Abstract：The United Arab Emirates lacks conventional water resources and relies primarily on desalination plants powered by fossil fuels to produce fresh water. Nuclear desalination is a proven technology, cost-competitive, and sustainable option capable of integrating the existing large-scale desalination plants to produce both freshwater and electricity. However, Small Modular Reactors (SMRs) are promising designs with advanced simplified configurations and inherent safety features. In this study, an Integrated Desalination SMR that produces thermal energy compatible with the capacity of a fossil fuel-powered desalination plant in the UAE was designed. First, the APR-1400 reactor core was used to investigate two 150 MWth conceptual SMR core designs, core A and core B, based on two-dimensional parameters, radius, and height. Then, the CASMO-4 lattice code was used to generate homogenized few-group constants for optimized fuel assembly loading patterns. Finally, to find the best core configuration, SIMULATE-3 was used to calculate the core key physics parameters such as power distribution, reactivity coefficients, and critical boron concentration. In addition, different reflector materials were investigated to compensate for the expected high leakage of the small-sized SMR cores. The pan shape core B model (142.6132 cm diameter, 100 cm height, and radially reflected by Stainless Steel) was selected as the best core configuration based on its calculated physics parameters. Core B met the design and safety criteria and indicated low total neutron leakage of 11.60% and flat power distribution with 1.50 power peaking factor. Compared to core A, it has a more negative MTC value of -6.93 pcm/℉ with lower CBC. In a 2-batch scheme, the fuel is discharged at 42.25 GWd/MTU burnup after a long cycle length of 1.58 years. The core B model offers the highest specific power of 36.56 kW/kgU while utilizing the smallest heavy metal mass compared with the SMART and NuScale models.
Abstract：In molten salt reactors (MSRs), the liquid fuel salt circulates through the primary loop and a part of the delayed neutron precursors (DNPs) decays outside the reactor core. To model and analyze the flow field effect of DNPs in channel-type liquid-fueled MSRs, a three-dimensional space-time dynamics code, named ThorCORE3D, that couples neutronics, core thermal-hydraulics, and a molten salt loop system was developed and validated with the Molten Salt Reactor Experiment (MSRE) benchmarks. The effects of external loop recirculation time, fuel flow rate, and core flow field distribution on the delayed neutron fraction loss of MSRE at steady-state were modeled and simulated using the ThorCORE3D code. Then, the flow field effect of the DNPs on the system responses of the MSRE in the reactivity insertion transient under different initial conditions was analyzed systematically for the channel-type liquid-fueled MSRs. The results indicate that the flow field condition has a significant effect on the steady-state delayed neutron fractions and will further affect the transient power and temperature responses of the reactor system. The analysis results for the effect of the DNP flow field can provide important references for the design optimization and safety analysis of liquid-fueled MSRs.
Keywords：Molten salt reactor;Delayed neutron precursor;Nodal expand method;Coupled neutronics and thermal-hydraulics
Abstract：In loss-of-coolant accidents (LOCAs), a passive containment heat removal system (PCS) protects the integrity of the containment by condensing steam. As a large amount of air exists in the containment, the steam condensation heat transfer can be significantly reduced. Based on previous research, traditional methods for enhancing pure steam condensation may not be applicable to steam-air condensation. In the present study, new methods of enhancing condensation heat transfer were adopted and several potentially enhanced heat transfer tubes, including corrugated tubes, spiral fin tubes, and ring fin tubes, were designed. STAR-CCM+ was used to determine the effect of enhanced heat transfer tubes on the steam condensation heat transfer. According to the calculations, the gas pressure ranged from 0.2 to 1.6 MPa, and air mass fraction ranged from 0.1 to 0.9. The effective perturbation of the high-concentration air layer was identified as the key factor for enhancing steam-air condensation heat transfer. Further, the designed corrugated tube performed well at atmospheric pressure, with a maximum enhancement of 27.4%, and performed poorly at high pressures. In the design of spiral fin tubes, special attention should be paid to the locations that may accumulate high-concentration air. Nonetheless, the ring-fin tubes generally displayed good performance under all conditions of interest, with a maximum enhancement of 24.2%.
