Vol.36,

Laser powder bed fusion (LPBF) is a widely used and well-developed approach in additive manufacturing. To meet the high material performance requirements of fourth-generation nuclear power reactors, the combination of LPBF processing with oxide dispersion strengthening (ODS) is currently of interest for the design and development of new materials. In this approach, nanoscale Y₂O₃ particles are dispersed into the feeding powders to produce LPBF-ODS materials. Oxygen exposure and the introduction of oxygen into the solvation cell during LPBF are usually considered as detrimental processes that are impossible to eliminate completely. However, our understanding of these unavoidable processes is still limited. In this study, we developed a new LPBF-ODS design approach based on in-situ oxygen content regulation during the LPBF process. The oxygen content of the environmental chamber was artificially adjusted using an online monitoring system to activate reactions between oxygen and the metallic elements for the in-situ formation of dispersed oxide particles. Four batches of LPBF 304L stainless steel samples were successfully processed under different oxygen levels to investigate the reinforcement effect of in-situ chemical alloying. The results show that dispersed oxide particles were formed with an average nanoscale size of approximately 46 nm through the LPBF in-situ alloying approach. The increase in the number density of oxide particles to 11.4 particles /μm² as the oxygen content increased played a role in refining and stabilizing the cellular structure. The yield strength of the in-situ alloyed ODS material was enhanced (to up to ~675 MPa) while its ductility was not significantly degraded (elongation of up to ~39%). These tensile properties are competitive within the ranges reported for ODS alloys prepared by mechanical alloying. The main mechanisms for yield strength enhancement through interactions between nanoscale oxide particles and dislocation entanglement cells were analyzed. This study provides a new approach for the future preparation of high-performance LPBF-ODS alloys.

114

The reduced-activation ferritic/martensitic (RAFM) steel CLF-1 has been designed as a candidate structural material for nuclear fusion energy reactors. For engineering mechanical design, the effects of temperature on the strain distribution of CLF-1 steel during uniaxial tensile tests were explored within the temperature range from room temperature to 650 ℃ using uniaxial tensile tests combined with in-situ digital image correlation analysis. Strain-concentrated regions alternately distributed ±45° along the tensile direction could be attributed to the shear stress having the maximum value at ±45° along the tensile direction and the coordinated deformation of the microstructure. The total strain distribution changed from a normal distribution to a lognormal distribution with increasing deformation owing to the competition between the elastic and plastic strains at all test temperatures. Strain localization has a strong relationship with temperature at the same engineering strain because of the temperature effects on dynamic strain ageing (DSA). The stronger the DSA effect, the stronger the strain localization. With increasing temperature, the stronger the strain localization at the same strain, the weaker the plasticity, that is, DSA-induced embrittlement, and the slower the strength decline, that is, DSA-induced hardening.

104

With the increasing demand for controllable source logging, research on data-processing algorithms that meet accuracy requirements has become key to the development of controllable-source-logging tools. This study theoretically derives the relationship between the formation density and inelastic gamma count rate to investigate the data-processing methods for deuterium-tritium (D-T) source neutron-gamma density logging while drilling. Then, algorithms for the net inelastic gamma count-rate extraction and neutron transport correction are studied using Monte Carlo simulations. A new method for fast-neutron effect identification and additional correction is proposed to improve the density-calculation accuracy of gas-filled and heavy-mineral formations. Finally, the effectiveness and accuracy of the proposed data-processing methods are verified based on simulated and measured data. The results show that the density-calculation accuracy of water-bearing conventional formations in simulated data is ±0.02 g/cm³. The accuracy of gas-filled and heavy-mineral formations after the additional fast-neutron effect correction is ±0.025 g/cm³. For the measured data from the actual tool, the algorithms perform well in the density calculation. The density results obtained using the processing algorithms are consistent with the density data provided by NeoScope. Therefore, the D-T source neutron-gamma density-logging algorithms proposed in this study can obtain relatively accurate data-processing results for a variety of formations. This study provides technical support for engineering applications and the development of logging tools for controllable-source neutron-density logging.

