Papers by Author: Fei Xue

Abstract: IASCC of stainless steel has been the most important issue for internals BFBs. The inspection data analysis indicates that there is a closed relation between irradiation fluence and cracked BFBs distribution. Then the nanoindentation and 3DAP tests were carried out to study the hardening and radiation induced segregation (RIS) behaviors of the reactor internals stainless steel specimens irradiated with 6 MeV Xe ions at room temperature. It is indicated that higher irradiation damage will cause more significant hardening and RIS and consequently increase the IASCC susceptibility.

Abstract: The stress corrosion cracking (SCC) sensitivity of aged Z3CN20.09M stainless steel (SS) was investigated by scanning electrochemical microscopy (SECM), nanoindenter and slow strain rate tensiometer (SSRT). The results indicated that the hardness and modulus of the samples increased with increasing aging time at 475 °C, which increased about 80% and 15% respectively after aging for 1000h. After immersed in NaCl+HCl solution (pH=2) for 7 h, the pitting corrosion point appeared of specimen aged for 1000h. While it was not found even for 24 h of as-received (AR) and aged for 500 h specimens at the same condition. The SCC sensitivity was increased about one time of the specimen aged for 1000 h tested in 300 °C high temperature water. The combined effect associated the embrittlement of mechanical properties and the decrease of corrosion resistance is regarded as the main reason for the increasing of SCC sensitivity.

Abstract: Nanosized Cu-enriched clusters formed in Cu-containing reactor pressure vessel (RPV) steels during service have a deleterious effect on mechanical properties, which can result in RPV embrittlement and limit reactor operation life. To understand the effect of Cu-enriched clusters (CECs) behavior on mechanical properties, thermal aging at 370°C for times up to 13200 h was performed on the high-copper ferritic steels. The microstructure evolution of CECs was investigated by positron annihilation spectroscopy (PAS) and transmission electron microscope (TEM). The results show that the CECs formed after aging times up to 3000 h, which composition is composed of Fe, Cu, Ni, Mn, and Si, are 9R structures. The CECs lead to precipitation hardening/embrittlement effects. The changes of hardness have a linear relationship with transition temperature shifts.

Abstract: Most of the French Nuclear Power Plants (NPPs) are currently embarking upon efforts to renew their operating license, while the pressurized thermal shock (PTS) events and environmentally assisted fatigue (EAF) pose potentially significant challenges to the structural integrity of the reactor pressure vessel (RPV) which has the potential to be NPP life-limiting conditions. In the assessment of the PTS events, the deterministic fracture mechanics (DFM) is still used as the basic mechanics in most countries except for the USA. While the maximum nil-ductility-transition temperature (RT_NDT) is about 80°C for 54 French RPVs after 40 years operation, the maximum allowable RT_NDT is only about 70 ^oC and 80 ^oC for the typical PTS events in the IAEA and NEA reports, respectively. On the other hand, the effects of light water reactor (LWR) environmental (other than moderate environment in the code) were not considered in the original design, while the effects of LWR environmental are needed to be considered in the LRA according to the USA regulations. In this paper, the challenges of the PTS and EAF are discussed, and some suggestions are also given for the LRA

Abstract: Socket welds are widely used in nuclear power plants. According to industry experiences, vibration fatigue of socket welds is becoming one of the major ageing issues. It is very important for the operating engineers to monitor the vibration condition and detect the damage before leak occurs. This paper studies the damage identification technology applying wavelet transform method. Small bore pipes with socket welds are installed on the vibrating table and vibrate at the frequencies that near its first natural frequency. The acceleration response signal is acquired and decomposed by wavelet method. The energy of decomposition signal shows a suddenly variation when crack occurs. From this study, a parameter that is sensitive to vibration fatigue is defined and has the potential application value in the nuclear power plants to identify the vibration fatigue damage.

Abstract: In this paper, the role of the pearlite-banded structure on fatigue crack growth behavior was investigated on carbon vessel plate material SA516, which is commonly used in the nuclear power plants. Along pearlite-banded orientation, in situ fatigue tests indicate that the crack initiated and propagated in the ferrite and then extended along the ferrite-pearlite interface when it met pearlitic colony. For comparison, the cyclic loading was also carried out perpendicular to the banding direction of the microstructure, and an intense crack branching was observed which led to fatigue crack retardation. Besides, the orientation perpendicular to banded pearlite in the investigated ferrite-pearlite steel was found to have a lower fatigue crack growth rate.

Abstract: In order to confirm the structural integrity of pressurizer surge line affected by thermal stratification and thermal shock, the thermo-mechanical fatigue (TMF) behavior of the material used for surge line was investigated based on the real situation in the pressurized water reactor (PWR). Smooth, hollow specimens were subjected to in-phase (IP) and out-of-phase (OP) cycling in air under a mechanical strain control mode. For the sake of comparison, low cycle fatigue (LCF) tests were also performed at the peak temperatures of TMF cycling. The Nano Hardness Tester was used to test the nano hardness of the sample on the cut section surface. The results are shown that there is no significant difference between the IP, OP and IF lives in the investigated temperature ranges. The fracture analysis reveals that the crack initiation and propagation occurred in a transgranular mode under OP, IP and IF cycling condition, and a harden layer occurrence may be the cause of the crack initiation.

Abstract: At the present time, as the steam conditions and capability of the supercritical power unit increasing, the unit reliability is an important factor for the unit efficiency. High temperature, thick walled pipes are widely used in power plants and chemical plants. In this paper, life of the welded joint was predicted by the methods of skeletal point (SP) rupture stress rupture stress, which was calculated by finite element method (FEM). For the life prediction of welded component, the continuum damage mechanics was employed too. The life prediction of the welded joint by SP rupture stress was compared with the life prediction by the method of continuum damage mechanics (CDM). The research results showed that the two predicted methods were consistent. So, it can be concluded that the SP rupture stress can be used for predicting life of the high temperature welded component. The SP rupture stress method was used conveniently for the structure of power plant or other high temperature components.

Abstract: In this study, based on ASME Code Section III, France RCC-MR, ANSYS simulation and experimental data, ratcheting and ratcheting boundary are obtained to determine allowed loading of primary auxiliary pipeline in nuclear power plant. A software of pressurized water reactor auxiliary pipeline anti-ratcheting design is compiled. The calculation method to determine the boundary of ratcheting effect is proposed in order to provide a basis for pipe structural design. This work focuses on the work of the establishment of the structure of software system. The structure mainly composed by three program modules, i.e. the database module, data computing module and data display module. The function of each module and the relationship between the modules are explained. An example to determine ratcheting boundary is presented in the paper.

Abstract: A series of ratcheting experiments under bending loading for Z2CND18.12 stainless steel were carried out on a dynamic mechanical analyzer. The characteristic of progressive inelastic deformation of the material in the different temperatures and different bending loadings were investigated. The difference of the domestic and imported stainless steel on the bending ratcheting properties was studied. It is shown that the temperature and the bending loading affect the ratcheting greatly. In addition, the imported steel is better than the domestic one on the resistance to the ratcheting deformation at various temperatures and bending loadings.