benchmark and the detection efficiency of the main detector;

[0013] The true radioactivity concentration of the flowing fluid is calculated based on the compensated count rate and the updated detection efficiency, and the mass thickness of the sediment is output.

[0014] Further, the transmission attenuation pair is obtained, including:

[0015] Two reference sources emitting two different energies of gamma rays are set at 180-degree intervals along the circumference outside the clean section of the pipeline. Two detectors are set on the opposite side of the pipeline, directly opposite each reference source, so that each detector receives the rays from the reference source on the opposite side that propagate in a straight line along the diameter of the pipeline, and at the same time, two transmission count pairs are measured.

[0016] Based on two transmission count pairs, the ratio of the two energy count rates received by each detector is calculated. The ratio is compared with the initial calibration ratio. If the deviation exceeds the preset threshold, the original count rates of the two energies are reversed according to the deviation amount to obtain the corrected transmission count pair.

[0017] The reference source is operated in pulse mode, and the count rate of the transmitted signal plus the background signal is obtained during the window opening time and the count rate of the pure background signal is obtained during the window closing time by time gating synchronized with the pulse source. The pure transmission attenuation pair is obtained by subtracting the window closing count rate from the window opening count rate in the same period.

[0018] Furthermore, the mass thickness of the sediment within the pipe is obtained through inversion, including:

[0019] Based on two sets of pure transmission attenuation pairs, attenuation feature vectors corresponding to each channel are constructed. The two sets of attenuation feature vectors are spatially aligned and compared. The non-uniform distribution pattern of sediments in the circumferential direction is deduced from the comparison results.

[0020] Based on the non-uniform distribution morphology of sediments, the cross-section of the pipe is divided into multiple micro-regions. For each micro-region, the non-uniform distribution morphology parameters are taken as known quantities and substituted into a set of physical constraint equations based on the attenuation characteristics of two types of energy in sediments and fluids. The local mass thickness of each micro-region is obtained by solving the equations. The total mass thickness of sediments is obtained by spatial integration of all local mass thicknesses.

[0021] Furthermore, the main count rate is measured, including:

[0022] Based on the circumferential non-uniform distribution morphological parameters of sediments, the spatial orientation of the detection field of view is adjusted so that the orientation is aligned with the fluid equivalent center.

[0023] Based on the detection field of view aligned with the fluid equivalent center, photons passing through the field of view are screened based on energy-angle coordinated discrimination, and the main count rate after topological suppression of the screened photons is recorded.

[0024] Furthermore, the compensated count rate is obtained, including:

[0025] The pulse signals corresponding to the main count rate after topological suppression are sorted by amplitude to construct the count rate of multiple energy channels corresponding to the characteristic energy of the radionuclide to be tested;

[0026] Based on the circumferential non-uniform distribution of sediments and the spatial orientation of the detection field of view, the sediment thickness distribution traversed by rays reaching the detector from the fluid equivalent center region along different directions is calculated. Combined with the pre-acquired attenuation coefficients of each characteristic energy in the sediment, the attenuation correction factor corresponding to each energy channel is generated.

[0027] Preliminary compensation is performed using the count rate of each energy channel and the corresponding attenuation correction factor. Then, based on the branching ratio of each characteristic energy of the radionuclide to be measured, the count rate of each energy channel after preliminary compensation is self-consistently iteratively corrected to eliminate the influence of scattering crosstalk between channels, and the count rate of each energy after energy self-consistency correction is obtained.

[0028] Furthermore, the compensated count rate also includes:

[0029] Based on the total mass thickness of the sediment, the energy spectrum hardening correction coefficient is obtained from the pre-constructed nonlinear mapping relationship between sediment thickness and energy response. The energy count rate after energy self-consistency correction is then corrected twice to obtain the energy count rate after energy spectrum hardening correction.

[0030] Based on the spatial coverage of the detection field of view and the non-uniform distribution of sediments, a weighting function for the contribution of different spatial locations within the field of view to the detector count is constructed. The count rates of each energy after energy spectrum hardening correction are summed by energy weight and then divided by the integral of the weighting function over the field of view to obtain the spatially normalized total compensated count rate.

[0031] The current fluid density is inverted using pure transmission attenuation. Based on the correlation between fluid density and radioactivity concentration, the consistency of the spatially normalized total compensation count rate is checked. If the deviation exceeds the preset threshold, the energy spectrum hardening correction coefficient or the corresponding correction coefficient in the contribution weight function is adjusted, and the process of obtaining the spatially normalized total compensation count rate is re-executed until the deviation converges within the threshold. The final compensation count rate after verification is output.

[0032] Furthermore, a zero-deposition verification is performed, including:

[0033] Zero sediment check is triggered when the total sediment mass thickness is below a preset threshold.

[0034] In a zero-deposit state, the transmittance of the reference source rays after passing through the pipe and fluid is measured to obtain an updated clean pipe transmittance benchmark, and the fluid density is inverted based on this transmittance.

[0035] The detection field of the main detector is redirected to the direction of the reference source, and the count rate of the reference source rays is measured to obtain the main detector's count rate of the reference source.

[0036] Furthermore, performing zero-deposition verification also includes:

[0037] Based on the fluid density and transmittance obtained under zero sediment conditions, combined with the relative geometric positions of the reference source and the main detector, the attenuation correction coefficient of the ray from the reference source to the main detector is calculated. The attenuation correction coefficient is used to correct the count rate measured by the main detector to the reference source. Based on the corrected count rate and the known activity of the reference source, the detection efficiency of the main detector is determined.

[0038] The detection field of view of the main detector is restored to the pipeline axis area, and the updated clean pipeline transmittance benchmark and main detector detection efficiency are stored.

[0039] Further, the true radioactivity concentration of the flowing fluid is calculated, including:

[0040] Based on the final compensated count rate and the updated main detector detection efficiency, the response matrix is ​​constructed and solved jointly using the detection field of view spatial weight distribution function and the pre-acquired branch ratio to obtain the radioactivity concentration after preliminary geometric correction.

[0041] Based on the radioactive concentration and pure transmission attenuation pair after preliminary geometric correction, the fluid equivalent density is obtained by inversion. The expected concentration is calculated based on the fluid equivalent density. The radioactive concentration after preliminary geometric correction is compared with the expected concentration. If the deviation exceeds the preset threshold, the sediment attenuation coefficient used in the attenuation correction factor generation process is adjusted, and the process of calculating the radioactive concentration after preliminary geometric correction is iteratively executed until the deviation converges within the threshold. The final radioactive concentration is then output.

[0042] Based on the final radioactivity concentration, total sediment mass thickness, and circumferential non-uniform distribution morphology parameters, the concentration change rate and sediment growth rate are obtained by combining historical data, and the sediment eccentricity index is calculated. The above parameters are then integrated into a comprehensive state vector output.

[0043] In a second aspect, the present invention also provides an online monitoring system for gas-liquid two-phase flow in a radioactive separation system, comprising:

[0044] The transmission measurement module is used to set up a reference source emitting two different energies of gamma rays on the outside of the clean section of the pipe to be tested, and to set up a reference source detector on the opposite side of the pipe to measure the transmittance of the two energies of the reference source rays after passing through the pipe, fluid and sediment, so as to obtain the transmission attenuation pair.

[0045] The mass inversion module is used to invert the mass thickness of deposits inside the pipe based on the transmission attenuation pair and the pre-acquired clean pipe transmittance benchmark.

[0046] The main counting module is used to set the main detector and its narrow field-of-view collimator, so that the detection field of the main detector is limited to the pipe axis area, and the main counting rate is measured.

[0047] The counting compensation module is used to compensate the main count rate by utilizing the mass thickness of the sediment and the attenuation coefficient of the radionuclide to be tested in the sediment, so as to obtain the compensated count rate.

[0048] The zero-deposition calibration module is used to perform zero-deposition calibration at predetermined time intervals to update the clean pipeline transmittance benchmark and the detection efficiency of the main detector.

[0049] The concentration calculation module is used to calculate the true radioactive concentration of the flowing fluid based on the compensated count rate and the updated detection efficiency, and output the mass thickness of the sediment.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0051] This solution employs a combination of techniques: dual-energy gamma reference source transmission measurement to invert the mass thickness and circumferential non-uniform distribution of sediments within the pipeline; a narrow field-of-view collimated main detector combined with energy-angle collaborative discrimination to limit the detection field; and multi-dimensional count rate attenuation compensation combined with zero sediment calibration to dynamically update system baseline parameters. This overcomes the technical challenges of existing radioactive separation systems operating under gas-liquid two-phase flow conditions, where increased sediment adhesion to the pipe wall, complex fluid states, and the inability to effectively distinguish between the static radiation of radioactive deposits on the pipe wall and the dynamic radiation of the flowing fluid, lead to persistently high monitoring results and cumulative and uncertain biases due to sediment attenuation, scattering crosstalk, and energy spectrum hardening effects, making it impossible to accurately obtain the true radioactive concentration of the flowing fluid. This solution achieves precise decoupling of sediment interference and full-link measurement deviation correction, eliminating cumulative measurement errors caused by sediment adhesion. It enables real-time, high-precision online monitoring of fluid radioactive concentration under gas-liquid two-phase flow conditions in the radioactive separation system, while simultaneously acquiring sediment adhesion status parameters. This provides reliable data support for system process control, pipeline cleaning management, and compliance assessment of radioactive waste discharge. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0053] Figure 1 This is a flowchart of the online monitoring method for gas-liquid two-phase flow in a radioactive separation system according to the present invention;

[0054] Figure 2 This is a data flow diagram between various modules in the gas-liquid two-phase flow online monitoring system of the radioactive separation system of the present invention. Detailed Implementation

[0055] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0056] Example 1

[0057] Please see Figure 1 A method for online monitoring of gas-liquid two-phase flow in a radioactive separation system, the method comprising:

[0058] Step 1: Set up a reference source emitting two different energies of gamma rays on the outside of the clean section of the pipe to be tested, and set up a reference source detector on the opposite side of the pipe. Measure the transmittance of the two energies of the reference source rays after passing through the pipe, fluid, and sediment to obtain the transmission attenuation pair. The specific operation is as follows:

[0059] The clean section of the pipe under test is a straight pipe section with a uniform cross-section and no abrupt changes in flow path, and no built-in obstructive components on the inner wall. This section of the pipe can ensure a stable flow state when the fluid flows through it, avoiding unexpected interference to the X-ray propagation path caused by changes in the flow path structure. The reference source is a radionuclide that can simultaneously emit two different energies of gamma rays. The selection of the two energies must satisfy the requirement that there are distinguishable differences in the mass attenuation coefficients of the pipe wall material, the deposits inside the pipe, and the gas-liquid two-phase fluid, so as to achieve decoupled calculation of the contribution of different media to X-ray attenuation. The intensity attenuation of gamma rays when passing through a homogeneous medium follows an attenuation law jointly determined by the photoelectric effect, Compton scattering, and pair production of photons. This law can be expressed by a mathematical formula, which is derived as follows: the ratio of the transmitted intensity to the incident intensity of the X-ray when passing through the medium decreases exponentially with the mass attenuation coefficient of the medium and the product of the medium density and the medium thickness. This relationship can be verified by transmission experiments of single-energy narrow-beam gamma rays, specifically:

[0060]

[0061] In the formula, The transmission intensity of gamma rays after passing through the medium; The initial intensity of the gamma rays before they enter the medium; The mass attenuation coefficient of gamma rays in the corresponding medium; d represents the density of the corresponding medium; d represents the thickness of the corresponding medium through which the gamma rays pass.

