Vol.34,

Sustainable energy sources are an immediate need to cope with the imminent issue of climate change the world is facing today. In particular, the long-lasting miniatured power sources that can supply energy continually to power handheld gadgets, sensors, electronic devices, unmanned airborne vehicles in space and extreme mining are some of the examples where this is an acute need. It is known from basic physics that radioactive materials decay over few years and some nuclear materials have their half-life until thousands of years. The past five decades of research have been spent harnessing the decay energy of the radioactive materials to develop batteries that can last until the radioactive reaction continues. Thus, an emergent opportunity of industrial symbiosis to make use of nuclear waste by using radioactive waste as raw material to develop batteries with long shelf life presents a great opportunity for sustainable energy resource development. However, the current canon of research on this topic is scarce. This perspective draws fresh discussions on the topic while highlighting future directions in this wealthy arena of research.

760

Research reactors with neutron fluxes higher than 10¹⁴ n/cm²/s are widely used in nuclear fuel and material irradiation, neutron-based scientific research, and medical and industrial isotope production. Such high flux research reactors are not only important scientific research facilities for the development of nuclear energy but also represent the national comprehensive technical capability. China has several high flux research reactors that do not satisfy the requirements of nuclear energy development. A high flux research reactor has the following features: a compact core arrangement, high power density, plate type fuel elements, a short refueling cycle, and high coolant velocity in the core. These characteristics make it difficult to simultaneously realize high neutron flux and optimal safety margin. A new multi-mission high flux research reactor was designed by the Institute of Nuclear and New Energy Technology at Tsinghua University in China; the reactor can simultaneously realize an average neutron flux higher than 2.0×10¹⁵ n/cm²/s and fulfill the current safety criterion. This high flux research reactor features advanced design concepts and has sufficient safety margins according to the preliminary safety analysis. Based on the analysis of the station blackout accident, loss of coolant accident, and reactivity accident of a single control drum rotating out accidently, the maximum temperature of the cladding surface, minimum departure from nucleate boiling ratio, and temperature difference to the onset of nucleate boiling temperature satisfy the design limits.

761

Motivated to understand the pressure-buildup characteristics in a circumstance of a water droplet immerged inside a heavy liquid metal pool, which is a key phenomenon during a Steam Generator Tube Rupture accident of Lead-cooled Fast Reactor, many experiments have been conducted by injecting water lumps into a molten lead pool at Sun Yat-sen University. In order to deepen the understanding of the influence of melt material, this lead experiment was compared with a Lead-Bismuth-Eutectic (LBE) experiment in the literature. For both experiments, a steam explosion occurred in a small part of the experimental runs, which generally leads to strengthened pressure buildup. Regarding the non-explosion experimental cases, the impact of all parameters employed in lead experiments (i.e., water lump volume, water lump shape, molten pool depth, and temperature of water and melt) on the pressure buildup is non-negligible and similar to that in our previous experiments using LBE. Notably, limited pressure buildup with an increase in water lump volume was also observed. A slightly more violent pressure buildup tends to appear in the lead experiments than in the LBE experiments under the same experimental conditions, which may be due to the higher thermal conductivity of lead than of LBE. In a few experimental runs with a relatively low melt temperature close to the melting point of lead, local solidification of liquid lead was observed, restricting pressure buildup. For the lead and LBE experiments, the calculated melt kinetic energy conversion efficiency η has a relatively small value (not exceeding 1.6%), and the η values have an overall positive correlation with the impulse on the molten pool.

614

Considering the growing global demand for energy and the need for countries to achieve climate goals, there is an increasing global interest in small modular reactors (SMRs) and their applications. Accident source term and radiological consequence evaluations of SMRs are key components of nuclear and radiation safety reviews, which affect the site, exclusion area (EAB), and low population zone (LPZ) outer boundaries. Based on the design characteristics of the SMR and accident analysis results, a theoretical model of a whole-core fuel cladding damage accident was constructed to study the radioactivity released into the environment and its consequences. The accident source term and radiation dose calculation models were established to analyze the released amounts of radionuclides and the total effective dose affecting individuals at the site boundary. The results showed that the amount of radionuclides released into the environment after a whole-core fuel cladding damage accident reached 10¹⁴ Bq, among which the release amount of ¹³³Xe was the largest. The total effective dose at the site boundary 30 days after the accident was 8.65 mSv. The highest total effective dose affecting individuals occurred to the east-north-east. The results of the accident source term and radiological consequence provide technical support for site boundary dose assessments and reviews of SMRs.

800

The lightweight shielding design of small reactors is a popular research topic. Based on a small helium-xenon-cooled solid reactor, the effects of neutron and photon shielding sequence and the number of shielding layers on the radiation dose were first studied. It was found that when photons were shielded first and the number of shielding layers was odd, the radiation dose could be significantly reduced. To reduce the weight of the shielding body, the relative thickness of the shielding layers was optimized using the genetic algorithm. The optimized scheme can reduce the radiation dose by up to 57% and reduce the weight by 11.84%. To determine the total thickness of the shielding layers and avoid the local optimal solution of the genetic algorithm, a series of formulas that describes the relationship between the total thickness and the radiation dose was developed through large-scale calculations. A semi-empirical and semi-quantitative lightweight shielding design algorithm is proposed to integrate the above shielding optimization method that verified by the Monte Carlo method. Finally, a code, SDIC1.0, was developed to achieve the optimized lightweight shielding design for small reactors. It was verified that the difference between the SDIC1.0 and the RMC code is approximately 10% and that the computation time is shortened by 6.3 times.