119

Industrial linear accelerators often contain many bunches when their pulse widths are extended to microseconds. As they typically operate at low electron energies and high currents, the interactions among bunches cannot be neglected. In this study, an algorithm is introduced for calculating the space charge force of a train with infinite bunches. By utilizing the ring charge model and the particle-in-cell (PIC) method and combining analytical and numerical methods, the proposed algorithm efficiently calculates the space charge force of infinite bunches, enabling the accurate design of accelerator parameters and a comprehensive understanding of the space charge force. This is a significant improvement on existing simulation software such as ASTRA and PARMELA that can only handle a single-bunch or a small number of bunches. The PIC algorithm is validated in long-drift space transport by comparing it with existing models, such as the infinite-bunch, ASTRA single-bunch, and PARMELA several-bunch algorithms. The space charge force calculation results for the external acceleration field are also verified. The reliability of the proposed algorithm provides a foundation for the design and optimization of industrial accelerators.

Promoting the development of deep-sea mineral exploration instrumentation can help alleviate the global resource shortage faced by mankind. X-ray fluorescence (XRF) spectrometry has been widely used in the in situ analysis of deep-sea minerals owing to its fast analytical speed, nondestructive nature, and wide analytical range. This study focused on the structural safety and detection efficiency of X-ray fluorescence in situ measurement equipment under high pressure for deep-sea XRF analysis. This study first combined finite element analysis and experiments to design and optimize the structure of an X-ray probe tube required for deep-sea mineral exploration and to determine the Be window thickness to ensure stress safety. Subsequently, the Monte Carlo method was used to analyze and optimize the Be window thickness on the X-ray probe tube to improve the accuracy of the elemental analyses. Finally, the effect of seawater thickness between the transmitter outer tube and rock wall was also considered. The results show that based on ocean depth in different detection environments, Be windows with a thickness of 1.5 mm or 2.0 mm can be selected to improve the detection efficiency of the device while ensuring the structural safety of the instrument. According to the design features and detection requirements of the device, in deep-sea exploration of minerals with characteristic peak energies below 10 keV, the transmitter outer tube should be as close as possible to the rock wall inside the logging. When the characteristic peak energy of the minerals is more than 10 keV, the distance between the transmitter outer tube and rock wall inside the logging should be controlled to approximately 2 mm. This study provides feasible solutions for future deep-sea mineral resource development and a useful reference for elemental analysis of minerals in the deep sea or other extreme working environments.

107

Superconducting radio-frequency (SRF) cavities are the core components of SRF linear accelerators, making their stable operation considerably important. However, the operational experience from different accelerator laboratories has revealed that SRF faults are the leading cause of short machine downtime trips. When a cavity fault occurs, system experts analyze the time-series data recorded by low-level RF systems and identify the fault type. However, this requires expertise and intuition, posing a major challenge for control-room operators. Here, we propose an expert feature–based machine learning model for automating SRF cavity fault recognition. The main challenge in converting the "expert reasoning" process for SRF faults into a "model inference" process lies in feature extraction, which is attributed to the associated multidimensional and complex time-series waveforms. Existing autoregression-based feature-extraction methods require the signal to be stable and autocorrelated, resulting in difficulty in capturing the abrupt features that exist in several SRF failure patterns. To address these issues, we introduce expertise into the classification model through reasonable feature engineering. We demonstrate the feasibility of this method using the SRF cavity of the China Accelerator Facility for superheavy Elements (CAFE2). Although specific faults in SRF cavities may vary across different accelerators, similarities exist in the RF signals. Therefore, this study provides valuable guidance for fault analysis of the entire SRF community.

100

In recent years, due to the scarcity of domestic radioisotopes, the Chinese government has strongly supported the development of dedicated radioisotope production facilities. This paper presents conceptual design simulations of an 11 MeV, 50 μA, H^- compact superconducting cyclotron for radioisotope production. This paper focuses primarily on four aspects: magnet system design, central region configuration, beam dynamics analysis, and extraction system design. This paper outlines the cyclotron's primary parameters and key steps in the development process.