[0062] A reference source is fixedly installed on the outer wall of the clean section of the pipe to be tested. A reference source detector is fixedly installed on the outer wall of the pipe opposite to the reference source. The line connecting the emission center of the reference source and the center of the detector surface passes through the center of the pipe cross-section, ensuring that the ray propagation path completely covers all the media inside the pipe. During the measurement, the reference source continuously emits two gamma rays of different energies. The rays pass through the pipe wall, the deposits attached to the inner wall of the pipe, and the gas-liquid two-phase fluid inside the pipe before reaching the reference source detector on the opposite side. The detector counts and collects the two gamma rays of different energies respectively, obtaining the transmission count rate corresponding to each energy ray. Based on the incident count rates of the two energy rays obtained in advance under the condition of a clean pipe without deposits, the transmittance corresponding to the two energy rays is calculated. The transmittance is the ratio of the transmission count rate of the corresponding energy to the calibrated incident count rate. The two sets of transmittance together constitute a transmission attenuation pair.

[0063] Obtaining the transmission attenuation pair also includes the following steps:

[0064] Step 11: Two reference sources emitting gamma rays of different energies are set up at 180-degree intervals along the circumference outside the clean section of the pipe. Two detectors are set up on the opposite side of the pipe, directly opposite each reference source, so that each detector receives the rays from the opposite reference source that are propagating in a straight line along the diameter of the pipe. At the same time, two transmission count pairs are obtained. The specific operation is as follows:

[0065] On the outside of the clean section of the pipeline, two installation positions spaced 180 degrees apart along the circumference of the pipeline are selected to fix two reference sources. The types of radionuclides, nominal activities, and emitted gamma ray energies of the two reference sources are kept consistent to ensure that the initial response characteristics of the two measurement channels are consistent. On the opposite side of the pipeline, a reference source detector is fixed at a position directly opposite each reference source. The line connecting the center of the detection surface of each detector to the emission center of the corresponding reference source coincides perfectly with the diameter of the pipeline at the corresponding position. This ensures that the rays received by each detector are from the reference source on the opposite side and travel along the pipeline. Gamma rays propagate in a straight line in the radial direction to avoid scattering and causing measurement deviations. Two reference sources synchronously initiate the ray emission process, and two reference source detectors synchronously initiate the data acquisition process. All acquisition operations are completed within the same measurement time to ensure that the two sets of measurement data correspond to the medium and fluid state in the pipe at the same moment. During the measurement time, each detector collects the count rate of two different energies of gamma rays emitted by the corresponding reference source. Each detector outputs a transmission count pair containing the two energy count rates. After the two detectors complete the synchronous measurement, a total of two transmission count pairs are obtained.

[0066] Step 12: Based on the two transmission count pairs, calculate the ratio of the two energy count rates received by each detector. Compare the ratio with the initial calibration ratio. If the deviation exceeds a preset threshold, reverse the original count rates of the two energies according to the deviation amount to obtain the corrected transmission count pairs. The specific operation is as follows:

[0067] The initial calibration ratio is the ratio of the count rates of the two energy gamma rays received by each detector under the conditions that the pipeline is clean and free of deposits and filled with a known homogeneous medium. This ratio is only related to the emission branching ratio of the reference source nuclide, the energy response characteristics of the detector, and the attenuation characteristics of the pipeline wall material, and is not affected by subsequent changes in the state of the medium inside the pipeline. The initial calibration ratio after calibration is stored as an inherent parameter of the corresponding detector. For the two transmission count pairs obtained synchronously in step 11, the ratio of the count rates of the two energy gamma rays in the corresponding transmission count pair for each detector is calculated to obtain the real-time measurement ratio. The real-time measurement ratio corresponding to each detector is compared with the initial calibration ratio stored in the detector beforehand, and the deviation of the real-time measurement ratio relative to the initial calibration ratio is calculated. When the deviation exceeds a preset threshold, the original count rates of the two energies corresponding to the detector are reversed according to the deviation. The correction process adjusts the relative ratio of the two energy count rates so that the ratio of the two energy count rates after correction returns to the allowable deviation range of the initial calibration ratio, thereby eliminating the systematic errors caused by detector energy response drift, reference source activity decay, and electronic system gain fluctuations. After the original transmission count pairs corresponding to the two detectors have been corrected, two sets of corrected transmission count pairs are obtained.

[0068] Step 13: Operate the reference source in pulse mode, and through time gating synchronized with the pulse source, acquire the count rate of the transmitted signal plus the background signal during the window opening time, and acquire the count rate of the pure background signal during the window closing time. Subtract the window closing count rate from the window opening count rate within the same period to obtain the pure transmission attenuation pair. The specific operation is as follows:

[0069] The reference source switches to pulse mode. In pulse mode, the emission process of the reference source is controlled by the pulse drive circuit. Within a preset pulse period, there is a windowing period for emission and a windowing period for emission to stop. These two periods are consecutively arranged within the same pulse period. The signal acquisition system of the reference source detector is synchronously triggered with the pulse source driving the reference source, ensuring that the detector's acquisition time window is completely synchronized with the pulse period of the reference source. During the windowing period of each pulse period, the reference source continuously emits gamma rays. The count rate acquired by the detector during this period includes the transmitted signal after the reference source rays pass through the medium inside the pipe, as well as the background signal caused by the environmental background and the dark noise of the detector itself. This is the transmission signal superimposed on the background signal. The total count rate of the background signal; during the window-off period of the same pulse cycle, the reference source stops emitting gamma rays, and the count rate collected by the detector during this period includes only the count rate of the pure background signal caused by the environmental background and the dark noise of the detector itself. The two sets of count rates within the same pulse cycle are calculated by subtracting the pure background count rate obtained during the window-off period from the total count rate obtained during the window-open period, thereby eliminating the interference of the background signal on the transmission measurement results and obtaining the pure transmission count rate of the corresponding energy. After performing the above background subtraction operation on the two energies of gamma rays respectively, a set of pure transmission attenuation pairs is obtained. After performing the above background subtraction operation on the two sets of corrected transmission count pairs corresponding to the two detectors respectively, two sets of pure transmission attenuation pairs are obtained.

[0070] In a preferred embodiment of the present invention, step 2 is further included: based on the transmission attenuation pair and the pre-acquired clean pipe transmittance benchmark, the mass thickness of the deposits inside the pipe is obtained by inversion. The specific operation is as follows:

[0071] The clean pipeline transmittance benchmark is based on the transmittance values ​​of two different energy gamma rays obtained through calibration measurements under zero-deposit conditions (no deposits on the inner wall of the pipeline), consistent with actual operating conditions, and using pipeline material, inner diameter parameters, and a preset fluid medium type. This benchmark fully characterizes the inherent attenuation characteristics of the pipeline wall material and the pure fluid medium within the pipeline for both energy gamma rays. After calibration, the values ​​are stored as a reference for subsequent attenuation separation. The transmission attenuation of gamma rays in multilayer media follows a linear superposition exponential attenuation law, with the total transmittance being the product of the transmittances of each layer. This law is derived from the physical mechanism of the interaction between narrow-beam gamma rays and matter and is applicable to multilayer media scenarios where the pipeline wall, deposits, and fluid are arranged sequentially along the ray propagation path. This physical relationship can be expressed as:

[0072]

[0073] This formula is based on the fact that when monoenergetic gamma rays pass through multiple layers of parallel media, the attenuation effect of each layer of media on the rays is independent, and the ratio of the total transmitted intensity to the incident intensity is equal to the product of the transmittance of each layer of media. This relationship is derived from the basic law of exponential attenuation of narrow-beam gamma rays and can accurately describe the intensity change process of rays as they pass through pipe walls, sediments and fluids in sequence.

[0074] In the formula, T is the transmittance of monoenergetic gamma rays obtained from actual measurement; The transmittance of the pipe wall material to this energy of gamma rays; The transmittance of the deposits on the inner wall of the pipe to this energy of gamma rays; The transmittance of the gas-liquid two-phase fluid in the pipe is the transmittance of gamma rays of this energy. The transmittance benchmark of the clean pipe corresponds to the ray attenuation caused by the pipe wall material and the fluid in the pipe. It can be expressed as the transmittance values ​​of the two energies of gamma rays in the clean state. By comparing the actual measured transmission attenuation with the transmittance benchmark of the clean pipe, the ray transmittance caused only by the sediment can be separated. The attenuation effect of the sediment on gamma rays also follows the exponential decay law. The mass thickness of the sediment is the product of the sediment density and the sediment thickness. It is a surface density parameter characterizing the amount of sediment adhesion. The mass attenuation coefficients of the two different energies of gamma rays in the same sediment medium have a definite difference. This difference is obtained through pre-calibrated laboratory calibration. To fix the known parameters, based on the sediment-specific transmittance corresponding to the two energies of gamma rays, combined with the pre-calibrated mass attenuation coefficient, a solution relationship for the mass thickness of the sediment can be constructed. The mass thickness of the sediment in the pipe can be obtained by numerical inversion.

