Vol.28,

Integral experiments on tungsten slab samples were carried out on the D-T neutron source facility at China Institute of Atomic Energy. Leakage neutron spectra from the irradiated tungsten target were measured by the time-of-flight technique. Accuracy of the nuclear data for tungsten was examined by comparing the measured neutron spectra with the leakage neutron spectra simulated using the MCNP-4C code with evaluated nuclear data of the JEFF-3.2, FENDL-3.0 and TENDL-2014 libraries. The results show that the calculations with JEFF-3.2 agree well with the measurements in the whole energy range and all angles, whereas the spectra calculated with FENDL-3.0 and TENDL-2014 have some discrepancies with the experimental data.

540

The low energy muon (LEM) facility at PSI provides nearly fully polarized positive muons with tunable energies in the keV range to carry out muon spin rotation (LE-μSR) experiments with nanometer depth resolution on thin films, heterostructures, and near-surface regions. The low energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes, which can be operated at different electric potential. In LE-μSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies (0.5-30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.

403

Electrochemical logical operations utilizing biological molecules (protein or DNA), which can be used in disease diagnostics and bio-computing, have attracted great research interest. However, the existing logic operations, being realized on macroscopic electrode, are not suitable for implantable logic devices. Here, we demonstrate DNA-based logic gates with electrochemical signal as output combined with gold flower microelectrodes. The designed logic gates are of fast response, enzyme free and micrometer scale. They perform well in either pure solution or complex matrices, such as fetal bovine serum, suggesting great potential for in vivo applications.

324

In this article, we present the promise of a new method generating double electron pulses in picosecond-scale pulse length and tunable interpulse spacing at several picoseconds. This has witnessed an impressive potential of application in pump-probe techniques, two-color X-ray free electron laser (FEL), high-gradient witness bunch acceleration in a plasma, etc. Three-dimensional simulations are carried out to analyze the dynamic of the electron beam in a linear accelerator. Comparisons are made between the new method and existing ways.

403

Technetium (⁹⁹Tc), a major fission product in nuclear reactors, of high yield, long-half-life and high mobility in the environment must be removed in nuclear fuel reprocessing. Considering rhenium (Re) and Tc are both VIIB elements, Re is a good chemical analogue to ⁹⁹Tc. Herein, we use Re as a substitution of ⁹⁹Tc to study adsorption and desorption behavior. Porous 4-vinylpyridine–divinylbenzene-based (4VP-DVB) adsorbent containing tertiary amine groups is synthesized by suspension polymerization and characterized by BET, TGA, SEM and laser particle size analyzer. The adsorbent has high adsorption efficiency toward Re (VII) in 0.1 mol/L nitric acid solution, and the adsorption equilibrium can be achieved in 30 min. The adsorption kinetics of Re (VII) follows pseudo-second-order rate equation, the adsorption isotherm matches well with the Langmuir isotherm, and the adsorption capacity of Re (VII) on 4VP-DVB adsorbent is 352.1 mg/g at 298 K. Thermodynamic study reveals that the adsorption process is exothermic. This adsorbent is of separation convenience when a fixed-bed column is used, compared to the batch adsorption treatment.

341

Atomic configuration and connectivity of Sb₂Te₃ thin film are investigated using high energy X-ray diffraction and reverse Monte Carlo simulation. Atomic model details of Sb₂Te₃ thin film are compared with liquid and amorphous Sb₂Te₃ reported in other article. Simulations show that both Sb-Sb and Te-Te homopolar bonds are present in the models. In phase transition process, atomic configuration of the sample rearrange gradually through the forming of Sb–Te bonds, and the breaking of Sb-Sb and Te-Te bonds.

