Search Results (88)

Early-age strength development and carbon emissions represent specific operational constraints in underground cemented tailings backfill (CTB) operations. A pH and ionic pre-conditioning-assisted CO₂ mineralization process was evaluated for carbonate-rich cemented tailings backfill designed to improve early UCS while retaining measurable CO₂ uptake through systematic process control and optimization. Skarn-type tailings (CaO 16.74 wt%, total carbonates 34.7 wt%) were subjected to screening under nominal pH and ionic pre-conditioning treatments (4.0–11.5), CO₂ pressure (0–0.5 MPa), cement-to-tailings ratio (1:3–1:12), and slurry concentration (66–78%). Strength evolution (1–28 d), mineralization products were characterized using TGA as the primary CO₂-uptake method, with XRD used for semi-quantitative phase-trend assessment, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) with selected-area electron diffraction (SAED), X-ray computed tomography (CT), and nuclear magnetic resonance (NMR). Under optimal conditions (pH 8.5, 0.3 MPa CO₂ pressure, 48 h mineralization, 72–74% solids), mineralized specimens achieved 2-day uniaxial compressive strength equivalent to 1.47-times the 3-day control strength (p < 0.01), with peak net CO₂ sequestration of 37.1 g/kg. EBSD analysis of 347 grain boundaries and TEM-SAED examination of multiple foil sections supported the occurrence of syntaxial calcite overgrowth on primary carbonate debris as a major interfacial transition zone strengthening mechanism. Interconnected pore cluster volume decreased by 70.6%; Zn²⁺ and Pb²⁺ leaching decreased by 67.2% and 71.8%, respectively. A shrinking-core kinetics-Ryshkewitch model with pH-dependent correction functions predicted 3-day strength with acceptable accuracy for TW-A and TW-B, whereas TW-C showed a −27.3% deviation, identifying acidic and sulfate-rich wastewater as a boundary condition outside the reliable model domain. Field coring at −500 m depth provided pilot-scale evidence that a 23 mm mineralized shell was consistent with localized reduction of shallow exposed-face instability risk during the early free-standing period. Overall, the pH and ionic pre-conditioning-assisted CO₂ mineralization process is proposed as a laboratory-supported and field-informed screening framework for simultaneous early-strength enhancement and partial carbon sequestration in carbonate-rich cemented tailings systems. The resulting models and parameter guidance should be interpreted as preliminary design tools requiring further factorial optimization and long-term field validation before full site-specific deployment. Full article

This review traces how our understanding of low- and intermediate-mass stars (hereafter LMS and IMS, respectively) evolved in time, in parallel with our knowledge of slow neutron-capture phenomena (the s-process). I shall focus in particular on the main component of this nucleosynthesis phenomenon, occurring in the above-mentioned stars close to the end of their lifetimes. They start ascending the Asymptotic Giant Branch (AGB), where both H- and He-shells exist, burning alternatively during the phases most relevant to our discussion: the so-called thermal pulses (hence, the name of TP-AGB stages for the final evolutionary period of these stars). I shall outline how such final stages were discovered to be a crucial source for neutron captures. Finally, I will briefly discuss what observational constraints and nuclear measurements have taught us about the status of our theoretical models in this field of nuclear and stellar physics. Full article

In the theoretical understanding of nuclear structure, different models play a crucial role due to the complications of the quantum mechanical many-body problem. One of the fundamental models is the cluster model, based on the molecular picture. We investigate here the possible phases of nuclear clusterization in a quantitative way. In particular, the semimicroscopic algebraic cluster model is applied, in which the phases are defined by the dynamical symmetry limits. We construct detailed spectra corresponding to the shell-like, rigid-molecule-like and weak-coupled phases, and compare them. Special attention is focused on the role of the Pauli principle. The spectra of the limiting cases show dramatic differences, and only one of them harmonizes with this basic natural law. The experimentally observed ¹²C + $\alpha$ spectrum is considered for the discussion. Full article

