Subjects: Nuclear Science and Technology >> Nuclear Detection Technology and Nuclear Electronics submitted time 2024-07-23
Abstract： Common radioactive aerosol monitors are often not portable and are difficult to deploy quickly, which means they cannot meet the needs of nuclear emergency response. [Purpose]: This study aims to develop a robust and compact portable radioactive aerosol monitor. And it can carry out real-time measurement and remote monitoring to realize the function of identification and analysis of nuclides. [Methods]:This monitor utilises 3D printing technology to design a unique housing and gas path structure, employs an anticoincidence detector, and uses an Artery ultra-high performance microcontroller for signal acquisition via a two-channel energy discrimination method. Based on the Intel HD Graphics processor, the monitor processes and analyses the signal using the α/β ratio method, snip de-localisation method, and second derivative peak search method to achieve accurate measurement and identification and analysis of nuclides. [Results]: The theoretical detection limit for α and β of the monitor are 0.72 Bq/m³ and 1.71 Bq/m³, respectively. The monitor demonstrates excellent stability and detection efficiency. [Conclusions]: The monitor can be deployed on unmanned inspection robots and drones, offering significant advantages for real-time monitoring and emergency response. This capability ensures adaptability to various scenarios involving radioactive aerosols, enhancing both efficiency and responsiveness in critical situations.
Subjects: Nuclear Science and Technology >> Nuclear Science and Technology submitted time 2024-07-12
Abstract： [Background] The imperative need for high-performance propulsion systems in deep space exploration missions has led to a focus on improving the design of nuclear thermal propulsion reactors (NTPRs). The existing methods for designing NTPRs have been identified as lacking in systematic and integral approaches. [Purpose] The purpose of this study is to propose a novel multi-objective optimization design method for NTPRs to achieve a core design that offers high thrust, high specific impulse, extended service life, and reduced weight. [Methods] The methodology involves several key steps: Constructing a heat transfer model between assemblies based on their thermal interaction characteristics. Integrating this model with the flight performance model of the nuclear rocket and the two-dimensional criticality model of the assemblies. Proposing a multi-objective parameter screening method that combines the aforementioned models for coupled iterative calculations to optimize the core layout. Ensuring that the design meets comprehensive standards in thermal engineering, flight performance, and neutron physics while minimizing the core mass. Utilizing the open-source Monte Carlo software OpenMC to perform detailed three-dimensional neutronics calculations and conduct a comprehensive assessment of the reactor's criticality, safety, and burnup performance. [Results] The study's findings demonstrate that the low-enriched uranium (LEU) NTPR conceptual design, developed using the proposed method, has preliminarily satisfied the design criteria for high thrust, high specific impulse, long service life, and lightweight. [Conclusions] The results suggest that the proposed method for NTPR core design is effective in meeting the demanding requirements of future manned deep space exploration missions, offering a promising direction for further research and development in this field.
Subjects: Nuclear Science and Technology >> Nuclear Detection Technology and Nuclear Electronics submitted time 2024-07-04
Abstract： [Background]: Accurate localization of radioactive material is essential for finding "orphan sources", decontaminating and decommissioning nuclear facilities, and optimizing radiation protection. Silicon Photomultiplier (SiPM) has been widely used in scintillator detection systems. [Purpose]: To realize a low-cost large-field-of-view high-resolution detection system, a mixed-mode readout circuit combining a resistive network, a preamplifier circuit and an ASIC module is designed and verified. [Methods]: Firstly, by changing the rising edge, falling edge, pulse width and amplitude of the input pulse, the requirements of the A5202 module on the input pulse are experimentally measured to achieve the best data acquisition performance. When the rise time of the input pulse is less than 150ns and the amplitude is greater than 20mV, the data measured by the A5202 module has less noise and higher energy resolution. Then simulation is carried out by Multisim software. This simulation analyzes in detail the relationship between the resistor resistance and the rise time of the output signal. It determines the optimum resistor resistance value for the symmetric charged division circuit. The rise time of the output signal is relatively minimized when the resistance value of the first stage shunt resistor is 1 kOhm and the resistance value of the second stage shunt resistor is 100 ohms. Finally, in order to simultaneously take into account the characteristics of the output signal of the symmetric charged division circuit and the requirements of the A5202 module for the input signal, an inverse proportional operational amplifier circuit with the AD8066ARZ chip as the core is designed. It is used to connect the A5202 module and the symmetric charged division circuit. After the scintillator detection system was assembled, the stability of the system was examined, then the RMS noise of the system was measured, and finally the positioning accuracy of the system was examined. In order to improve the robustness of localization, the localization threshold was first calibrated with a single LYSO. The LYSO was further replaced with an array of Cerium-doped Gadolinium Aluminum Gallium Garnet (GAGG(Ce)) crystals and the calibration results were examined with a 241Am source. [Results]: The test results show that the readout circuit has an RMS noise of about 3 mV, retains the energy and position information of the signal well, and has an average energy resolution of about 12.13%. [Conclusions]: The readout circuit designed in this paper simplifies the 64-channel SiPM signal into 4 channels, and reduces the number of detector output signal channels by 16 times. A single ASIC module can read out 1024 SiPMs at the same time, which can greatly reduce the cost of readout for large-area SiPM arrays.
