Dynamic micro-computed tomography (micro-CT) using monochromatic X-ray offers higher density resolution and lower radiation damage compared to that using white X-ray, however balancing its imaging spatial and temporal resolution is challenging. Currently, the reported highest temporal resolution of monochromatic X-ray dynamic micro-CT is 13.3 Hz with a detector effective pixel size of 5 μm.

This study aims to develop a monochromatic X-ray dynamic micro-CT system with a higher spatial and temporal resolution to meet the experimental needs of the fast X-ray imaging beamline (BL16U2) users at Shanghai Synchrotron Radiation Facility (SSRF).

Firstly, an experimental system of dynamic micro-CT with the high flux density monochromatic X-ray from an undulator source was established by combination of a high-speed rotary stage and a large numerical aperture triple-lens fast X-ray imaging detection system on the BL16U2 beamline at SSRF. Then, a demonstration experiment with a fast-foaming polyurethane material as a sample was performed to examine the spatial-temporal resolution of this experimental system, moreover a quantitative analysis of the bubble motion during foaming process was performed.

Experimental results of foaming process of the fast-foaming polyurethane material based on the monochromatic X-ray dynamic micro-CT system show that a temporal resolution of 20 Hz of the dynamic micro-CT was achieved with 15 keV monochromatic X-ray and an effective detector pixel size of 2.2 μm.

The developed monochromatic X-ray dynamic micro-CT system has a high spatial-temporal resolution and can perform four-dimensional quantitative analysis of complex motion systems, providing a powerful experimental research platform for users of BL16U2 beamline at SSRF.

Shanghai High Repetition rate XFEL and Extreme light facility (SHINE) employs a White Rabbit (WR)-based timing system. This timing system operates via the utilization of beamline–endstation division, which receives external reference timing signals and distributes them to each beamline and endstation via WR timing network devices, including master nodes, WR switches and slave nodes.

This study aims to develop a timing equipment control system (TECS) to address the requirements of remote monitoring and control of distributed timing equipment.

Based on Experiment Physics and Industrial Control System (EPICS) and Simple Network Management Protocol (SNMP), an approach for acquiring timing equipment parameters was employed. These parameters was stored in the resident memory database though EPICS Input/Output Controller (IOC) and accessed via a user interface developed with PyDM (Python Display Manager). Archive and retrieval of timing equipment parameters were implemented in the Archiver Appliance historical archiving system. Finally, test environment was set up in laboratory to verify the validity and reliability of this TECS.

This control system underwent testing exhibits its effective functionalities, including real-time monitoring equipment parameters, as well as remote control of equipment signal delay and pulse width. These capabilities are essential in meeting the requirements of SHINE beamlines and endstations.

The extraction of uranium (U) and its alternative resources, such as thorium (Th) and plutonium (Pu), from seawater is essential to address the scarcity of terrestrial U resources. The development of a separation material with high adsorption properties is the key to solving this problem.

This study aims to reveal the adsorption behavior of actinides (U, Th, and Pu) on the surface of a two-dimensional metal material, antimonene.

The Hubbard U values, U_eff, were determined for the on-site Coulomb interactions of 5f electrons of U and Pu atoms using the linear response method. Furthermore, the adsorption energy, adsorption configuration, electronic structures, charge transfer, and highest occupied molecular orbital wavefunction of a U, Th, or Pu atom adsorbed on the surface of monolayer antimonene were analyzed using the DFT+U approximation. The variation of the adsorption rate with temperature was further calculated by the equilibrium adsorption rate equation.

