分类： 核科学技术 >> 核科学与技术 提交时间： 2024-06-20
摘要： 近年来我国能源清洁化率不断提高，以风电和光伏为代表的规模化新能源出力存在明显的波动性和不确定性，另一方面，电网的负荷需求、增长和总量达不到预期，这对电网的调峰能力提出了新的考验和挑战，为确保厂网安全，核电机组参与调峰越来越频繁,这对核电机组的核安全又带来了新的挑战，甚至可能会影响中国核电事业的长远发展。本文对核电机组参与电网调峰可能给电厂安全及系统设备造成的影响进行了分析，重点分析了参与电网调峰对电厂安全性、可靠性、经济性以及对三废处理的影响，并提出了合理化建议和改进方向，为我国核电机组的运行和参与调峰提供了示范思路。
分类： 核科学技术 >> 核科学与技术 提交时间： 2024-06-21
摘要： 氦氙冷却反应堆以氦氙混合气体作为布雷顿循环运行工质，具有循环效率高、功率质量比高和运行可靠等特点，在深空大功率核反应堆电源和无人潜航器核动力等领域具有广阔的应用前景。针对氦氙布雷顿循环系统运行特性，本文建立了涡轮机、压缩机、紧凑型换热器等氦氙布雷顿循环热力设备仿真模型，开发了氦氙冷却反应堆布雷顿循环运行性能分析仿真工具。以“普罗米修斯”氦氙冷却反应堆布雷顿循环系统为研究对象，分析循环各点参数与各部件性能对系统效率和系统比功的影响。结果表明：系统效率与系统比功均存在最佳压比，循环最高温度越高、最低温度越低，系统效率与系统比功越大；压力对循环的影响不明显，压力越大，系统效率与系统比功略微减小；回热器总热导率越大，系统效率越大，系统比功不变。
分类： 核科学技术 >> 核科学技术其他学科 提交时间： 2024-06-24
摘要： 在牙化石ESR测年中辐照剂量点拟合函数的选择对等效剂量DE的确定至关重要。目前早期遗址老化石（＞1Ma）的DE拟合常采用双饱和指数（DSE）函数，但在使用该函数时一般需要15个以上剂量点和＞20kGy的最大辐照剂量（Dmax）才能保证DE值的拟合精度，这对老化石测年构成了很大制约。本研究对涵盖晚中新世至早更新世的化石样品进行了不同拟合函数的对比分析，着重探讨单饱和指数（SSE）函数在老化石样品DE拟合中的适用性。研究表明在15个剂量点和Dmax=50kGy条件下，SSE函数的平均拟合优度与DSE函数接近，但平均拟合精度明显优于后者；对于DE＞4500Gy和DE＜4500Gy的样品，分别在Dmax≥6.5*DE和1.3*DE＜Dmax＜2.2*DE条件下采用SSE函数拟合，其结果可以作为DSE函数的良好近似值。
分类： 物理学 >> 核物理学 提交时间： 2024-06-24
Zhi-Jun Chi
Hong-Ze Zhang
Jin Lin
Xuan-Qi Zhang
Hao Ding
Qi-Li Tian
Zhi Zhang
Ying-Chao Du
Wen-Hui Huang
Chuan-Xiang Tang
摘要： Owing to the Thomson scattering between relativistic electrons and a laser, continuously polarization-tunable X-rays can be easily generated, providing an excellent probe for advanced X-ray imaging. In this paper, a method for simultaneous fluorescence and Compton scattering computed tomography is proposed using linearly polarized X-rays. The proposed method feasibility was verified using Monte Carlo simulations. In the simulations, the phantom is a polytetrafluoroethylene (Teflon) cylinder inside which are cylindrical columns containing aluminum, water, and gold (Au)-loaded water solutions with Au concentrations ranging between 0.5--4.0 wt%, and a parallel hole collimator imaging geometry was adopted. By adjusting the incident X-ray polarization direction, both the X-ray fluorescence computed tomography (XFCT) and Compton scattering computed tomography (CSCT) images of the phantom were accurately reconstructed using a maximum-likelihood expectation maximization algorithm. A similar attenuation contrast problem for the different cylindrical columns in the phantom can be resolved in the XFCT and CSCT images. The interplay between XFCT and CSCT was analyzed and the contrast-to-noise ratio (CNR) of the reconstruction was improved by correcting for the mutual influence between the two imaging modalities. Compared with K-edge subtraction imaging, XFCT exhibits a CNR advantage for the phantom.
