Abstract：Radioactive tritium leakage from high-pressure storage vessels is a common nuclear leakage event. Different leakage conditions have different effects on tritium diffusion, resulting in different degrees of radioactive hazards. This study focuses on tritium leakage from high-pressure storage vessels and analyzes the influence of different leakage orifice shapes, leakage positions, and the presence of obstacles in the scene space on tritium leakage diffusion. The results show that there is little difference in the radial diffusion velocity of tritium gas along the jet axis between circular and square leakage orifices. The radial diffusion velocity of tritium gas in the long-axis direction of the rectangular leakage orifice is larger than that in the short-axis direction, and the larger the aspect ratio of the rectangle is, the greater the difference is in the diffusion velocity. In addition, leakage from the storage vessel below the air inlet is beneficial to the dilution of tritium, whereas leakage from the air vents leads to a slow decrease in the tritium concentration. The obstacles present in the tritium scene space hinder the migration of tritium gas and prolong the time for the tritium concentration to reach stabilization. This study provides a theoretical basis for the disposal of tritium in tritium leakage accidents by analyzing the influence of different leakage conditions in storage vessels on tritium gas diffusion.
Abstract：Irradiated low-enriched uranium as target plates are used to produce, via neutron radiation and from the molybdenum-99 fission product, technetium-99m, which is a radio-element widely used for diagnosis in the field of nuclear medicine. The behavior of this type of target must be known to prevent eventual failures during radiation.The present study aims to assess, via prediction, the thermal mechanical behavior, physical integrity, and geometric stability of targets under neutron radiation in a nuclear reactor. For this purpose, a numerical simulation using a three-dimensional finite element analysis model was performed to determine the thermal expansion and stress distribution in the target cladding. The neutronic calculation results, target material properties, and cooling parameters of the KAERI research group were used as inputs in our developed model. Thermally induced stress and deflection on the target were calculated using Ansys-Fluent codes, and the temperature profiles, as inputs of this calculation, were obtained from a CFD thermal-hydraulic model. The stress generated, induced by the pressure of fission gas release at the interface of the cladding target was also estimated using the Redlich-Kwong equation of state.The results obtained using the bonded and unbonded target models considering the effect of the radiation heat combined with a fission gas release rate of approximately 3% show that the predicted thermal stress and deflection values satisfy the structural performance requirement and safety design. It can be presumed that the integrity of the target cladding is maintained under these conditions.
Keywords：Irradiated LEU target;Mo-99 production;Integrity evaluation;Thermo-mechanical analyses;Fission gas pressure
Abstract：Scaling analysis is widely used to design scaled-down experimental facilities through which the prototype phenomena can be effectively evaluated. As a new method, dynamic system scaling (DSS) must be verified as a rational and applicable method. A DSS method based on dilation transformation was evaluated using single-phase natural circulation in a simple rectangular loop. The scaled-down cases were constructed based on two parameters-length ratio and dilation number-and the corresponding transient processes were simulated using the Relap5 computational code. The results show that this DSS method can simulate the dynamic flow characteristics of scaled-down cases. The transient deviation of the temperature difference and mass flow rate of the scaled cases decrease with increases in the length ratio and dilation number. The distortion of the transient temperature difference is smaller than that of the mass flow; however, the overall deviation is within a reasonable range.
Keywords：Dynamical System Scaling analysis;Single-phase natural circulation;Transient scaling deviation;Dilation transformation
Abstract：The neutron energy spectrum was measured using a Bonner sphere spectrometer at six locations inside the containment vessel of a nuclear reactor at the Qinshan nuclear power plant. The structures of the neutron spectra obtained by the maximum entropy, iteration, and genetic algorithm methods were consistent with one another and could be interpreted as the spectral superposition of different energy regions. The characteristic parameters of the neutron spectrum, including the fluence rate, average energy, and neutron ambient dose equivalent rate (10), were in good agreement among the three methods. In addition, an LB6411 neutron ambient dose equivalent meter was employed to obtain the (10) directly for comparison. These findings indicate that neutron spectrum unfolding methods can be used to overcome the problems associated with the response functions of dosimeters to provide more accurate (10) values. In this study, the following three evaluation criteria were systematically addressed to ensure the accuracy of the unfolded spectra: count rates of the inverse solutions, neutron spectrum structures, and comparison of key parameters.