The calculated U_eff values of U and Pu atoms are 2.24 eV and 2.84 eV, respectively. The Pu atom is energetically unfavorable to be adsorbed on antimonene (with a negative adsorption energy for each adsorption site), whereas the U and Th atoms exhibit strong chemical adsorption on its surface. Antimonene also offers abundant surficial stable adsorption sites for the U and Th adatoms. The most energetically stable sites for the U and Th adatoms are the B (Bridge)-H (Hollow) site and H (Hollow) site, with adsorption energies of 4.40 eV and 3.62 eV, respectively. The impurity states are generated in the band gap of antimonene upon the adsorption of the U or Th atom, and the strong p-d coupling between the U or Th adatom and antimonene in the impurity states contributes to the strong adsorption of the adatoms. The desorption temperatures of U and Th on the surface of antimonene reach 837 K and 660 K, respectively.

The results indicate that antimonene is an excellent two-dimensional adsorbent material for U and Th and has potential for several applications such as in the extraction of actinides from seawater.

Complete kinematic measurements in the medium or high-energy region is a common experimental method to study the structure and properties of exotic nuclides on the neutron-rich side. The experiment setup in the Cooling Storage Ring - Radioactive Ion Beam Line in Lanzhou (CSR-RIBLLII), a typical nuclear external target facility, comprises many detectors with different requirements. The anticoincidence (Veto) detector is an essential part of the external target facility for eliminating the interference of charged particles and measuring medium or high-energy neutrons with high reliability and performance by combining them with a neutron wall detector. The original Veto detector with photomultiplier (PMT) readouts has many disadvantages, such as low detection efficiency and poor uniformity, resulting in significant differences or contradictions between experimental and calculation results.

This study aims to upgrade the original Veto detector using wave length shifter fiber (WLS) and silicon photomultiplier (SiPM) to improve the detection efficiency of charged particles.

Firstly, a new configuration for the anticoincidence Veto detector unit was designed and the detector thickness was increased by 5 mm compared to the previous Veto detector, resulting in a final thickness of 1 cm. The Veto detector was embedded with 15, 7, and 3 WLS fibers from both ends, and read using SiPM. Furthermore, to systematically explore the performance of the detector unit, a linear relationship was calibrated between the number of photons of the SiPMs and the number of Analog-to-Digital Converter (ADC) channels. This relationship was used to accurately calculate the threshold value, laying a foundation for calculating detection efficiency. Then, based on Multi-Wire Proportional Chamber (MWPC), a detection efficiency test platform was established, and time position conversion and track selection data analysis methods were developed as test methods. Finally, a detailed test on the whole and each part of the anticoincidence Veto detector unit was carried out on the MWPC test platform.

Test results show the highest anticoincidence efficiencies of SiPMs at both ends for the Veto detector embedded with 15, 7, and 3 WLS fibers are 99.99%, 99.94%, and 99.82%, respectively; increased by over 22.74% compared with the original Veto detector.

The new Veto detector based on WLS fiber and SiPM readout meets the needs of the CSR-RIBLLII external target facility.

Recently, global concerns regarding the illicit transportation and trafficking of nuclear materials and other radioactive sources have increased, leading to increased demands for efficient and rapid security and non-proliferation technologies. The International Atomic Energy Agency's Incident and Trafficking Database has reported 3 235 confirmed incidents involving nuclear and other radioactive materials out of regulatory control from 1993 to 2017. Of these incidents, 278 are associated with trafficking or malicious use of materials such as highly enriched uranium, plutonium, and plutonium-beryllium neutron sources. Therefore, developing depth-of-interaction detector for neutrons and gamma rays is important for effective control of nuclear and radiation materials at national and international cross points such as borders, ports, and airports.

This study aims to design a depth-of-interaction detector for neutrons and gamma rays and characterize its performance.

Hereby, an EJ276 plastic scintillator (Φ3 cm× 15 cm) coupled with two silicon photomultipliers (SiPMs) in both sides was designed as a depth-of-interaction detector for neutrons and gamma rays. The short gate time was optimized to achieve better neutron/gamma-ray discrimination, and the reaction position was determined based on the amplitude ratio and time of flight (TOF) difference between signals from two sides. Finally, Am-Be neutron source and ¹³⁷Cs γ source were applied to detector parameter optimization and resolution calibration for performance characterization.