[0075] The inversion of the mass thickness of sediments inside the pipe also includes the following steps:

[0076] Step 21: Based on the two sets of pure transmission attenuation pairs, construct the attenuation feature vector corresponding to each channel. Compare the two sets of attenuation feature vectors spatially and deduce the non-uniform distribution pattern of the sediment in the circumferential direction based on the comparison results. The specific operation is as follows:

[0077] Two sets of pure transmission attenuation pairs correspond to two measurement channels arranged 180 degrees apart along the circumference of the pipe. Each measurement channel corresponds to an independent reference source and reference source detector combination. The pure transmission attenuation pair of each channel fully characterizes the attenuation characteristics of all media along the ray propagation path of that channel for the two energy gamma rays. For each pure transmission attenuation pair, combined with the transmittance benchmark of the clean pipe, the sediment-specific attenuation amount corresponding to the two energy gamma rays is extracted. Using the sediment-specific attenuation amount of the two energy gamma rays as elements, an attenuation feature vector is constructed for each channel. The attenuation feature vector can fully reflect the sediment adhesion characteristics of the area covered by the ray propagation path of the corresponding channel. The ray propagation paths of the two measurement channels are arranged 180 degrees apart along the circumference of the pipe, respectively covering two opposite circumferential pipe walls on the pipe cross-section. In this region, two sets of attenuation feature vectors are spatially compared. The process of spatial comparison involves mapping the attenuation contribution corresponding to the two attenuation feature vectors to the circumferential positions of the pipe wall covered by their ray propagation paths, forming two sampling nodes for the circumferential attenuation distribution of the pipe. The difference in amplitude and energy ratio of the attenuation feature vectors of the two channels directly reflects the difference in sediment adhesion at two positions 180 degrees apart on the circumference of the pipe. By performing continuous fitting calculation on the numerical relationship of the two sets of attenuation feature vectors, the relative distribution relationship of sediment attenuation within the entire circumference of the pipe can be obtained, and then the non-uniform distribution pattern of sediment in the circumference of the pipe can be deduced. The non-uniform distribution pattern can be characterized by a continuous function of circumferential angle and relative thickness of sediment, completely covering the inner wall area of ​​the entire circumference of the pipe.

[0078] Step 22: Based on the non-uniform distribution morphology of the sediments, the pipe cross-section is divided into multiple micro-regions. For each micro-region, the non-uniform distribution morphology parameters are taken as known quantities and substituted into a set of physical constraint equations based on the attenuation characteristics of the two types of energy in the sediments and fluids. The local mass thickness of each micro-region is then obtained by spatial integration of all local mass thicknesses. The specific operation is as follows:

[0079] Based on the circumferential non-uniform distribution morphology of sediments obtained from step 21, the pipe cross-section is discretized, dividing it into multiple micro-regions. The division of these micro-regions occurs simultaneously along the pipe's circumference and radial direction. The step size for the circumferential division matches the spatial resolution of the non-uniform distribution morphology, while the step size for the radial division is determined based on the pipe's inner diameter and the maximum expected sediment thickness. Each micro-region is a small fan-shaped area on the pipe cross-section, ensuring that the sediment thickness within a single micro-region can be considered uniformly distributed. The non-uniform distribution morphology parameters obtained from step 21 include the relative sediment thickness ratio at each circumferential position and the relevant parameters of the circumferential distribution continuous function. These parameters are taken as known parameters. The solution process is improved by substituting quantities into the equations, which limits the relative distribution of sediments within each micro-element region and reduces the degree of freedom in the solution process. Based on the attenuation characteristics of two types of gamma rays in sediments and fluids, a set of physical constraint equations is constructed. The constraints of the equations include: the attenuation of sediments in each micro-element region to the two types of rays must match the non-uniform distribution morphology parameters corresponding to that micro-element; the mass attenuation coefficients of the two types of rays in sediments are pre-calibrated known parameters; the contribution of sediment mass thickness in the same micro-element region to the attenuation of the two types of rays must conform to their respective exponential attenuation laws; and the sum of the attenuation amounts of all micro-element regions must completely match the two sets of pure transmission attenuation pairs obtained by actual measurement.

[0080] For each micro-element region, the non-uniformly distributed morphological parameters are substituted into the physical constraint equations as known constraints. The local mass thickness of the sediment within each micro-element region is obtained through numerical solutions. This local mass thickness represents the areal density of the sediment within the corresponding micro-element region, accurately characterizing the actual amount of sediment adhered at that location. For the local mass thickness of all micro-element regions along the entire cross-section of the pipe's inner wall, spatial integration is performed along the pipe's circumference. During the integration process, weights are applied based on the circumferential arc length corresponding to each micro-element region, ultimately yielding the total mass thickness of the sediment on the pipe's inner wall. This integration process is specifically as follows:

[0081]

[0082] The formula is derived as follows: the total mass thickness of the sediment is the circumferential weighted average of the local mass thickness at each position on the circumference of the inner wall of the pipe. This relationship is derived from the definition of the surface density of mass thickness. The inner wall of the pipe is a continuous circumferential surface. The contribution of the local mass thickness at each circumferential position to the total mass thickness is proportional to the weight of the circumferential arc length corresponding to that position. The result of continuous integral can be approximated by summing discrete infinitesimal elements.

[0083] In the formula, The total mass thickness of the sediment; θ represents the local mass thickness of sediment at the corresponding angular position along the circumference of the pipe; θ is the angular variable along the circumference of the pipe, and the integration range covers the entire circumferential range of the pipe; the total mass thickness can fully characterize the total amount of sediment adhering to the entire inner circumference of the pipe.

[0084] In a preferred embodiment of the present invention, step 3 is further included: setting up the main detector and its narrow field-of-view collimator so that the detection field of view of the main detector is limited to the pipe axis region, and measuring the main count rate. The specific operation is as follows:

[0085] The main detector is selected from radiation detectors that match the gamma-ray energy range of the radionuclide being measured. High-energy-resolution semiconductor detectors or high-efficiency scintillator detectors can be used to accurately identify and count the energy of incident gamma photons. The narrow-field collimator is made of high-density, high-atomic-number radiation shielding material, commonly including tungsten alloys, lead, or depleted uranium, which can effectively shield gamma rays propagating in directions other than the preset one. The narrow-field collimator is located at the radiation incident end of the main detector. A collimation aperture extending in a straight line is formed inside the collimator. The geometric parameters of the collimation aperture, including aperture diameter, channel length, and channel inner wall roughness, are designed and fabricated according to the preset field of view. One end of the collimation aperture faces the sensitive detection surface of the main detector, and the other end faces the outer wall of the pipe being measured. By adjusting the installation position and angle of the collimator and the main detector, the central axis of the collimation aperture is aligned with the axial region of the pipe, thereby limiting the detection field of view of the main detector.

[0086] The spatial range of the detection field of view is jointly determined by the geometric parameters of the collimation aperture and the spatial position of the sensitive volume of the main detector. Only when gamma photons propagate within the spatial angle range defined by the collimation aperture can they pass through the collimation aperture and reach the sensitive detection surface of the main detector. Gamma photons deviating from this angle range are absorbed by the shielding substrate of the collimator and cannot enter the main detector. This structural design ensures that the detection field of view of the main detector is completely confined to the axial region inside the pipe. The area around the pipe wall where the deposits attached to the inner wall are located is outside the coverage of the main detector's detection field of view, thereby reducing the interference of static radiation emitted by the pipe wall deposits on the measurement results from a geometrical perspective. The count rate measured by the main detector has a definite physical correlation with parameters such as the activity of the radioactive source within the detection field of view, the intrinsic detection efficiency of the detector, and the solid angle of the incident rays. This correlation can be expressed by a formula, specifically:

[0087]

[0088] The formula is derived as follows: the number of effective photons recorded by the detector per unit time is equal to the total number of corresponding energy photons emitted by the radioactive source per unit time, multiplied by the solid angle ratio of the photons reaching the sensitive volume of the detector, and then multiplied by the intrinsic detection efficiency of the detector for that energy photon. The attenuation effect of the medium along the ray propagation path is also taken into account. This relationship is derived from the statistical law of radioactive decay and the basic principle of gamma ray detection, and can accurately describe the counting response characteristics of the main detector.

[0089] In the formula, C is the main count rate measured by the main detector; A is the activity of the radionuclide to be measured within the detection field; Ω is the effective solid angle of the main detector relative to the radioactive source within the detection field; and ε is the intrinsic detection efficiency of the main detector for this characteristic energy gamma photon. This represents the mass attenuation coefficient of the medium along the propagation path of the gamma rays. The main detector continuously collects and counts gamma photons entering the detection field of view within a preset measurement time, obtaining the photon count value per unit time, which is the initial main count rate.

[0090] The process of measuring the main count rate also includes the following steps:

[0091] Step 31: Based on the circumferential non-uniform distribution morphological parameters of the sediments, adjust the spatial orientation of the detection field of view so that it is aligned with the equivalent center of the fluid. The specific operation is as follows:

[0092] The non-uniform circumferential distribution of deposits adhering to the inner wall of the pipe causes the geometric center of the cross-section available for fluid flow to shift from the physical geometric axis of the pipe. The fluid equivalent center is the geometric centroid of this flow cross-section, which can accurately characterize the spatial location of the concentrated fluid distribution within the pipe. Based on the circumferential non-uniform distribution morphological parameters of the deposits obtained from step 21, that is, the local thickness values ​​of the deposits at various angles within the entire circumference of the pipe, the flow cross-section of the pipe can be geometrically reconstructed, and the centroid coordinates of the flow cross-section can be calculated. The spatial location corresponding to this centroid is the fluid equivalent center. The calculation of the centroid of the flow cross-section is as follows:

[0093]

[0094] The formula is derived as follows: the centroid coordinates of the planar figure are the weighted average of the coordinates of all the micro-elements within the figure, with the weight being the area of ​​the corresponding micro-element. This relationship is derived from the basic geometric definitions of the static moment and centroid of the planar figure. The flow section of the pipe is an irregular planar figure formed by removing the area occupied by the inner wall sediment from the circular cross section. The coordinate values ​​of the centroid can be accurately calculated by weighted summation of the areas of discrete micro-elements. This is applicable to the solution scenario of fluid equivalent center under non-uniform sediment distribution in this scheme.

[0095] In the formula, This represents the abscissa value of the centroid of the flow section in the pipe cross-section coordinate system. This represents the ordinate value of the centroid of the flow section in the pipe cross-section coordinate system; The x-coordinate value of the i-th discrete infinitesimal element within the flow cross section; The ordinate value of the i-th discrete element within the flow cross section; Let be the area of ​​the i-th discrete element; n is the total number of discrete elements after discretization of the flow section; the spatial orientation of the detection field of view is determined by the spatial orientation of the central axis of the collimation aperture. A high-precision angle adjustment mechanism, installed on the mounting base of the main detector and collimator, finely adjusts the overall installation angle of the main detector and collimator, ensuring that the orientation of the central axis of the collimation aperture completely coincides with the spatial position of the fluid equivalent center. This completes the adjustment of the spatial orientation of the detection field of view. During the adjustment process, the update of the circumferential non-uniform distribution morphological parameters of the sediment is synchronized with the adjustment of the detection field of view, ensuring that the detection field of view can always accurately align with the fluid equivalent center under the current operating conditions when the sediment distribution changes. This adjustment process allows the detection field of view to cover the concentrated flow area of ​​the fluid within the pipe to the maximum extent, while further avoiding the surrounding area of ​​the pipe wall with a large sediment thickness, reducing the probability of static radiation emitted by the pipe wall sediment entering the main detector, and improving the signal-to-noise ratio of the main count rate measurement results.

