Vol.30,

A compact 15.0-MeV, 1.5-kW electron linear accelerator (LINAC) was successfully constructed to provide an electron beam for the first photoneutron source at the Shanghai Institute of Applied Physics, Shanghai, China. This LINAC consists of five main parts: a thermal cathode grid-controlled electron gun, a pre-buncher, a variable-phase-velocity buncher, a light-speed accelerating structure, and a high-power transportation beamline. A digital feedforward radio frequency compensator is adopted to reduce the energy spread caused by the transient beam loading effect. Furthermore, a real-time electron gun emission feedback algorithm is used to keep the beam stable. After months of efforts, all the beam parameters successfully met the requirements of the facility. In this paper, the beam commissioning process and performance of the LINAC are presented.

541

To date, two-color pulses are widely used in pump–probe experiments. For a ring-based light source, the power of the spontaneous radiation fluctuates randomly in the longitudinal direction. It is difficult to produce two-color double pulses by optical methods. In this paper, we introduce a method based on the echo-enabled harmonic generation scheme that generates two-color pulses in a storage ring light source. By adopting crossed undulators and a phase shifter, the polarization of the two-color pulses can be easily switched. A numerical simulation of a diffraction-limited storage ring, the Hefei Advanced Light Source, suggests that the time delay and spectral separation of the two pulses can be adjusted linearly by changing the pulse duration and chirp parameters of the seed laser. A circular polarization degree above 80% could be achieved.

530

This work aims at evaluating the reliability of the GEANT4 (GEometry ANd Tracking 4) Monte Carlo (MC) toolkit in calculating the power deposition on the Megawatt Pilot Experiment (MEGAPIE), the first liquid-metal spallation target worldwide. A new choice of codes to study and optimize this target is provided. The evaluation of the GEANT4 toolkit is carried out in comparison with the MCNPX and FLUKA MC codes. The MEGAPIE is an international project led by the Paul Scherrer Institute (PSI) in Switzerland. It aims to demonstrate the safe operation of an intense neutron source to power the next generation of nuclear reactors, accelerator driven systems (ADSs). In this study, we used the GEANT4 MC toolkit to calculate the power deposited by fast protons on the MEGAPIE target. The calculation focuses on several structures and regions. The predictions of our calculations were compared and discussed with that of the MCNPX and FLUKA codes, adopted by the MEGAPIE project. The comparison shows that there is a very good agreement between our results and those of the reference codes.

469

After the Fukushima disaster, interest in the evaluation of severe accidents in nuclear power plants and off-site consequences has significantly increased. Because experimental studies are difficult to conduct, computational methods play a substantial role in accident analysis. In this study, a severe accident in the Bushehr pressurized water reactor power plant caused by a station blackout with a total loss of alternating current power supply has been evaluated. This analysis presents the in-core damage of fuel rods and the release of fission products as well as the thermal hydraulic response of the station components during the loss of active emergency cooling systems. In this manner, a perfect model of the Bushehr nuclear power plant using the MELCOR code is prepared. The accident progression is simulated and the thermal responses of the fuels and hydraulic components are presented. It is shown that, without operator intervention, steam generators will become dry in approximately 3000 s, and the heat sink of the reactor will be lost. The simulation results show that at approximately 8600 s, the upper parts of the core start melting. This model calculates the shortest available time for accident prevention and proves that the time available is sufficient for operator manual action to prevent a nuclear disaster.

566

To explore the behavior of radiolytically produced hydrogen release from the waste resin stored in a high integrated container (HIC), and the mechanism of hydrogen diffusion in a near-surface disposal facility, both experimental studies and numerical simulations were performed through an accelerated irradiation test and simulated disposal, respectively. Results indicated that, 100 years after disposal, the highest hydrogen concentration appeared in the cell where the HICs were placed. The volume fraction for different scenarios postulated in the numerical simulation was 2.64% for Scenario 1, 2.28% for Scenario 2, and 3.965% for Scenario 3, all of which are lower than the hydrogen explosion limit of 4.1%. The results indicated that the simulated HIC disposal scheme is safe.