Experimental results demonstrate that good consistency in the detection efficiency of the detector at different incident positions, where the resolution of the one-dimensional reaction position is approximately 4.4 cm.

The designed depth-of-interaction detector can be used toreplace detector arrays in neutron scatter cameras and coded-aperture imagers to reduce costs and system complexity.

Diamond material demonstrates excellent temperature and radiation resistance properties, and detectors made from diamond exhibit good potential for use under harsh environments.

This study aims to analyze the structure and working principle of diamond thermal neutron detectors, and establish a physical model of such a detector applied to 2 MW thorium molten salt experimental reactor-liquid fueled (TMSR-LF1) radiation field by using MCNP program.

First of all, ⁶Li and ¹⁰B were selected as neutron conversion materials considering the neutrons of TMSR-LF1 mainly concentrated in the 10^-8~10^-6 MeV energy range, and the Stopping and the Range of the Ions in Matter (SRIM) program was employed to calculate the range of secondary charged particles generated by the reaction in the neutron conversion layer and diamond layer. Then, the MCNP program was used to establish a physical model of diamond neutron detector applied to 2 MW TMSR-LF1 radiation field. Finally, the effects of the neutron conversion layer thickness (⁶LiF, ¹⁰B), diamond thickness, and γ screening threshold on the neutron detection efficiency, γ detection efficiency, and n/γ suppression ratio of the detector were determined through simulation results.

The results reveals that ⁶LiF is more suitable than ¹⁰B for use in the neutron conversion layer in neutron and γ mixed fields. With the increase of the ⁶LiF thickness, the neutron detection efficiency first increases and then decreases, and the optimal thickness of ⁶LiF is 25 μm. The n/γ discrimination performance of the detector deteriorates with the increase of diamond thickness, but the diamond thickness must be greater than 20 μm to ensure insensitivity of the detector to γ, hence a γ screening threshold is needed to prevent excessive γ interference for thick diamond layers.

The influence of detector structural parameters on detector performance obtained by this study has guiding significance for the subsequent fabrication of and research on such detectors.

Elliptic flow (v₂) is one of the most important observations for exploring the properties of nuclear matter using heavy-ion collisions. v₂ is not only affected by dynamic processes but is also related to the Fermi momentum of the initial nucleus.

This study aims to quantitatively determine the effect of the initial Fermi momentum on the time evolution of v₂.

First, based on the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model, gold-gold (Au+Au) collisions at beam energies of 0.4A GeV and 0.8A GeV with impact parameter b = 6 fm were simulated. In the initial stage, three cases were considered: without Fermi momentum, with Fermi momentum, and with half-Fermi momentum. Then, by reverse tracing the nucleons that were emitted at mid-rapidity (|y₀|<0.1) throughout the reaction process, the time evolution of v₂ for these traced nucleons was investigated in detail. Finally, the influence of the initial Fermi momentum on v₂ of the nucleons in the mid-rapidity region in heavy-ion collisions at intermediate energies was examined.

The yield of free nucleons calculated by considering the Fermi momentum was much larger than that obtained without the Fermi momentum, owing to the reduction in nucleon-nucleon collisions. However, v₂ shows the opposite effect; it is obtained by considering that the Fermi momentum is much smaller than that in the latter case because of the stronger blocking effect of the spectator nucleons.

Our results indicate that the initialization of the nucleon momentum must be carefully considered in the transport model.

Traditional X-ray fluorescence spectrum analysis has the limitations of poor accuracy of the characteristic peak counting rate and shadow peak.

This study aims to propose a long and short term memory (LSTM) neural network model based on deep learning for the loss correction of the characteristic peak count rate and shadow peak.