[0096] Step 32: Based on aligning the detection field of view with the fluid equivalent center, perform energy-angle co-selection on photons passing through the field of view, and record the main count rate after topological suppression of the selected photons. The specific operation is as follows:

[0097] Even after the geometric shielding of the narrow field-of-view collimator and the adjustment of the field-of-view pointing, there will still be some gamma photons that do not meet the requirements entering the main detector. These photons mainly include scattered photons that enter the detection field-of-view after being scattered by gamma photons emitted from the tube wall deposits, and scattered photons that deviate from the original propagation direction after being scattered by the pipe wall and the fluid medium by gamma photons emitted from the radionuclides in the fluid. These photons will interfere with the measurement results of the main count rate; energy-angle coincidence discrimination is to perform energy characteristic discrimination and incident angle discrimination on each gamma photon incident on the sensitive volume of the main detector at the same time. Only when the photon meets both the energy screening condition and the angle screening condition, it is counted as an effective count. Energy discrimination is achieved through the multi-channel pulse amplitude analysis system supporting the main detector. This system can convert the pulse signal generated by the incident photon into the corresponding energy value, and preset the energy window corresponding to the characteristic gamma ray energy of the radionuclide to be measured. Only when the measured energy of the photon falls within the range of this energy window, does it meet the energy screening condition; angle discrimination is achieved through the position-sensitive detection function of the main detector. The sensitive volume of the main detector is divided into multiple independent position-sensitive detection units, which can record the interaction position of the incident photon within the sensitive volume. Combining the spatial geometric parameters of the collimation through-hole, the incident angle of this photon can be calculated. The calculation of the incident angle is as follows:

[0098]

[0099] The derivation of the formula is that the incident angle of the gamma photon is the angle between the photon incident direction and the central axis of the collimation through-hole. This angle can be calculated by combining the relative position of the incident position of the photon on the sensitive surface of the detector and the center of the exit end of the collimation through-hole, and the perpendicular distance between the exit end of the collimation through-hole and the sensitive surface of the detector. This relationship is derived from the basic principles of linear propagation and angle calculation in spatial geometry, and can accurately characterize the deviation degree of the propagation direction of the incident photon from the field-of-view axis.

[0100] In the formula, θ is the incident angle of the incident photon; x is the abscissa value of the incident position of the photon on the sensitive surface of the detector; y is the ordinate value of the incident position of the photon on the sensitive surface of the detector; is the abscissa value of the projection of the center of the exit end of the collimation through-hole on the plane where the sensitive surface of the detector is located; The vertical coordinate of the projection of the center of the collimated aperture exit end onto the plane of the detector sensitive surface is given; L is the vertical distance between the collimated aperture exit end and the detector sensitive surface. An angle receiving window corresponding to the detection field of view is pre-set. Angle selection criteria are met only when the incident angle of a photon falls within this window. The energy-angle coordinated discrimination process synchronously judges the energy and angle of each incident photon. Only photons that simultaneously meet both selection criteria are considered valid photons; all other photons are discarded. This discrimination process can suppress scattered photons from pipe wall deposits and interfering photons from non-field-of-view directions from a topological perspective, retaining only characteristic photons directly incident along the field-of-view axis from the fluid's equivalent center region, thus achieving topological suppression of interference signals. Within a preset measurement time, the main detector counts the valid photons after energy-angle coordinated discrimination, obtaining the valid photon count value per unit time, which is the main count rate after topological suppression.

[0101] In a preferred embodiment of the present invention, step 4 is further included: using the mass thickness of the sediment and the attenuation coefficient of the radionuclide to be tested in the sediment obtained in advance to compensate the main count rate, thereby obtaining the compensated count rate. The specific operation is as follows:

[0102] The main count rate measured by the main detector after topological suppression corresponds to the characteristic gamma rays emitted by the radionuclide being tested in the fluid flowing in the pipe axis region. As the rays travel from the fluid emission point to the main detector, they need to pass through the gas-liquid two-phase fluid in the pipe, the deposits attached to the inner wall of the pipe, and the pipe wall material in sequence. Each layer of medium will attenuate the gamma rays, resulting in the actual count rate measured by the main detector being lower than the theoretical count rate under the no-attenuation state. The attenuation caused by the deposits is directly related to the mass thickness of the deposits and the mass attenuation coefficient of the characteristic gamma rays of the radionuclide being tested in the deposits. The mass thickness of the deposits has been obtained through the inversion process in step 2. The attenuation coefficient of the radionuclide being tested in the deposits is a fixed known parameter obtained through a pre-existing laboratory calibration experiment. The calibration process uses a standard sample with the same composition as the deposits in the actual working conditions and conducts a transmission experiment within the same radiation energy range as the actual measurement to obtain the mass attenuation coefficient values ​​corresponding to different characteristic energies. After calibration, the values ​​are stored.

[0103] The basic logic of compensation is to reverse the gamma-ray attenuation caused by sediments, based on the exponential decay law of gamma rays, to eliminate the influence of sediment attenuation on the main count rate. Simultaneously, it involves multi-dimensional correction of various influencing factors such as fluid density changes under gas-liquid two-phase flow conditions, gamma-ray energy spectrum hardening, scattering crosstalk between different energy channels, and uneven spatial distribution of the field of view. The final result is a compensated count rate that accurately reflects the true activity of radionuclides in the flowing fluid. The fundamental physical relationship of this compensation process can be expressed by the following formula:

[0104]

[0105] This formula is derived from the fundamental law of exponential decay of monoenergetic narrow-beam gamma rays. The ratio of the transmitted intensity to the incident intensity of gamma rays passing through the sediment medium decreases exponentially with the product of the sediment mass thickness and the mass attenuation coefficient. By reversing the derivation, the mathematical relationship between the incident intensity and the actual measured transmitted intensity under no-attenuation conditions can be obtained. This relationship can accurately characterize the reverse correction process of sediment attenuation and is the basis for the calculation of the main count rate compensation. It is applicable to the attenuation correction scenarios of gamma rays with different characteristic energies in this scheme.

[0106] In the formula, The attenuation-free count rate after compensation; This represents the local mass thickness of the sediment at the corresponding angular position along the circumference of the pipe. The main count rate is obtained from actual measurement; The mass attenuation coefficient of the characteristic gamma rays of the radionuclide to be measured in the sediment is given. The entire compensation process is divided into multiple continuous processing steps. First, the pulse signal corresponding to the main count rate is sorted by energy to construct the count rate of multiple energy channels. Then, the attenuation correction factor of each energy channel is calculated based on the non-uniform distribution of the sediment. After the initial compensation is completed, the energy self-consistency iterative correction is performed to eliminate the scattering crosstalk between channels. Then, the energy spectrum hardening correction is performed. After that, spatial normalization is performed. Finally, the closed-loop correction is completed by the consistency verification of fluid density, and the final compensated count rate is output.

[0107] The process of obtaining the compensated count rate also includes the following steps:

[0108] Step 41: The pulse signals corresponding to the main count rate after topological suppression are sorted by amplitude to construct the count rates of multiple energy channels corresponding to the characteristic energies of the radionuclide to be measured. The specific operation is as follows:

[0109] The main detector generates corresponding electrical pulse signals for incident effective gamma photons. The amplitude of the pulse signal is linearly positively correlated with the energy of the incident gamma photon. This linear relationship is calibrated using a standard radiation source before the detector is used, obtaining the corresponding conversion coefficient between pulse amplitude and photon energy. After calibration, this coefficient is stored as a fixed parameter. All effective pulse signals corresponding to the main count rate after topological suppression are sent to a multichannel pulse amplitude analysis system. This system sorts all pulse signals according to a pre-set amplitude threshold interval. Each amplitude threshold interval corresponds to an independent energy channel. The center energy and channel width of the energy channel are set according to the characteristic gamma ray energy of the radionuclide to be measured. Each energy channel corresponds to one characteristic gamma ray of the radionuclide to be measured. The pulse signals sorted in each energy channel are counted and statistically analyzed to calculate the pulse count value per unit time. This value is the count rate of the corresponding energy channel. The count rates of all energy channels corresponding to the characteristic energy of the radionuclide to be measured together constitute a multi-energy channel count rate set.

[0110] Step 42: Based on the circumferential non-uniform distribution of sediments and the spatial orientation of the detection field of view, calculate the sediment thickness distribution traversed by rays arriving at the detector from the fluid equivalent center region along different directions. Combined with the pre-acquired attenuation coefficients of each characteristic energy in the sediment, generate the attenuation correction factor corresponding to each energy channel. The specific operation is as follows:

[0111] As gamma rays emitted from the fluid equivalent center region travel along different spatial directions to reach the main detector, the thickness of the sediment on the inner wall of the pipe that they need to pass through varies with the relative angle between the emission direction of the rays and the spatial orientation of the detection field of view. This variation is jointly determined by the circumferential non-uniform distribution morphology of the sediment and the spatial coverage of the detection field of view. Based on the circumferential non-uniform distribution morphology parameters of the sediment obtained in step 21, and combined with the spatial orientation of the detection field of view adjusted in step 31, all spatial angles covered by the detection field of view are discretized to obtain multiple discrete ray propagation directions. For each discrete ray propagation direction, the ray propagation path from the fluid equivalent center to the sensitive surface of the main detector is calculated, and the intersection point of this path with the inner wall of the pipe is determined. Based on the circumferential angle corresponding to the intersection point, the local thickness of the sediment at the corresponding position is retrieved from the sediment non-uniform distribution morphology parameters. This thickness is the thickness of the sediment traversed by the ray in that propagation direction. The sediment thickness values ​​corresponding to all discrete directions together constitute the sediment thickness distribution.