835

Transplutonium isotopes are scarce and need to be produced by irradiation in high flux reactors. However, their production is inefficient, and optimization studies are necessary. This study analyzes the physical nature of transplutonium isotope production using ²⁵²Cf, ²⁴⁴Cm, ²⁴²Cm, and ²³⁸Pu as examples. Traditional methods based on the Monte Carlo burnup calculation have the limitations of many calculations and cannot analyze the individual energy intervals in detail; thus, they cannot support the refined evaluation, screening, and optimization of the irradiation schemes. After understanding the physical nature and simplifying the complexity of the production process, we propose a rapid diagnostic method for evaluating radiation schemes based on the concepts "single energy interval value (SEIV)" and "Energy Spectrum Total Value (ESTV)". The rapid diagnostic method not only avoids tedious burnup calculations but also provides a direction for optimization. The optimal irradiation schemes for producing ²⁵²Cf, ²⁴⁴Cm, ²⁴²Cm, and ²³⁸Pu are determined based on a rapid diagnostic method. Optimal irradiation schemes can significantly improve production efficiency. Compared with the initial scheme, the optimal scheme improved the production efficiency of ²³⁸Pu by 7.41 times; ²⁴²Cm, 11.98 times; ²⁴⁴Cm, 65.20 times; and ²⁵²Cf, 15.08 times. Thus, a refined analysis of transplutonium isotope production is conducted and provides a theoretical basis for improving production efficiency.

960

The Shanghai Laser Electron Gamma Source (SLEGS) is a powerful tool for exploring photonuclear physics, such as giant dipole resonance (GDR) and pygmy dipole resonance (PDR), which are the main mechanisms of collective nuclear motion. The goal of the SLEGS neutron time-of-flight (TOF) spectrometer is to measure GDR and specific nuclear structures in the energy region above the neutron threshold. The SLEGS TOF spectrometer was designed to hold 20 sets of EJ301 and LaBr₃ detectors. Geant4 was used to simulate the efficiency of each detector and the entire spectrometer, which provides a reference for the selection of detectors and layout of the SLEGS TOF spectrometer. Under the events of ²⁰⁸Pb, implementations of coincidence and time-of-flight technology for complex experiments are available; thus, γ and neutron decay events can be separated. The performance of SLEGS TOF spectrometer was systematically evaluated using offline experiments, in which the time resolution reached approximately 0.9 ns.

595

A Zr-Gd alloy with neutron poisoning properties and resistance to boiling concentrated HNO3 corrosion was developed based on a corrosion-resistant Zr-702 alloy to meet the demand for neutron shielding in the closed-loop treatment of spent fuel and the nuclear chemical industry. In this study, 1 wt. %, 3 wt. %, 5 wt. %, 7 wt. %, and 9 wt. % Zr-Gd alloys were designed and fabricated with Zr-702 as the control element. The electrochemical behavior of the Zr-Gd alloys in boiling concentrated HNO3 was investigated, and the neutron shielding effect on plate thickness and Gd content was simulated. The experimental results demonstrate that the corrosion resistance of the alloy decreased slightly before ~7 wt. %–9 wt. % with increasing Gd content; this is the inflection point of its corrosion resistance. The alloy uniformly dissolved the Gd content that could not be dissolved in the Zr lattice, resulting in numerous micropores on the passivation coating, which deteriorated and accelerated the corrosion rate. The MCNP simulation demonstrated that when the Gd content was increased to 5 wt. %, a 2-mm-thick plate can shield 99.9 % neutrons; an alloy with a Gd content ≥7 wt. % required only a 1-mm-thick plate, thereby showing that the addition of Gd provides an excellent neutron poisoning effect. Thus, the corrosion resistance and neutron shielding performance of the Zr-Gd alloy can meet the harsh service requirements of the nuclear industry.

767

Spectral computed tomography (CT) based on photon counting detectors can resolve the energy of every single photon interacting with the sensor layer and be used to analyze material attenuation information under different energy ranges, which can be helpful for material decomposition studies. However, there is a considerable amount of inherent quantum noise in narrow energy bins, resulting in a low signal-to-noise ratio, which can consequently affect the material decomposition performance in the image domain. Deep learning technology is currently widely used in medical image segmentation, denoising, and recognition. In order to improve the results of material decomposition, we propose an attention-based global convolutional generative adversarial network (AGC-GAN) to decompose different materials for spectral CT. Specifically, our network is a global convolutional neural network based on an attention mechanism that is combined with a generative adversarial network. The global convolutional network based on the attention mechanism is used as the generator, and a patchGAN discriminant network is used as the discriminator. Meanwhile, a clinical spectral CT image dataset is used to verify the feasibility of our proposed approach. Extensive experimental results demonstrate that AGC-GAN achieves a better material decomposition performance than vanilla U-Net, fully convolutional network, and fully convolutional denseNet. Remarkably, the mean intersection over union, structural similarity, mean precision, PAcc, and mean F1-score of our method reach up to 87.31%, 94.83%, 93.22%, 97.39%, and 93.05%, respectively.