Keywords：Air-steam condensation;Numerical simulation;Heat transfer enhancement;Fin tube
Abstract：The HTR-PM600 high-temperature gas-cooled reactor nuclear power plant is based on the technology of the high-temperature gas-cooled reactor pebble-bed module (HTR-PM) demonstration project. It utilizes proven HTR-PM reactor and steam generator modules with a thermal power of 250 MWth and power generation of approximately 100 MWe per module. Six modules in parallel, connected to a steam turbine, form a 600 MWe nuclear power plant. In addition, its system configuration in the nuclear island is identical to that of the HTR-PM in which the technical risks are minimized. Under this principle, the HTR-PM600 achieves the same level of inherent safety as the HTR-PM. The concept of a ventilated low-pressure containment (VLPC) is unchanged; however, a large circular VLPC accommodating all six reactor modules is adopted rather than the previous small-cavity-type VLPC, which contains only one module, as defined for the HTR-PM. The layout of the nuclear island and its associated systems refer to single-unit pressurized water reactor (PWR) practices. With this layout, the HTR-PM600 achieves a volume size of the nuclear island that is comparable to a domestic PWR of the same power level. This will be a Generation IV nuclear energy technology that is economically competitive.
Keywords：High-temperature gas-cooled reactor;Module;HTR-PM600;Generation IV
Abstract：The transient performance and optimization of a passive residual-heat removal heat exchanger (PRHR HX) were investigated. First, a calculation method was developed for predicting the heat transfer of the PRHR HX. The calculation results were validated through comparisons with ROSA experimental data. The heat-transfer performance of the AP1000 PRHR HX in the initial period was predicted, and it satisfied the design requirements. Second, the distributions of the heat flux, tube-inside/outside heat-transfer coefficients, and heat load for the AP1000 PRHR HX over 2000 s were examined. Third, an optimization study was conducted by adjusting the horizontal length and tube diameter. Their effects on the four main heat-transfer parameters and the heat-transfer area were analyzed. Furthermore, the influence of the initial in-containment refueling water storage tank (IRWST) temperature was investigated using an established simulation procedure. The results indicated that it significantly affected the trends of the IRWST temperature and reactor outlet temperature. Finally, the minimum required flow rates over time to maintain the reactor outlet temperature at the safety line were determined for different start-up times. The trends of the minimum required flow rate and the peak flow rate were analyzed.
Abstract：JMCT is a large-scale, high-fidelity, three-dimensional general neutron-photon-electron-proton transport Monte Carlo software system. It was developed based on the combinatorial geometry parallel infrastructure JCOGIN and the adaptive structured mesh infrastructure JASMIN. JMCT is equipped with CAD modeling and visualizes the image output. It supports the geometry of the body and the structured/unstructured mesh. JMCT has most functions, variance reduction techniques, and tallies of the traditional Monte Carlo particle transport codes. Two energy models, multi-group and continuous, are provided. In recent years, some new functions and algorithms have been developed, such as Doppler broadening on-the-fly (OTF), uniform tally density (UTD), consistent adjoint driven importance sampling (CADIS), fast criticality search of boron concentration (FCSBC), domain decomposition (DD), adaptive control rod moving (ACRM), and random geometry (RG) etc. The JMCT is also coupled with the discrete ordinate SN code JSNT to generate source-biasing factors and weight-window parameters. At present, the number of geometric bodies, materials, tallies, depletion zones, and parallel processors are sufficiently large to simulate extremely complicated device problems. JMCT can be used to simulate reactor physics, criticality safety analysis, radiation shielding, detector response, nuclear well logging, and dosimetry calculations. In particular, JMCT can be coupled with depletion and thermal-hydraulics for the simulation of reactor nuclear-hot feedback effects. This paper describes the progress in advanced modeling, high-performance numerical simulation of particle transport, multiphysics coupled calculations, and large-scale parallel computing.
