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- 摘要：BackgroundPredicting and delineating the dispersion pattern and extent of radioactive plumes is crucial in nuclear accident. Unmanned aerial vehicle (UAV) γ-ray spectrometry can determine radionuclides types and their concentration distributions within radioactive plume. Meanwhile, computational fluid dynamics (CFD) can simulate the concentration distributions of radionuclides in the air following dispersion. Under the extreme conditions of a nuclear accident, coupling these two methods offers an effective approach for conducting detailed assessments of radioactive contamination.PurposeThis study aims to obtain emergency response of UAV-borne γ-ray spectrometry to radioactive plumes, and statistically analyze the anomalous response characteristics for emergency monitoring in nuclear accidents.MethodsFirst of all, a mathematical model for UAV-borne γ-ray spectrometry with a cylindrical detector in the size of Ø7.62 cm×7.62 cm was established to calculate the full-energy peak detection efficiency for an equivalent spherical detector across all volume cells within the effective detection range for airborne radionuclides. Subsequently, the activity concentrations from the CFD dispersion model were interpolated using the natural neighbor interpolation method, and the activity concentration grid was remapped according to the detection efficiency grid coordinates. Then, a coupled analysis of the results from the mathematical model for UAV-borne γ-ray spectrometry of airborne radionuclides with non-uniform, irregular distributions and those from the CFD dispersion model was conducted. Finally, the counting rate, and the variation in counting rate yielded from the product of these two values were used to indicate the concentration boundaries and leakage points of the radioactive plume.ResultsSimulation results show that the impact of anomalous patterns and different radionuclides on boundary identification are obtained by analyzing the response characteristics of UAV-borne γ-ray spectrometry in the downwind, tangential, and vertical directions relative to the plume. The identification of abrupt changes in the deviation of the maximum value position at a fixed vertical height determines the horizontal boundary of the radioactive plume, while the pattern of the maximum counting rates on vertical transects rising with the downwind direction reflects the upper and lower boundary. The peak counting rates along the downwind survey lines and the lowest altitude at which peak counting rates are observed in the vertical survey lines indicate the approximate coordinates of the leak point. In boundary identification, nuclides with a short effective detection range can be used to precisely locate the leak point or the plume's central axis, while those with a long effective detection range are used to assess the overall extent of the contaminated area and to delineate the boundary contours of the plume.ConclusionsResults of this study demonstrate that the emergency monitoring response characteristics of the UAV-borne γ-ray spectrometry to radioactive plume can be applied to rapidly delineating the dispersion range of airborne radionuclides following a nuclear accident.关键词：Nuclear emergency response;Computational fluid dynamics;UAV γ-ray spectrometry;Radioactive plume;Boundary identification2|0|0更新时间：2026-08-18
- 摘要：BackgroundSingle-crystal 3C-SiC is a promising material for nuclear and micro/nano-device applications because of its excellent irradiation resistance, thermal stability, and mechanical properties. However, the swelling behavior of 3C-SiC under ion irradiation, together with the associated changes in electronic and mechanical properties, has not been systematically clarified, especially in relation to its potential use for surface micro/nano structuring.PurposeThis study aims to explore the irradiation-induced swelling behavior of single-crystal 3C-SiC under Ar-ion irradiation, establish its relationship with work function and hardness evolution, and assess the feasibility of exploiting this swelling effect for three-dimensional (3D) micro/nanostructure fabrication.MethodsFirstly, single crystals of 3C-SiC sample at size of 10 mm×10 mm×0.8 mm (including Si substrate) were obtained by laser cutting from a wafer with an epitaxial layer thickness of (300±30) nm. Then, these samples