[0112] The pre-acquired attenuation coefficients of each characteristic energy in the sediment are mass attenuation coefficients corresponding one-to-one with the central characteristic energy of each energy channel. For each energy channel, combined with the mass attenuation coefficient of the corresponding characteristic energy and the sediment thickness distribution, the average attenuation corresponding to that energy channel is calculated. The calculation process of the average attenuation involves performing a solid angle-weighted average of the attenuation in all ray propagation directions within the detection field of view, with the weight being the contribution ratio of the ray in the corresponding propagation direction to the main detector count. Based on the average attenuation, an attenuation correction factor corresponding to that energy channel is generated through the reverse derivation of the exponential attenuation law. The attenuation correction factor is the ratio of the theoretical count rate under no-attenuation conditions to the actual measured count rate, and can be directly used to compensate for the attenuation of the count rate of that energy channel. The calculation process of the attenuation correction factor is as follows:

[0113]

[0114] This formula is derived from the exponential decay law of gamma rays. For gamma rays of a certain characteristic energy, the average transmittance of rays in all propagation directions within the detection field of view is the solid angle weighted average of the transmittance in each direction. The attenuation correction factor is the reciprocal of the average transmittance, which can directly correct the measured count rate in reverse and eliminate the influence of sediment attenuation. This relationship can accurately characterize the average attenuation correction process of multi-directional rays and is suitable for the calculation scenario of multi-energy channel correction factor under non-uniform sediment distribution in this scheme.

[0115] In the formula, This is the attenuation correction factor corresponding to the j-th energy channel; θ is the mass attenuation coefficient of the characteristic energy corresponding to the j-th energy channel in the sediment; t is the sediment thickness traversed by the ray at the corresponding spatial angle; θ and A spatial angular parameter characterizing the direction of ray propagation; This is the solid angle of the infinitesimal element corresponding to the spatial angle.

[0116] Step 43: Initial compensation is performed using the count rate of each energy channel and the corresponding attenuation correction factor. Then, based on the branching ratio of each characteristic energy of the radionuclide to be measured, the count rate of each energy channel after initial compensation is self-consistently iteratively corrected to eliminate the influence of scattering crosstalk between channels, and the count rate of each energy after energy self-consistent correction is obtained. The specific operation is as follows:

[0117] The preliminary compensation process involves multiplying the measured count rate of each energy channel by the corresponding attenuation correction factor to obtain the preliminary compensated count rate for that channel. The preliminary compensated count rate eliminates the main influence of sediment attenuation on the count rate of that channel. The branching ratio of each characteristic gamma ray of the radionuclide being measured is the probability of emitting gamma rays of the corresponding characteristic energy during the decay process of that radionuclide. It is an inherent physical characteristic of that radionuclide and is obtained through a radionuclide database or a pre-calibration experiment. As a fixed known parameter, there is a definite proportional relationship between the branching ratios of different characteristic energies of the same radionuclide. This proportional relationship is not affected by factors such as medium attenuation and scattering during the measurement process. In the actual measurement process, after a gamma ray of a certain characteristic energy undergoes Compton scattering, its energy decreases and it may fall into an adjacent low-energy channel, resulting in scattering crosstalk between different energy channels. This causes the proportional relationship between the preliminary compensated count rates of each channel to deviate from the proportional relationship of the inherent branching ratio of the radionuclide being measured.

[0118] The self-consistent iterative correction process first calculates the ideal proportional relationship of the theoretical count rate for each energy channel based on the inherent branching ratio of each characteristic energy of the radionuclide under test. Then, the actual proportional relationship of the count rate after preliminary compensation for each channel is compared with the ideal proportional relationship to calculate the deviation of the count rate for each channel. Based on the deviation, a crosstalk correction matrix is ​​constructed. The elements of the crosstalk correction matrix represent the probability of scattering crosstalk between different energy channels. The crosstalk probability is obtained through prior Monte Carlo simulations or calibration experiments and is related to the energy resolution of the detector, the difference in characteristic energies, and the scattering characteristics of the medium. The count rates of each channel after preliminary compensation are substituted into the crosstalk correction matrix for iterative solution. After each iteration, the proportional relationship of the corrected count rate for each channel is recalculated and compared with the ideal branching ratio. The iteration stops when the deviation is less than a preset convergence threshold. The final count rate obtained is the energy count rate after energy self-consistent correction. This count rate eliminates the influence of scattering crosstalk between channels, and the proportional relationship of the count rate for each channel remains consistent with the inherent branching ratio of the nuclide.

[0119] Step 44: Based on the total mass thickness of the sediment, retrieve the energy spectrum hardening correction coefficient from the pre-constructed nonlinear mapping relationship between sediment thickness and energy response. Perform a secondary correction on each energy count rate after energy self-consistency correction to obtain each energy count rate after energy spectrum hardening correction. The specific operation is as follows:

[0120] The energy spectrum hardening effect refers to the phenomenon where, when a multi-energy gamma-ray beam passes through a medium, low-energy gamma photons are more easily absorbed and attenuated by the medium. This results in a relatively higher proportion of high-energy photons in the beam after passing through the medium, increasing the average energy of the beam and altering the energy spectrum distribution. This effect leads to a nonlinear deviation in the detector's energy response, and the degree of deviation is directly related to the thickness of the medium. In this scheme, the greater the thickness of the sediment, the more significant the impact of the energy spectrum hardening effect on the energy response. The nonlinear mapping relationship between sediment thickness and energy response was established through pre-calibration experiments. The calibration process used standard sediment samples with the same composition as the actual operating conditions, set a series of different mass thickness gradients, and measured the detector energy response after gamma rays of various characteristic energies of the radionuclide under test passed through samples of different thicknesses. This yielded the results for different sediment mass thicknesses. The nonlinear deviation of the energy response corresponding to each characteristic energy is calculated, and the corresponding energy spectrum hardening correction coefficient is obtained based on the deviation. Finally, a one-to-one mapping relationship between the total mass thickness of the sediment and the energy spectrum hardening correction coefficient of each characteristic energy is constructed. This mapping relationship is stored in the form of a lookup table. Based on the total mass thickness of the sediment obtained in step 22, the energy spectrum hardening correction coefficient of each energy channel corresponding to the characteristic energy is retrieved from the pre-stored lookup table. The energy spectrum hardening correction coefficient is the ratio of the ideal response count rate without hardening effect to the actual measured response count rate. The count rate of each energy channel after energy self-consistency correction is multiplied by the energy spectrum hardening correction coefficient of the corresponding channel to complete the secondary correction and obtain the count rate of each energy after energy spectrum hardening correction. This count rate eliminates the nonlinear influence of the energy spectrum hardening effect caused by sediment on the detector energy response.

[0121] Step 45: Based on the spatial coverage of the detection field of view and the non-uniform distribution of sediments, construct a weighting function for the contribution of different spatial locations within the field of view to the detector count. After energy-weighted summation of the count rates after energy spectrum hardening correction, divide by the integral of this weighting function over the field of view to obtain the spatially normalized total compensated count rate. The specific operation is as follows:

[0122] Within the pipe axis region covered by the detection field of view, the contribution of gamma rays emitted by radionuclides at different spatial locations to the main detector count varies. This difference is jointly determined by the solid angle of the spatial location relative to the main detector, the amount of sediment attenuation along the ray propagation path, and whether the location is within the effective coverage area of ​​the detection field of view. The contribution weighting function is a continuous function characterizing the proportion of contribution of different spatial locations within the field of view to the detector count. Based on the spatial coverage of the detection field of view, the effective domain of the weighting function is determined. This domain is the three-dimensional spatial region inside the pipe covered by the field of view, based on the non-uniformity of the sediment. For uniformly distributed morphology, the thickness of sediment that the rays emitted from each spatial location within the region pass through during their journey to the main detector is calculated. Combined with the attenuation coefficient of the corresponding characteristic energy, the contribution weight value of that location is calculated. The weight value is proportional to the ray transmittance and solid angle ratio corresponding to that location, thus constructing the contribution weight function for different spatial locations within the field of view. The count rates of each energy channel after energy spectrum hardening correction are weighted and summed according to the branch ratio of the characteristic energy corresponding to the radionuclide to be measured, resulting in the weighted total count rate. During the weighted summation, the weight of each energy channel is the branch ratio of the characteristic energy corresponding to that channel.

[0123] The contribution weighting function is integrated over the entire spatial region covered by the field of view to obtain the total integral value of the weighting function. This integral value represents the total contribution weight of all spatial locations within the field of view. The total count rate obtained by weighted summation is divided by the total integral value of the weighting function to complete the spatial normalization process, resulting in a spatially normalized total compensated count rate. This count rate eliminates the influence of uneven contribution at different spatial locations within the field of view on the total count rate and can accurately represent the counting response corresponding to the radioactivity activity of a unit volume of fluid within the field of view. The calculation of the integral of the weighting function is as follows:

[0124]

[0125] This formula is derived from the basic principle of detector counting response of a radioactive source in three-dimensional space. The total count rate in the field of view is the volume integral of the counting contribution of all spatial micro-elements. The contribution of each spatial micro-element is proportional to the activity of that micro-element and the contribution weight function value. The total integral value is the theoretical total count rate when the unit activity is uniformly distributed in the field of view. It is used to spatially normalize the actual measured total count rate and eliminate the influence of non-uniformity in the spatial response of the field of view.

[0126] In the formula, Let w be the total integral value of the contribution weighting function, and w be the contribution weighting function value corresponding to the spatial position within the field of view. The three-dimensional coordinate parameters characterize the spatial position, where V is the three-dimensional spatial region inside the pipe covered by the detection field of view, and dV is the infinitesimal volume corresponding to the spatial position.

[0127] Step 46: The current fluid density is retrieved using pure transmission attenuation. Based on the correlation between fluid density and radioactivity concentration, the consistency of the spatially normalized total compensation count rate is checked. If the deviation exceeds a preset threshold, the energy spectrum hardening correction coefficient or the corresponding correction coefficient in the contribution weighting function is adjusted. The process of obtaining the spatially normalized total compensation count rate is repeated until the deviation converges within the threshold. The final, verified compensation count rate is then output. The specific operations are as follows:

[0128] The pure transmission attenuation pair, obtained from step 13, represents the pure transmittance values ​​of two different energy gamma rays. The mass attenuation coefficients of the two energy gamma rays in the gas-liquid two-phase fluid exhibit a definite difference, obtained through prior calibration experiments and thus a known parameter. Based on the pure transmission attenuation pair of the two energies, combined with the transmittance benchmark of the clean pipeline, the attenuation amount caused solely by the gas-liquid two-phase fluid can be separated. Based on this attenuation amount, the equivalent density of the current gas-liquid two-phase fluid in the pipeline is inverted using the physical principle of dual-energy ray density measurement. The correlation between fluid density and radioactivity concentration is determined based on the process characteristics of the radioactivity separation system. When the radionuclide to be measured is dissolved or suspended in the fluid medium, under stable process operation, a definite linear correlation exists between the radioactivity concentration of the fluid and the equivalent density of the fluid. This correlation is obtained through process calibration experiments and is a known correspondence. Based on the inverted current equivalent density of the fluid, the expected value of the current fluid radioactivity concentration can be calculated using this correlation. Combined with the detection efficiency parameter of the main detector, the expected count rate corresponding to the expected concentration can be calculated.

