JI Xiaoyu1, CHEN Nanyu1, CHEN Mufeng2, ZHANG Shuaijun1, HOU Gangling1, CAI Xuesong1
Small modular reactor (SMR) refers to a new generation of reactors with a unit power output of less than 300 MW. These reactors utilize innovative technologies for modular design and rapid on-site assembly. The assurance of structural seismic safety becomes a crucial prerequisite for the commercial application of SMR. Traditional seismic resistance theories enhance the strength and stiffness of the structure itself to resist earthquake-induced damage. In contrast, seismic isolation theory employs isolation devices to absorb and dissipate seismic energy, thereby reducing structural deformation and damage and better protecting the internal equipment and piping. To verify the effectiveness of different seismic isolation strategies for SMR under safe shutdown earthquake (SSE) conditions, this study uses the finite element method (FEM) to conduct three-dimensional modeling of the SMR containment structure. Modal analysis is performed to extract the first four modes of vibration and natural frequencies of the structure. Lead rubber bearings (LRB) and friction pendulum systems (FPS) were utilized for the seismic isolation design of the SMR structure, and finite element models of the isolated SMR structures were established. Subsequently, seismic response analyses of the SMR containment structure were conducted. By studying the structural response under SSE and double SSE conditions, the applicability of different seismic isolation strategies for SMR was evaluated. The results show that the natural vibration periods of the SMR containment structure are extended to 2.46 s and 2.53 s based on the LRB and FPS isolation schemes. Under the SSE, the acceleration reduction rates at the peak of the LRB and FPS isolated structures are 74.6% and 63.2%, and the peak horizontal deformation of the containment structure can be reduced by 75.1% and 68.4%. Under the double SSE, the maximum tensile stress peaks of the containment structure can be reduced by 33.5% and 35.8% with the LRB and FPS isolation strategies. In non-isolated structures, tensile damage is mostly concentrated at the connections between the bottom and the side walls. After the damping effect of the isolation devices, no tensile damage was observed in the isolated containment structures, indicating that the LRB and FPS isolation schemes can effectively reduce the seismic response and structural damage of SMR nuclear power plants. This study emphasizes the importance of adopting effective seismic isolation strategies to ensure the seismic resilience of SMR. The LRB and FPS systems, by extending the natural vibration period and reducing the seismic response, offer promising solutions for the seismic protection of SMR. These results provide valuable insights for the design and implementation of seismic isolation in nuclear reactor structures, promoting the safe and reliable operation of SMR in seismically active regions.
The SnLi alloy has good prospects to be used as a material of intra-chamber elements of fusion facilities, as it has a number of advantages over pure lithium. The results of a series of experiments on deuterium adsorption/desorption by a Sn73Li27 alloy sample are presented. To prepare an alloy sample with the required tin and lithium content, a technique was developed and a special experimental device was constructed. An ampoule device was manufactured to conduct a series of experiments to study sample saturation with deuterium and desorption of deuterium and deuterium-containing molecules from it. Saturation was carried out at alloy temperatures of 650, 600, 550, 500 and 450 °C. TDS experiments were carried out at 20 °C/min. The possible mechanism of deuterium dissolution and release from the tin-lithium alloy was considered and temperature dependences of the effective deuterium solubility constant KS in the tin-lithium alloy were calculated within the framework of the proposed mechanism. The temperature dependence of the Sieverts’ constant for the test sample in the temperature range of 500–650 °C was determined as KST=3.6·106∙exp-32400(J)RT∙Pa12.