111

Most synchrotron light storage rings are equipped with a higher harmonic cavity (HHC) and are currently predominantly used to increase beam life. With the enhancement of the beam current intensity, it is necessary to consider instability problems that may be caused by heavy beam loading effects. In this study, we incorporated a HHC into the small-signal Pedersen mathematical model and used system signal analysis to investigate the mode-zero Robinson instability driven by the passive superconducting harmonic cavity (PSHC) and active superconducting harmonic cavity (ASHC) fundamental modes. To further study and alleviate this instability, we introduced direct radio-frequency feedback (DRFB), an automatic voltage control loop (AVC), and a phase-lock loop (PLL) into the model, discussed the impact of the feedback loop parameter settings on the stability margin, and provided suggestions for parameter settings.

105

Radio frequency (RF) cavities for advanced storage rings, also known as diffraction-limited storage rings, are under development. To this end, a competitive and promising approach involves normal-conducting continuous wave technology. The design and preliminary test of a 499.654 MHz RF cavity for the Wuhan Advanced Light Source (WALS) based on specific beam parameters were conducted at the SSRF. Multi-objective evolutionary algorithms have been utilized to optimize RF properties, such as the power loss and power density, resulting in better performance in the continuous wave mode. Further improvements were made to suppress multipacting effects in the working area. To operate stably with the beam, higher-order mode dampers were applied to better address the coupling bunch instability than in previous designs, along with thermal analysis to achieve the desired RF performance. Comprehensive simulation studies demonstrated the stable operation of the RF cavity at the defined beam parameters in the WALS design. A prototype RF cavity was then developed, and the RF performance results in a low-power test showed good agreement with the design and simulation, exhibiting readiness for high-power experiments and operation.

112

This study presents a real-time tracking algorithm derived from the retina algorithm, designed for the rapid, real-time tracking of straight-line particle trajectories. These trajectories are detected by pixel detectors to localize single-event effects in two-dimensional space. Initially, we developed a retina algorithm to track the trajectory of a single heavy ion and achieved a positional accuracy of 40 μm. This was accomplished by analyzing trajectory samples from the simulations using a pixel sensor with a 72 × 72 pixel array and an 83 μm pixel pitch. Subsequently, we refined this approach to create an iterative retina algorithm for tracking multiple heavy-ion trajectories in single-events. This iterative version demonstrated a tracking efficiency of over 97%, with a positional resolution comparable to that of single-track events. Furthermore, it exhibits significant parallelism, requires fewer resources, and is ideally suited for implementation in field-programmable gate arrays on board-level systems, facilitating real-time online trajectory tracking.

106

High-power laser pulses interacting with targets can generate intense electromagnetic pulses (EMPs), which can disrupt physical experimental diagnostics and even damage diagnostic equipment, posing a threat to the reliable operation of experiments. In this study, EMPs resulting from multi-petawatt laser irradiating nitrogen gas jets were systematically analyzed and investigated. The experimental results revealed that the EMP amplitude is positively correlated with the quantity and energy of the electrons captured and accelerated by the plasma channel. These factors are reflected by parameters such as laser energy and nitrogen gas jet pressure. Additionally, we propose several potential sources of EMPs produced by laser-irradiated gas jets and separately analyzed their spatiotemporal distributions. The findings provide insight into the mechanisms of EMP generation and introduce a new approach to achieve controllable EMPs by regulating the laser energy and gas jet pressure.

112

Utilizing the laser-driven Z-pinch effect, we propose an approach for generating an ultrashort, intense MeV neutron source with femtosecond pulse duration. The self-generated magnetic field driven by a petawatt-class laser pulse compressed the deuterium in a single nanowire to more than 120 times its initial density, achieving an unprecedented particle number density of 10²⁵ cm^-3. Through full-dimensional kinetic simulations, including nuclear reactions, we found that these Z-pinches can generate high-intensity and short-duration neutron pulses, with the peak flux reaching 10²⁷ cm^-2s^-1. Such laser-driven neutron sources are beyond the capabilities of existing approaches and pave the way for groundbreaking applications in r-process nucleosynthesis studies and high-precision time-of-flight neutron data measurements.