472

Microelectronic power converters such as buck and boost converter are required to be tolerant to radiations including electron radiation. This paper examines electron radiation effects on the I-V characteristics of VDMOSFET and its corresponding effects in buck converter. Analysis of the electrical characteristics shows that after irradiation the threshold voltage and drain current for all VDMOSFETs degraded more than 2 orders of magnitude. The impact of this electrical degradation has been investigated in an application of typical buck converter circuit. The buck converter with n-channel switching transistor shows that after irradiation its output voltage increased with the drain current in the n-channel ZVN4424A VDMOSFET, while the buck converter with p-channel switching transistor shows its output voltage decreased with the drain current in the p-channel ZVP4424A VDMOSFET after irradiation.

323

An extensible high-speed accelerator data acquisition system (ADAS) for the Dragon-I linear induction accelerator (LIA) has been developed. It comprises a VXI crate, a controller, four data acquisition plugins, and a host computer. A digital compensation algorithm is used to compensate for the distortion of high-speed signals arising from long-distance transmission. Compared with the traditional oscilloscope wall, ADAS has significant improvements in system integration, automation and reliability. It achieves unified management of data acquisition and waveform monitoring, and performs excellently with a 107-ps high-accuracy trigger and 32-channel signal monitoring. In this paper, we focus on the system architecture and hardware design of the ADAS, and realization of the trigger and digital compensation algorithm.

416

In this paper, a versatile time and charge measurement (MQT) board for muon tomography is described in detail. For time measurement, the general-purpose time-to-digital converter (TDC) chip TDC-GP2 is employed; while for charge measurement, digitization plus numerical integration in field programmable gate array (FPGA) is employed. Electronic tests demonstrate that the total 32 channels of 2 MQT boards have a time resolution of superior than 100 ps, with excellent linearity for time and charge measurement.

529

In order to investigate the effect of Ag doping (ZnS(Ag)) and Zn vacancy (V_Zn) on the alpha particle detection performance of wurtzite (WZ) ZnS as a scintillation cell component, the electronic structure and optical properties of ZnS, ZnS(Ag), and V_Zn were studied by first-principles calculation based on the density functional theory (DFT). The results show that the band gaps of ZnS, ZnS(Ag), and V_Zn are 2.17 eV, 1.79 eV, and 2.37 eV, respectively. Both ZnS(Ag) and V_Zn enhance the absorption and reflection of the low energy photons. A specific energy, about 2.9 eV, leading to decrease of detection efficiency is observed. The results indicate that Ag-doping has a complex effect on the detection performance. It is beneficial to produce more visible light photons than pure WZ ZnS when exposed to the same amount of radiation while the increase of the absorption to visible light photons weakens the detection performance. Zn vacancy has negative effect on the detection performance. If we want to improve the detection performance of WZ ZnS, Ag-doping will be a good way, but we should reduce the absorption to visible light photons and control the number of Zn vacancy rigorously.

461

Success criteria analysis (SCA) bridges the gap between deterministic and probabilistic approaches for risk assessment of complex systems. To develop a risk model, SCA evaluates systems behavior in response to postulated accidents using deterministic approach to provide required information for the probabilistic model. A systematic framework is proposed in this article for extracting the frontline systems success criteria. In this regard, available approaches are critically reviewed and technical challenges are discussed. Application of the proposed methodology is demonstrated on a typical Westinghouse type nuclear power plant. Steam Generator Tube Rupture (SGTR) is selected as the postulated accident. The methodology is comprehensive and general; therefore, it can be implemented on the other types of plants and complex systems.