China is accelerating the development of sodium-cooled fast reactor technology. For nuclear reactors, whether it is a pressurized water reactor or a fast reactor, core flow distribution is a key concern, which directly determines whether the reactor can operate safely and reliably. Sodium-cooled fast reactor core adopts a three-stage flow distribution method consisting of diagrid, distribution headers and assemblies. Distribution headers are installed on diagrid, and various types of assemblies are installed on distribution headers. Pressure drop of the core is composed of distribution header pressure drop and assembly pressure drop. The distribution header pressure drop itself affects the flow distribution of the assemblies, thereby affecting the safety of the core. Therefore, it is of great significance to study the impact of distribution header pressure drop on the flow distribution of assemblies for the sodium-cooled fast reactors. In order to reduce the flow distribution deviation of assemblies caused by the distribution header pressure drop, it is necessary to carry out a reasonable assembly pressure drop design. Based on the mechanism of flow distribution deviation of assemblies caused by distribution header pressure drop, a theoretical calculation model was proposed, and an optimized design of assembly pressure drop was carried out for the China Experimental Fast Reactor (CEFR) core. Based on the actual layout of CEFR core, the maximum deviation of flow distribution of fuel assemblies was obtained, and the optimization direction of nominal assembly pressure drop was determined, indicating that optimization design of nominal assembly pressure drop should be carried out for the first five rings. After adjusting the nominal pressure drop of the first five rings of assemblies from 250 kPa (the original nominal pressure drop) to 249 kPa, 248.5 kPa, and 248 kPa, respectively, the maximum deviation of flow distribution of fuel assemblies firstly decreases from −0.99% to −0.95%, and then increases to −1.02% and −1.08%, which indicates that nominal assembly pressure drop should be elaborately determined to obtain a minimum flow distribution deviation of fuel assemblies. In conclusion, when conducting core thermal hydraulic design for sodium-cooled fast reactors, it is necessary to analyze the optimization direction of nominal assembly pressure drop based on actual core layout, and sensitivity analysis should be conducted to finally determine the nominal assembly pressure drop to reduce the impact of distribution header pressure drop on flow distribution of assemblies to the lowest extent.
UEDGE simulations with density scans for various input power, transport coefficients and outer poloidal leg length are performed to study the conditions for the existence of a bifurcation-like drop of Te at the outer strike point, commonly referred to as a detachment cliff, when transitioning to a detached plasma from an attached plasma in the outer divertor as the upstream density increases (McLean et al., 2015). The simulation results show that a detachment cliff tends to occur with a higher power input regardless of diffusivities and leg length. Further analysis of change of plasma profiles at a cliff indicate that, in addition to the sharp reduction of the E×B drift fluxes in the outer divertor studied in Jaervinen et al., (2018), the substantial change of the Mach number in the outer divertor and the decrease of the outer mid-plane Te due to the radiation front moving across the separatrix into the confinement region above the X-point consistently occur for all UEDGE density scans that have a detachment cliff. UEDGE time-dependent simulation of the evolution of a detachment cliff shows that the rapid increase of radiation above the X-point occurs in a time scale of ∼0.3–0.5ms, which could possibly be the trigger for the formation of a detachment cliff, quicker than the Mach number change in a time scale of ∼1ms and the drop of Te in a time scale of ∼2–3ms in the outer divertor.
Rajnikant V. Umretiya, Atharva Chikhalikar, Barret Elward
et al.
The APMT FeCrAl alloy is a cladding candidate for the accident-tolerant fuel (ATF) systems in light water reactors (LWRs) due to its ability to form a protective Al2O3 film on the surface at temperatures greater than 1000 °C. In order to understand the alumina evolution at the early stages of high-temperature exposure in short periods, an APMT tube specimen was heated up rapidly to melting temperature in a flowing 100 % water and steam environment. Using transmission electron microscopy (TEM), the presence of a ∼ 90 nm thick oxide layer was confirmed. The surface chemistry of APMT was characterized layer by layer using X-ray photoelectron spectroscopy (XPS) depth profiling. The results indicated a thin layer composed of oxides and hydroxides of Al, Cr, and Fe with varying proportions at different depths in the oxide layer. The microstructure of the oxide layer was characterized using X-ray diffraction and showed the presence of α-Al2O3 and γ-Fe2O3/Fe3O4 after ramp heating. The results depict the ability of the APMT FeCrAl alloy to form a protective oxide layer in less than a second on exposure to steam under high ramp rates.
Atomic nuclei are self-organized, many-body quantum systems bound by strong nuclear forces within femtometer-scale space. These complex systems manifest a variety of shapes, traditionally explored using non-invasive spectroscopic techniques at low energies. However, at these energies, their instantaneous shapes are obscured by long-timescale quantum fluctuations, making direct observation challenging. Here we introduce the ``collective flow assisted nuclear shape imaging'' method, which images the nuclear global shape by colliding them at ultrarelativistic speeds and analyzing the collective response of outgoing debris. This technique captures a collision-specific snapshot of the spatial matter distribution within the nuclei, which, through the hydrodynamic expansion, imprints patterns on the particle momentum distribution observed in detectors. We benchmark this method in collisions of ground state Uranium-238 nuclei, known for their elongated, axial-symmetric shape. Our findings show a large deformation with a slight deviation from axial symmetry in the nuclear ground state, aligning broadly with previous low-energy experiments. This approach offers a new method for imaging nuclear shapes, enhances our understanding of the initial conditions in high-energy collisions and addresses the important issue of nuclear structure evolution across energy scales.
