Nuclear Science and Techniques

With the development of silicon photomultiplier (SiPM) technology, front-end electronics for SiPM signal processing have been highly sought after in various fields. A compact 64-channel front-end electronics (FEE) system achieved by field-programmable gate array-based charge-to-digital converter (FPGA-QDC) technology was built and developed. The FEE consists of an analog board and FPGA board. The analog board incorporates commercial amplifiers, resistors, and capacitors. The FPGA board is composed of a low-cost FPGA. The electronics performance of the FEE was evaluated in terms of noise, linearity, and uniformity. A positron emission tomography (PET) detector with three different readout configurations was designed to validate the readout capability of the FEE for SiPM-based detectors. The PET detector was made of a 15 × 15 lutetium–yttrium oxyorthosilicate (LYSO) crystal array directly coupled with a SiPM array detector. The experimental results show that FEE can process dual-polarity charge signals from the SiPM detectors. In addition, it shows a good energy resolution for 511-keV gamma photons under the dual-end readout for the LYSO crystal array irradiated by a Na-22 source. Overall, the FEE based on FPGA-QDC shows promise for application in SiPM-based radiation detectors.

This study presents the design and performance results for compact plastic scintillator strips using a wavelength shifting fiber (WLS -fiber) readout with dimensions of 0.1×0.02×2 m³. This approach was evaluated as a candidate for a cosmic-ray muon detector for the Taishan Antineutrino Observatory (JUNO-TAO). The strips coupled with 3-inch photomultiplier tubes (PMTs) were measured and compared between the single-end and double-end readout options. Additionally, a strip using the double-end option coupling with a silicon photomultiplier (SiPM) was further evaluated and compared with the results obtained using PMTs. The performance of the strips was determined by a detailed survey along their length with a cosmic-ray muon after detailed characterization of the 3-inch PMTs and SiPMs. The proposed design employing a compact plastic scintillator strip with WLS-fiber coupling to a SiPM provides a good choice for cosmic-ray muon veto detectors, particularly when detector dimensions must be limited.

The novel pulsed liquid chromatography radionuclide separation method presented here provides a new and promising strategy for the extraction of uranium from seawater. In this study, a new chromatographic separation method was proposed, and a pulsed nuclide automated separation device was developed, alongside a new chromatographic column. The length of this chromatographic column was 10 m, with an internal warp of 3 mm and a packing size of 1 mm, whilst the total separation units of the column reached 12,250. The most favorable conditions for the separation of nuclides were then obtained through optimizing the separation conditions of the device: Sample pH in the column = 2, sample injection flow rate = 5.698 mL/min, chromatographic column heating temperature = 60 ℃. Separation experiments were also carried out for uranium, europium, and sodium ions in mixed solutions; Uranium and sodium ions in water samples from the Ganjiang River; and uranium, sodium, and magnesium ions from seawater samples. The separation factors between the different nuclei were then calculated based on the experimental data, and a formula for the separation level was derived. The experimental results showed that the separation factor in the mixed solution of uranium and europium (1:1) was 1.088, whilst achieving the initial separation of uranium and europium theoretically required a 47-stage separation. Considering the separation factor of 1.50 for the uranium and sodium ions in water samples from the Ganjiang River, achieving the initial separation of uranium and sodium ions would have theoretically required at least a 21-stage separation. Furthermore, for the seawater sample separation experiments, the separation factor of uranium and sodium ions was 1.2885, therefore more than 28 stages of sample separation would be required to achieve uranium extraction from seawater. The novel pulsed liquid chromatography method proposed in this study was innovative in terms of uranium separation and enrichment, whilst expanding the possibilities of extracting uranium from seawater through chromatography.