Abstract：The evolution of lead halide perovskites used for X-ray imaging scintillators has been facilitated by the development of solution-processable semiconductors characterized by large-area, flexible, fast photoresponse. The stability and durability of these new perovskites are insufficient to achieve extended computed tomography scanning times with hard X-rays. In this study, we fabricated a self-assembled CsPbBr3-based scintillator film with a flexible large-area uniform thickness using a new room-temperature solution-processable method. The sensitivity and responsivity of X-ray photon conversion were quantitatively measured and showed a good linear response relationship suitable for X-ray imaging. We also demonstrated, for the first time, that the self-assembled CsPbBr3-based scintillator has good stability for hard X-ray microtomography. Therefore, such an inexpensive solution-processed semiconductor easily prepared at room temperature can be used as a hard X-ray scintillator and equipped with flexible CsPbBr3-based X-ray detectors. It has great potential in three-dimensional high-resolution phase-contrast X-ray-imaging applications in biomedicine and material science because of its heavy Pb and Br atoms.
Keywords：X-ray scintillator;X-ray illumination;Computed tomography;CsPbBr3-based film perovskite;Solution-processable semiconductor
Abstract：A waterproof nanocrystalline soft magnetic alloy (MA) core with a size of O.D.850 mm×I.D.316 mm×H.25 mm for radio frequency (RF) acceleration was successfully developed by winding 18 μm 1k107b MA ribbons. The products reached 7.5, 10, and 12 GHz at 1, 3, and 5 MHz respectively. The products of the MA core (O.D.250 mm×I.D.100 mm×H.25 mm) manufactured using a 13 μm MA ribbon further increased by 30%. Detailed improvements on the MA core manufacture process are discussed herein. Continuous high-power tests on the new MA cores demonstrated its good performance of waterproofness, particularly its stability of high products. The MA core with high product and large size can operate under a high average RF power, high electric field, and in deionized water, which will be used in the China Spallation Neutron Source Phase II (CSNS-II).
Keywords：Large size magnetic alloy core;High insulation and low stress coating;Waterproof structure;Transverse magnetic field annealing;High power MA loaded cavity
Abstract：X-band high-gradient linear accelerators are a challenging and attractive technology for compact electron linear-accelerator facilities. The Very Compact Inverse Compton Scattering Gamma-ray Source (VIGAS) program at Tsinghua University will utilize X-band high-gradient accelerating structures to boost the electron beam from 50 to 350 MeV over a short distance. A constant-impedance traveling-wave structure consisting of 72 cells working in the 2π/3 mode was designed and fabricated for this project. Precise tuning and detailed measurements were successfully applied to the structure. After 180 h of conditioning in the Tsinghua high-power test stand, the structure reached a target gradient of 80 MV/m. The breakdown rate versus gradient of this structure was measured and analyzed.
Keywords：Traveling-wave accelerating structure;X-band high gradient;Tuning method;High-power test
Abstract：The neutron supermirror is an important neutron optical device that can significantly improve the efficiency of neutron transport in neutron guides and has been widely used in research neutron sources. Three types of algorithms, including approximately 10 algorithms, have been developed for designing high-efficiency supermirror structures. In addition to its applications in neutron guides, in recent years the use of neutron supermirrors in neutron-focusing mirrors has been proposed to advance the development of neutron scattering and neutron imaging instruments, especially those at compact neutron sources. In this new application scenario, the performance of supermirrors strongly affects the instrument performance; therefore, a careful evaluation of the design algorithms is needed. In this study, we examine two issues: the effect of nonuniform film thickness distribution on a curved substrate and the effect of the specific neutron intensity distribution on the performance of neutron supermirrors designed using existing algorithms. The effect of film thickness nonuniformity is found to be relatively insignificant, whereas the effect of the neutron intensity distribution over Q (where Q is the magnitude of the scattering vector of incident neutrons) is considerable. Selection diagrams that show the best design algorithm under different conditions are obtained from these results. When the intensity distribution is not considered, empirical algorithms can obtain the highest average reflectivity, whereas discrete algorithms perform best when the intensity distribution is taken into account. The reasons for the differences in performance between algorithms are also discussed. These findings provide a reference for selecting design algorithms for supermirrors for use in neutron optical devices with unique geometries and can be very helpful for improving the performance of focusing supermirror-based instruments.