分类： 核科学技术 >> 核动力工程技术 提交时间： 2024-06-23
摘要： 为了进一步提高球床式高温气冷堆堆芯物理计算精度，西安交通大学核工程计算物理（Nuclear Engineering Computational Physics, NECP）实验室自主研发了适用于球床式高温气冷堆物理热工计算程序NECP-Panda的中子学计算模块。本文介绍了NECP-Panda的计算框架，重点阐述了中子学计算部分的理论方法并进行了验证计算。计算问题包括简化混合球床堆算例以及高温气冷堆核电示范工程（High Temperature Reactor Pebble-bed Module, HTR-PM）的净堆装料和吸收体价值计算。数值结果表明，NECP-Panda对简化混合球床堆的keff计算与蒙特卡罗连续能量结果符合良好，计算的HTR-PM临界装料高度与蒙特卡罗连续能量结果高度一致，吸收体价值非常吻合，证明了NECP-Panda针对球床式高温气冷堆的中子学计算具有良好的计算能力和精度，为后续模块的开发奠定了坚实基础。
分类： 核科学技术 >> 核科学与技术 提交时间： 2024-06-23
摘要： 核电厂核岛机械设备在役检查规则（简称RSE-M，下同）是国内核电站机械设备在役期间通用的规范。随着制造工艺、焊接水平、无损检测手段以及试验数据的积累，RSE-M历经多个版本。文中就1997版到2018版RSE-M规范中裂纹扩展方法进行了对比研究，并参考1997版和2010版对某电站反应堆压力容器筒体与接管焊缝位置深埋裂纹开展疲劳裂纹扩展分析计算，结果表明参考2010版RSE-M规范得到的结果更为精确，能够更为精确的对核电站设备的寿命进行评估，降低电厂运行成本。
分类： 核科学技术 >> 粒子加速器 提交时间： 2024-06-25
摘要： 随着核技术的不断发展，射线防护需求日益增加，对防护材料的优化研究愈发受到重视。针对常用的医疗诊断X射线管电压范围（＜150 kV），首先着重研究80、100、120 kV管电压下的X射线能谱特征，对其韧致辐射与特征辐射特点进行分析；其次利用Xcom程序进行不同元素的光子吸收截面计算和采用MCNP程序进行屏蔽性能模拟预测；最后对实验制备的柔性X射线防护功能材料进行屏蔽性能测试验证。理论预测表明，吸收截面随能量呈衰减趋势，但在低能区域存在明显的K吸收边效应，W、Bi和Gd元素对X射线均具有较高的质量吸收系数，而且K吸收边还具有优势互补特点，可同时实现对能谱中的韧致与特征辐射进行高效屏蔽。实验也验证了W+Bi基复合材料叠加Gd基材料屏蔽性能优异，在120 kV管电压下屏蔽率可达82.98%，质量衰减系数为6.47 cm2·g-1，线性衰减系数为10.12 cm-1，半值层为0.07 cm。通过本研究可深化对医用X射线屏蔽策略的认识，可对轻质、无铅X射线柔性防护材料研发提供指导。关键词 X射线；光电效应；质量衰减系数；辐射防护
分类： 核科学技术 >> 核科学与技术 提交时间： 2024-06-23
摘要： 自动卸压系统(ADS)作为非能动安全技术的典型代表，执行事故后加速反应堆一回路卸压，衔接高压、中压和低压安全注入系统，维持堆芯冷却的功能。为了研究自动卸压系统卸压阀启闭特性及其对反应堆各系统的影响，基于系统分析程序以中国先进压水堆为研究对象，将典型ADS触发事故作为始发事件，模拟了ADS前三级阀门不同开启速度及ADS第四级卸压阀关闭的工况，分析不同工况下各系统的响应情况。结果表明：ADS-1卸压阀需采用快开的方式；ADS-2和ADS-3卸压阀需采用慢开的方式；ADS-4对与小尺寸破口事故至关重要。通过ADS卸压阀启闭特性的模拟分析，为自动卸压系统的设计提供了参考，也为先进核电厂安全分析提供理论和数据支持。
分类： 物理学 >> 核物理学 提交时间： 2024-06-25
摘要： In conventional isochronous mass spectrometry (IMS) performed at a storage ring, the precision of mass measurement for short-lived nuclei depends on the precise determination of the revolution times (Ts) of stored ions. However, the resolution of T inevitably deteriorates due to the magnetic rigidity spread of the ions, resulting in limited mass resolving power. In this work, we measure the betatron tune Q (the number of betatron oscillations within a single revolution) of the ions, and construct a correlation between T and Q. From this correlation, the T are transformed corresponding to a fixed Q with higher resolution. Using the transformed Ts, we re-determine the masses of 63Ge, 65As, 67Se, and 71Kr, which agree well with the mass values measured by the newly developed IMS (Bρ-IMS). We also study the systematics of Coulomb displacement energies (CDEs) and find that the anomalous staggering in CDEs is removed using the new mass values. This method of T transformation is very useful for the conventional IMS equipped with a single time-of-flight detector.