Keywords：Neutron spectrum;(10);Nuclear power plant;Evaluation criteria
Abstract：This study evaluated the nuclear data libraries for a small 100 Mega Watt electric (MWe) Molten Salt Reactor with plutonium fuel. The reactor has a power output of 100 MWe, which meets the demand for electricity generation in several regions or provinces outside Java Island. Several nuclear data libraries, such as JEFF 3.1, ENDF/B-VII.0, JENDL 3.3, and JENDL 4.0, were used for a more comprehensive evaluation. LiF-BeF2-ThF4-PuF4 was used as the initial fuel composition. The thorium and plutonium concentrations in the fuel salt were varied to obtain the optimum fuel composition, leading to critical conditions. The results showed some neutronic parameters, such as the conversion ratio, neutron spectra, and effective multiplication factors, from three different nuclear data libraries. By changing the plutonium concentration in the initial fuel salt composition, the minimum plutonium loaded for the reactor criticality during 2,000 days of operation time was determined to be 0.995, 0.91, 0.87, and 0.90 mol% for JEFF 3.1, ENDF/B-VII.0, JENDL 3.3, and JENDL 4.0, respectively. The differences in the values of each parameter were due to several factors, such as the cross-section values and number of nuclides in the nuclear data libraries. Several safety parameters were also investigated to ensure the possibility of utilizing PuF4 in the reactor.
Abstract：Nuclear charge density distribution plays an important role in both nuclear and atomic physics, for which the two-parameter Fermi (2pF) model has been widely applied as one of the most frequently used models. Currently, the feedforward neural network has been employed to study the available 2pF model parameters for 86 nuclei, and the accuracy and precision of the parameter-learning effect are improved by introducing A1/3 into the input parameter of the neural network. Furthermore, the average result of multiple predictions is more reliable than the best result of a single prediction and there is no significant difference between the average result of the density and parameter values for the average charge density distribution. In addition, the 2pF parameters of 284 (near) stable nuclei are predicted in this study, which provides a reference for the experiment.
Keywords：Charge density distribution;Two-parameter Fermi model;Feedforward neural network approach
Abstract：Modern rare isotope beam (RIB) factories will significantly enhance the production of extremely rare isotopes (ERI) at or near drip lines. As one of the most important methods employed in RIB factories, the production of ERIs in projectile fragmentation reactions should be theoretically improved to provide better guidance for experimental research. The cross-sections of ERIs produced in 140 MeV/u 78,86Kr/58,64Ni/40,48Ca + 9Be projectile fragmentation reactions were predicted using the newly proposed models [i.e., Bayesian neural network (BNN), BNN + FRACS, and FRACS, see Chin. Phys. C, 46: 074104 (2022)] and the frequently used EPAX3 model. With a minimum cross-section of 10-15 mb, the possibilities of ERIs discovery in a new facility for rare isotope beams (FRIB) are discussed.
Abstract：Compton scattering with bound electrons contributes to a significant atomic effect in low-momentum transfer, yielding background structures in direct light dark matter searches as well as low-energy rare event experiments. We report the measurement of Compton scattering in low-momentum transfer by implementing a 10-g germanium detector bombarded by a 137Cs source with a radioactivity of 8.7 mCi and a scatter photon captured by a cylindrical NaI(Tl) detector. A fully relativistic impulse approximation combined with multi-configuration Dirac-Fock wavefunctions was evaluated, and the scattering function of Geant4 software was replaced by our calculation results. Our measurements show that the Livermore model with the modified scattering function in Geant4 is in good agreement with the experimental data. It is also revealed that atomic many-body effects significantly influence Compton scattering for low-momentum transfer (sub-keV energy transfer).