[0129] The consistency verification process involves comparing the spatially normalized total compensation count rate with the calculated expected count rate and calculating the relative deviation between them. If the relative deviation is within a preset threshold range, the total compensation count rate is considered to have passed the consistency verification and is directly output as the final compensation count rate. If the relative deviation exceeds the preset threshold range, the current correction process is considered to have residual deviation, requiring adjustment of the corresponding correction coefficients in the energy spectrum hardening correction coefficients or contribution weighting functions. The adjustment magnitude corresponds to the magnitude and direction of the deviation. After adjustment, the complete process from energy spectrum hardening correction to obtaining the spatially normalized total compensation count rate is re-executed to obtain a new total compensation count rate. The consistency verification is then performed again, and this iterative process is repeated until the relative deviation between the total compensation count rate and the expected count rate converges within the preset threshold range. At this point, the verified final compensation count rate is output.

[0130] In a preferred embodiment of the present invention, step 5 is further included, which involves performing zero-deposit calibration at predetermined time intervals to update the clean pipe transmittance benchmark and the detection efficiency of the main detector. The specific operation is as follows:

[0131] During the long-term continuous operation of the radioactive separation system, the radioactivity of the reference source will naturally decay over time, the electronic system of the detector will experience gain drift, the pipe wall material will undergo slow changes in physical properties due to irradiation, and the composition and density of the fluid medium inside the pipe will fluctuate with the process conditions. These factors will cause a systematic deviation between the initially calibrated clean pipe transmittance benchmark and the detection efficiency of the main detector, thereby affecting the accuracy of sediment mass thickness inversion and radioactivity concentration calculation results. The predetermined time interval is set in advance based on the half-life of the reference source, the long-term stability index of the detector, and the process conditions required for system operation. The system will periodically start the zero sediment calibration process according to this time interval, and will also trigger calibration in conjunction with the zero sediment state after pipe cleaning.

[0132] The basic logic of zero-sediment calibration is as follows: under a zero-sediment state where the total mass thickness of sediment on the inner wall of the pipe is negligible, the interference of sediment on X-ray measurement is completely eliminated. The inherent response parameters of the system are then recalibrated, and the transmittance benchmark and the detection efficiency of the main detector are updated. The updated parameters replace the original stored benchmark parameters and are applied to all subsequent sediment mass thickness inversion, main count rate compensation, and radioactivity concentration calculation processes. This eliminates the cumulative deviation caused by long-term system operation and ensures the long-term accuracy and reliability of online monitoring results. The physical definition of the main detector detection efficiency can be expressed by the formula:

[0133]

[0134] The formula is derived as follows: the intrinsic detection efficiency of the detector is the ratio of the effective photon count rate recorded by the detector to the total number of corresponding energy photons incident on the sensitive volume of the detector per unit time. This relationship is derived from the statistical law of radioactive decay and the basic principle of gamma-ray detection. It can accurately characterize the detector's ability to detect gamma photons of a specific energy and is the fundamental physical parameter connecting the detector count rate and the activity of the radioactive source. In the formula, N is the total number of corresponding energy gamma photons incident on the sensitive volume of the main detector per unit time; ε is the intrinsic detection efficiency of the main detector for this characteristic energy gamma photon.

[0135] The zero-deposition verification process also includes the following steps:

[0136] Step 51: Based on the total sediment mass thickness being lower than a preset threshold, a zero sediment check is triggered. The specific operation is as follows:

[0137] The triggering of zero-deposition verification requires that the total mass thickness of sediment on the inner wall of the pipeline be lower than a preset threshold. This preset threshold is determined through pre-calibration experiments and numerical simulations based on the accuracy requirements of the system's online monitoring, the lower limit of sediment interference with gamma ray attenuation, and the acceptance criteria of the pipeline cleaning process. When the total mass thickness of sediment is lower than this threshold, the contribution of sediment to gamma ray attenuation can be completely ignored, and the inner wall of the pipeline can be regarded as a zero-deposition state with no sediment attachment. After each inversion calculation of the total mass thickness of sediment, the calculated value is continuously compared with the preset threshold. When the value is lower than the preset threshold, a trigger signal is automatically generated to start the zero-deposition verification process. At the same time, the arrival time of the predetermined time interval is monitored. When the preset verification time point is reached, it is first checked whether the current total mass thickness of sediment meets the condition of being lower than the preset threshold. If the condition is met, the verification process is started directly. If the condition is not met, the pipeline cleaning operation is completed, and the total mass thickness of sediment is confirmed to meet the standard before the verification process is started again, ensuring that the verification process is always carried out in a zero-deposition state that meets the requirements.

[0138] Step 52: Under zero-deposit conditions, measure the transmittance of the reference source rays after passing through the pipe and fluid to obtain an updated clean pipe transmittance benchmark. Based on this transmittance, the fluid density is then deduced. The specific operation is as follows:

[0139] After the zero-deposit calibration is triggered, the flow state, temperature and pressure parameters of the fluid in the pipeline are kept completely consistent with the normal operating conditions to avoid unexpected interference to the transmittance measurement results caused by changes in the fluid state. The system activates two sets of reference sources and their corresponding detectors. Following the same measurement procedure as in step 1, it synchronously acquires the transmission count rates of two different energy gamma rays emitted by the reference sources after passing through the pipe and fluid. Based on the nominal activity of the reference sources after metrological calibration and the inherent response parameters of the detectors pre-calibrated, the transmittance values ​​corresponding to the two energy gamma rays are calculated respectively. This set of transmittance values ​​fully characterizes the inherent attenuation characteristics of the pipe wall material and the fluid medium under the current operating conditions for the two energy gamma rays in a zero-deposit state. This value is the updated clean pipe transmittance benchmark. The system will temporarily store this benchmark value for subsequent parameter correction and final storage update. Based on the updated transmittance benchmark of the two energy gamma rays, combined with the pre-calibrated mass attenuation coefficients of the two energy gamma rays in the fluid medium, the equivalent density of the gas-liquid two-phase fluid in the current pipe is calculated by inversion using the physical principle of dual-energy ray transmission measurement. This density value will be used as a known parameter for attenuation correction calculation in the subsequent main detector detection efficiency correction process.

[0140] Step 53: Reorient the detection field of the main detector to the reference source direction, measure the count rate of the reference source rays, and obtain the main detector's count rate of the reference source. The specific operation is as follows:

[0141] The main detector and the narrow field-of-view collimator are mounted together on a pre-calibrated high-precision two-dimensional angle adjustment mechanism. This mechanism has nanometer-level angle adjustment resolution and micrometer-level repeatability, enabling precise adjustment and reset of the spatial orientation of the detection field of view. Under stable zero-deposit conditions, the system sends control commands to the angle adjustment mechanism to adjust the overall installation angle of the main detector and the narrow field-of-view collimator. This ensures that the central axis of the collimator's internal aperture, which is also the center of the main detector's detection field of view, is perfectly aligned with the emission center of one of the reference sources. This guarantees that the gamma rays emitted by the reference sources can propagate linearly along the central axis of the collimation aperture and directly incident on the target. The gamma rays are directed to the sensitive detection surface of the main detector to eliminate interference from non-direct scattered rays on the measurement results. After the angle adjustment is completed, the corresponding reference source is activated to emit gamma rays in a stable continuous working mode. The main detector continuously collects the incident gamma photons within a preset measurement time. At the same time, the energy-angle co-discrimination method, which is exactly the same as in step 32, is used to screen each incident photon, removing interference photons and scattered photons that do not meet the requirements of the energy window and angle acceptance window. Finally, the effective photons after screening are counted and statistically analyzed to obtain the effective photon count value per unit time. This value is the measurement count rate of the main detector to the reference source.

[0142] Step 54: Based on the fluid density and transmittance obtained under zero sediment conditions, and combined with the relative geometric positions of the reference source and the main detector, calculate the attenuation correction factor of the ray from the reference source to the main detector. Use the attenuation correction factor to correct the count rate measured by the main detector at the reference source. Based on the corrected count rate and the known activity of the reference source, determine the detection efficiency of the main detector. The specific operation is as follows:

[0143] As the gamma rays emitted from the reference source propagate from the emission center to the sensitive surface of the main detector, they must pass through the pipe wall material and the fluid medium inside the pipe in sequence. Both types of media attenuate the gamma rays, causing the actual count rate measured by the main detector to be lower than the theoretical count rate under the no-attenuation state. It is necessary to perform reverse correction on the measured count rate using an attenuation correction coefficient. Based on the fluid density and clean pipe transmittance benchmark obtained in step 52 under the zero-deposit state, and combined with the relative geometric position of the reference source and the main detector, the straight-line propagation path of the gamma rays from the emission center of the reference source to the sensitive surface of the main detector is determined. The thickness of the pipe wall material and the thickness of the fluid medium through which the rays pass along this path are determined. Combining the mass attenuation coefficient of the energy corresponding to the pipe wall material, the mass attenuation coefficient of the energy corresponding to the fluid medium, and the fluid density obtained in step 52, the total attenuation during the ray propagation process is calculated. The reciprocal of the total attenuation is the attenuation correction coefficient of the ray from the reference source to the main detector.

[0144] Multiplying the measured count rate of the reference source by the attenuation correction coefficient yields the corrected count rate. This count rate eliminates the attenuation effect of the pipe wall material and fluid medium on the radiation, corresponding to the theoretical count rate of the reference source incident on the sensitive surface of the main detector in an attenuation-free state. The known activity of the reference source is the nominal activity calibrated by a national legal metrology institution. Combining this with the emission branching ratio of the corresponding energy gamma rays of the reference source, the total number of corresponding energy gamma photons emitted by the reference source per unit time can be calculated. Based on this total number and the corrected count rate, the detection efficiency of the main detector for the corresponding energy gamma rays of the reference source is calculated using the physical definition formula of detection efficiency. Then, combined with the energy calibration relationship pre-completed by the detector, the detection efficiency of the main detector for all characteristic energy gamma rays of the radionuclide under test is extended to obtain the detection efficiency of the main detector, thus completing the updated calculation of the main detector's detection efficiency.