分类： 物理学 >> 核物理学 提交时间： 2024-06-25
摘要： 传统的中子俘获反应截面测量主要通过测量靶核与中子反应后生成的所有伽马射线，再利用理论方法计算目标反应的比例进而得到中子俘获截面。这类方法对理论具有依赖性，并且多种反应道的综合效应会掩盖目标反应的结构特征，在理论预测的共振区得到的也是平滑的截面数据。利用能量分辨高的伽马探测器针对可以代表反应产额的特征伽马谱线进行测量，可以排除其它反应道的干扰，得到准确的中子俘获反应的截面。本文以91Zr(n,gamma) 92Zr反应为例，在中国散列白光中子源上利用此方法对反应截面进行了测量。在理论预测的共振区测到了明显的共振现象，在非共振区的结果与前人的数据在误差范围内保持一致。这表明此方法具有可靠性，并比传统方法具有更高的准确性，希望为其它反应截面的测量提供一种新的思路。
分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2024-06-25
摘要： X-ray detectors show potential applications in medical imaging, materials science, and nuclear energy. To achieve high detection efficiency and spatial resolution, many conventional semiconductor materials, such as amorphous selenium, cadmium telluride zinc, and perovskites have been utilized in direct conversion X-ray detectors. However, these semiconductor materials are susceptible to temperature-induced performance degradation, crystallization, delamination, uneven lattice growth, radiation damage, and high dark current. This study explores a new approach by coupling an FC40 electronic fluorinated liquid with a specialized high-resolution and high-readout-speed complementary metal-oxide-semiconductor (CMOS) pixel array, specifically the Topmetal $ textrm{ uppercase expandafter{ romannumeral2}}^{-}$ chip, to fabricate a direct conversion X-ray detector. The fluorinated liquid FC40 (molecular formula: $ ce{C^{21}F^{48}N^2}$) is an electronic medium that is minimally affected by temperature and displays no issues with uniform conductivity. It exhibits a low dark current and minimal radiation damage and enables customizable thickness in X-ray absorption. This addresses the limitations inherent in conventional semiconductor-based detectors. In this study, simple X-ray detector imaging tests were conducted, demonstrating the excellent coupling capability between FC40 electronic fluorinated liquid and CMOS chips by the X-ray detector. A spatial resolution of SI{4.0}{lp/mm} was measured using a striped line par card, and a relatively clear image of a cockroach was displayed in the digital radiography imaging results. Preliminary test results indicated the feasibility of fabricating an X-ray detector by combining FC40 electronic fluorinated liquid and CMOS chips. Owing to the absence of issues related to chip-material coupling, a high spatial resolution could be achieved by reducing the chip pixel size. This method presents a new avenue for studies on novel liquid-based direct conversion X-ray detectors.