This article describes the transient models of the neutronics code VITAS that are used for solving time-dependent, pin-resolved neutron transport equations. VITAS uses the stiffness confinement method (SCM) for temporal discretization to transform the transient equation into the corresponding transient eigenvalue problem (TEVP). To solve the pin-resolved TEVP, VITAS uses a heterogeneous variational nodal method (VNM). The spatial flux is approximated at each Cartesian node using finite elements in the x-y plane and orthogonal polynomials along the z-axis. Angular discretization utilizes the even-parity integral approach at the nodes and spherical harmonic expansions at the interfaces. To further lower the computational cost, a predictor-corrector quasi-static SCM (PCQ-SCM) was developed. Within the VNM framework, computational models for the adjoint neutron flux and kinetic parameters are presented. The direct-SCM and PCQ-SCM were implemented in VITAS and verified using the two-dimensional (2D) and three-dimensional (3D) exercises on the OECD/NEA C5G7-TD benchmark. In the 2D and 3D problems, the discrepancy between the direct-SCM solver’s results and those reported by MPACT and PANDAS-MOC was under 0.97% and 1.57%, respectively. In addition, numerical studies comparing the PCQ-SCM solver to the direct-SCM solver demonstrated that the PCQ-SCM enabled substantially larger time steps, thereby reducing the computational cost 100-fold, without compromising numerical accuracy.

Knowledge graph technology has distinct advantages in terms of fault diagnosis. In this study, the control rod drive mechanism (CRDM) of the liquid fuel thorium molten salt reactor (TMSR-LF1) was taken as the research object, and a fault diagnosis system was proposed based on knowledge graph. The Subject-Relation-Object triples are defined based on CRDM unstructured data, including design specification, operation and maintenance manual, alarm list, and other forms of expert experience. In this study, we constructed a fault event ontology model to label the entity and relationship involved in the corpus of CRDM fault events. A three-layer robustly optimized bidirectional encoder representation from transformers (RBT3) pretraining approach combined with a text convolutional neural network (TextCNN) was introduced to facilitate the application of the constructed CRDM fault diagnosis graph database for fault query. The RBT3-TextCNN model along with the Jieba tool is proposed for extracting entities and recognizing the fault query intent simultaneously. Experiments on the dataset collected from TMSR-LF1 CRDM fault diagnosis unstructured data demonstrate that this model has the potential to improve the effect of intent recognition and entity extraction. Additionally, a fault alarm monitoring module was developed based on WebSocket protocol to deliver detailed information about the appeared fault to the operator automatically. Furthermore, the Bayesian inference method combined with the variable elimination algorithm was proposed to enable the development of a relatively intelligent and reliable fault diagnosis system. Finally, a CRDM fault diagnosis Web interface integrated with graph data visualization was constructed, making the CRDM fault diagnosis process intuitive and effective.

Dry storage containers must be secure and reliable during long-term storage, and the effect of decay heat released from the internal spent fuel on the cask has become an important research topic. In this paper, a 3D computational fluid dynamics (CFD) model is presented, and the accuracy of the calculation is verified, with computational errors of less than 6.2%. The thermal stress of the dry storage cask was estimated by coupling it with a transient temperature field. The total power remained constant and adjusting the power ratio of the inner and outer zones had a small effect on the stress results, with a maximum equivalent stress of approximately 5.2 kPa, which occurred at the lower edge of the shell. In the case of tilt, the temperature gradient varied in a wavy distribution, and the wave crest moved from right to left. Altering the tilt angle affects the air distribution in the annular gap, leading to the shell temperature being transformed, with a maximum equivalent stress of 202MPa at the bottom of the shell. However, the equivalent stress in both cases was less than the yield stress (205MPa).

The high-temperature molten salt pump is the core equipment in a molten salt reactor that drives the flow of the molten salt coolant. Rotor stability is key to the continuous and reliable operation of the molten salt pump, and the liquid seal at the wear ring can affect the dynamic characteristics of the rotor system. When the molten salt pump is operated in the high-temperature molten salt medium, thermal deformation of the submerged parts inevitably occurs, changing clearance between the stator and rotor, affecting the leakage and dynamic characteristics of the seal. In this study, the seal leakage, seal dynamic characteristics, and rotor system dynamic characteristics are simulated and analyzed using finite element simulation software based on two cases of considering the effect of seal thermal deformation effect or not. The results show a significant difference in the leakage characteristics and dynamic characteristics of the seal obtained by considering the effect of seal thermal deformation and neglecting the effect of thermal deformation. The leakage flow rate decreases, and the first-order critical speed of the seal-bearing-rotor system decrease after considering the seal's thermal deformation.