First-principles calculations related to defect complexes formed from a monovacancy and multiple interstitial impurity atoms (hydrogen, carbon, nitrogen, and oxygen atoms) in tungsten were performed. The most stable atomic configurations, the electron density distributions, the binding energies of impurity atoms, and the positron lifetimes of each defect complex were calculated. In calculating positron lifetimes, slight deviations in the initial positions of the H atoms were found to be enhanced by positron localization, which affected the positron lifetimes of the vacancy-hydrogen complexes. In addition, the positron lifetimes of vacancy-nitrogen and vacancy-oxygen complexes were found to become longer in some cases with increasing numbers of impurity atoms that bound to the vacancy. Such longer positron lifetimes with increasing numbers of binding impurity atoms were attributed to the fact that the impurity atoms bind slightly further away from the vacancy, expanding the tungsten lattice.
Background: Recently, a new direction in the field of electric propulsion has emerged – the multidirectional plasma thrusters. These thrusters are capable of producing propulsive forces in multiple directions. The thrusters are proposed to be used for orbit maintenance and alterations, formation flights, and interplanetary flights of space artificial objects ranging in size from CubeSats to fusion-powered interplanetary spacecraft. In this paper, the results of numerical simulation of the iodine propellant supply system for the multidirectional plasma thruster are presented. Methods: The geometry and temperature parameters of propellant supply system various elements are varied to determine the stable modes of iodine propellant ejection into the gas discharge chamber of the thruster. The temperatures of the thermo throttle and filter are found to ensure iodine mass flow rate in the range of 0.1 to 1.5 mg/s. The thermo throttle and filter temperatures are altered in the range of 65 to 200 °C and 65 to 100 °C, correspondingly. Results: The mass flow rate is critically dependent on the filter temperature and iodine saturated vapor pressure, as well as the filter and throttle geometries. The required values of iodine flow rate have been achieved by using the throttle with a diameter of 0.5 mm and a length of 60 mm and a filter with 56 holes, each hole diameter is 0.2 mm, and temperature from 90 C to 200 C. Conclusions: According to the data obtained, the iodine storage and supply system is preferably equipped with a thermos throttle, which provides precise control of the flow rate, as well as reduces sharp jumps of the flow rate when the temperature of the filter changes. Preferred filter geometry: 56 holes, each hole 0.2 mm in diameter.
Nuclear engineering. Atomic power, Medical physics. Medical radiology. Nuclear medicine
This paper describes an hp-angular adaptivity algorithm in the discrete ordinates method for Boltzmann transport applications with strong angular effects. This adaptivity uses discontinuous finite element quadrature sets with different degrees, which updates both angular mesh and the degree of the underlying discontinuous finite element basis functions, allowing different angular local refinement to be applied in space. The regular and goal-based error metrics are considered in this algorithm to locate some regions to be refined. A mapping algorithm derived by moment conservation is developed to pass the angular solution between spatial regions with different quadrature sets. The proposed method is applied to some test problems that demonstrate the ability of this hp-angular adaptivity to resolve complex fluxes with relatively few angular unknowns. Results illustrate that a reduction to approximately 1/50 in quadrature ordinates for a given accuracy compared with uniform angular discretization. This method therefore offers a highly efficient angular adaptivity for investigating difficult particle transport problems.
In past years the Paul Scherrer Institute (PSI, Switzerland) and the Karlsruhe Institue of Technology (KIT, Germany)) collaborated to develop a model to account for the active role of nitrogen in the air oxidation of a Zircalloy cladding. The “PSI-KIT Nitriding Model for Zirconium based Fuel Cladding” model was implemented at PSI into PSI-MELCOR 1.8.6.In order to make a preliminary evaluation of the effect of the new model on the evolution of full-scale spent fuel pool accidents, one spent fuel pool event was analyzed using the PSI research version of PSI-MELCOR 1.8.6, which includes the nitriding model. To adapt an existing input deck for the calculations, a sensitivity study was conducted to find an optimal nodalization for the analyses. The nitriding model results were compared to those calculated with the MELCOR 1.8.6-PSI without the new nitriding model.The results demonstrate the effect of the nitriding reactions in spent fuel pool accident progression. Moreover, they confirm the impact of ZrN formation during cladding oxidation in air when the oxidation reactions lead to oxygen starvation inside the fuel assemblies. The nitriding reaction led to higher chemical heat generation during the accident and to an earlier failure of the cladding than when the effect of nitrogen reactions was not considered.It should be noted that the nitriding model, as implemented in the PSI version of MELCOR 1.8.6 has not yet been conclusively validated. Thereby the results presented in this paper should be treated as a preliminary demonstration of the capabilities of the model.