分类： 核科学技术 >> 裂变堆工程技术 提交时间： 2024-06-26
摘要： Small modular reactors have received widespread attention owing to their inherent safety, low investment, and flexibility. Small pressurized water reactors (SPWRs) have become important candidates for SMRs owing to their high technological maturity. Since the Fukushima accident, research on accident-tolerant fuels (ATFs), which are more resistant to serious accidents than conventional fuels, has gradually increased. This study analyzes the neutronics and thermal hydraulics of an SPWR (ACPR50S) for different ATFs, BeO+UO2-SiC, BeO+UO2-FeCrAl, U3Si2-SiC, and U3Si2-FeCrAl, based on a PWR fuel-management code, the Bamboo-C deterministic code. In the steady state, the burnup calculations, reactivity coefficients, power and temperature distributions, and control-rod reactivity worth were studied. The transients of the control-rod ejection accident for the two control rods with the maximum and minimum reactivity worth were analyzed. The results showed that 5% B-10 enrichment in the wet annular burnable absorbers assembly can effectively reduce the initial reactivity and end-of-life reactivity penalty. The BeO+UO2 -SiC core exhibited superior neutronic characteristics in terms of burnup and negative temperature reactivity compared with the other three cases owing to the strong moderation ability of BeO+UO2 and low neutron absorption of SiC. However, the U3Si2 core had a marginally better power-flattening effect than BeO+UO2, and the differential worth of each control-rod group was similar between different ATFs. During the transient of a control-rod ejection, the changes in the fuel temperature, coolant temperature, and coolant density were similar. The maximum difference was less than 10◦C for the fuel temperature and 2 ◦ C for the coolant temperature.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We measure for the first time the outermost edges of the Milky Way (MW) halo in terms of the depletion and turnaround radii. The inner depletion radius, $r_\mathrm{id}$, identified at the location of maximum infall velocity, separates a growing halo from the draining environment, while the turnaround radius, $r_\mathrm{ta}$, marks the outermost edge of infalling material towards the halo, both of which are located well outside the virial radius. Using the motions of nearby dwarf galaxies within $3\mathrm{Mpc}$, we obtain a marginal detection of the infall zone around the MW with a maximum velocity of $v_\mathrm{inf, max}=-46_{-39}^{+24}\mathrm{km s^{-1}}$. This enables us to measure $r_\mathrm{id}=559\pm 107 \mathrm{kpc}$ and $r_\mathrm{ta}=839\pm 121 \mathrm{kpc}$. The measured depletion radius is about 1.5 times the MW virial radius ($R_\mathrm{200m}$) measured from internal dynamics. Compared with halos in the cosmological simulation Illustris TNG100, the factor 1.5 is consistent with that of halos with similar masses and dynamical environments to the MW but slightly smaller than typical values of Local Group analogs, potentially indicating the unique evolution history of the MW. These measurements of halo edges directly quantify the ongoing evolution of the MW outer halo and provide constraints on the current dynamical state of the MW that are independent from internal dynamics.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Solar System's orbital structure is thought to have been sculpted by an episode of dynamical instability among the giant planets. However, the instability trigger and timing have not been clearly established. Hydrodynamical modeling has shown that while the Sun's gaseous protoplanetary disk was present the giant planets migrated into a compact orbital configuration in a chain of resonances. Here we use dynamical simulations to show that the giant planets' instability was likely triggered by the dispersal of the gaseous disk. As the disk evaporated from the inside-out, its inner edge swept successively across and dynamically perturbed each planet's orbit in turn. The associated orbital shift caused a dynamical compression of the exterior part of the system, ultimately triggering instability. The final orbits of our simulated systems match those of the Solar System for a viable range of astrophysical parameters. The giant planet instability therefore took place as the gaseous disk dissipated, constrained by astronomical observations to be a few to ten million years after the birth of the Solar System. Terrestrial planet formation would not complete until after such an early giant planet instability; the growing terrestrial planets may even have been sculpted by its perturbations, explaining the small mass of Mars relative to Earth.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： A general covariant local field theory of the holographic dark energy model is presented. It turns out the low energy effective theory of the holographic dark energy is the massive gravity theory whose graviton has 3 polarisations, including one scalar mode and two tensor modes. The Compton wavelength is the size of the future event horizon of the universe. The UV-IR correspondence in the holographic dark energy model stems from the scalar graviton's strong coupling at the energy scale that marks the breaking down of the effective field theory.