Nuclear Science and Techniques最新文献

The layout and characteristics of the hard X-ray spectroscopy beamline (BL11B) at the Shanghai synchrotron radiation facility are described herein. BL11B is a bending-magnet beamline dedicated to conventional and millisecond-scale quick-scanning X-ray absorption fine structures. It is equipped with a cylindrical collimating mirror, a double-crystal monochromator comprising Si(111) and Si(311), a channel-cut quick-scanning Si(111) monochromator, a toroidal focusing mirror, and a high harmonics rejection mirror. It can provide 5–30 keV of X-rays with a photon flux of ~ 5 × 10¹¹ photons/s and an energy resolution of ~ 1.31 × 10^–4 at 10 keV. The performance of the beamline can satisfy the demands of users in the fields of catalysis, materials, and environmental science. This paper presents an overview of the beamline design and a detailed description of its performance and capabilities.

The ultrahard X-ray multifunctional application beamline (BL12SW) is a phase-II beamline project at the Shanghai Synchrotron Radiation Facility. The primary X-ray techniques used at the beamline are high-energy X-ray diffraction and imaging using white and monochromatic light. The main scientific objectives of ultrahard X-ray beamlines are focused on two research areas. One is the study of the structural properties of Earth’s interior and new materials under extreme high-temperature and high-pressure conditions, and the other is the characterization of materials and processes in near-real service environments. The beamline utilizes a superconducting wiggler as the light source, with two diamond windows and SiC discs to filter out low-energy light (primarily below 30 keV) and a Cu filter assembly to control the thermal load entering the subsequent optical components. The beamline is equipped with dual monochromators. The first was a meridional bending Laue monochromator cooled by liquid nitrogen, achieving a full-energy coverage of 30–162 keV. The second was a sagittal bending Laue monochromator installed in an external building, providing a focused beam in the horizontal direction with an energy range of 60–120 keV. There were four experimental hutches: two large-volume press experimental hutches (LVP1 and LVP2) and two engineering material experimental hutches (ENG1 and ENG2). Each hutch was equipped with various near-real service conditions to satisfy different requirements. For example, LVP1 and LVP2 were equipped with a 200-ton DDIA press and a 2000-ton dual-mode (DDIA and Kawai) press, respectively. ENG1 and ENG2 provide in situ tensile, creep, and fatigue tests as well as high-temperature conditions. Since June 2023, the BL12SW has been in trial operation. It is expected to officially open to users by early 2024.

The heavy water-moderated molten salt reactor (HWMSR) is a newly proposed reactor concept, in which heavy water is adopted as the moderator and molten salt dissolved with fissile and fertile elements is used as the fuel. Issues arising from graphite in traditional molten salt reactors, including the positive temperature coefficient and management of highly radioactive spent graphite waste, can be addressed using the HWMSR. Until now, research on the HWMSR has been centered on the core design and nuclear fuel cycle to explore the viability of the HWMSR and its advantages in fuel utilization. However, the core safety of the HWMSR has not been extensively studied. Therefore, we evaluate typical accidents in a small modular HWMSR, including fuel salt inlet temperature overcooling and overheating accidents, fuel salt inlet flow rate decrease, heavy water inlet temperature overcooling accidents, and heavy water inlet mass flow rate decrease accidents, based on a neutronics and thermal–hydraulics coupled code. The results demonstrated that the core maintained safety during the investigated accidents.

Aluminum is the primary structural material in nuclear engineering, and its cross section induced by 14-MeV neutrons is of great significance. To address the issue of insufficient accuracy for the (^{27}hbox {Al})(n,2n)(^{26}hbox {Al}) reaction cross section, the activation method and accelerator mass spectrometry (AMS) technique were used to determine the (^{27}hbox {Al})(n,2n)(^{26}hbox {Al}) cross section, which could be used as a D-T plasma ion temperature monitor in fusion reactors. At the China Academy of Engineering Physics, neutron activation was performed using a K-400 neutron generator produced by the T(d,n)(^{4}hbox {He}) reaction. The (^{26}hbox {Al}/^{27}hbox {Al}) isotope ratios were measured using the newly installed GYIG 1 MV AMS at the Institute of Geochemistry, Chinese Academy of Sciences. The neutron flux was monitored by measuring the activity of (^{mathrm{92,m}}hbox {Nb}) produced by the (^{93}hbox {Nb})(n,2n)(^{mathrm{92,m}}hbox {Nb}) reaction. The measured results were compared with available data in the experimental nuclear reaction database, and the measured values showed a reasonable degree of consistency with partially available literature data. The newly acquired cross-sectional data at 12 neutron energy points through systematic measurements clarified the divergence, which has two different growth trends from the existing experimental values. The obtained results are also compared with the corresponding evaluated database, and the newly calculated excitation functions with TALYS(-)1.95 and EMPIRE(-)3.2 codes, the agreement with CENDL(-)3.2, TENDL-2021 and EMPIRE(-)3.2 results are generally acceptable. A substantial improvement in the knowledge of the (^{27}hbox {Al})(n,2n)(^{26}hbox {Al}) reaction excitation function was obtained in the present work, which will lay the foundation for the diagnosis of the fusion ion temperature, testing of the nuclear physics model, evaluation of nuclear data, etc.