363

Fault diagnostics is important for safe operation of nuclear power plants (NPPs). In recent years, data-driven approaches have been proposed and implemented to tackle the problem, e.g. neural networks, fuzzy and neuro-fuzzy approaches, support vector machine, K-nearest neighbors classifiers and inference methodologies. Among these methods, Dynamic Uncertain Causality Graph (DUCG) has been proved effective in many practical cases. However, the causal graph construction behind the DUCG is complicate and, in many cases, results redundant on the symptoms needed to correctly classify the fault. In this paper, we propose a method to simplify causal graph construction in an automatic way. The method consists in transforming the expert knowledge-based DCUG into a Fuzzy Decision Tree (FDT) by extracting from the DUCG a Fuzzy Rule Base (FRB) that resumes the used symptoms at the basis of the FDT. Genetic algorithm (GA) is, then, used for the optimization of the FDT, by performing a wrapper search around the FDT: the set of symptoms selected during the iterative search are taken as the best set of symptoms for the diagnosis of the faults that can occur in the system. The effectiveness of the approach is shown with respect to a DUCG model initially built to diagnose 23 faults originally using 262 symptoms of Unit-1 in the Ningde NPP of the China Guangdong Nuclear Power Corporation (CGNPC). The results show that the FDT, with GA-optimized symptoms and diagnosis strategy, can drive the construction of DUCG and lower the computational burden without loss of accuracy in diagnosis.

356

In this paper, a novel model is proposed to investigate the neutron transport in scattering and absorbing medium. This solution to the linear Boltzmann equation is expanded from the idea of lattice Boltzmann method (LBM) with the collision and streaming process. The theoretical derivation of lattice Boltzmann model for transient neutron transport problem is proposed for the first time. The fully implicit backward difference scheme is used to ensure the numerical stability, and relaxation time and equilibrium particle distribution function are obtained. To validate the new lattice Boltzmann model, the LBM formulation is tested for a homogenous media with different sources, and both transient and steady-state LBM results get a good agreement with the benchmark solutions.

348

Lead and lead-alloys are proposed in future advanced nuclear system as coolant and spallation target. To test the natural circulation and gas-lift, and obtain thermal-hydraulics data for computational fluid dynamics (CFD) and system code validation, a lead-bismuth eutectic (LBE) rectangular loop, the KYLIN-II Thermal Hydraulic natural circulation test loop, has been designed and constructed by the FDS team. In this paper, theoretical analysis on natural circulation thermal-hydraulic performance is described and the steady state natural circulation experiment is performed. The results indicated that the natural circulation capability depends on the loop resistance and the temperature and center height differences between the hot and cold legs. The theoretical analysis results agree well with, while the CFD deviate from, the experimental results.

415

The release of fission products from coated particle fuel to primary coolant, as well as the activation of coolant and impurities, were analysed for a fluoride salt-cooled high-temperature reactor (FHR) system, and the activity of radionuclides accumulated in the coolant during normal operation was calculated. The release rate (release fraction per unit time) of fission products was calculated with STACY code, which is modelled mainly based on the Fick’s law, while the activation of coolant and impurities was calculated with SCALE code. The accumulation of radionuclides in the coolant has been calculated with a simplified model, which is generally a time integration considering the generation and decay of radionuclides. The results show that activation products are the dominant gamma source in the primary coolant system during normal operation of the FHR while fission products become the dominant source after shutdown. In operation condition, health-impacts related nuclides such as ³H, and ¹⁴C originate from the activation of lithium and coolant impurities including carbon, nitrogen, and oxygen. According to the calculated effective cross sections of neutron activation, ⁶Li and ¹⁴N are the dominant ³H production source and ¹⁴C production source, respectively. Considering the high production rate, ³H and ¹⁴C should be treated before being released to the environment.

475

Structural integrity of the flywheel of reactor coolant pump (RCP) is important for safe operation of a nuclear power plant. A shrink- fit multi-ring flywheel is designed with a fall-off function, i.e. it will separate from the shaft at a designed fall-off rotation speed, which is determined by the assembly process and the gravity. However, the two factors are ignored in the analytical method based on the Lame’s equation. In this work, we conducted fall-off experiments to analyze the two factors, and used the experimental data to verify the validity of the analytical method and the finite element method (FEM). The results show that FEM performs better than the analytical method in designing the fall-off function of the flywheel, though FEM cannot successfully predict the strain variation with the rotational speed.

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