were irradiated by 140 keV Ar-ions at fluences ranging from 5×1015 ions∙cm-2 to 2×1017 ions∙cm-2 at room temperature, and the distributions of displacement damage (DPA) and Ar concentration were calculated using Stopping and Range of Ions in Matter (SRIM). Subsequently, irradiation-induced swelling was characterized by the step-height method using atomic force microscopy (AFM) between adjacent irradiated and unirradiated regions, and Kelvin probe force microscopy (KPFM) was employed to measure the surface potential difference and evaluate the work function variation. Finally, nanoindentation testing was carried out to determine the hardness evolution with irradiation fluence, and cross-sectional transmission electron microscopy (TEM) was used to analyze the damaged layer, amorphization, and Ar bubble formation at high fluence. In addition, mask-assisted ion beam irradiation (MAIBI) was applied to fabricate 3D micro/nanopatterned structures on single-crystal 3C-SiC substrates.ResultsExperimental results show that irradiation-induced swelling is increased from ~27 nm to ~56 nm with increasing fluence from 5×1015 ions∙cm-2 to 2×1017 ions∙cm-2, and the formation of nanoscale Ar bubbles make an important contribution to the enhanced irradiation-induced swelling at a high fluence. The work function of irradiated 3C-SiC shifts to negative values at high fluences, contrasting with 4H-SiC, where the work function remains positive and tends to stabilize near its pristine value. The nanoindentation hardness of irradiated 3C-SiC is initially increased with fluence, then is decreased to 77% of the pristine sample's hardness. Based on these irradiation-induced effects, 3D micro/nanopatterned structures are fabricated on single-crystal 3C-SiC substrates via MAIBI.ConclusionsThese findings in this study demonstrate that the irradiation swelling effect in single-crystal 3C-SiC can be effectively utilized for the one-step fabrication of 3D micro/nanostructures, providing a viable means of tuning its surface electronic properties.关键词：Single-crystal 3C-SiC;Irradiation swelling;Work function;Micro/nanostructure2|0|0更新时间：2026-08-18
- 摘要：BackgroundSodium-cooled fast reactors (SFR) represent one of six reactor types in fourth-generation nuclear energy systems. The heat exchanger tubes in SFRs operate at approximately 500 ℃ and are fabricated from 2.25Cr1Mo steel, a low-alloy ferritic heat-resistant material. During prolonged service, these tubes are susceptible to corrosion fatigue cracking, which gradually reduces their pressure-bearing capacity and poses the risk of catastrophic sodium-water reaction accidents. However, existing research on corrosion fatigue crack propagation of 2.25Cr1Mo steel is primarily experimental in nature, and the extended duration and high costs of such tests result in limited data. Current standards lack fatigue crack extension rate curves specific to the high-temperature high-pressure water environment relevant to this study.PurposeThis study aims to establish the Paris formula for 2.25Cr1Mo steel under high-temperature high-pressure water corrosion conditions and validate the Extended Finite Element Method (XFEM) simulation approach for predicting corrosion fatigue crack propagation in heat exchanger tubes.MethodsTwo integrated stages were comprised in this study. In the first stage, constant-amplitude fatigue loading tests were conducted on 2.25Cr1Mo steel compact tension (CT) specimens in simulated heat exchanger conditions of 350 ℃ and 17.5 MPa in high-temperature high-pressure deionized water. The test apparatus consisted of a load control system, high-temperature high-pressure autoclave, water chemistry circulation loop, and six-channel Direct Current Potential Drop (DCPD) monitoring system. The water chemistry loop maintained dissolved oxygen below 5 μg∙L-1 and pH at 9.2±0.1 through nitrogen degassing and ammonia adjustment. Sinusoidal cyclic loading with load ratio R=0.1 was applied through five stages: pre-cracking at 1.5 Hz followed by four formal stages at 1 Hz with maximum loads of 4 550 N, 4 700 N, 5 500 N, and 6 500 N, respectively. Crack extension rates were calculated using the secant line method, and data dimensionality was reduced through logarithmic binning averaging to obtain the Paris formula via linear regression. In the second stage, time-independent elastic-plastic constitutive models were employed