A realistic description of halo nuclei, characterized by low-lying breakup thresholds, requires a proper treatment of continuum effects. We have developed an ab initio approach, the No-Core Shell Model with Continuum (NCSMC), capable of describing both bound and unbound states in light nuclei in a unified way. With chiral two- and three-nucleon interactions as the only input, we can predict the structure and dynamics of halo and other light nuclei and, by comparing to available experimental data, test the quality of chiral nuclear forces. We review NCSMC calculations of weakly bound states and resonances of the exotic halo nuclei ⁶He, ⁸B, ¹¹Be, and ¹⁵C. For the latter, we discuss its production in the capture reaction ¹⁴C(n,$\gamma$)¹⁵C. We highlight the challenges of a description of ⁶He as a Borromean n-n-⁴He system. Finally, we present our calculations of excited states in ¹⁰Be exhibiting a one-neutron halo structure and a large scale No-Core Shell Model investigation of ¹¹Li as a precursor of a full n-n-⁹Li NCSMC study. Full article

After the global cessation of nuclear tests, there is a lack of experimental methods and conditions for evaluating the residual nuclear radiation protection performance of vehicles. To address this, this paper proposes a vehicle residual nuclear radiation protection performance evaluation method based on an equivalent model. Using a certain type of vehicle as the research sample, the theoretical model for calculating the internal dose rate of the vehicle is first applied to determine the equivalent surface source radius of an infinitely large residual nuclear radiation field. A Monte Carlo simulation model of the vehicle is then established to obtain the residual nuclear radiation protection factors for each surface of the vehicle’s outer shell, which forms the basis for designing an equivalent model for residual nuclear radiation protection performance testing. Finally, a point radiation source is used to simulate the residual nuclear radiation field and conduct experimental testing on the equivalent model, in order to obtain the residual nuclear radiation protection factors. The experimental results show that this method can measure the residual nuclear radiation protection factor of vehicles in a laboratory environment, and provide technical support for the evaluation of the residual nuclear radiation protection performance of any type of vehicle. Full article

The proxy-SU(3) approximation to the shell model, which restores the SU(3) symmetry of the 3-dimensional harmonic oscillator beyond the $sd$ shell, predicts the collective deformation variables $\beta$ and $\gamma$ of even–even atomic nuclei in a parameter-free way based on the most symmetric irreducible representation (irrep) of SU(3) allowed by the Pauli principle and the short-range nature of the nucleon–nucleon interaction, which in group theoretical language is the highest-weight (hw) irrep. In the few cases in which the hw irrep turns out to be completely symmetric, thus being able to accommodate only the ground-state band, the next hw (nhw) irrep becomes indispensable. In the present article, complete tables of the hw and nhw irreps are given for all atomic nuclei ranging from $Z=28$, $N=28$ to $Z=82$, $N=126$, along with the corresponding parameter-free predictions for the deformation variables $\beta$ and $\gamma$. A few examples using the tabulated results to provide microscopic insight for specific effects in various regions of the nuclear chart are also given. Full article

Recent measurements performed by the LUNA(Laboratory for Underground Nuclear Astrophysics) collaboration between 2019 and 2024 have provided the most precise direct determinations to date of several key reaction rates in the NeNa cycle, specifically the ²⁰Ne(p,γ)²¹Na and the ²²Ne(p,γ)²³Na reactions, as well as its bridge to the MgAl cycle, i.e., the ²³Na(p,γ)²⁴Mg reaction. Despite their improved accuracy, these updated rates are not yet consistently incorporated into widely used nuclear reaction network compilations. We explore the astrophysical impact of adopting the new LUNA rates by performing nucleosynthesis calculations, focusing on the case of ²⁶Al nucleosynthesis and considering four different stellar environments: low-mass AGB stars, massive stars, very massive stars and core-collapse supernovae. Our results show substantial sensitivity of ²⁶Al production to the revised rates. In the AGB model, the surface ²⁶Al abundance decreases by up to 30%, while in the massive star model, the ²⁶Al abundance in the C-burning shell increases by 51%. In contrast, the impact on both the ²⁶Al yields ejected by very massive stars and on the explosive nucleosynthesis in the supernova model is negligible. These findings have direct implications for galactic chemical evolution, the global budget of ²⁶Al, and theoretical predictions of the ⁶⁰Fe/²⁶Al ratio, which will be critically tested by forthcoming γ-ray observations from missions such as the Compton Spectrometer and Imager (COSI). Full article