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Thermoelastic loss is one of the main energy dissipation mechanisms in resonant systems. A careful analysis of the thermoelastic loss is critical to design low-noise resonators for high-precision applications, such as gravitational-wave detectors. This paper presents an analytical solution to the thermoelastic loss in multimaterial coated finite substrates with realistic assumptions on the model structure and the elastic fields. The mechanism responsible for thermoelastic loss is taken as a function of material properties, operating temperature and frequency, and other design parameters. We calculate the thermoelastic loss for specific applications over a wide range of frequencies (1 Hz to 10 GHz) and temperatures (1 K to 300 K), and for a variety of substrate and coating materials. The result is relevant for gravitational-wave detectors and for experiments sensitive to mechanical dissipation.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Building accurate and predictive models of the underlying mechanisms of celestial motion has inspired fundamental developments in theoretical physics. Candidate theories seek to explain observations and predict future positions of planets, stars, and other astronomical bodies as faithfully as possible. We use a data-driven learning approach, extending that developed in Lu et al. ($2019$) and extended in Zhong et al. ($2020$), to a derive stable and accurate model for the motion of celestial bodies in our Solar System. Our model is based on a collective dynamics framework, and is learned from the NASA Jet Propulsion Lab's development ephemerides. By modeling the major astronomical bodies in the Solar System as pairwise interacting agents, our learned model generate extremely accurate dynamics that preserve not only intrinsic geometric properties of the orbits, but also highly sensitive features of the dynamics, such as perihelion precession rates. Our learned model can provide a unified explanation to the observation data, especially in terms of reproducing the perihelion precession of Mars, Mercury, and the Moon. Moreover, Our model outperforms Newton's Law of Universal Gravitation in all cases and performs similarly to, and exceeds on the Moon, the Einstein-Infeld-Hoffman equations derived from Einstein's theory of general relativity.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Presolar grains are microscopic dust grains that formed in the stellar winds or explosions of ancient stars that died before the formation of the solar system. The majority (~90% in number) of presolar silicon carbide (SiC) grains, including types mainstream (MS), Y, and Z, came from low-mass C-rich asymptotic giant branch (AGB) stars, which is supported by the ubiquitous presence of SiC dust observed in the circumstellar envelope of AGB stars and the signatures of slow neutron-capture process preserved in these grains. Here, we review the status of isotope studies of presolar AGB SiC grains with an emphasis on heavy-element isotopes and highlight the importance of presolar grain studies for nuclear astrophysics. We discuss the sensitives of different types of nuclei to varying AGB stellar parameters and how their abundances in presolar AGB SiC grains can be used to provide independent, detailed constraints on stellar parameters, including 13C formation, stellar temperature, and nuclear reaction rates.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Messenger Interface Monte-Carlo Mappings V (M^3) is a photoionization code adopting the fully self-consistent Monte-Carlo radiative transfer technique, which presents a major advance over previous photoionization models with simple geometries. M^3 is designed for modeling nebulae in arbitrary three-dimensional geometries. In this paper, we describe the Monte-Carlo radiative transfer technique and the microphysics implemented in M^3, including the photoionization, collisional ionization, the free-free and free-bound recombination, and two-photon radiation. We put M^3 through the Lexington/Meudon benchmarks to test the reliability of the new code. We apply M^3 to three HII region models with fiducial geometries, demonstrating that M^3 is capable of dealing with nebulae with complex geometries. M^3 is a promising tool for understanding emission-line behavior in the era of SDSS-V/LVM and JWST, which will provide high-quality data of spatially-resolved nearby HII regions and highly turbulent local and high-redshift HII regions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The exchange of a pair of neutrinos between two objects, seperated by a distance $r$, leads to a long-range effective potential proportional to $1/r_{}^5$, assuming massless neutrinos and four-fermion contact interactions. In this paper, we investigate how this known form of neutrino-mediated potentials might be altered if the distance $r$ is sufficiently short, corresponding to a sufficiently large momentum transfer which could invalidate the contact interactions. We consider two possible scenarios to open up the contact interactions by introducing a $t$-channel or an $s$-channel mediator. We derive a general formula that is valid to describe the potential in all regimes as long as the external particles remain non-relativistic. In both scenarios, the potential decreases as $1/r_{}^5$ in the long-range limit as expected. In the short-range limit, the $t$-channel potential exhibits the Coulomb-like behavior (i.e. proportional to $1/r$), while the $s$-channel potential exhibits $1/r_{}^4$ and $1/r_{}^2$ behaviors.
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