Vol.31,

Carbonic composite materials and ceramics appear to be excellent structural materials for parts subjected to very high temperatures in molten salt reactors (MSRs), in which the reactor core outlet temperature is normally above 700 °C. Because of the high temperature, there are major challenges in the sealing of flanged connections for tubes made of alloys and nonmetallic materials. In this study, an improved method for sealing bolted flange connections for tubes made of dissimilar materials at high temperature is analyzed. The study focuses on the compensation mechanism for the difference in thermal expansion between the bolts and the flanges. An angle is introduced for the sealing surface in the flanged connection to provide effective sealing. The arctangent of the angle is the ratio of the thickness between the theoretical core of the sealing surface and the outside end face of the flange to the distances between the axis of the flanged joint and the theoretical core of the sealing surface of the flange; the sealing surface of the flange, which is made of the same material as the fastening assemblies, faces the fastening assemblies. To ensure effective sealing, the frictional coefficient between the two sealing surfaces should not exceed the tangent of the angle. This result does not agree well with the solution given by previous researchers. Further, in the modified flanged connection, the compression of each bolt in the clamped condition is increased to maintain the compaction force unchanged without increasing the number of bolts on the flanged joint.

501

The study of accelerator-driven subcritical reactor systems (ADSs) has been an important research topic in the field of nuclear energy for years. The main code applied in ADS research is MCNPX, which was developed by Los Alamos National Laboratory. We studied the application of the open-source Monte Carlo codes FLUKA and OpenMC to a coupled ADS calculation. The FLUKA code was used to simulate the reaction of high-energy protons with the nucleus of the target material in the ADS, which produces spallation neutrons. Information on the spallation neutrons, such as their energy, position, direction, and weight, can be recorded by a user-defined routine called FLUSCW provided by FLUKA. Then the information was stored in an external neutron source file in HDF5 format by using a conversion code, as required by the OpenMC calculation. Finally, the fixed-source calculation function of OpenMC was applied to simulate the transport of spallation neutrons and obtain the distribution of the neutron flux in the core region. In the coupled calculation, the high-energy cross section library JENDL4.0/HE in ACE format produced by NJOY2016 was applied in the OpenMC transport simulation. The OECD-ADS benchmark problem was calculated, and the results were compared with those obtained using MCNPX. It was found that the flux calculations performed by FLUKA–OpenMC and MCNPX were in agreement, so the coupling calculation method for ADS is reasonable and feasible.

687

With the advantages of high reliability, power density, and long life, nuclear power reactors have become a promising option for space power. In this study, the Reactor Excursion and Leak Analysis Program 5 (RELAP5), with the implementation of sodium-potassium eutectic alloy (NaK-78) properties and heat transfer correlations, is adopted to analyze the thermal-hydraulic characteristics of the space nuclear reactor TOPAZ-II. A RELAP5 model including thermionic fuel elements (TFEs), reactor core, radiator, coolant loop, and volume accumulator is established. The temperature reactivity feedback effects of the fuel, TFE emitter, TFE collector, moderator, and reactivity insertion effects of the control drums and safety drums are considered. To benchmark the integrated TOPAZ-II system model, an electrical ground test of the fully integrated TOPAZ-II system, the V-71 unit, is simulated and analyzed. The calculated coolant temperature and system pressure are in acceptable agreement with the experimental data for the maximum relative errors of 8% and 10%, respectively. The detailed thermal-hydraulic characteristics of TOPAZ-II are then simulated and analyzed at the steady state. The calculation results agree well with the design values. The current work provides a solid foundation for space reactor design and transient analysis in the future.