for XFEM simulation to treat fatigue damage as purely cycle-dependent rather than time-dependent processes, and XFEM simulations were performed using Abaqus software integrated with Python "restart" scripts to model constant-ΔK corrosion fatigue crack propagation. A two-dimensional finite element model of the CT specimen with a thickness of 12.7 mm was established with refined mesh at the crack tip with a minimum element size of 0.03 mm. Four-node bilinear plane strain elements were employed based on the maximum tangential stress criterion. The Benzeggagh-Kenane criterion (η=1.5) was adopted for mixed-mode fracture. Finally, two formal test stages were modeled by simulation: stage one at 1 Hz until a/W≥0.55, and stage two at 0.1 Hz until a/W≥0.6 or time t≥96 h. The Python script controlled constant ΔK=30 MPa∙m0.5 by iteratively adjusting loading amplitude based on crack length extracted from the level set function.ResultsThe fitted Paris formula yieldes constants C=9.68×10-9 and m=2.754 with goodness of fit R²≥0.861. At 1 Hz loading frequency with 0.45≤a/W≤0.55, simulated crack extension rates agree with experimental results with only 6.9% relative error. Simulated crack propagation paths match the experimental observations. However, when the loading frequency is decreased to 0.1 Hz with a/W≥0.55, the XFEM simulation significantly overestimate crack growth rate compared to experimental measurements, with relative error increasing to 48.2%. This "simulation overestimation" phenomenon is attributed to insufficient consideration of time-dependent factors affecting corrosion fatigue crack growth rates. According to the Bažant-Li viscoelastic fracture model, stress relaxation effects reduce the effective stress amplitude as loading period increases, causing a notable difference in effective stress intensity factor ΔKeff between 1 Hz and 0.1 Hz conditions. Furthermore, at 0.1 Hz, the extended loading period allows the cyclic plastic zone (CPZ) at the crack tip to fully develop within each cycle, leading to significant stress redistribution that the rate-independent constitutive model cannot capture, thereby further amplifying the overestimation error.ConclusionsThe XFEM methodology based on the derived Paris formula demonstrates effectiveness for evaluating corrosion fatigue crack extension at 1 Hz, showing practical engineering value. However, the model's inadequate treatment of time-dependent effects, including crack-tip CPZ development, stress relaxation, and stress/strain field redistribution, limits its applicability to lower frequency scenarios. Future research requires conducting corrosion fatigue tests at various frequencies to develop frequency-dependent Paris formulas and establish rate-dependent constitutive models, enabling quantitative description of low-frequency crack-tip mechanical behaviors and more accurate simulation of real-service corrosion fatigue crack propagation in sodium-cooled fast reactor heat exchangers.关键词：Heat exchanger tube;2.25Cr1Mo steel;Corrosion fatigue;Paris law;Extended Finite Element Method (XFEM)2|0|0更新时间：2026-08-18
- 摘要：BackgroundIsotope separation technology plays a crucial role in basic scientific research, the national economy, and national security strategies. Existing separation technologies face challenges such as high energy consumption, low efficiency or limited applicability.PurposeThis study aims to verify the feasibility of single-photon separation of SF6 isotopes and to explore the effects of key parameters on separation performance.MethodsSeparation was achieved by combining supersonic molecular beam cooling with selective single-photon infrared laser excitation. A quadrupole mass spectrometer was used for online monitoring, experimental parameters were adjusted, and their impact on the separation factor was calculated.ResultsThe experimental results show that under the optimal conditions (laser close to the nozzle, sample gas pressure at 0.4 MPa, and laser power at 18 W), the separation selectivity exceeds 5.ConclusionsThe research results confirm the feasibility of single-photon separation of SF6 isotopes and provide important foundational data for the application of laser isotope separation methods domestically.关键词：Single-photon;Supersonic molecular beam cooling;Mass spectrometer online monitoring;Isotope4|11|0更新时间：2026-05-13
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