Owing to the inhomogeneous distribution of FLiNaK salt impregnated into graphite which is observed by scanning electron microscopy and an element probe micro-analyzer, a map scan of in situ real-time tensile synchrotron-based two-dimensional X-ray diffraction (2D-XRD) at several fixed external forces was implemented to reveal the local microstructure evolution of graphite and FLiNaK salt. Notably, a stress concentration area (SCA), that is, the main interaction area between graphite and salt, was found and then transformed from one region to another region because of the unbalanced squeeze interaction between graphite and FLiNaK salt with the increase of external force. During the external stress load process, a smaller grain size, poorer crystallinity of graphite and a larger grain size, better crystallinity of FLiNaK salt appear in the SCA; meanwhile, the changes of crystallographic preferred orientation of FLiNaK salt domains in SCA imply that the external load force makes better the ordered stacking of the larger crystal grains of the FLiNaK salt impregnated into graphite. Most importantly, we have found for the first time that the fracture position of graphite impregnated with FLiNaK salt always occurs near the SCA rather than at a fixed region under the external stress load. Thus, the present study not only helps to reveal the interaction mechanism between graphite and FLiNaK salt under the external stress load but also contributes to accurately predict and analyze the stress state of components, which would have an effective impact on the design of a molten salt reactor and the reliability of the component safety assessment.

To optimize the performance of the carbon fiber reinforced carbon matrix (C/C) composites by controlling the microstructure for more reliable and safety application in thorium molten salt reactor (hereafter, TMSR), we have investigated the irradiation effects of fiber, matrix, and their interfaces in C/C composite induced by He+ ions and further reveal their corresponding micromechanism. Compared with fibers, an obviously fragmented surface morphology in matrix appears and then gradually becomes widespread around the surface of C/C composite with increasing dose of irradiation. This found is attributed to the breakage of crystallites observed by synchrotron-based grazing incidence X-ray diffraction (GIXRD) and the increase of defect state density revealed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, respectively. Three different microstructure evolutions in fiber, matrix and fiber-matrix interface induced by irradiation damage have been further revealed in detail by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). It is found that the layered structure gradually loses its initial ordering and the nanostructural degradation in carbon matrix is much more serious than that of the fiber, resulting in breaks and bends in the lattice with increasing dose. Observed by nanoindentation experiment, the enhancement of the hardness and modulus of the matrix is more significant than that in fiber, which can be attributed to the more obviously pinning of basal plane dislocations in the matrix due to lattice defects induced by He+ irradiation. These discoveries are properly contribute to improve the performance of the C/C composites by regulatory microstructure composition, such as fiber and matrix.

Binderless nanopore-isotropic graphite (NPIG) produced from mesocarbon microbeads by isostatic pressing method was irradiated with 7 MeV Xe26+ to a total peak dose of 0.1, 0.5, 2.5 and 5.0 dpa. The effect of the irradiation on the microstructure and physical properties of NPIG was then evaluated and compared against the performance of isostatic nuclear graphite (IG-110, TOYO TANSO CO., LTD). Ion-irradiation has a different effect on the microstructure (crystallinity, crystallite size) and mechanical properties (hardness, Young's modulus) of NPIG and IG-110 graphite. At lower irradiation doses, the surface morphology of NPIG was fragmented in a similar way to that of IG-110, but the NPIG gradually balled at 5 dpa. X-ray diffraction results show that NPIG has a lower degree of graphitization than IG-110. Raman studies indicated that NPIG reached saturation at lower doses. The nanoindentation showed that the hardness and Young's modulus of the NPIG and IG-110 increased after irradiation. Transmission electron microscopy images also provide clear evidence for an irradiation-induced increase in the number of basal dislocations and defects. Thus, although NPIG is generally more sensitive to irradiation than IG-110, its hardness is actually less affected.

为了保障钍基熔盐堆核能系统(Thorium Molten Salt Reactor Nuclear Energy System,TMSR)项目的实验安全运行,需要构建一套实验室安全监控系统,该系统需要解决以下问题:实验室地域覆盖广、环境差异大、信号种类繁多、软件接口复杂.现有的商业监控系统很难满足以上需求,因此开发了一套基于Node-Web技术的实验室安全监控系统.展示了该系统的结构框架,并阐述了基于视频接口进行软件开发的流程.该系统实现了EPICS(Experimental Physics and Industrial Control System)信号采集系统和海康威视(Hikvsion)视频采集系统的集成,通过Node-Web前端可视化接口的开发,实现了监测界面中EPICS变量和视频流联动的功能.系统具有分布式、网络化、扩展性好、低成本的特点,可适用于建设大型科研机构实验室安全监控系统.