564

In 2007, the license for the second reactor unit of the Ignalina nuclear power plant was renewed considering the safety-related modifications introduced in this reactor. The Safety Analysis Report for this reactor unit was prepared with more strict criteria. The bounding reactivity-initiated accident (RIA) performed by the Lithuanian Energy Institute could be mentioned as an example. The performed analysis demonstrated that even when the worst initial conditions and possible uncertainties are considered, the fuel cladding remains intact. However, the analysis was performed assuming a fresh fuel assembly. In this study, an analysis of the fuel-rod cladding behavior in the RBMK-1500 reactor following a bounding RIA is performed using the computational codes FEMAXI-6 and RELAP5. The analysis is extended by modeling an oxide layer (nodular corrosion) on the external surface cladding. An uncertainty and sensitivity analysis was performed using a method developed by the Society for Plant and Reactor Safety, employing the Software for Uncertainty and Sensitivity Analyses (SUSA), in order to evaluate the effect of the oxide layer on the inside and outside fuel-rod temperatures. The results of the thermo-mechanical analysis (stress, strain, and enthalpy) for a local oxide layer with a thickness of 70 μm show that despite the exceeded limit of allowed linear power density, the fuel rod is under acceptable safety conditions.

432

A molten salt reactor (MSR) is one of the six advanced reactor concepts selected by the Generation IV International Forum because of its advantages of inherent safety, and the promising capabilities of Th-U breeding and transuranics (TRU) transmutation. A dynamics model for the channel-type MSR is developed in this work based on a three-dimensional thermal-hydraulic model (3DTH) and a point reactor model. The 3DTH couples a three-dimensional heat conduction model and a one-dimensional single-phase flow model that can accurately consider the heat conduction between different assemblies. The 3DTH is validated by the RELAP5 code in terms of the temperature and mass flow distribution calculation. A point reactor model considering the drift of delayed neutron precursors (DNP) is adopted in the dynamics model. To verify the dynamics model, three experiments from the Molten Salt Reactor Experiment (MSRE) are simulated. The agreement of the experimental data and simulation results was excellent. With the aid of this model, the unprotected step reactivity addition and unprotected loss of flow of the 2 MWt experimental MSR are modeled, and the reactor power and temperature evolution are analyzed.

644

Neutron capture therapy with Sulfur-33, similar to boron neutron capture therapy with Boron-10, is effective in treating some types of tumors including ocular melanoma. The key point in sulfur neutron capture therapy is whether the neutron beam flux and the resonance capture cross-section of ³³S(n,α)³⁰Si reaction at 13.5 keV can achieve the requirements of radiotherapy. In this research, the authors investigated the production of 13.5 keV neutron production and moderation based on an accelerator neutron source. A lithium glass detector was used to measure the neutron flux produced via near threshold ⁷Li(p,n)⁷Be reaction using the time of flight method. Furthermore, the moderation effects of different kinds of materials were investigated using Monte Carlo simulation.

477

Cross-sections of the (n,2n) reactions for neodymium (Nd) isotopes induced by 14 MeV neutrons were measured in this work by using the activation and relative methods. The measured cross-sections of the ¹⁵⁰Nd(n,2n)¹⁴⁹Nd, ¹⁴⁸Nd(n,2n)¹⁴⁷Nd, and ¹⁴²Nd(n,2n)¹⁴¹Nd reactions were 1854±81, 1789±119, and 1559±98 mb, respectively, at a neutron energy of 14.2±0.2 MeV, and 1485±74, 1726±85, and 1670±119 mb, respectively, at 14.9±0.2 MeV. The results were compared with the experimental values from the reported literature, with the evaluated data from the ENDF/B-VII.1, CENDL-3.1, and JENDL-4.0 libraries, and with the curves calculated by the Talys-1.8 code.

581

For a characteristic γ-ray with interlaced overlap peak, and the case where its reliable and credible net count cannot be obtained using the current high-purity germanium (HPGe) multichannel γ-ray spectrum software, two new methods are proposed herein to obtain the γ-ray net peak count from the interlaced overlap peak in the HPGe γ-ray spectrometer system, of which one is the symmetric conversion method based on Gaussian distribution and the other is where the energy average value of two close γ-rays is regarded as the γ-ray energy. The experimental results indicate that the two methods mentioned above are reliable and credible. This study is significant for the development of better γ-ray spectrum processing software for measuring complex γ-ray spectra concerning the nuclear reaction cross section, neutron activation analysis, and analysis of transuranium elements, using an HPGe detector.