106

Liquid-fueled molten-salt reactors have dynamic features that distinguish them from solid-fueled reactors, such that conventional system-analysis codes are not directly applicable. In this study, a coupled dynamic model of the Molten-Salt Reactor Experiment (MSRE) is developed. The coupled model includes the neutronics and single-phase thermal-hydraulics modeling of the reactor and validated xenon-transport modeling from previous studies. The coupled dynamic model is validated against the frequency-response and transient-response data from the MSRE. The validated model is then applied to study the effects of xenon and void transport on the dynamic behaviors of the reactor. Plant responses during the unique initiating events such as off-gas system blockages and loss of circulating voids are investigated.

114

With the rapid development of the nuclear power industry on a global scale, the discharge of radioactive effluents from nuclear power plants and their impact on the environment have become important issues in radioactive waste management, radiation protection, and environmental impact assessments. β-detection of nuclides requires tedious processes, such as waiting for the radioactive balance of the sample and pretreatment separation, and there is an urgent need for a method specifically designed for mixing β rapid energy spectrum measurement method for nuclide samples. The analysis of hybrid β-energy spectrum is proposed in this study as a new algorithm, which takes advantage of the spectral analysis of β-logarithmic energy spectrum and fitting ability of Fourier series. The logarithmic energy spectrum is obtained by logarithmic conversion of the hybrid linear energy spectrum. The Fourier fitting interpolation method is used to fit the logarithmic energy spectrum numerically. Next, the interpolation points for the ‘effective high-energy window’ and ‘effective low-energy window’ corresponding to the highest E_m nuclide in the hybrid logarithmic fitted energy spectrum are set, and spline interpolation is performed three times to obtain the logarithmic fitted energy spectrum of the highest E_m nuclide. Finally, the logarithmic-fitted spectrum of the highest E_m nuclide is subtracted from the hybrid logarithmic-fitted spectrum to obtain a logarithmic-fitted spectrum comprised of the remaining lower E_m nuclides. The aforementioned process is iterated in a loop to resolve the logarithmic spectra of each nuclide in the original hybrid logarithmic spectra. Then, the radioactivity of E_m nuclides to be measured is calculated. In the experimental tests, ¹⁴C, ⁹⁰Sr, and ⁹⁰Y spectra, which are obtained using the Fourier fitting interpolation method are compared with the original simulated ¹⁴C, ⁹⁰Sr, and ⁹⁰Y spectra of GEANT4. The measured liquid scintillator data of ⁹⁰Sr/⁹⁰Y sample source and simulated data from GEANT4 are then analyzed. Analysis of the experimental results indicates that the Fourier fitting interpolation method accurately solves ¹⁴C, ⁹⁰Sr, and ⁹⁰Y energy spectra, which is in good agreement with the original GEANT4 simulation. The error in ⁹⁰Y activity, calculated using the actual detection efficiency, is less than 10% and less than 5% when using the simulated full-spectrum detection efficiency, satisfying the experimental expectations.

108

A floating nuclear power plant (FNPP) is an offshore facility that integrates proven light-water reactor technologies with floating platform characteristics. However, frequent contact with marine environments may lead to wave-induced vibrations and oscillations. This study aimed to evaluate the wave danger on FNPPs, which can negatively impact FNPP functionality. We developed a hydrodynamic model of an FNPP using potential flow theory and computed the frequency-domain fluid dynamic responses. After verifying the hydrodynamic model, we developed a predictive model for FNPP responses. This model utilizes a genetic aggregation methodology for batch prediction while ensuring accuracy. We analyzed all the wave data from a selected sea area over the past 50 years using the constructed surrogate model, enabling us to identify dangerous marine areas. By utilizing the extreme value distribution of important wave heights in these areas, we determined the wave return period, which poses a threat to FNPPs. This provides an important method for analyzing wave hazards to FNPPs.