Nanopore pyrolytic graphite coatings (PyC, average pore size ∼64 nm) were prepared on graphite to inhibit liquid fluoride salt and Xe135 penetration. The samples were irradiated with 7 MeV Xe26+ to a total peak dose of 0.1, 0.5, 2.5 and 5.0 displacements per atom at room temperature to study the irradiation resistance of the PyC. The effect of irradiation on the properties of the graphite was evaluated. With the increase of irradiation dose, the surface morphology of the coatings tends to be smoother. At the total peak dose of 2.5 dpa, peeling and spalling on the surface of the samples have been identified, indicating the surface microstructure of the graphite has been damaged by Xe26+ bombardment. Raman results indicated the increase in the degree of disorder and decrease of in-plane crystallite size with the irradiation dose, and the new PyC was more sensitive to irradiation than IG-110 graphite. The nanohardness at peak dose increased with the irradiation dose, but decreased at 2.5 dpa. The results of a hardness test also show PyC has a higher irradiation sensitivity.

钍基熔盐堆(Thorium Molten Salt Reactor,TMSR)是以核石墨为反射体及慢化体、2LiF-BeF2(FLiBe)熔盐为主冷却剂的反应堆.在TMSR中,核石墨直接与熔盐接触.由于石墨的多孔特性,熔盐有可能渗入石墨的孔隙中,引发其力学、热学性能的变化.研究熔盐在TMSR环境下是否渗入候选核石墨及其浸渗量,对于反应堆的运行安全至关重要.基于自行研制的熔盐浸渗实验装置,采用静态熔盐浸渗试验方法,测试TMSR候选核石墨T220在不同压强下的熔盐浸渗量,并研究了温度、时间对T220、NBG-18及IG-110石墨材料熔盐浸渗行为的影响.研究结果表明:T220石墨的临界浸渗压强介于600～700 kPa之间,这说明在TMSR工况下(<500 kPa)该石墨不发生FLiBe熔盐浸渗.温度(600°C和700°C)及时间(20～2000 h)对三个牌号石墨熔盐浸渗行为影响不大.

In thermal Molten Salt Reactors, the nuclear graphite core is in direct contact with the molten salt coolant. Due to the porous nature of nuclear graphite, the molten salt may infiltrate the nuclear graphite, which may affect the mechanical strength and irradiation behavior of the nuclear graphite. In order to evaluate the infiltration behavior of molten salt in nuclear graphite, both FLiNaK and FLiBe salts were used to infiltrate two typical nuclear graphite grades: IG110 and NBG18. The pressure dependence of the infiltration weight gain ratio was measured. The influence of molten salt infiltration on the thermal properties of these two graphite grades, such as their thermal expansion behavior and thermal conductivity, was also measured. The mechanical strength of the FLiNaK-infiltrated graphite was measured at room temperature and elevated temperature, and showed that the mechanical strength of the nuclear graphite was enhanced at room temperature and weakened at elevated temperature by molten salt infiltration. Finally, the thermal expansion coefficient and the fracture surface analysis measured after FLiNaK infiltration indicated that the stress induced by molten salt infiltration could be one of the reasons for the graphite property changes.

The crystallite size of the three different carbon fibers (K223HE,HTA40 and T700SC) was characterized by Raman spectroscopy.The transverse elastic modulus and hardness of the carbon fibers were measured by nano indentation technique,and the data scatter was analyzed by two-parameter Weibull function.The results show that the crystallite length of the mesophase pitch based carbon fiber K223HE is the longest,about 39.43 nm±2.63 nm,and that of HTA40 and T700SC PAN based carbon fiber is almost the same,about 4.63 nm±0.09 nm and 4.89 nm±0.06 nm,respectively.In the nano indentation load-depth curve,the residual deformation of K223HE is the biggest (75.34 nm±17.07 nm),indicating the lowest recovery ratio of indentation work (65.89%).The characteristic transverse elastic modulus of the three carbon fibers is 19.52 GPa,11.99 GPa and 17.92 GPa.The Weibull modulus of the transverse elastic modulus of the three different carbon fibers (HTA40,K223HE and T700SC) is 25.26,6.85 and 8.07,which displays the consistence in the properties of HTA40 is the best.The differences in the nano indentation behavior of the three carbon fibers are attributed to the differences in the integrity and preferred orientation of the crystallite of carbon fibers.