AbstractSmall modular reactors (SMRs) could be key to providing developing regions with clean and affordable (and cost-effective) electricity. Deployment of SMRs requires a transparent and balanced legal framework that will define the specifics and boundaries of shared responsibility between the host and supplier country, especially in the case of innovative floating SMR projects. Legal experience in nuclear-powered vessels and nuclear installations can be used in the development of regulatory approaches for floating SMRs. This chapter provides an analysis of the applicability of the existing international conventions, including the 1974 International Convention for the Safety of Life at Sea, the IAEA safeguards agreements, and civil liability instruments, to the floating SMRs. In addition, some considerations for the future development of the legal framework for floating SMRs are proposed.
A new method of dose calculation algorithm, called GPU-accelerated Monte Carlo and collapsed cone Convolution (GMCC) was developed to improve the calculation speed of BNCT treatment planning system. The GPU-accelerated Monte Carlo routine in GMCC is used to simulate the neutron transport over whole energy range and the Collapsed Cone Convolution method is to calculate the gamma dose. Other dose components due to alpha particles and protons, are calculated using the calculated neutron flux and reaction data. The mathematical principle and the algorithm architecture are introduced. The accuracy and performance of the GMCC were verified by comparing with the FLUKA results. A water phantom and a head CT voxel model were simulated. The neutron flux and the absorbed dose obtained by the GMCC were consistent well with the FLUKA results. In the case of head CT voxel model, the mean absolute percentage error for the neutron flux and the absorbed dose were 3.98% and 3.91%, respectively. The calculation speed of the absorbed dose by the GMCC was 56 times faster than the FLUKA code. It was verified that the GMCC could be a good candidate tool instead of the Monte Carlo method in the BNCT dose calculations.
BackgroundIn recent years, electron cyclotron wave (ECW) heating and current drive (ECCD) have been widely used in tokamak discharge experiments. The inevitable presence of impurity particles in the tokamak plasma affects the ECCD through radiation energy, inhibition of turbulent transport, and change the collision rate. Changes in plasma density, temperature and other transport quantities caused by the change of impurity concentration, induce the changes of Shafranov displacement at the center of magnetic surface of the plasma.PurposeThis study aims to investigate the influence of impurity concentration changes on the ECW deposition position and current drive efficiency theoretically with consideration of all above related variations.MethodsThe One Modeling Framework for Integrated Tasks (OMFIT) platform was used to conduct integrated simulation study of the effect of impurity effect on ECW heating and current drive. The HL-2M Tokamak device parameters were combined with self-consistent coupled plasma equilibrium, external auxiliary heating and current drive, transport and other physical processes for simulation computation with the carbon ions as the unique impurity ions.ResultsThe simulation results show that when the influence of impurities on the plasma is considered, with the increase of the impurity concentration, the radial position of the ECW deposition first moves to the plasma core and then moves to the edge, and the current drive efficiency first increases and then decreases. Due to the competition between the radiation effect and the dilution effect of the impurity-plasma interaction, the radiation loss power basically increases linearly with the increase of Zeff, while the dilution effect suppresses the turbulence and improve the confinement, but the stabilization effect slows down with the increase of Zeff.ConclusionsWhen the influence of impurities on the plasma is not considered, the deposition position of ECW is basically unchanged, and the current drive efficiency decreases. Results of this study have guiding significance for electron cyclotron current drive (ECCD) to control the plasma current profile and control the instability of magnetic fluid.
OPF problems are formulated and solved for power system operations, especially for determining generation dispatch points in real-time. For large and complex power system networks with large numbers of variables and constraints, finding the optimal solution for real-time OPF in a timely manner requires a massive amount of computing power. This paper presents a new method to reduce the number of constraints in the original OPF problem using a graph neural network (GNN). GNN is an innovative machine learning model that utilizes features from nodes, edges, and network topology to maximize its performance. In this paper, we proposed a GNN model to predict which lines would be heavily loaded or congested with given load profiles and generation capacities. Only these critical lines will be monitored in an OPF problem, creating a reduced OPF (ROPF) problem. Significant saving in computing time is expected from the proposed ROPF model. A comprehensive analysis of predictions from the GNN model was also made. It is concluded that the application of GNN for ROPF is able to reduce computing time while retaining solution quality.