In recent years, the development of new types of nuclear reactors, such as transportable, marine, and space reactors, has presented new challenges for the optimization of reactor radiation-shielding design. Shielding structures typically need to be lightweight, miniaturized, and radiation-protected, which is a multi-parameter and multi-objective optimization problem. The conventional multi-objective (two or three objectives) optimization method for radiation-shielding design exhibits limitations for a number of optimization objectives and variable parameters, as well as a deficiency in achieving a global optimal solution, thereby failing to meet the requirements of shielding optimization for newly developed reactors. In this study, genetic and artificial bee-colony algorithms are combined with a reference-point-selection strategy and applied to the many-objective (having four or more objectives) optimal design of reactor radiation shielding. To validate the reliability of the methods, an optimization simulation is conducted on three-dimensional shielding structures and another complicated shielding-optimization problem. The numerical results demonstrate that the proposed algorithms outperform conventional shielding-design methods in terms of optimization performance, and they exhibit their reliability in practical engineering problems. The many-objective optimization algorithms developed in this study are proven to efficiently and consistently search for Pareto-front shielding schemes. Therefore, the algorithms proposed in this study offer novel insights into improving the shielding-design performance and shielding quality of new reactor types.

121

Prompt fission neutron uranium logging (PFNUL) is an advanced method for utilizing pulsed neutron bombardment of the ore layer and a fission reaction with uranium (²³⁵U) to detect the transient neutrons produced by fission and then directly measure and quantify uranium; however, the stability and lifetime performance of pulsed neutron sources are the key constraints to its rapid promotion. To address these problems, this study proposes a PFNUL technique for acquiring the time spectrum of dual-energy neutrons (epithermal and thermal neutrons) from the upper and lower detection structures and establishes a novel uranium quantification algorithm based on the ratio of epithermal and thermal neutron time windows (E/T) via a mathematical-physical modeling derivation. Through simulations on well logging models with different uranium contents, the starting and stopping times of the time window (Δt) for uranium quantification in the dual-energy neutron time spectrum are determined to be 200 and 800 μs, respectively. The minimum radius and height of the model wells are 60 and 120 cm, respectively, and the E/T values in the time window show an excellent linear relationship with the uranium content. The scale factor is K_E/T=1.92 and R²=0.999, which verifies the validity of the E/T uranium quantification algorithm. In addition, experiments were carried out in the Nu series of uranium standard model wells, and the results showed that under different neutron source yields, the E/T-based uranium quantification method reduced the relative standard deviation of the scale factor of the uranium content from 33.41% to 1.09%, compared with a single epithermal neutron quantification method. These results prove that the E/T value uranium quantification method is unaffected by the change in the neutron source yield, effectively improves the accuracy and service life of the logging instrument, and has great scientific and popularization value.

Molten salt reactors (MSRs) are a promising candidate for Generation IV reactor technologies, and the small modular molten salt reactor (SM-MSR), which utilizes low-enriched uranium and thorium fuels, is regarded as a wise development path to accelerate deployment time. Uncertainty and sensitivity analyses of accidents guide nuclear reactor design and safety analyses. Uncertainty analysis can ascertain the safety margin, and sensitivity analysis can reveal the correlation between accident consequences and input parameters. Loss of forced cooling (LOFC) represents an accident scenario of the SM-MSR, and the study of LOFC could offer useful information to improve physical thermohydraulic and structural designs. Therefore, this study investigates the uncertainty of LOFC consequences and the sensitivity of related parameters. The uncertainty of the LOFC consequences was analyzed using the Monte Carlo method, and multiple linear regression was employed to analyze the sensitivity of the input parameters. The uncertainty and sensitivity analyses showed that the maximum reactor outlet fuel salt temperature was 725.5 ℃, which is lower than the acceptable criterion, and five important parameters influencing LOFC consequences were identified.

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