Subjects: Nuclear Science and Technology >> Nuclear Science and Technology submitted time 2024-06-21
Abstract： [Background] The helium-xenon mixture closed Brayton cycle system has significant advantages of high cycle efficiency, small specific power volume, and large output specific power, and has broad application prospects in the field of special nuclear power. The coupling of a helium xenon mixed working fluid closed Brayton cycle system with a nuclear reactor to form a megawatt level special nuclear reactor power supply can effectively adapt to high-power energy supply scenarios such as deep space exploration, star catalog nuclear power supply, and deep-sea submersibles. At present, there are few tools available for steady-state simulation research of helium xenon closed Brayton cycles, making it difficult to grasp the steady-state characteristics of the system. [Purpose] In order to grasp the characteristics of equipment and systems before actual engineering design and operation, and reduce research costs, it is necessary to develop relevant helium xenon closed Brayton cycle steady-state simulation tools. [Methods] By establishing component models of core equipment such as reheaters, coolers, turbines, and compressors in the steady-state thermodynamic system of helium xenon closed Brayton cycles, a simulation tool for steady-state analysis of helium xenon Brayton cycles was obtained. And by comparing the design values of the Prometheus project in the United States with the calculated values of simulation software built under the same conditions, the accuracy of the simulation software is verified. The construction model was validated and the effects of parameters such as the highest temperature, lowest temperature, highest pressure, and total thermal conductivity of the regenerator on the cycle were analyzed. The influence of parameters and component performance at various points of the space helium xenon closed Brayton cycle system with an output power of 200kW on system efficiency and specific power was analyzed. [Results] The calculation results of the helium xenon thermodynamic cycle calculation model constructed in this article are in good agreement with the "Prometheus" design values, with a maximum node parameter error of 0.212% and a maximum system parameter error of 3.419%, all of which are within an acceptable range, proving the accuracy and reliability of the helium xenon closed Brayton cycle model. The results also show that there is an optimal pressure ratio for both system efficiency and system specific power, and it is reasonable to use the pressure ratio at the maximum system efficiency in the design; The higher the maximum temperature of the cycle, the lower the minimum temperature, and the greater the system efficiency and specific power. The impact of the minimum temperature of the cycle on the cycle is more significant; The impact of pressure on circulation is not significant. The higher the pressure, the slightly smaller the system efficiency and specific power of the system; The higher the total thermal conductivity of the regenerator, the greater the system efficiency. The specific power of the system remains unchanged, and the higher the pressure ratio, the less significant the impact of the total thermal conductivity of the regenerator on the cycle efficiency. [Conclusions] This study provides a reference and basis for the design and optimization of helium xenon closed Brayton cycles.