Aldo Antognini, Sonia Bacca, Andreas Fleischmann
et al.
Recent progress in laser and x-ray spectroscopy of muonic atoms offers promising long-term possibilities at the intersection of atomic, nuclear and particle physics. In muonic hydrogen, laser spectroscopy measurements will determine the ground-state hyperfine splitting (HFS) and additionally improve the Lamb shift by a factor of 5. Precision spectroscopy with cryogenic microcalorimeters has the potential to significantly improve the charge radii of the light nuclei in the $Z=3-8$ range. Complementary progress in precision should be achieved on the theory of nucleon- and nuclear-structure effects. The impact of this muonic-atom spectroscopy program will be amplified by the upcoming results from H and He$^+$ spectroscopy, simple molecules such as HD$^+$ and Penning trap measurements. In this broader context, one can test ab-initio nuclear theories, bound-state QED for two- or three-body systems, and determine fundamental constants, such as the Rydberg ($R_\infty$) and the fine-structure ($α$) constants.
Principal Component Analysis (PCA) via Singular Value Decomposition (SVD) of large datasets is an adaptive exploratory method to uncover natural patterns underlying the data. Several recent applications of the PCA-SVD to event-by-event single-particle azimuthal angle distribution matrices in ultra-relativistic heavy-ion collisions at RHIC-LHC energies indicate that the sine and cosine functions chosen {\it a priori} in the traditional Fourier analysis are naturally the most optimal basis for azimuthal flow studies according to the data itself. We perform PCA-SVD analyses of mid-central Au+Au collisions at $E_{\rm beam}/A$=1.23 GeV simulated using an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model to address the following two questions: (1) if the principal components of the covariance matrix of nucleon azimuthal angle distributions in heavy-ion reactions around 1 GeV/nucleon are naturally sine and/or cosine functions and (2) what if any advantages the PCA-SVD may have over the traditional flow analysis using the Fourier expansion for studying the EOS of dense nuclear matter. We find that (1) in none of our analyses the principal components come out naturally as sine and/or cosine functions, (2) while both the eigenvectors and eigenvalues of the covariance matrix are appreciably EOS dependent, the PCA-SVD has no apparent advantage over the traditional Fourier analysis for studying the EOS of dense nuclear matter using the azimuthal collective flow in heavy-ion collisions.
This paper focuses on scrape-off layer and divertor modelling of the medium-density single-null scenario of the Divertor Test Tokamak facility (DTT), under construction in Italy. The modelling was performed using the 2D coupled fluid-Monte Carlo code SOLEDGE2D-EIRENE. For DTT pump designing, neutral pressure at the pump aperture below the dome is calculated in deuterium-only cases as well as with impurity seeding with various puffing levels. This scenario analysis also allowed the characterization of detachment in DTT and the influence of pumping on detachment itself. Two different radiating impurities, neon and nitrogen, were tested in the high power scenario to evaluate the minimum impurity concentration required to achieve sustainable conditions at DTT divertor. The sensitivity of the model was studied by varying the impurity concentration; the model shows a hysteresis-like behaviour between the impurity influx and the total impurity content by which detachment is strongly influenced.
The International Atomic Energy Agency has developed a tomographic imaging system for accomplishing the total fuel rod-by-rod verification time of fuel assemblies within the order of 1–2 h, however, there are still limitations for some fuel types. The aim of this study is to develop a deep learning-based de-noising process resulting in increasing the tomographic image acquisition speed of fuel assembly compared to the conventional techniques. Convolutional AutoEncoder (CAE) was employed for de-noising the low-quality images reconstructed by filtered back-projection (FBP) algorithm. The image data set was constructed by the Monte Carlo method with the FBP and ground truth (GT) images for 511 patterns of missing fuel rods. The de-noising performance of the CAE model was evaluated by comparing the pixel-by-pixel subtracted images between the GT and FBP images and the GT and CAE images; the average differences of the pixel values for the sample image 1, 2, and 3 were 7.7%, 28.0% and 44.7% for the FBP images, and 0.5%, 1.4% and 1.9% for the predicted image, respectively. Even for the FBP images not discriminable the source patterns, the CAE model could successfully estimate the patterns similarly with the GT image.