The safety assessment of high-level radioactive waste repositories requires a high predictive accuracy for radionuclide diffusion and a comprehensive understanding of the diffusion mechanism. In this study, a through-diffusion method and six machine-learning methods were employed to investigate the diffusion of ({hbox {ReO}_{4}^{-}}), ({hbox {HCrO}_{4}^{-}}), and ({hbox {I}^{-}}) in saturated compacted bentonite under different salinities and compacted dry densities. The machine-learning models were trained using two datasets. One dataset contained six input features and 293 instances obtained from the diffusion database system of the Japan Atomic Energy Agency (JAEA-DDB) and 15 publications. The other dataset, comprising 15,000 pseudo-instances, was produced using a multi-porosity model and contained eight input features. The results indicate that the former dataset yielded a higher predictive accuracy than the latter. Light gradient-boosting exhibited a higher prediction accuracy ((R^2 = 0.92)) and lower error ((MSE = 0.01)) than the other machine-learning algorithms. In addition, Shapley Additive Explanations, Feature Importance, and Partial Dependence Plot analysis results indicate that the rock capacity factor and compacted dry density had the two most significant effects on predicting the effective diffusion coefficient, thereby offering valuable insights.

Neutron-skin thickness is a key parameter for a neutron-rich nucleus; however, it is difficult to determine. In the framework of the Lanzhou Quantum Molecular Dynamics (LQMD) model, a possible probe for the neutron-skin thickness ((delta _text {np})) of neutron-rich (^{48})Ca was studied in the 140A MeV (^{48})Ca + (^{9})Be projectile fragmentation reaction based on the parallel momentum distribution ((p_parallel )) of the residual fragments. A Fermi-type density distribution was employed to initiate the neutron density distributions in the LQMD simulations. A combined Gaussian function with different width parameters for the left side ((Gamma _text {L})) and the right side ((Gamma _text {R})) in the distribution was used to describe the (p_parallel ) of the residual fragments. Taking neutron-rich sulfur isotopes as examples, (Gamma _text {L}) shows a sensitive correlation with (delta _text {np}) of (^{48})Ca, and is proposed as a probe for determining the neutron skin thickness of the projectile nucleus.

The utilization of a proton beam from the China Spallation Neutron Source (CSNS) for producing medical radioisotopes is appealing owing to its high current intensity and high energy. The medical isotope production based on the proton beam at the CSNS is significant for the development of future radiopharmaceuticals, particularly for the α-emitting radiopharmaceuticals. The production yield and activity of typical medical isotopes were estimated using the FLUKA simulation. The results indicate that the 300-MeV proton beam with a power of 100 kW at CSNS-II is highly suitable for proof-of-principle studies of most medical radioisotopes. In particular, this proton beam offers tremendous advantages for the large-scale production of alpha radioisotopes, such as ²²⁵Ac, whose theoretical production yield can reach approximately 57 Ci/week. Based on these results, we provide perspectives on the use of CSNS proton beams to produce radioisotopes for medical applications.

The study of nuclide production and its properties in the ({N}=126) neutron-rich region is prevalent in nuclear physics and astrophysics research. The upcoming High-energy FRagment Separator (HFRS) at the High-Intensity heavy-ion Accelerator Facility (HIAF), an in-flight separator at relativistic energies, is characterized by high beam intensity, large ion-optical acceptance, high magnetic rigidity, and high momentum resolution power. This provides an opportunity to study the production and properties of neutron-rich nuclei around ({N}=126). In this paper, an experimental scheme is proposed to produce neutron-rich nuclei around ({N}=126) and simultaneously measure their mass and lifetime based on the HFRS separator; the feasibility of this scheme is evaluated through simulations. The results show that under the high-resolution optical mode, many new neutron-rich nuclei approaching the r-process abundance peak around ({A}=195) can be produced for the first time, and many nuclei with unknown masses and lifetimes can be produced with high statistics. Using the time-of-flight corrected by the measured dispersive position and energy loss information, the cocktails produced from ({}^{208})Pb fragmentation can be unambiguously identified. Moreover, the masses of some neutron-rich nuclei near ({N}=126) can be measured with high precision using the time-of-flight magnetic rigidity technique. This indicates that the HIAF-HFRS facility has the potential for the production and property research of neutron-rich nuclei around ({N}=126), which is of great significance for expanding the chart of nuclides, developing nuclear theories, and understanding the origin of heavy elements in the universe.

Small-break superposed station blackout (SBO) accidents are the basic design accidents of nuclear power plants. Under the condition of a small break in the cold leg, SBO further increases the severity of the accident, and the steam bypass discharging system (GCT) in the second circuit can play an important role in guaranteeing core safety. To explore the influence of the GCT on the thermal–hydraulic characteristics of the primary circuit, RELAP5 software was used to establish a numerical model based on a typical pressurized water reactor nuclear power plant. Five different small breaks in the cold-leg superposed SBO were selected, and the impact of the GCT operation on the transient response characteristics of the primary and secondary circuit systems was analyzed. The results show that the GCT plays an indispensable role in core heat removal during an accident; otherwise, core safety cannot be guaranteed. The GCT was used in conjunction with the primary safety injection system during the placement process. When the break diameter was greater than a certain critical value, the core cooling rate could not be guaranteed to be less than 100 K/h; however, the core remained in a safe state.

Based on the dinuclear system model, the calculated evaporation residue cross sections matched well with the current experimental results. The synthesis of superheavy elements (Z=121) was systematically studied through combinations of stable projectiles with (Z = 21)–30 and targets with half-lives exceeding 50 d. The influence of mass asymmetry and isotopic dependence on the projectile and target nuclei was investigated in detail. The reactions (^{254})Es ((^{46})Ti, 3n) (^{297}121) and (^{252})Es ((^{46})Ti, 3n) (^{295}121) were found to be experimentally feasible for synthesizing superheavy element (Z = 121), with maximal evaporation residue cross sections of 6.619 and 4.123 fb at 219.9 and 223.9 MeV, respectively.