768

304L H-shaped stainless steel is used as the support frame of the passive residual heat removal heat exchanger (PRHR HX) in a nuclear fission reactor. The extrusion process is adopted to manufacture the 304L H-shaped stainless steel. Finite element method (FEM) simulation is herein used to analyze metal flow characteristics, optimize the extrusion die and predict the extrusion force at different temperatures and speeds. A Φ400 mm container and Φ388 mm forging billet are selected and the 304L H-shaped stainless steel is successfully manufactured using a Germany SMS 60 MN horizontal extruder. The mechanical properties and microstructure of the manufactured 304L H-shaped stainless steel meet the requirements of the PRHR HX, and the surfaces of the product pass the dye penetration test (PT). The H-shaped stainless steels are used in Haiyang nuclear power plant in Shandong Province.

526

The reactivity of a nuclear reactor is the most important safety and operating parameter. Due to short reactor period, the Light Water Reactor (LWR) designs require the compensations of rapid unfavorable reactivity increases. The increase in fuel or moderator temperature leads to compensate the reactivity jumps as inherent safety characteristics. The safe and reliable reactor operation requires the accurate assessment of these reactivity changes. This paper highlights the improvements in the methodology to determine the feedback reactivity changes for IAEA MTR Benchmark. This method incorporates the reactivity effects of fuel temperature in moderator regions and vice versa. For this purpose, a detailed 3-D model of the IAEA 10 MW MTR benchmark reactor is developed employing OpenMC computer code. OpenMC is a probabilistic computer code for neutronic calculations. This work uses temperature dependent JEFF 3.2 cross-section library. The model is validated against the reference results of eigenvalues for control rods (inserted and in fully withdrawn position), control rod reactivity worth, averaged thermal flux in the central flux trap, and power fraction for each fuel element (FE) at beginning of life (BOL). The validated model is applied to simulate the feedback reactivity coefficients against the conventional reference results. In order to improve the methodology, the effect of the moderator temperature and void on fuel is incorporated to improve the value of the fuel temperature coefficient (FTC). Similarly the moderator temperature coefficient (MTC) and void coefficient (VC) are improved by incorporating the coupling effects of fuel temperature on moderator. This methodology can be applied to improve the LWRs designs.

534

In this paper, non-equilibrium ignition conditions for magnetized cylindrical deuterium-tritium plasma in the presence of an axial magnetic field have been investigated. It is expected that temperature imbalance between ions and electrons as well as the axial magnetic field will relax the threshold of ignition conditions. Therefore, ignition conditions for this model are derived numerically involving the energy balance equation at the stagnation point. It has been derived using parametric space including electron and ion temperature (T_e, T_i), areal density (ρR), and seed magnetic field depended free parameters of B/ρ, mB, and BR. For B/ρ<10⁶ G cm³ g^-1, mB<4×10⁴ G cm g^-1, and BR<3×10⁵ G cm, the minimum fuel areal density exceeds between ρR>0.002 g cm^-2, ρR>0.25 g cm^-2 and ρR>0.02 g cm^-2, respectively. The practical equilibrium conditions also addressed which is in good agreement with the corresponding one temperature magnetized mode proposed in previous studies. Moreover, it has been shown that the typical criterion of BR≥(6.13-4.64)×10⁵ G cm would be expectable. It is also confirmed that the minimum product of areal density times fuel temperature in equilibrium model is located in the range of T=6-8 keV for all these free parameters, depending on the magnitude of the magnetic field. This is the entry point for the non-equilibrium model consistent with equilibrium model.