Firstly, a LSTM neural network model based on deep learning was proposed to estimate accurately the amplitudes of nuclear pulse signals by learning samples. Then, a convolutional neural network (CNN) with unique convolutional kernel structure was introduced to deal with the challenges of large sample size of the nuclear pulse signal and the low training efficiency of the model by extracting the sample features layer by layer, thereby effectively reducing the number of samples and the complexity of model training. Finally, a series of offline nuclear pulse sequences of powdered iron ore samples were used to generate the dataset required for model training. Among the 64 000 entries in this dataset, 44 800 were used as training sets, 12 800 were used as validation sets, and the remaining 6 400 were used as testing sets.

The trained CNN-LSTM model saves considerable training time, overcomes the defects of local convergence of traditional methods, and accurately estimates the parameters of input pulse under different degrees of distortion. Results show that the accuracy rate of the training and verification sets is greater than 99%. An analysis of the count repair results reveals that the average value of the correction ratio of the three shadow peaks, that is, the correction ratio of the depth learning model trained in this study to the count loss derived from the distorted pulses, is 91.52%.

The CNN-LSTM model can effectively correct the shadow peaks derived from the amplitude loss of distorted pulses and improve the accuracy of the characteristic peak count rate in X-ray fluorescence spectra. The model is shown to have high application value for the field of X-ray fluorescence spectroscopy.

Molten salt reactors, one of the important types of fourth-generation advanced reactors, use high-boiling-point molten salt as a nuclear fuel carrier after melting, hence have the characteristics of high-temperature output and normal-pressure operation. A heat-pipe molten salt reactor based on thermoelectric power generation has the advantages of its components, that is, high output temperature, high thermoelectric conversion efficiency, simple structure, safety, and reliability. Therefore, the reactor of heat-pipe molten salt has significant advantages in the field of energy systems as it is an ideal energy source for outer space and deep-sea exploration missions. However, because of the low thermal conductivity of the molten salt in the core, the dense arrangement of heat pipes complicates the heat transfer design of the thermal power generator in the condensing section of the heat pipes.

This study aims to design a heat-pipe–thermal power generation coupling system structure suitable for molten salt reactors, and analyze its heat transfer characteristics on the basis of design requirements of the reactor.

Firstly, the condensing section of the core heat pipe was designed using a tower thermoelectric power generation system. A thermoelectric generator was placed between the outer wall of the hot-side tower and the inner wall of the cold-side tower, and the gap between the generators was made of an insulating material to reduce heat leakage. Then, a heat transfer simulation of a four-layer tower thermoelectric power generation system suitable for a heat-pipe molten salt reactor was performed using the ANSYS Workbench. Finally, temperature distribution and variation under different power values at each layer of the thermoelectric generator and every thermoelectric generator, etc., were analyzed.

The analysis results reveal that, when the system is running with maximum heat-pipe temperature of 696 ℃, the temperature distribution in the overall tower is uniform, the effective heat utilization rate is >96%, the system leakage heat is <4%, and the temperature difference between the two sides of the generator is >490 ℃, which is conducive for improving the thermoelectric conversion efficiency.

The structural design of this study is feasible and conducive for promoting the application of thermoelectric power generation in a heat-pipe molten salt reactor.

The metallic materials utilized for nuclear reactors undergo corosion due to the inherient high-temperature and high-pressure environment. Consequently, the corrosion products may be deposited in the core, called crud, and impact the fuel operation, core reactivity, and primary radioactivity, such as crud-induced localized corrosion or crud-induced power shift.

Thus, this study aimed to establish a model that can quantitatively analyze these corrosion products, the results of which can then be used to evaluate the impact of these products.

Based on the corrosion and release dynamic theory, combined with the assumption of metallic oxide volume ratio (Pilling-Bedworth Ratio), a corrosion and release model of metallic materials was developed. The model was validated based on experimental data from Inconel 690.

The verification result indicates that the proposed model is reasonable and scientific, and hence can be used to quantify the amount of main corrosion and release products of metallic materials for nuclear reactors.