To improve the safety of road transportation of Spent Nuclear Fuel (SNF), this paper proposes a novel approach for risk identification and chaotic synchronous control in SNF road transportation systems. Firstly, a dynamic risk evolution model for the road transportation of SNF is developed by analyzing the nonlinear interactions among vehicles, environmental conditions, and human factors using complex network analysis and nonlinear dynamics. Secondly, an enhanced K-shell decomposition method is applied to identify key risk nodes and assess the relative importance of different risk factors, providing a basis for targeted risk control. Finally, a chaotic synchronization control strategy based on Lyapunov stability is proposed to suppress risk divergence and restore system stability. Three targeted control schemes are evaluated by varying the control gain coefficients across the ‘Vehicle–Environment–Human’ dimensions. Simulation results indicate that the strategy prioritizing environmental and human risk control yields the fastest convergence, significantly outperforming vehicle-centric approaches. The results show that prioritizing both environmental and human-factor control is most effective for suppressing chaotic divergence. This provides a solid quantitative basis for the strategic shift from passive defense to active environmental warning, thereby significantly optimizing the dynamic risk management of the SNF transportation system. Full article

Despite several efforts to investigate the accretion disk and torus, near-simultaneous broadband studies of the nuclear regions of radio-quiet AGNs remain lacking. NGC 4151, one of the closest and brightest Seyfert galaxies, provides an excellent laboratory for probing the circum-nuclear regions of AGNs. A detailed, near-simultaneous broadband spectral study of NGC 4151 is carried out during one of its historic minimum activity states, using archival data from the Ultraviolet (UV) to the Infrared (IR) regions. We used the radiative transfer code SKIRT to model the source and to constrain the properties of the torus. We found that the observed broadband spectral energy distribution is best explained by a two-torus geometry with a polar conical shell structure. Full article

The accurate determination of nuclear level density (NLD) is essential for a wide range of applications in nuclear science, including reactor design, nuclear astrophysics, and nuclear data evaluation. Traditional phenomenological models often face challenges in capturing key physical effects, such as collective excitations and shell structure, particularly in heavy and transitional nuclei, where the level density grows exponentially. Machine learning (ML) approaches have shown promise in improving predictive accuracy but are often limited by their purely data-driven nature, leading to challenges in interpretability and performance in regions with sparse experimental data. In this study, we propose a Physics-Informed Neural Network (PINN) framework, enhanced through multi-task learning (MTL), to address these limitations. The proposed model simultaneously predicts cumulative levels and mean resonance spacings by integrating experimental data with theoretical constraints, ensuring consistency with nuclear structure theory and robustness in extrapolating beyond the training data. Validation against both cumulative and yrast levels highlights the model’s ability to accurately capture rotational and vibrational excitations across a wide range of isotopes. Comparative evaluations demonstrate that the PINN model significantly outperforms traditional phenomenological models and purely data-driven approaches, offering a comprehensive and interpretable framework for advancing nuclear level density predictions and supporting practical applications in nuclear energy and astrophysics. Full article

Shell-and-tube heat exchangers serve as critical energy conversion equipment in marine nuclear power systems, where their thermal performance directly determines operational safety and reliability. This study proposes a kind of shark-skin bionic structure tube to enhance compactness and power density. Key findings are: (1) The microstructures induce intensive secondary flows and helical vortices, substantially disrupting the thermal boundary layer and amplifying near-wall perturbations. Maximum enhancement reaches 56.7% in heat transfer coefficient and 33.1–58.3% in heat exchange capacity, with PEC consistently maintained at 1.25–1.30. (2) Fouling deposition significantly degrades heat transfer performance. The fouling layer is simplified using a homogenized model, where the thickness reaches 0.20 mm, the heat transfer capacity of the shark-skin bionic structure tube becomes essentially equivalent to that of a smooth tube, and the heat transfer enhancement effect is largely lost. (3) This study reveals the coupling mechanism between enhanced heat exchange and fouling deposition. On a macroscopic scale, the design and manufacturing of a shark-skin bionic structure tube are achieved, laying a theoretical and design foundation for the development of a new generation of marine heat exchangers with high anti-fouling performance. Full article