[0145] Step 55: Restore the detection field of view of the main detector to the pipe axis region, and store the updated clean pipe transmittance reference and the main detector detection efficiency. The specific operation is as follows:

[0146] After the main detector's detection efficiency is updated and calculated, a reset control command is sent to the angle adjustment mechanism to adjust the installation angle between the main detector and the narrow field-of-view collimator. This ensures that the central axis of the collimation orifice points back to the pipe axis region, completely restoring the normal measurement position aligned with the fluid equivalent center before calibration. After adjustment, the system confirms the adjustment accuracy using a high-precision position sensor, ensuring that the spatial orientation of the detection field is completely consistent with the normal measurement state before calibration, avoiding any positional deviation from affecting subsequent normal monitoring processes. The updated clean pipe transmittance benchmark obtained in step 52 and the updated main detector's detection efficiency for each characteristic energy obtained in step 54 are written into the system's non-volatile... The storage unit, using non-volatile memory, replaces the original old reference parameters and old detection efficiency parameters. Simultaneously, it records the completion time of this calibration, pipeline operating parameters during the calibration process, and auxiliary information such as the total sediment mass thickness at the time of calibration triggering. This information is used for subsequent system status tracing and data traceability. After the parameters are stored, the system automatically exits the zero-sediment calibration mode and reverts to the normal gas-liquid two-phase flow radioactivity online monitoring process. All subsequent sediment mass thickness inversion, main count rate compensation calculation, and flow fluid true radioactivity concentration determination processes use the updated reference parameters and detection efficiency values ​​from this calibration, thereby ensuring the long-term accuracy and stability of the online monitoring results.

[0147] In a preferred embodiment of the present invention, step 6 is further included: calculating the true radioactivity concentration of the flowing fluid based on the compensated count rate and the updated detection efficiency, and outputting the mass thickness of the sediment. The specific operation is as follows:

[0148] The true radioactivity concentration of the flowing fluid refers to the activity of the radionuclide to be measured in a unit volume of flowing fluid. It is a key basic parameter for process control, product collection, and compliance judgment of waste discharge during the operation of the radioactive separation system. The final compensation count rate has eliminated the interference of various factors such as sediment attenuation, scattering crosstalk, energy spectrum hardening, and spatial response inhomogeneity. The detection efficiency of the updated main detector has completed the correction of system deviation through zero sediment calibration. Together, they provide basic data for the accurate calculation of radioactivity concentration. The fundamental physical laws of gamma-ray detection dictate that the detector's count rate is linearly and positively correlated with the total activity of radionuclides within the detection field of view. The total activity is the product of the radioactive concentration and the effective fluid volume within the detection field of view. By combining parameters such as detection efficiency, nuclide branching ratio, and ray attenuation, a quantitative correlation between the count rate and radioactive concentration can be established. The entire calculation process consists of three consecutive stages. First, preliminary geometric correction is achieved through joint solution of the response matrix to obtain the initial radioactive concentration. Then, consistency verification and closed-loop iteration are performed using the correlation between fluid density and concentration to eliminate residual system biases and obtain the final true radioactive concentration. Finally, by combining measurement data from the current and historical moments, dynamic parameters characterizing the system's operating state are calculated and integrated into a comprehensive state vector for synchronous output. Simultaneously, the system outputs the total mass thickness of the inverted sediment and the circumferential non-uniform distribution morphology parameters, along with the final radioactive concentration, providing operators with complete monitoring information on the sediment adhesion status on the pipeline inner wall and the fluid radioactivity level. This supports system process adjustments, pipeline cleaning plan formulation, and compliance control operations.

[0149] Calculating the true radioactivity concentration of the flowing fluid also includes the following steps:

[0150] Step 61: Based on the final compensated count rate and the updated main detector detection efficiency, the response matrix is ​​constructed and solved jointly using the detection field-of-view spatial weight distribution function and the pre-acquired branch ratio to obtain the radioactivity concentration after preliminary geometric correction. The specific operations are as follows:

[0151] The spatial weight distribution function of the detection field of view is a continuous function characterizing the proportion of contribution of different spatial locations within the field of view to the counting of the main detector. The pre-acquired branch ratio is the emission probability of each characteristic gamma ray of the radionuclide under test, which is an intrinsic physical parameter of the nuclide. The updated detection efficiency of the main detector includes the detection efficiency values ​​of gamma rays of all characteristic energies of the radionuclide under test. The construction process of the response matrix uses discrete spatial elements of the detection field of view as row vectors and energy channels corresponding to each characteristic energy as column vectors. Each element in the matrix is ​​the response coefficient of the corresponding spatial element and the corresponding energy channel. The value of the response coefficient is determined by... The weighting function value corresponding to the spatial micro-element, the detection efficiency of the main detector for the corresponding energy, the branching ratio for the corresponding characteristic energy, and the transmittance of the ray from the spatial micro-element to the main detector are all jointly determined. The final compensated count rate includes the count rate values ​​of each energy channel after complete correction. The count rates of each energy channel are combined into a measurement vector, which is then jointly solved with the constructed response matrix. The solution process uses a least-squares fitting numerical method to obtain the activity value corresponding to a unit volume of fluid within the detection field of view. This value is the radioactivity concentration after preliminary geometric correction. This solution process can be expressed by a matrix formula, specifically:

[0152]

[0153] This formula is derived from the basic principle of linear response of gamma-ray detection. When the radioactivity concentration of the flowing fluid in the detection field is uniformly distributed, the measured count rate of each energy channel is equal to the product of the radioactivity concentration and the total response coefficient of the corresponding energy channel. The total response coefficient is the volume integral of the response coefficients of all spatial infinitesimal elements in the detection field. By integrating the linear relationship of multiple energy channels into a matrix form, a unique radioactivity concentration value can be obtained by solving the least squares method. This relationship can accurately characterize the quantitative correlation between the count rate of multiple energy channels and the radioactivity concentration of the fluid, and is the basic mathematical model for preliminary geometric correction.

[0154] In the formula, This is a column vector composed of the final compensation count rates of each energy channel, with the dimension being the number of characteristic energies of the radionuclide to be measured. The radioactivity concentration of the flowing fluid is the activity of the radionuclide to be measured per unit volume of fluid. K is a column vector composed of the total response coefficients corresponding to each energy channel. Each element is the volume integral of the response coefficient of the corresponding energy channel in the entire detection field of view. The response coefficient is determined by the spatial weight distribution function of the detection field of view, the detection efficiency of the corresponding energy of the main detector, and the branching ratio of the corresponding characteristic energy. The radioactivity concentration after preliminary geometric correction has eliminated the response deviation caused by the non-uniformity of the spatial response of the detection field of view, the energy difference of the detector detection efficiency, and the branching ratio of the nuclide. It can accurately reflect the preliminary value of the radioactivity concentration of the fluid in the detection field of view, and provide a basis for subsequent consistency verification and iterative correction.

[0155] Step 62: Based on the radioactivity concentration and pure transmission attenuation pair after preliminary geometric correction, the fluid equivalent density is inverted. The expected concentration is calculated based on the fluid equivalent density. The radioactivity concentration after preliminary geometric correction is compared with the expected concentration. If the deviation exceeds a preset threshold, the sediment attenuation coefficient used in the attenuation correction factor generation process is adjusted, and the process of calculating the radioactivity concentration after preliminary geometric correction is iteratively executed until the deviation converges within the threshold. The final radioactivity concentration is then output. The specific operations are as follows:

[0156] The pure transmission attenuation pair consists of the pure transmittance values ​​of two different energy gamma rays after background subtraction and correction. Based on the radioactivity concentration after preliminary geometric correction, the mass proportion of the radionuclide to be measured in the fluid can be determined. Combining the physical density of the radionuclide and the inherent density of the fluid matrix, a quantitative correlation between radioactivity concentration and fluid equivalent density can be established. Based on the pure transmission attenuation pair, combined with the physical principles of clean pipeline transmittance benchmark and dual-energy ray density measurement, the equivalent density of the gas-liquid two-phase fluid in the current pipeline can be inverted. This density value is obtained only by ray transmission measurement and is independent of the radioactivity concentration calculation process, and can be used as an independent verification benchmark for the concentration calculation results. Based on the fluid equivalent density obtained by inversion, the expected value of the fluid radioactivity concentration under the current operating conditions is calculated through the pre-calibrated correlation between fluid density and radioactivity concentration. The radioactivity concentration after preliminary geometric correction is compared with the expected concentration, and the relative deviation between the two is calculated.

[0157] If the relative deviation is within the preset threshold range, the radioactive concentration after preliminary geometric correction is considered the final radioactive concentration and is output directly. If the relative deviation exceeds the preset threshold range, it is considered that the sediment attenuation coefficient currently used deviates from the actual attenuation characteristics of the sediment under actual working conditions. This deviation is the main source of error in the concentration calculation result. The system will adjust the sediment attenuation coefficient used in the attenuation correction factor generation process according to the magnitude and direction of the deviation. After the adjustment is completed, the complete process from main count rate compensation to preliminary geometric correction radioactive concentration calculation is re-executed to obtain a new preliminary geometric correction radioactive concentration. This is then compared with the expected concentration, and the iterative process is repeated until the relative deviation between the two converges to the preset threshold range. At this point, the output radioactive concentration is the final true radioactive concentration of the flowing fluid.

[0158] Step 63: Based on the final radioactivity concentration, total sediment mass thickness, and circumferential non-uniform distribution morphology parameters, and combined with historical data, the concentration change rate and sediment growth rate are obtained, and the sediment eccentricity index is calculated. These parameters are then integrated into a comprehensive state vector output. The specific operations are as follows:

[0159] Historical data refers to the complete measurement data stored by the system at each sampling time prior to this measurement, including the final radioactivity concentration, total sediment mass thickness, and circumferential non-uniform distribution morphology parameters. The time interval between adjacent sampling times is the system's preset fixed sampling period. The concentration change rate is calculated by dividing the difference between the final radioactivity concentration at the current time and the final radioactivity concentration at the previous sampling time by the time interval between the two sampling times to obtain the change in fluid radioactivity concentration per unit time, which is the concentration change rate. The sediment growth rate is calculated by dividing the difference between the total sediment mass thickness at the current time and the total sediment mass thickness at the previous sampling time by the time interval between the two sampling times to obtain the increase in the mass thickness of sediment on the inner wall of the pipe per unit time, which is the sediment growth rate.

[0160] The sediment segregation index is a parameter characterizing the degree of non-uniform sediment adhesion around a pipe. Based on the circumferential non-uniform distribution morphology parameters of sediments, the ratio of the maximum to the average local mass thickness of sediments at each location within the entire circumference of the pipe is calculated. This ratio is the sediment segregation index. The closer the segregation index is to 1, the more uniform the circumferential distribution of sediments; the larger the value, the more severe the circumferential segregation phenomenon. The system integrates the current final radioactivity concentration, total sediment mass thickness, circumferential non-uniform distribution morphology parameters of sediments, concentration change rate, sediment growth rate, and sediment segregation index into a one-dimensional comprehensive state vector according to a preset order. This vector is synchronously output to the system's host computer control system, data storage unit, and display terminal, providing operators with complete quantitative information on the operating status of the radioactive separation system. This supports real-time process adjustments, pipeline cleaning timing judgment, product collection control, and compliance management of radioactive waste discharge.