Background:The distribution of nanoscale pore is of great significance to irradiation damage behavior of nuclear graphite under intense radiation. Small angle X-ray scattering (SAXS) is an important method used to study the number distribution and its fractal characteristics of pore in nanoscale.Purpose: This study aims at the changes in number distribution and its fractal characteristics of nanoscale pore in nuclear graphite.Methods:Two typical nuclear graphite, i.e., IG-110 and NBG-18 were sampled and tested at synchrotron radiation SAXS beamline station at temperatures of 25 oC, 100 oC, 200 oC, 300 oC and 400 oC, respectively.Results: The results showed that there was a non-uniform area in the microstructure of nuclear graphite, and the solid-gas structure of the nuclear graphite pore had a sharp interface, but the change of solid-gas interface does not show obvious regularity with the increase of temperature. In addition, the number of nanoscale pore in IG-110 nuclear graphite increases with the temperature, and is more obvious than that of NBG-18. The fractal dimension of the solid-gas interface decreases with the temperature increasing, indicating that the fractal structure of the graphite become smoother with the increasing of temperature. And the change of IG-110 is more obvious than that of NBG-18.Conclusion: The temperature has a significant impact on the pore number distribution and its fractal characteristics.

The elastic modulus and hardness of T800SC carbon fiber with different orientation respect to its axis direction were tested by nanoindentation,and the scatter in the data was treated in terms of the two-parameter Weibull statistical analysis.It is shown that with the increase of the intersection angle between the test plane and the axis direction,the elastic modulus and hardness of T800SC increase.When the intersection angle increases from 0° to 90°,the elastic modulus of T800SC rises to (50.96±5.73) GPa from (5.84±2.00) GPa,and the hardness increases from (2.71±0.51) GPa to (5.24±0.91) GPa.For the elastic modulus and hardness of T800SC carbon fiber with different orientation,the modulus of Weibull distribution ranges from 9.0 to 10.5 and from 6.0 to 8.0,respectively.

Developing a molten salt reactor needs molten salt–impermeable nuclear graphite. Ultra-fine grain graphite is a good choice as it is better in permeability than fine grain graphite. In this paper, ultra-fine grain graphite (HPG-510) and fine grain graphite (IG-110) samples are irradiated at room temperature by 7 MeV Xe ions to doses of 1 × 1014–5 × 1015 ions/cm2. Scanning electron microscopy, transmission electron microscopy (TEM), Raman spectroscopy and nano-indentation are used to study the radiation-induced changes. After irradiation of different doses, all the HPG-510 samples show less surface fragment than the IG-110 samples. The TEM and Raman spectra, and the hardness and modulus characterized by nano-indentation, also indicate that HPG-510 is more resistant to irradiation.

With the aim of developing neutron moderator and neutron reflector materials for fluoride-salt-cooled high-temperature reactors (FHRs), static infiltration tests were performed on graphite materials in molten 2LiF–BeF2 (FLiBe) salt, which is a potential primary coolant, at 700 °C and various pressures. The weight gain ratios of four grades (NBG-18, IG-110, NG-CT-10, and NG-CT-50) of graphite after infiltration were measured to determine their infiltration curves. The threshold pressure for FLiBe salt infiltration for the ultrafine-grained graphite (NG-CT-50) was greater than 600 kPa and much higher than those of the other three grades (medium-grained/fine-grained graphites), indicating that this graphite grade more probably resists salt infiltration in FHRs than other grades of graphite. However, if the threshold pressure is exceeded, it has the highest potential capacity for infiltrated salt over the pressures tested. The four grades were also characterized using mercury intrusion porosimetry. It was found that the infiltration curves of these two unwetting liquids were very similar. Scanning electron microscopy characterization showed that the FLiBe salt was distributed relatively uniformly in all four grades, indicating the presence of interconnected networks of open pores throughout the samples. X-ray diffraction patterns showed that infiltration test at high pressure led to an improved structural order and a decreased d-spacing in graphite.

An in-situ real-time synchrotron-based grazing incidence X-ray diffraction was systematically used to investigate the crystal structural evolution of carbon fiber reinforced carbon matrix (C/C) composite impregnated with FLiNaK molten salt during the heat-treatment process. It was found that the crystallographic thermal expansion and contraction rate of interlayer spacing d 002 in C/C composite with FLiNaK salt impregnation is smaller than that in the virgin sample, indicating the suppression on interlayer spacing from FLiNaK salt impregnated. Meanwhile the crystallite size L C002 of C/C composite with FLiNaK salt impregnation is larger than the virgin one after whole heat treatment process, indicating that FLiNaK salt impregnation could facilitate the crystallization of C/C composite after heat treatment process. This improved crystallization in C/C composite with FLiNaK salt impregnation suggests the synthetic action of the salt squeeze effect on crooked carbon layer and the release of internal residual stress after heating-cooling process. Thus, the present study not only contribute to reveal the interaction mechanism between C/C composite and FLiNaK salt in high temperature environment, but also promote the design of safer and more reliable C/C composite materials for the next generation molten salt reactor.