Steam flow-induced vibration (FIV) of cooling tubes poses critical failure risks in nuclear power plant condensers. However, accurate FIV prediction remains challenging due to the complex three-dimensional flow structures in full-scale condensers, which are often oversimplified in existing models. To address this gap, this study develops a novel full-scale Computational Fluid Dynamics (CFD) model that uniquely integrates the low-pressure exhaust cylinder, condenser throat, and tube bundles. This approach enables a comprehensive evaluation of shell-side flow characteristics and FIV phenomena under both Valve Wide Open (VWO) and partial-load conditions (with either Modules A/C or B/D active). The results quantitatively identify peak FIV risk coefficients in specific zones—particularly at branch-shaped channel inlets and certain tube bundle corners where steam impingement is most intense—with values reaching 0.7 under VWO, 0.67 with Modules A/C active, and 0.74 with Modules B/D active. Notably, the peak FIV risk under B/D active condition is approximately 10.4% higher than under A/C active condition, indicating that partial-load operation with Modules B/D active presents the highest FIV risk among investigated scenarios. These findings provide novel insights into FIV mechanisms and establish a critical theoretical foundation for optimizing condenser design and enhancing operational safety protocols. Full article

Helical coiled tube (HCT) heat exchangers (HXs) are used in the nuclear industry, particularly in the residual heat removal systems of nuclear power plants (NPPs) and steam generators for small modular reactors. In this study, a single-phase CFD model was developed to investigate non-uniform circumferential distributions in the local wall heat transfer characteristics of a vertical HCT to obtain localized information critical for the safety of NPPs. In a comparison, the predicted circumferential heat transfer characteristics agreed well with the measured data. Governed by centrifugal/gravitational forces, these non-uniform distributions are clearly visible in the results, explaining the test data. We performed additional simulations of the conjugated heat transfer from the hot fluid of the shell side to the cold fluid of the tube side, confirming that the inhomogeneity of circumferential distributions in HCTs is due to the assumption of a constant heat flux boundary condition. Full article

Bis(2-ethylhexyl) phosphate (P204) is widely used in extraction processes in the nuclear and rare earth industries. However, its high solubility in water results in high levels of total organic carbon and phosphorus in aqueous environments, and may also lead to radioactive contamination when it is used to combine with radionuclides. In this paper, we characterized a coconut shell activated carbon (CSAC) and a coal-based activated carbon (CBAC) for the adsorption of P204 and then evaluated their adsorption performance through batch and column experiments. The results found that, except for the main carbon matrix, CSAC and CBAC carried rich oxygen-containing functional groups and a small amount of inorganic substances. Both adsorbents had porous structures with pore diameters less than 4 nm. CSAC and CBAC showed good removal performance for P204 under low pH conditions, with removal efficiencies significantly higher than those of commonly used adsorption resins (XAD-4 and IRA900). The adsorption kinetics of P204 conformed to the pseudo-second-order kinetic model, and the adsorption isotherms conformed to the Langmuir model, indicating a monolayer chemical reaction mechanism. Both adsorbents exhibited strong anti-interference capabilities; their adsorption performance for P204 did not change greatly with the ambient temperature or the concentrations of common interfering ions. Column experiments demonstrated that CSAC could effectively fix dissolved P204 with a removal efficiency exceeding 90%. The fixed P204 could be desorbed with acetone. The findings provide an effective method for the recovery of P204 and the regeneration of spent activated carbon, which shows promise for practical applications in the future. Full article

Nuclear density functional theory (DFT) is able to reproduce the saturation properties of nuclear matter, as well as properties of finite nuclei. Consequently, the DFT calculations are applicable to nuclei across a wide range of masses on the nuclear chart. The Gogny-type density functional, which is equivalent to the mean-field calculations with finite-range density-dependent effective interactions, is a successful example. In contrast, the shell model (configuration interaction) calculation is a powerful tool to describe nuclear structure, especially spectroscopic properties. The shell model is able to take into account correlations beyond mean-field in a truncated model space. In this work, we report an investigation on $sd$-shell nuclei and Ca isotopes using a hybrid approach of the shell model and Gogny-type DFT. Full article