[0161] Example 2

[0162] Please see Figure 2 Based on Example 1, this embodiment provides an online monitoring system for gas-liquid two-phase flow in a radioactive separation system, comprising:

[0163] The transmission measurement module is used to set up a reference source emitting two different energies of gamma rays on the outside of the clean section of the pipe to be tested, and to set up a reference source detector on the opposite side of the pipe to measure the transmittance of the two energies of the reference source rays after passing through the pipe, fluid and sediment, so as to obtain the transmission attenuation pair.

[0164] The mass inversion module is used to invert the mass thickness of deposits inside the pipe based on the transmission attenuation pair and the pre-acquired clean pipe transmittance benchmark.

[0165] The main counting module is used to set the main detector and its narrow field-of-view collimator, so that the detection field of the main detector is limited to the pipe axis area, and the main counting rate is measured.

[0166] The counting compensation module is used to compensate the main count rate by utilizing the mass thickness of the sediment and the attenuation coefficient of the radionuclide to be tested in the sediment, so as to obtain the compensated count rate.

[0167] The zero-deposition calibration module is used to perform zero-deposition calibration at predetermined time intervals to update the clean pipeline transmittance benchmark and the detection efficiency of the main detector.

[0168] The concentration calculation module is used to calculate the true radioactive concentration of the flowing fluid based on the compensated count rate and the updated detection efficiency, and output the mass thickness of the sediment.

[0169] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A method for online monitoring of gas-liquid two-phase flow in a radioactive separation system, characterized in that, include: A reference source emitting two different energies of gamma rays is set outside the clean section of the pipe to be tested, and a reference source detector is set on the opposite side of the pipe. The transmittance of the two energies of the reference source rays after passing through the pipe, fluid and sediment is measured to obtain the transmission attenuation pair. The process of obtaining transmission attenuation pairs includes: setting two reference sources emitting two different energies of gamma rays at 180-degree circumferential intervals on the outside of the clean section of the pipe; setting two detectors on the opposite side of the pipe, directly opposite each reference source, so that each detector receives rays from the opposite reference source that propagate in a straight line along the pipe diameter, and simultaneously measuring to obtain two transmission count pairs; based on the two transmission count pairs, calculating the ratio of the count rates of the two energies received by each detector, comparing the ratio with the initial calibration ratio, and if the deviation exceeds a preset threshold, then correcting the original count rates of the two energies in reverse according to the deviation amount to obtain the corrected transmission count pairs; making the reference sources operate in pulse mode, and through time gating synchronized with the pulse sources, obtaining the count rate of the transmission signal plus the background signal during the window opening time, and obtaining the count rate of the pure background signal during the window closing time; subtracting the window closing count rate from the window opening count rate within the same period to obtain the pure transmission attenuation pair; Based on the transmission attenuation pairs and the pre-obtained clean pipe transmittance benchmark, the mass thickness of the deposits inside the pipe is obtained by inversion. The inversion process for obtaining the mass thickness of sediments within the pipe includes: constructing attenuation feature vectors for each channel based on two sets of pure transmission attenuation pairs; comparing the two sets of attenuation feature vectors spatially; and inferring the non-uniform distribution pattern of sediments in the circumferential direction based on the comparison results; dividing the pipe cross-section into multiple micro-regions based on the non-uniform distribution pattern of sediments; substituting the non-uniform distribution pattern parameters as known quantities for each micro-region into a set of physical constraint equations based on the attenuation characteristics of two types of energy in sediments and fluids; solving for the local mass thickness of each micro-region; and spatially integrating all local mass thicknesses to obtain the total mass thickness of sediments. By setting up a main detector and its narrow field-of-view collimator, the detection field of the main detector is limited to the pipe axis area, and the main count rate is measured. The main count rate is compensated by using the mass thickness of the sediment and the attenuation coefficient of the radionuclide to be tested in the sediment, and the compensated count rate is obtained. Zero-deposit calibration is performed at predetermined time intervals to update the clean pipe transmittance benchmark and the detection efficiency of the main detector; The true radioactivity concentration of the flowing fluid is calculated based on the compensated count rate and the updated detection efficiency, and the mass thickness of the sediment is output.

2. The method for online monitoring of gas-liquid two-phase flow in a radioactive separation system according to claim 1, characterized in that, The main count rate is measured, including: Based on the circumferential non-uniform distribution morphological parameters of sediments, the spatial orientation of the detection field of view is adjusted so that the orientation is aligned with the fluid equivalent center. Based on the detection field of view aligned with the fluid equivalent center, photons passing through the field of view are screened based on energy-angle coordinated discrimination, and the main count rate after topological suppression of the screened photons is recorded.

3. The online monitoring method for gas-liquid two-phase flow in a radioactive separation system according to claim 2, characterized in that, The compensated count rate includes: The pulse signals corresponding to the main count rate after topological suppression are sorted by amplitude to construct the count rate of multiple energy channels corresponding to the characteristic energy of the radionuclide to be tested; Based on the circumferential non-uniform distribution of sediments and the spatial orientation of the detection field of view, the sediment thickness distribution traversed by rays reaching the detector from the fluid equivalent center region along different directions is calculated. Combined with the pre-acquired attenuation coefficients of each characteristic energy in the sediment, the attenuation correction factor corresponding to each energy channel is generated. Preliminary compensation is performed using the count rate of each energy channel and the corresponding attenuation correction factor. Then, based on the branching ratio of each characteristic energy of the radionuclide to be measured, the count rate of each energy channel after preliminary compensation is self-consistently iteratively corrected to eliminate the influence of scattering crosstalk between channels, and the count rate of each energy after energy self-consistency correction is obtained.

4. The online monitoring method for gas-liquid two-phase flow in a radioactive separation system according to claim 3, characterized in that, The compensated count rate also includes: Based on the total mass thickness of the sediment, the energy spectrum hardening correction coefficient is obtained from the pre-constructed nonlinear mapping relationship between sediment thickness and energy response. The energy count rate after energy self-consistency correction is then corrected twice to obtain the energy count rate after energy spectrum hardening correction. Based on the spatial coverage of the detection field of view and the non-uniform distribution of sediments, a weighting function for the contribution of different spatial locations within the field of view to the detector count is constructed. The count rates of each energy after energy spectrum hardening correction are summed by energy weight and then divided by the integral of the weighting function over the field of view to obtain the spatially normalized total compensated count rate. The current fluid density is inverted using pure transmission attenuation. Based on the correlation between fluid density and radioactivity concentration, the consistency of the spatially normalized total compensation count rate is checked. If the deviation exceeds the preset threshold, the energy spectrum hardening correction coefficient or the corresponding correction coefficient in the contribution weight function is adjusted, and the process of obtaining the spatially normalized total compensation count rate is re-executed until the deviation converges within the threshold. The final compensation count rate after verification is output.

5. The online monitoring method for gas-liquid two-phase flow in a radioactive separation system according to claim 4, characterized in that, Perform zero-deposition verification, including: Zero sediment check is triggered when the total sediment mass thickness is below a preset threshold. In a zero-deposit state, the transmittance of the reference source rays after passing through the pipe and fluid is measured to obtain an updated clean pipe transmittance benchmark, and the fluid density is inverted based on this transmittance. The detection field of the main detector is redirected to the direction of the reference source, and the count rate of the reference source rays is measured to obtain the main detector's count rate of the reference source.

6. The online monitoring method for gas-liquid two-phase flow in a radioactive separation system according to claim 5, characterized in that, Performing zero-deposit verification also includes: Based on the fluid density and transmittance obtained under zero sediment conditions, combined with the relative geometric positions of the reference source and the main detector, the attenuation correction coefficient of the ray from the reference source to the main detector is calculated. The attenuation correction coefficient is used to correct the count rate measured by the main detector to the reference source. Based on the corrected count rate and the known activity of the reference source, the detection efficiency of the main detector is determined. The detection field of view of the main detector is restored to the pipeline axis area, and the updated clean pipeline transmittance benchmark and main detector detection efficiency are stored.

7. The method for online monitoring of gas-liquid two-phase flow in a radioactive separation system according to claim 6, characterized in that, Calculating the true radioactivity concentration of the flowing fluid includes: Based on the final compensated count rate and the updated main detector detection efficiency, the response matrix is ​​constructed and solved jointly using the detection field of view spatial weight distribution function and the pre-acquired branch ratio to obtain the radioactivity concentration after preliminary geometric correction. Based on the radioactive concentration and pure transmission attenuation pair after preliminary geometric correction, the fluid equivalent density is obtained by inversion. The expected concentration is calculated based on the fluid equivalent density. The radioactive concentration after preliminary geometric correction is compared with the expected concentration. If the deviation exceeds the preset threshold, the sediment attenuation coefficient used in the attenuation correction factor generation process is adjusted, and the process of calculating the radioactive concentration after preliminary geometric correction is iteratively executed until the deviation converges within the threshold. The final radioactive concentration is then output. Based on the final radioactivity concentration, total sediment mass thickness, and circumferential non-uniform distribution morphology parameters, the concentration change rate and sediment growth rate are obtained by combining historical data, and the sediment eccentricity index is calculated. The above parameters are then integrated into a comprehensive state vector output.

8. An online monitoring system for gas-liquid two-phase flow in a radioactive separation system, applied to the online monitoring method for gas-liquid two-phase flow in a radioactive separation system according to any one of claims 2-7, characterized in that, include: The transmission measurement module is used to set up a reference source emitting two different energies of gamma rays on the outside of the clean section of the pipe to be tested, and to set up a reference source detector on the opposite side of the pipe to measure the transmittance of the two energies of the reference source rays after passing through the pipe, fluid and sediment, so as to obtain the transmission attenuation pair. The mass inversion module is used to invert the mass thickness of deposits inside the pipe based on the transmission attenuation pair and the pre-acquired clean pipe transmittance benchmark. The main counting module is used to set the main detector and its narrow field-of-view collimator, so that the detection field of the main detector is limited to the pipe axis area, and the main counting rate is measured. The counting compensation module is used to compensate the main count rate by utilizing the mass thickness of the sediment and the attenuation coefficient of the radionuclide to be tested in the sediment, so as to obtain the compensated count rate. The zero-deposition calibration module is used to perform zero-deposition calibration at predetermined time intervals to update the clean pipeline transmittance benchmark and the detection efficiency of the main detector. The concentration calculation module is used to calculate the true radioactive concentration of the flowing fluid based on the compensated count rate and the updated detection efficiency, and output the mass thickness of the sediment.

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