Subjects: Nuclear Science and Technology >> Nuclear Science and Technology submitted time 2024-06-20
Abstract： [Background]: The single-phase reversed flow in inverted U-tubes of steam generator (SG) leads to increasing flow resistance and decreasing heat transfer area, so it is meaningful to study this phenomenon. [Purpose]: The water level of the secondary side in SG can influence the single-phase reversed flow, it is necessary to clarify its influence mechanism from a more general viewpoint. [Methods]: The dimensionless conservation equations were derived first, and the extreme point was obtained based on the equations. Then the effect of the water level of the secondary side under conditions of different lengths, dimensionless resistance number, and dimensionless heat transfer number was analyzed. [Results]: The decrease in the water level leads to the critical point of the single-phase reversed flow gradually approaching the origin, the influence law of the water level is the same under different pipe length conditions. As the water level decreases, the influence of the dimensionless resistance number and dimensionless heat transfer number on the critical point gradually reduces. [Conclusions]: This study theoretically proves that the effect of secondary water level on single-phase reversed flow is not conducive to the occurrence of backflow, and explains the reasons from a mechanistic perspective, which can assist in accident analysis of related nuclear power plants.
Subjects: Nuclear Science and Technology >> Nuclear Science and Technology submitted time 2024-05-30
Abstract： [Background]: The single-phase reversed flow in inverted U-tubes of steam generator (SG) leads to increasing flow resistance and decreasing heat transfer area, so it is meaningful to study this phenomenon. [Purpose]: The water level of the secondary side in SG can influence the single-phase reversed flow, it is necessary to clarify its influence mechanism from a more general viewpoint. [Methods]: The dimensionless conservation equations were derived first, and the extreme point was obtained based on the equations. Then the effect of the water level of the secondary side under conditions of different lengths, dimensionless resistance number, and dimensionless heat transfer number was analyzed. [Results]: The decrease in the water level leads to the critical point of the single-phase reversed flow gradually approaching the origin, the influence law of the water level is the same under different pipe length conditions. As the water level decreases, the influence of the dimensionless resistance number and dimensionless heat transfer number on the critical point gradually reduces. [Conclusions]: This study theoretically proves that the effect of secondary water level on single-phase reversed flow is not conducive to the occurrence of backflow, and explains the reasons from a mechanistic perspective, which can assist in accident analysis of related nuclear power plants.
Subjects: Nuclear Science and Technology >> Particle Accelerator submitted time 2024-04-25
Abstract： Abstract:
Objective: Cone beam CT（CBCT） can provide more accurate target location for patients during radiotherapy. However， due to the low contrast， loud noise and large artifacts caused by many scattered lines， the image quality is poor， and it cannot be used for dose calculation in real-time radiotherapy. This study aims to generate CBCt-based synthetic CT（sCTs） using three kinds of deep learning networks， namely Unet， CyclaGAN and CGAN， and study and compare the image quality of the three sCTs.
Methods: The CBCT and pCTs data of 78 patients with prostate cancer were preprocessed， including 63 training sets， 10 test sets， and 5 validation sets， to train and evaluate the image quality based on the three models， respectively. Image evaluation indexes such as mean absolute error （MAE）， mean error （ME）， mean square error （MSE）， peak signal-to-noise ratio （PSNR）， structural similarity （SSIM） and spatial non-uniformity （SNU） and frequency domain information were used for evaluation.
Results: Among the three models， CGAN model showed the best performance in each index. In terms of image quality under global conditions， the average MAE is reduced to 7.77HU， MSE is reduced to 4.99， PSNR is increased to 54.95， SSIM is increased to 96%.
Conclusion: The deep learning method can significantly modify the HU value of cbct and generate the corresponding high-quality sCT. For patients with prostate cancer， the sCT generated by cGAN has better image quality. The CBCt-based sCT generated by this model can provide the target dose calculation for prostate cancer radiotherapy.
Subjects: Physics >> Nuclear Physics submitted time 2024-03-27
Abstract： Background: The propagation and power deposition process of ion cyclotron waves in plasma is the key to ICRH.
Purpose: The purpose of this study is to evaluate the effect of single absorption assumption and non-single absorption assumption on ion cyclotron wave coupling and heating in the EAST.
Methods: Under different antenna current phases, the simulation results of the EAST 3D full vacuum chamber ICRH program and the 1/4 vacuum chamber ICRH program were compared.
Results: When the antenna current phase is (0 π 0 π), there is a significant difference between the simulation results of the two models.
Conclusion: The ion cyclotron wave propagating multiple times in the toroidal direction is the main reason for the difference in results. For fusion devices, the applicability of the single absorption assumption needs further systematic research.
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