636

Imaging plates are widely used to detect alpha particles to track information, and the number of alpha particle tracks is affected by the overlapping and fading effects of the track information. In this study, an experiment and a simulation were used to calibrate the efficiency parameter of an imaging plate, which was used to calculate the grayscale. Images were created by using grayscale, which trained the convolutional neural network to count the alpha tracks. The results demonstrated that the trained convolutional neural network can evaluate the alpha track counts based on the source and background images with a wider linear range, which was unaffected by the overlapping effect. The alpha track counts were unaffected by the fading effect within 60 min, where the calibrated formula for the fading effect was analyzed for 132.7 min. The detection efficiency of the trained convolutional neural network for inhomogeneous ²⁴¹Am sources (2π emission) was 0.6050 ± 0.0399, whereas the efficiency curve of the photo-stimulated luminescence (PSL) method was lower than that of the trained convolutional neural network.

747

Extremely low background experiments to measure key nuclear reaction cross sections of astrophysical interest are conducted at the world’s deepest underground laboratory, the Jingping Underground laboratory for Nuclear Astrophysics (JUNA). High precision measurements provide reliable information to understand nucleosynthetic processes in celestial objects and resolve mysteries on the origin of atomic nuclei discovered in the first generations of Pop. III stars in the universe and meteoritic SiC grains in the solar system.

585

A control and data acquisition system was implemented for the recently-developed collinear laser spectroscopy setup. This system is dedicated to data recording, storage, processing, monitoring of the beam intensity and energy, and visualization of various spectra. In comparison to the conventional resonance nuclear reaction system, the key technique is the precise synchronization of the detected counts with the actual scanning voltage (or probing laser frequency). The functions of the system were tested by measuring the hyperfine structure spectra of stable calcium (e.g.⁴⁰Ca⁺) and radioactive potassium (e.g.³⁸K) in the bunched and continuous modes, respectively. This system will be routinely applied and further improved in subsequent laser spectroscopy experiments on unstable isotopes at the Beijing Radioactive Ion-beam Facility (BRIF).

526

A gridded thermionic cathode electron gun was developed for the linear accelerator of the High Energy Photon Source (HEPS). An electron gun should provide a large maximum bunch charge with a wide adjustable range. To satisfy these requirements, the shape of the electrode was optimized using a multi-objective genetic algorithm. A large bunch charge with an adjustable range was achieved using the grid-limited gun, the flow of which was analyzed using 3-D simulations. The electron gun has been manufactured and tested, and the measured data of the grid-limited current and simulation results are compared and discussed in this study.

656

High-brightness electron beams are required to drive LINAC-based free-electron lasers (FELs) and storage-ring-based synchrotron radiation light sources. The bunch charge and RMS bunch length at the exit of the LINAC play a crucial role in the peak current; the minimum transverse emittance is mainly determined by the injector of the LINAC. Thus, a photoinjector with a high bunch charge and low emittance that can simultaneously provide high-quality beams for 4^th generation synchrotron radiation sources and FELs is desirable. The design of a 1.6-cell S-band 2998-MHz RF gun and beam dynamics optimization of a relevant beamline are presented in this paper. Beam dynamics simulations were performed by combining ASTRA and the multi-objective genetic algorithm NSGA II. The effects of the laser pulse shape, half-cell length of the RF gun, and RF parameters on the output beam quality were analyzed and compared. The normalized transverse emittance was optimized to be as low as 0.65 mm·mrad and 0.92 mm·mrad when the bunch charge was as high as 1 nC and 2 nC, respectively. Finally, the beam stability properties of the photoinjector, considering misalignment and RF jitter, were simulated and analyzed.

681

Due to their unique features, such as the inherent safety, simplified fuel cycle, and continuous on-line reprocessing, molten salt reactors (MSRs) are regarded as one of the six reference reactors in the Generation IV International Forum (GEN-IV). Molten chloride salt fast reactors (MCFRs) are a type of MSR. Compared to molten fluoride salt reactors (MFSRs), MCFRs have a higher solubility of heavy metal atoms, a harder neutron spectrum, lower accumulation of fission products (FPs), and better breeding and transmutation performance. Thus, MCFRs have been recognized as a type of MSR with great prospects for future development. However, as the most important feature for MSRs, the effect of different reprocessing modes on MCFRs must be researched in depth. As such, this study investigated the effect of different isotopes, especially FPs, on the neutronic performance of an MCFR, such as its breeding performance. Furthermore, the characteristics of the different reprocessing modes and MCFR rates were analyzed in terms of safety, radioactivity level, neutron economy, and breeding capacity. In the end, a reprocessing method suitable for MCFRs was determined through calculation and analysis, which provides a reference for the further research of MCFRs.

616