This study provides a model of the main elements of corrosion products including Ni and Fe ferrite for PWR plants, which can be used for evaluating the impact of corrosion products. However, some of the microelements of corrosion cannot be quantified by using this model as the corresponding equations were over-determined. Hence this aspect requires further research in the future.

In the international fourth-generation nuclear power system, the lead-bismuth fast reactor is one of the most concerned technologies. However, insoluble particulate matter generated in the flow of liquid lead-bismuth alloys will collect locally in the flow channel and affect the operation of lead-bismuth fast reactors.

This study aims to find the motion deposition of particulate matter in the flow channel, understand its influence on the safe operation of small lead-bismuth fast reactors, and provide a reference for the safe design of lead-bismuth reactors.

Firstly, based on the design scheme of 100 MWth small natural circulation lead cooled fast reactor SNCLFR-100, the particle deposition in the rod bundle channels that were divided into three types according to the relative position and wall conditions: triangle like channels, pentagon like channels and trapezoid like channels, was numerically simulated using ANSYS software, and the particle deposition movement was obtained. Then, the effects of particle type, particle size and particle velocity on particle deposition were obtained on the basis of grey correlation degree theory. Finally, the correlation degree of various factors affecting particle deposition rate was analyzed.

The results show that the particle deposition mainly occurs at the inlet stage,the surface of the inlet section is large area adhesion deposition,and the surface of the middle and rear sections is point-like deposition. With the increase of axial distance, the magnitude of turbulent kinetic energy is the main factor affecting the radial distribution of particulate matter. The increase of particle density and particle size will strengthen the deposition of particulate matter. The increase of particle velocity will reduce the particle deposition. The degree of influence on particle deposition is particle size>type> particle velocity.

During the operation of lead-bismuth fast reactor, attention should be paid to the deposition of particles in the inlet section and to remove the particles with larger particle size.

The core corium may melt through the reactor pressure vessel wall then lead to the failure of the second barrier during a serious accident. Core catcher can collect and cool the corium and prevent the development of severe accident.

This study aims to establish a computational model to explore the cooling process of crucible core catcher adopted by VVER (Vodo-Vodyanoi Energetichesky Reactor) designed by Russia.

According to the derived parameters based on VVER core catcher design data, non-isothermal flow calculation module of COMSOL was established to simulate the flow field, temperature field, and crust distribution of corium pool. The solidus temperature and liquidus temperature and the exponential form change of corium viscosity were referred to the research results of VULCANO item.

For the double layered structure of the corium pool in core catcher, the metal layer solidifies quickly after a core meltdown accident. Constantly changing natural convection flows are formed in the upper and middle part of the oxide layer and the temperature distribution is relatively uniform. No strong convection exists in the lower part of the oxide layer lead to obvious thermal stratification. Most of the corium cooled in the upper part of the oxide layer will transfer to the lower part by gravity and natural convection before full solidification, resulting in a slow increase in the thickness of the upper crust and a rapid increase in the bottom crust of the oxide layer.

The safety margin of crucible core catcher of VVER is sufficient, however the relevant equipment, support and auxiliary system are required to remain operational for a long time to realize the design function.

FLiBe is commonly used as the coolant and carrier salt in liquid molten salt reactors (MSRs). Its certain moderating properties and thermal neutron scattering attributes affect the neutronic performance of the MSR, and this in turn influences the physical design and safe operation of the reactor. Consequently, studying FLiBe's thermal neutron scattering data is essential for MSRs.

This study aims to analyze the influence of of FLiBe thermal neutron scattering on neutronic performances of a 65-MW MSR.

First, according to the requirements, a core model of a 65-MW MSR was established by using the general Monte Carlo procedure. Then, the neutronics performance of the MSR was calculated by considering the scattering cross-section of the free gas model and FLiBe thermal neutron scattering data (e.g., the neutron spectrum, effective multiplication factor, and nuclide reactivity rate). Finally, the changes in the influence of FLiBe thermal neutron scattering effect on neutronic properties under different energy spectra were compared.