Nuclear fuel performance modeling and simulation are critical tasks for nuclear fuel design optimization and safety analysis under normal and transient conditions. Fuel performance is a complicated phenomenon that involves thermal, mechanical, and irradiation mechanisms and requires special multiphysics modules. In this study, a fuel performance model was developed using the COMSOL Multiphysics platform. The modeling was performed for a 2D axis-symmetric geometry of a UO₂ fuel pellet in the E110 clad for VVER-1200 fuel. The modeling considers all relevant phenomena, including heat generation and conduction, gap heat transfer, elastic strain, mechanical contact, thermal expansion, grain growth, densification, fission gas generation and release, fission product swelling, gap/plenum pressure, and cladding thermal and irradiation creep. The model was validated using a code-to-code evaluation of the fuel pellet centerline and surface temperatures in the case of constant power, in addition to validation of fission gas release (FGR) predictions. This prediction proved that the model could perform according to previously published VVER nuclear fuel performance parameters. A sensitivity study was also conducted to assess the effects of uncertainty on some of the model parameters. The model was then used to predict the VVER-1200 fuel performance parameters as a function of burnup, including the temperature profiles, gap width, fission gas release, and plenum pressure. A compilation of related material and thermomechanical models was conducted and included in the modeling to allow the user to investigate different material/performance models. Although the model was developed for normal operating conditions, it can be modified to include off-normal operating conditions.

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Thorium-229 possesses the lowest first nuclear excited state, with an energy of approximately 8 eV. The extremely narrow linewidth of the first nuclear excited state, with an uncertainty of 53 THz, prevents direct laser excitation and realization of the nuclear clock. We present a proposal using the Coulomb crystal of a linear chain formed by ²²⁹Th³⁺ ions, where the nuclei of ²²⁹Th³⁺ ions in the ion trap are excited by the electronic bridge (EB) process. The 7P_1/2 state of the thorium-229 nuclear ground state is chosen for EB excitation. Using the two-level optical Bloch equation under experimental conditions, we calculate that two out of 36 prepared thorium ions in the Coulomb crystal can be excited to the first nuclear excited state, and it takes approximately 2 h to scan over an uncertainty of 0.22 eV. Taking advantage of the transition enhancement of EB and the long stability of the Coulomb crystal, the energy uncertainty of the first excited state can be limited to the order of 1 GHz.

The properties of exotic nuclei are the focus of the present research. Two-neutron halo structures of neutron-rich ^17,19B were experimentally confirmed. We studied the formation mechanism of halo phenomena in ^17,19B using the complex momentum representation method applied to deformation and continuum coupling. By examining the evolution of the weakly bound and resonant levels near the Fermi surface, s–d orbital reversals and certain prolate deformations were observed. In addition, by analyzing the evolution of the occupation probabilities and density distributions occupied by valence neutrons, we found that the ground state of ¹⁵B did not exhibit a halo and the ground states of ¹⁷B and ¹⁹B exhibited halos at 0.6≤β₂≤0.7 and 0.3≤β₂≤0.7, respectively. The low-l components in the valence levels that are weakly bound or embedded in the continuous spectrum lead to halo formation.

In the present study, on the basis of the screened electrostatic effect of the Coulomb potential, we propose an improved Gamow model within the centrifugal potential in which there are only two adjustable parameters, i.e., the screened parameters t and g, which represent the combined effect of the interaction pot ential and reduced mass of the emitted proton-daughter nucleus on the half-life of proton radioactivity in the overlapping region. Using this model, we systematically calculated the proton radioactivity half-lives of 31 spherical nuclei and 13 deformed nuclei and obtained corresponding root-mean-square deviations of 0.274 and 0.367, respectively. The relationship between the proton radioactivity half-life of ¹⁷⁷Tl^m and the corresponding angular momentum l removed by the emitted proton is also discussed. In addition, we used the proposed model to predict the proton radioactivity half-lives of 18 nuclei whose proton radioactivity is energetically allowed or observed but not yet quantified in NUBASE2020. For comparison, we used the universal decay law of proton radioactivity proposed by Qi et al. (Phys Rev C 85:011303, 2012. https://doi.org/10.1103/PhysRevC.85.011303), and the new Geiger–Nuttall law of proton radioactivity proposed by Chen et al. (Eur Phys J 55:214, 2019. https:// doi.org/10.1140/epja/i2019-12927-7).