621

When using the beam scanning method for particle beam therapy, the target volume is divided into many iso-energy slices and is irradiated slice by slice. Each slice may comprise thousands of discrete scanning beam positions. An optimized scanning path can decrease the transit dose and may bypass important organs. The minimization of the scanning path length can be considered as a variation of the traveling salesman problem (TSP); the simulated annealing (SA) algorithm is adopted to solve this problem. The initial scanning path is assumed as a simple zigzag path; subsequently random searches for accepted new paths are performed through cost evaluation and criteria-based judging. To reduce the optimization time of a given slice, random searches are parallelized by employing thousands of threads. The simultaneous optimization of multiple slices is realized by using many thread blocks of General-purpose computing on graphics processing units (GPGPU) hardware. Running on a computer with an Intel i7-4790 CPU and NVIDIA K2200 GPU, our new method required only 1.3 s to obtain optimized scanning paths with a total of 40 slices in typically studied cases. The procedure and optimization results of this new method are presented in this work.

568

Third-generation-semiconductor zinc oxide is utilized as an energy converting material in a betavoltaic battery, where 0.06 Ci ⁶³Ni and 8 Ci ¹⁴⁷Pm are used as the beta sources. Based on a Monte Carlo simulation, the full scales of the devices are derived as 17 and 118 μm, respectively, for both sources. The influences of semiconductor doping concentrations on the electrical properties of the devices are analyzed. For a typical doping concentration N_A=10¹⁷ cm^-3, N_D=10¹⁶ cm^-3, the conversion efficiencies are 7.177% and 1.658%, respectively, using ⁶³Ni and ¹⁴⁷Pm sources. The calculation results of energy deposition in materials for the two sources show that the doping concentrations drop to 1×10¹³~5×10¹⁴ cm^-3 and 1×10¹²~5×10¹³, and accordingly, the energy conversion efficiencies are rise to 14.212% and 18.359%, respectively.

456

Adsorption and desorption of hydrogen on/from single-vacancy and double-vacancy graphenes were studied by means of first-principles calculations. The structure and stability of continuous hydrogenation in single vacancy were investigated. Several new stable structures were found, along with their corresponding energy barriers. In double-vacancy graphene, the preferred sites of H atoms were identified, and H₂ molecule desorption and adsorption of from/on were calculated from the energy barriers. This work provides a systematic and comprehensive understanding of hydrogen behavior on defected graphene.

516

A prompt gamma neutron activation analysis (PGNAA) system was developed to detect the iron content of iron ore concentrate. Because of the self-absorption effect of gamma rays and neutrons, and the interference of chlorine in the neutron field, the linear relationship between the iron analytical coefficient and total iron content was poor, increasing the error in the quantitative analysis. To solve this problem, gamma-ray self-absorption compensation and a neutron field correction algorithm was proposed, and the experimental results have been corrected using this algorithm. The results show that the linear relationship between the iron analytical coefficient and total iron content was considerably improved after the correction. The linear correlation coefficients reached 0.99 or more.

571

Because of the growing concern over the radiation dose delivered to patients, X-ray cone-beam CT (CBCT) imaging of low dose is of great interest. It is difficult for traditional reconstruction methods such as Feldkamp (FDK) to reduce noise and keep resolution at low doses. A typical method to solve this problem is using optimization-based methods with careful modeling of physics and additional constraints. However, it is computationally expensive and very time consuming to reach an optimal solution. Recently, some pioneering work applying deep neural networks had some success in characterizing and removing artefacts from a low-dose data set. In this study, we incorporate imaging physics for a cone-beam CT into a residual convolutional neural network (Res-CNN) and propose a new end-to-end deep-learning-based method for slice-wise reconstruction. By transferring 3D projection to a 2D problem with a noise reduction property, we can not only obtain reconstructions of high image quality, but also lower the computational complexity. The proposed network is composed of three serially connected sub-networks: a cone-to-fan transformation sub-network, a 2D analytical inversion sub-network, and an image refinement sub-network. This provides a comprehensive solution for end-to-end reconstruction for CBCT. The advantages of our method are that the network can simplify a 3D reconstruction problem to a 2D slice-wise reconstruction problem and can complete reconstruction in an end-to-end manner with the system matrix integrated into the network design. Furthermore, reconstruction can be less computationally expensive and easily parallelizable compared with iterative reconstruction methods.