654

The nuclear data of n+^240,242,244Pu reactions for incident energy below 200 MeV are calculated and evaluated to meet the requirement in the design of an accelerator-driven sub-critical system. The optical model is used to calculate the total, nonelastic, shape elastic cross sections, shape elastic scattering angular distributions, and transmission coefficients. The distorted-wave Born approximation is applied to calculate the direct inelastic scatterings to the discrete excited states. The nuclear reaction statistical models and fission theory are applied to describe neutron, proton, deuteron, triton, helium-3, alpha and γ emissions, and fission consistently. The results thus obtained are compared with experimental data and the evaluated data obtained from ENDF/B-VII.1 and JENDL-4.0.

658

The collective properties along the yrast line in well-deformed even-even ^164-178 Yb isotopes are investigated by pairing self-consistent total-Routhian-surface (TRS) calculations and extended E-gamma over spin (E-GOS) curves. The calculated results from ground-state deformations, e.g., β₂, are in agreement with previous theoretical predictions and available experimental data. The basic behaviors of moment of inertia are reproduced by the present TRS calculations and discussed based on the aligned angular momenta. The centipede-like E-GOS curves indicate that the non-rotational components appear along the yrast sequences in these nuclei, which can explain the discrepancy in the moment of inertia between theory and experiment to some extent. The further extended E-GOS curves, which include the first-order rotation-vibration coupling, appear to provide possible evidence of vibrational effects in the well-deformed nuclei of ^164-178Yb.

731

The neutron-to-proton and ³H-to-³He yield ratios, and the directed flows of particles dependent on a reduced rapidity, the transverse momentum per nucleon, and a reduced impact parameter, are investigated for ²⁸S + ²⁸Si and ³²S + ²⁸Si systems at 50 and 400 MeV/u using an isospin-dependent quantum molecular dynamics model. The results show that these yield ratios of projectile-like fragments are approximately equal to the constituent neutron-to-proton ratio of the projectile. There are clear differences of the directed flows for isospin-related fragments neutron and proton, ³H and ³He from ²⁸S + ²⁸Si collisions. The differences in directed flows for neutrons and protons and ³H-³He from a proton-rich nucleus ²⁸S induced collisions are noticeably larger than those from a stable nucleus ³²S induced reactions under medium impact parameters. Thus, the yield ratios and differences in directed flows for the neutrons and protons and ³H-³He under medium impact parameters are proposed as possible observable items for studying isospin physics.

450

A bunch arrival-time monitor (BAM) based on an electro-optical intensity modulation scheme is currently in development at Shanghai soft X-ray Free Electron Laser (SXFEL) to meet the high-resolution requirements for bunch stability. The BAM uses a radio frequency (RF) signal generated by a pickup cavity to modulate the reference laser pulses in an electro-optical intensity modulator (EOM), and the bunch arrival time information is derived from the amplitude change of the laser pulse after laser pulse modulation. EOM is a key optical component in the BAM system. Through the basic principle analysis of BAM, many parameters of the EOM are observed to affect the measurement resolution of the BAM system. Therefore, a systematic analysis test of the EOM is crucial. In this paper, we present two schemes to compare and analyze an EOM and provide a reference for selecting a new version of the EOM.

596

The proton beam energy determines the range of particles and thus where the dose is deposited. According to the depth of tumors, an energy degrader is needed to modulate the proton beam energy in proton therapy facilities based on cyclotrons, because the energy of beam extracted from the cyclotron is fixed. The energy loss was simulated for the graphite degrader used in the beamline at the Superconducting Cyclotron of 200 MeV in Hefei (SC200). After adjusting the mean excitation energy of the graphite used in the degrader to 76 eV, we observed an accurate match between the simulations and measurements. We also simulated the energy spread of the degraded beam and the transmission of the degrader using theoretical formulae. The results agree well with the Monte Carlo simulation.