Background: Nuclear graphite is a porous material and its pores can be easily impregnated with the molten fuel salt in a high pressure environment in the molten salt reactor (MSR). A seepage of the fuel salt into the graphite leads to the formation of local hot spots, which significantly damage the graphite, thereby reducing the service life of the graphite components. Purpose: This study aims to investigate the relationship between porosity property and molten salt impregnation of nuclear graphite. Methods: The porosity properties were examined by optical microscopy (OM), mercury porosimetry, and helium gas pycnometry. The impregnation tests were performed by impregnating graphites with molten fluoride salt at a temperature of 650° centigrade and a pressure of 0.1 MPa and 0.5 MPa respectively. Results: The porosity results indicated that the IG-110/IG-430 showed uniformly-distributed gas-evolved pores, small entrance pore diameter 2?4 μm, and a high open porosity; NBG-17/NBG-18 showed a big gas-evolved pores, wide range entrance pore diameter, and a high closed porosity (numerous calcination cracks in filler). Conclusion: The impregnation results showed that the impregnation mechanism of molten salt was similar to mercury. Only the applied pressure is greater than threshold pressure, the impregnation starts. With the increase of pressure, the small pores will also be filled with salt. The distribution of molten salt indicated that most of the cracks (calcination cracks and Mrozowski cracks) were closed.

The properties of ceramic matrix composites strongly depend upon their complex internal structures. To better understand and improve the properties of the silicon carbide fiber-reinforced silicon carbide matrix composites (SiCf/SiC), we explored the microstructural properties of composites reinforced with either two-dimensional (2D) woven or three-dimensional (3D) braided preforms using synchrotron X-ray computed microtomography. Transects and volumetric images of the composites were reconstructed from objection images and the microstructures were investigated in three spatial directions. The network of void space in a composites was visualized in 3D and quantitative analysis of the porosity was performed to characterize the fiber-tissue structures. 2D-woven SiCf/SiC composite exhibited important fluctuations of porosity in different directions and the stacking of plies had a significant effect on the porosity distribution. In contrast, 3D-braided SiCf/SiC composites showed much less variation of porosity. We found the degree of densification of the composite also influenced the porosity distribution.

The magnetism of highly oriented pyrolytic graphite（HOPG） induced by ion implantation is investigated with electron spin resonance（ESR） spectroscopy and magnetization measurements.The results indicate that the ESR spectra of the HOPG sample correlate with ion species,incident energy and dose of implantation.The correlation of the ESR spectra and magnetism of the HOPG sample with 12 C + ion implantation and H + ion implantation are studied in detail.The ferromagnetism of the HOPG sample is likely related to the asymmetric L1 line,which may be attributed to the interaction between localized defects and itinerant electrons occupied in the ’impurity’band induced by ion implantation.

In this paper, SiC fiber reinforced SiC composite (SiCf/SiC) is joined to Hastelloy N alloy using 82.5Au–17.5Ni (wt%) foil as brazing filler. The microstructural evolution of the joints is investigated using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X‐ray diffraction (XRD), and Raman spectroscopy. The shear strengths of the joints are tested by the mechanical testing machine. The results show the formation of nanocrystalline graphites, Ni2Si layer, and Ni31Si12 phases. With increasing temperature, Ni2Si is transformed gradually into Ni31Si12. The shear strength reaches a maximum value of 24.5 MPa when the joint is brazed at 1 000 °C for 30 min.

Effects of Cr3+ on the corrosion of SiC in LiF-NaF-KF molten salt were investigated. Results reveal that Cr3+ can drive the corrosion of SiC. Thickness of the corroded region induced by Cr3+ is greater than 12 mu m for 400 h, while the corroded region induced by pure salt is similar to 2.5 mu m. Corrosion induced by Cr3+ should be attributed to the reactions of Cr3+ with SiC. Cr3+ reacts with SiC to form Cr-3 C-2, Cr7C3, and graphitic carbon in the corroded region of SiC, which results in the dissolution of element Si from SiC intothe salt. (C) 2016 Elsevier Ltd. All rights reserved.