471

Associated alpha particle imaging based on the time-of-flight (API–TOF) technique is an advanced neutron analysis method, which is capable of discriminating material nuclides and three-dimensional imaging of the spatial distribution of material nuclei. In this paper, the spatial resolution of API–TOF and its effects are studied using mathematical analysis and Monte Carlo numerical simulation. The results can provide guidance and assist in designing of API–TOF detection devices. First, a mathematical analysis of the imaging principles of the API–TOF was carried out, and the calculation formulas of the spatial resolution of API–TOF were deduced. Next, the relationship between the device layout and the spatial resolution of the API–TOF detection device was studied. The concept of a typical API–TOF detection device with an optimized structure was proposed. Then, the spatial distribution of the spatial resolution of the typical API–TOF detection device was analyzed, and the effects of the time resolution and the neutron emission angle resolution on the spatial resolution were studied. The results show that spatial resolutions better than 1 cm can be achieved by improving the time resolution and the neutron emission angle resolution to appropriate levels. Finally, a Monte Carlo numerical simulation program was developed for the study of the API–TOF, and was used to calculate the spatial resolutions of the API–TOF. The comparison of the results shows that the spatial resolutions calculated based on the Monte Carlo numerical simulation are in good agreement with those calculated based on the mathematical analysis. This verifies the mathematical analysis and the evaluation of the effects of the spatial resolution of the API–TOF in this study.

435

Residual thermal stress in the system is a serious problem that affects the application of tritium permeation barrier coatings in fusion reactors. The stress not only determines the adhesion between coating and substrate, but also changes the properties of the material. In this study, finite element analysis (FEA) was used to investigate the relationship between the residual thermal stress and the mechanical properties of Al₂O₃ tritium penetration barrier systems. Moreover, the residual thermal stress influenced by factors such as different substrates, temperature, and substrate roughness was also analyzed. The calculation showed that the hardness and elastic modulus increased with increasing compressive stress. However, the hardness and elastic modulus decreased with increasing tensile stress. The systems composed of Al₂O₃ coatings and different substrates exhibited different trends in mechanical properties. As the temperature increased, the hardness and the elastic modulus increased in an Al₂O₃/316L stainless steel system; the trend was opposite in an Al₂O₃/Si system. Apart from this, the roughness of the substrate surface in the system could magnify the change in hardness and elastic modulus of the coating. Results showed that all these factors led to variation in the mechanical properties of Al₂O₃ tritium permeation barrier systems. Thus, the detailed reasons for the changes in mechanical properties of these materials need to be analyzed.

601

The calculation of inelastic creep damage is important for the structural integrity evaluation of the elevated temperature structure in a thorium molten salt reactor (TMSR). However, a creep damage theory model and numerical simulation method have not been proposed for the key materials (UNS N10003 alloy) in the TMSR. In this study, creep damage characterization of UNS N10003 alloy is investigated using the Norton creep law and Kachanov-Rabotnov (K-R) creep damage model. First, the creep experimental data of the UNS N10003 alloy at 650 ℃ were adopted to fit the material constants of the two models. Then, the creep damage behavior of the UNS N10003 alloy were analyzed and discussed under uniaxial and multi-axial stress states. The results indicated that the K-R creep damage model is more suitable for the UNS N10003 alloy than the Norton model. Finally, the numerical simulation method was developed by a user-defined UMAT subroutine and subsequently verified through a finite element analysis (FEA). The FEA results are were in agreement with the theoretical solutions. This study provides an effective method for the inelastic creep damage analysis of the elevated temperature structure in the TMSR.

458

The new 1 kW power module for ADS project needs the optimization of cooling design including water flow and tunnel layout, the water flow of 3 tons per hour was chosen to be a goal for a 20kW power source. According to analysis from the insertion and integrated loss, about 24 modules were integrated into the rated power. Thus, every module has a cooling flow of 2.1 L/min for RF heat load and power supply loss, which is very hard to achieve if no special consideration and techniques. A new thermal simulation method was introduced for thermal analysis of cooling plate through CST Multi-Physics Suite, especially for temperature of power LDMOS transistor. Some specific measures carried out for the higher heat transfer were also presented in this paper.

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