Abstract：This study proposes a novel feature extraction approach for radionuclide identification to increase the precision of identification of the gamma-ray energy spectrum set. For easier utilization of the information contained in the spectra, the vectors of the gamma-ray energy spectra from Euclidean space, which are fingerprints of the different types of radionuclides, were mapped to matrices in the Banach space. Subsequently, to make the spectra in matrix form easier to apply to image-based deep learning frameworks, the matrices of the gamma-ray energy spectra were mapped to images in the RGB color space. A deep convolutional neural network (DCNN) model was constructed and trained on the ImageNet dataset. The mapped gamma-ray energy spectrum images were applied as inputs to the DCNN model, and the corresponding outputs of the convolution layers and fully connected layers were transferred as descriptors of the images to construct a new classification model for radionuclide identification. The transferred image descriptors consist of global and local features, where the activation vectors of fully connected layers are global features, and activations from convolution layers are local features. A series of comparative experiments between the transferred image descriptors, peak information, features extracted by the histogram of the oriented gradients (HOG), and scale-invariant feature transform (SIFT) using both synthetic and measured data were applied to 11 classical classifiers. The results demonstrate that although the gamma-ray energy spectrum images are completely unfamiliar to the DCNN model and have not been used in the pre-training process, the transferred image descriptors achieved good classification results. The global features have strong semantic information, which achieves an average accuracy of 92.76% and 94.86% on the synthetic dataset and measured dataset, respectively. The results of the statistical comparison of features demonstrate that the proposed approach outperforms the peak searching based method, HOG, and SIFT on the synthetic and measured datasets.
Keywords：Radionuclide identification;Feature extraction;Transfer learning;Gamma energy spectrum analysis;Image descriptor
Abstract：Within a transport model, we investigated the effects of the momentum dependence of the nuclear symmetry potential on the pion observables in central Sn + Sn collisions at 270 MeV/nucleon. To this end, the quantity (i.e., the value of the nuclear symmetry potential at the saturation density ρ0 and infinitely large nucleon momentum) was used to characterize the momentum dependence of the nuclear symmetry potential. With a certain L (i.e., the slope of the nuclear symmetry energy at ρ0), the characteristic parameter of the symmetry potential significantly affects the production of π- and π+ and their pion ratios. Moreover, by comparing the charged pion yields, pion ratios, and spectral pion ratios of the theoretical simulations for the reactions 108Sn + 112Sn and 132Sn + 124Sn with the corresponding data in the SπRIT experiments, we found that our results favor a constraint on (i.e., MeV), and L is also suggested within a range of 62.7 MeV<L<93.1 MeV. In addition, the pion observable for 197Au + 197Au collisions at 400 MeV/nucleon also supports the extracted value for .
Keywords：Nuclear symmetry potential;Momentum dependence;Symmetry energy
Abstract：In various monitoring and detection tools that use pulsed neutron generators as radiation sources, the gamma rays induced by the interaction with various nuclei at different stages of neutron transport can reflect information about the medium. These gamma rays are generated in two major interactions: inelastic scattering of fast neutrons and radiative capture of thermal neutrons, corresponding to the inelastic and capture gamma rays, respectively. However, the two types of gamma rays that reflect different properties of the medium are difficult to collect by normal detectors independently. The proportion of the two gamma rays needs to be solved for the separation of inelastic and capture gamma. Therefore, this study proposes an optimized spectra decomposition method to calculate the inelastic-to-capture ratio in the measured total gamma spectra based on the net inelastic and capture spectra obtained using the Geant4 simulation. Because the simulated data cannot reflect the energy resolution of the measured spectra, we introduce the Gaussian broadening function of the gamma detector while calculating the proportion of the spectra components, and achieve optimization of the proportion values and resolution parameters simultaneously. Based on the results, the total simulated spectra obtained by superimposing the broadened net inelastic and capture gamma spectra according to the calculated inelastic-to-capture ratio are in good agreement with their measured counterpart.