535

The detection technology of concealed bulk explosives is related to social security and national defense construction, and has important research significance. In this paper, an element analysis method of concealed explosives based on thermal neutron analysis (TNA) is proposed. This method could provide better reconstruction precision for hydrogen, carbon, and nitrogen ratios, making it possible to discriminate explosives from other compounds with the same elements but different proportions, as well as to identify the types of concealed bulk explosives. In this paper, the basic principles and mathematical model of this method are first introduced, and the calculation formula of the element number ratio (the ratio between the nucleus numbers of two different elements) of the concealed explosive is deduced. Second, a numerical simulation platform of this method was established based on the Monte Carlo JMCT code. By calibrating the absorption efficiencies of the explosive device to γ rays, the element number ratios of a concealed explosive model under the irradiation of thermal neutrons were reconstructed from the neutron capture prompt γ-ray spectrum. The reconstruction values were in good agreement with the actual values, which shows that this method has a high reconstruction precision of the element number ratio for concealed explosives. Lastly, it was demonstrated using the simulation study that this method can discriminate explosives, drugs, and common materials, with the capability of determining the existence of concealed bulk explosives and identifying explosive types.

431

519

Fundamental power couplers (FPC) are crucial components for feeding radiofrequency (RF) power to accelerating cavities. Couplers must be tested and conditioned on a room temperature test stand to evaluate and potentially improve their performance before being installed in an accelerating cavity. A new test system has been designed and is under construction at the institute of modern physics (IMP). For this test system, multiple conditioning modes, including the pulse mode, CW mode, and amplitude sweeping mode have been embedded in the low level radio frequency (LLRF) system of the test stand. All of these conditioning modes can be run manually or automatically. In addition, a novel test cavity is proposed and has been designed, which facilitates non-contact conditioning and a multi-purpose test stand.

605

Complementary metal–oxide–semiconductor (CMOS) sensors can convert X-rays into detectable signals; therefore, they are powerful tools in X-ray detection applications. Herein, we explore the physics behind X-ray detection performed using CMOS sensors. X-ray measurements were obtained using a simulated positioner based on a CMOS sensor, while the X-ray energy was modified by changing the voltage, current, and radiation time. A monitoring control unit collected video data of the detected X-rays. The video images were framed and filtered to detect the effective pixel points (radiation spots). The histograms of the images prove there is a linear relationship between the pixel points and X-ray energy. The relationships between the image pixel points, voltage, and current were quantified, and the resultant correlations were observed to obey some physical laws.

527

In this paper, we study how pixel size influences energy resolution for a proposed pixelated detector—a high sensitivity, low cost, and real-time radon monitor based on a Topmetal-II^- time projection chamber (TPC). This monitor was designed to improve spatial resolution for detecting radon alpha particles using Topmetal-II^- sensors assembled by a 0.35 μm CMOS integrated circuit process. Owing to concerns that small pixel size might have the side effect of worsening energy resolution due to lower signal to noise ratio, a Geant4-based simulation was used to investigate the dependence of energy resolution on pixel sizes ranging from 60 μm to 600 μm. A non-monotonic trend in this region shows the combined effect of pixel size and threshold on pixels, analyzed by introducing an empirical expression. Pixel noise contributes 50 keV full width at half maximum energy resolution for 400 μm pixel size at 1 ∼ 4 σ threshold that is comparable to the energy resolution caused by energy fluctuations in the TPC ionization process (∼ 20 keV). The total energy resolution after combining both factors is estimated to be 54 keV for a pixel size of 400 μm at 1 ∼ 4 σ threshold. The analysis presented in this paper would help choosing suitable pixel size for future pixelated detectors.

436