Neutron-induced fission is an important research object in basic science. Moreover, its product yield data are an indispensable nuclear data basis in nuclear engineering and technology. The fission yield tensor decomposition (FYTD) model has been developed and used to evaluate the independent fission product yield. In general, fission yield data are verified by the direct comparison of experimental and evaluated data. However, such direct comparison cannot reflect the impact of the evaluated data on application scenarios, such as reactor transport-burnup simulation. Therefore, this study applies the evaluated fission yield data in transport-burnup simulation to verify their accuracy and possibility of application. Herein, the evaluated yield data of ²³⁵U and ²³⁹Pu are applied in the transport-burnup simulation of a pressurized water reactor (PWR) and sodium-cooled fast reactor (SFR) for verification. During the reactor operation stage, the errors in pin-cell reactivity caused by the evaluated fission yield do not exceed 500 and 200 pcm for the PWR and SFR, respectively. The errors in decay heat and ¹³⁵Xe and ¹⁴⁹Sm concentrations during the short-term shutdown of the PWR are all less than 1%; the errors in decay heat and activity of the spent fuel of the PWR and SFR during the temporary storage stage are all less than 2%. For the PWR, the errors in important nuclide concentrations in spent fuel, such as ⁹⁰Sr, ¹³⁷Cs, ⁸⁵Kr, and ⁹⁹Tc, are all less than 6%, and a larger error of 37% is observed on ¹²⁹I. For the SFR, the concentration errors of ten important nuclides in spent fuel are all less than 16%. A comparison of various aspects reveals that the transport-burnup simulation results using the FYTD model evaluation have little difference compared with the reference results using ENDF/B-VIII.0 data. This proves that the evaluation of the FYTD model may have application value in reactor physical analysis.

In this paper, we propose a novel stacked laser dielectric acceleration structure. This structure is based on the inverse Cherenkov effect and represented by a parametric design formulation. Compared to existing dielectric laser accelerators relying on the inverse Smith–Purcell effect, the proposed structure provides an extended-duration synchronous acceleration field without requiring the pulse front tilting technique. This advantage significantly reduces the required pulse duration. In addition, the easy-to-integrate layered structure facilitates cascade acceleration, and simulations have shown that low-energy electron beams can be cascaded through high gradients over extended distances. These practical advantages demonstrate the potential of this new structure for future chip accelerators.

Carbon-ion radiotherapy (CIRT) offers unique physical and biological advantages over photon radiotherapy. However, some materials and devices in the CIRT treatment room become radioactive under bombardment by therapeutic carbon-ion beams due to nuclear reactions, thereby leading to possible radiation hazards to medical staff and additional and unwanted doses to patients. This study assessed the level of induced radioactivity in the treatment room of the Heavy Ion Medical Machine (HIMM) in Wuwei. Monte Carlo simulations using PHITS were performed for a conservative case under the conditions of maximum beam energy and intensity provided by the HIMM facility. The geometry and configuration of Treatment Room 2 of the HIMM facility in Wuwei were adopted. We evaluated the activation of air, the phantom, and the components of the beamline, such as the primary collimator (PC), ridge filter (RF), and multileaf collimator (MLC). For air activation, we calculated the medical staff immersion external exposure and inhalation internal exposure caused by the corresponding radionuclides. For phantom activation, we estimated the additional dose to the patient’s family members owing to secondary photons after treatment. In addition, the exemption or non-exemption of the component material activation was assessed. The results showed that external radiation caused by air activation was the main source of the annual effective dose at approximately 0.5 mSv/y. The induced radioactivity exposure to family members of a patient after CIRT was approximately 40 μSv, sufficiently lower than the public dose limit of 1 mSv/a. The induced radioactivity of the PC, RF, and MLC were all above the exempt levels after the devices were retired, whereas the induced radioactivity of the RS and compensator could reach the exempt levels after one patient session. Our study indicated that medical staff engaged in CIRT should stay away from the high dose-rate area of induced radioactivity along the beam direction, shorten the residence time in the treatment room as much as possible, and store the activated components in isolation after the equipment is out of use. Thus, this study provides guidance for accurately assessing the level of induced radioactivity in the treatment room for CIRT.