Keywords：Neutron-focusing supermirror;Design algorithm;Thickness nonuniformity;Intensity distribution over Q;Selection diagram
Abstract：This study investigates two secondary electron emission (SEE) models for photoelectric energy distribution curves f(Eph, hγ), B, Emean, absolute quantum efficiency (AQE), and the mean escape depth of photo-emitted electrons λ of metals. The proposed models are developed from the density of states and the theories of photo-emission in the vacuum ultraviolet and SEE, where B is the mean probability that an internal photo-emitted electron escapes into vacuum upon reaching the emission surface of the metal, and Emean is the mean energy of photo-emitted electrons measured from vacuum. The formulas for f(Eph, hγ), B, λ, Emean, and AQE that were obtained were shown to be correct for the cases of Au at hγ = 8.1-11.6 eV, Ni at hγ = 9.2-11.6 eV, and Cu at hγ = 7.7-11.6 eV. The photoelectric cross-sections (PCS) calculated here are analyzed, and it was confirmed that the calculated PCS of the electrons in the conduction band of Au at hγ = 8.1-11.6 eV, Ni at hγ = 9.2-11.6 eV, and Cu at hγ = 7.7-11.6 eV are correct.
Keywords：Absolute quantum efficiency;Photoelectric cross-section;Mean escape depth of photo-emitted electrons;Probability;Photo-emission from metals;Secondary electron emission;Vacuum ultraviolet;Mean energy of photo-emitted electrons
Abstract：During the last few decades, rare isotope beam facilities have provided unique data for studying the properties of nuclides located far from the beta-stability line. Such nuclei are often accompanied by exotic structures and radioactive modes, which represent the forefront of nuclear research. Among them, two-proton (2p) radioactivity is a rare decay mode found in a few highly proton-rich isotopes. The 2p decay lifetimes and properties of emitted protons hold invaluable information regarding the nuclear structures in the presence of a low-lying proton continuum; as such, they have attracted considerable research attention. In this review, we present some of the recent experimental and theoretical progress regarding the 2p decay, including technical innovations for measuring nucleon-nucleon correlations and developments in the models that connect their structural aspects with their decay properties. This impressive progress should play a significant role in elucidating the mechanism of these exotic decays, probing the corresponding components inside nuclei, and providing deep insights into the open quantum nature of dripline systems.
Keywords：Exotic decay;Two-proton radioactivity;Nucleon-nucleon correlation;Experimental and theoretical development
Abstract：In recent years, LaBr3(Ce) crystals and silicon photomultipliers (SiPMs) have been increasingly used in radiation imaging. This study involved the establishment of a detector model with a monolithic LaBr3(Ce) crystal and SiPM array for γ-radiation imaging on the GEANT4 platform. The optical process included in the detector model was defined by key parameters, such as the emission spectrum, scintillation yield, and intrinsic resolution of the LaBr3:5% Ce crystal, as well as the detection efficiency of the SiPM array. The response of the detector model to 57Co flooded field irradiation was simulated and evaluated. The radiation images generated by the detector model exhibited a compression effect that was very close to that on images acquired by the physical detector. The spatial resolution of the simulated detector closely approximates that of the physical experiment. A detector model without the optical process was also established for comparison with a detector using the optical process. Both were used in a near-field modified uniform redundant array (MURA) imaging system to acquire images of a point source and a ring source of 57Co at the center of the field-of-view of the imaging system. The spatial resolution and signal-to-noise ratio of the images that were reconstructed using the two detector models were determined and compared. Compared with the detector model without optical processes, although the images from the proposed detector model have slightly inferior signal-to-noise ratios and more artifacts, they are more consistent with the reconstructed versions of images acquired in real physical experiments. The results confirm that the detector model can be used to design a γ-radiation imaging detector and to develop an imaging algorithm that can significantly shorten the development time and reduce the cost.