The computation results show that, by considering the thermal scattering effect of FLiBe molten salt, the neutron energy spectrum in the core of the MSR becomes harder, ²³⁵U fission rate decreases, the k_eff value of the reactor decreases, but the density coefficient in the temperature reaction coefficient of the fuel keeps almost unchanged, and the Doppler coefficient decreases by 0.28×10^-5 K^-1. With the hardening of the energy spectrum, the variation in the ²³⁵U fission rate reduction decreases, and the decrease in k_eff caused by thermal neutron scattering changs from 9.2×10^-4 to 2×10^-4.

Therefore, it is necessary to incorporate FliBe's thermal neutron scattering data into the physical calculations for the MSR core.

In a pressurized water reactor (PWR) loss-of-coolant accident (LOCA), high temperature and high internal pressure of the fuel rod can lead to ballooning of fuel rod cladding, which causes a partial blockage of flow area in a subchannel. Such flow blockage would influence the core coolant flow and thus affect the core heat transfer during reflood phase and subsequent severe accidents. However, the commonly used integrated severe accident analysis codes use simple parametric models to simulate these aspects and therefore cannot consider the influence of multiple coupled factors. This results in a lack of accuracy of the simulation results.

This study aims to analyze the key phenomena in core degradation, and develop a thermal-mechanical (TM) behavior module for assessing the failure of cladding and analyzing the flow blockage.

First of all, the fuel rod thermal–mechanical behavior (FRTMB) module developed for analyzing the TM behavior of fuel rods was integrated into the integrated severe accident analysis code (ISAA). Then, on the basis of the FRTMB module, the flow blockage model of the ISAA-FRTMB code was improved to suit for simulating changes in coolant flow rate caused by fuel rod deformation. Finally, the QUENCH-LOCA-0 experiment was simulated by using improved ISAA-FRTMB code to verify the correctness and effectiveness of the model, and the peak cladding temperatures were compared in order to verify the validity of the flow blockage model.

The results including cladding failure time, circumferential strain, flow blockage rate and cladding temperature predicted by the code are in good agreement with the experimental data. The maximum circumferential strain of the simulated cladding, as indicated by the experimental results, is in the range of 25%?50%, and the errors of the predicted cladding rupture time and temperature are within 4%.

Under the stress caused by internal pressure, the cladding deforms outward owing to thermal creep with the increase of temperature. Rapid thermal creep and swelling lead to cladding failure. The maximum circumferential strain of the simulated cladding, as indicated by the experimental results, is in the range of 25%?50%, and the errors of the predicted cladding rupture time and temperature are within 4%. The correctness and effectiveness of FRTMB module are thus verified.

Currently, the destructive puncture manometry method is used to measure helium pressure inside fuel rods. However, this method is expensive and does not guarantee 100% coverage. Hence the non-destructive testing (NDT) equipment is introduced for non-destructive measurement of helium pressure inside fuel rods.

This study aims to analyze the reliability of NDT testing method for the measurement of helium pressure inside fuel rods.

Three standard rods with helium pressure values of 0.98 MPa, 1.76 MPa, 2.45 MPa, respectively, were selected for experimental test. The experimental fuel rods were first used to obtain the results comparison of heat transfer method and puncture manometry, then the control variates were employed to control the fuel rod temperature, the time interval of a single measurement, and the ambient temperature respectively, so as to determine influencing factors in the NDT method. Finally, reliability analysis of NDT method was performed according to experimental results.

The results of the NDT method are consistent with that of the puncture manometry method at a temperature range of 24~30 oC with less than 0.05 MPa deviation. Minimum repeat measurement time interval for NDT measuring helium pressure of the same standard rod or fuel rod is 2 min.

The NDT method for measuring the helium pressure of fuel rods is reliable, and the measurement results are stable in different environmental conditions.