Abstract：This study proposes a ladder gradient method for neutron and gamma-ray discrimination. The proposed method exhibited state-of-the-art performance with low time consumption, which incorporates two parts: information extraction and discrimination factor calculation. A quasi-continuous spiking cortical model was proposed to extract information from the radiation pulse signals, thus generating an ignition map corresponding to each pulse signal. The ignition map can be used to calculate the discrimination factor. A ladder gradient calculation was introduced to obtain a discrimination factor with low computational complexity. The proposed method was compared with five other discrimination methods to evaluate its robustness and efficacy. Furthermore, the filter adaptability of the pulse-coupled neural network and ladder gradient methods was investigated. Possible reasons for adapting the conditions with different discrimination methods and filters were analyzed. Experiments were conducted in 20 filtering situations with 11 types of filters to determine the most suitable filters for discrimination methods. The experimental results revealed that the three most adaptive filters of the pulse-coupled neural networks and ladder gradient methods are the wavelet, elliptic, and median filters and the elliptic, moving average, and wavelet filters, respectively.
Abstract：For nuclear measurements, it is necessary to obtain accurate information from nuclear pulses, which should be obtained by first shaping the pulses outputted by the detectors. However, commonly used pulse-shaping algorithms have certain problems. For example, certain pulse-shaping algorithms have long dead-times in high-counting-rate environments or are difficult to achieve in digital systems. Gaussian signals are widely used in analog nuclear instruments owing to their symmetry and completeness. A Gaussian signal is usually implemented by using a multilevel S-K filter in series or in parallel. It is difficult to construct a real-time digital Gaussian filter for the complex Gaussian filtering algorithm. Based on the multilevel cascade convolution, a pulse-shaping algorithm for double exponential signals is proposed in this study, which, in addition to double exponential signals, allows more complex output-signal models to be used in the new algorithm. The proposed algorithm can be used in high-counting-rate environments and has been implemented in an FPGA with fewer multipliers than those required in other traditional Gaussian pulse-shaping algorithms. The offline processing results indicated that the average peak base width of the output-shaped pulses obtained using the proposed algorithm was reduced compared with that obtained using the traditional Gaussian pulse-shaping algorithm. Experimental results also demonstrated that signal-to-noise ratios and energy resolutions were improved, particularly for pulses with a low energy. The energy resolution was improved by 0.1-0.2% while improving the counting rate.
Keywords：Impulse shaping;Multi-level cascade convolution;S-K filter;Gaussian-like distribution;Double exponential signal
Abstract：For modern scaling devices, multiple cell upsets (MCUs) have become a major threat to high-reliability field-programmable gate array (FPGA)-based systems. Thus, both performing the worst-case irradiation tests to provide the actual MCU response of devices and proposing an effective MCU distinction method are urgently needed. In this study, high- and medium-energy heavy-ion irradiations for the configuration random-access memory of 28 nm FPGAs are performed. An MCU extraction method supported by theoretical predictions is proposed to study the MCU sizes, shapes, and frequencies in detail. Based on the extraction method, the different percentages, and orientations of the large MCUs in both the azimuth and zenith directions determine the worse irradiation response of the FPGAs. The extracted largest 9-bit MCUs indicate that high-energy heavy ions can induce more severe failures than medium-energy ones. The results show that both the use of high-energy heavy ions during MCU evaluations and effective protection for the application of high-density 28 nm FPGAs in space are extremely necessary.
Abstract：A trigger system of the general function was designed using the commercial module of CAEN V2495 for heavy-ion nuclear reaction experiments at Fermi energies. The system was applied and verified on the compact spectrometer for heavy IoN experiment (CSHINE). Based on the field-programmable logic gate array (FPGA) technology of the command register access and remote computer control operation, trigger functions can be flexibly configured according to experimental physical goals. Using the trigger system on CSHINE, we conducted a beam experiment at 25 MeV/u 86Kr + 124Sn on the Radioactive Ion Beam Line 1 in Lanzhou (RIBLL1), China. The online results demonstrated that the trigger system worked normally and correctly. This system can be extended to other experiments as well.
Keywords：CSHINE;Trigger System;FPGA;Heavy Ion Experiment