| Neutron irradiation embrittlement of RPV is a key issue for the long-term safe operation. Irradiation embrittlement behavior and its mechanisms is an important concern in the nuclear science community in a long term. China’s nuclear power industry is now under the active development. Domestic RPVs can be independently produced, which will be used in the second generation and third generation of pressurized water reactor nuclear power plants. The irradiation-Induced microstructure evolution of the domestic A508-3steel is still a point and need to be cleared up.Firstly, according to the neutron irradiation parameters of the RPV steel in-service, proton irradiation experiments of domestic A508-3steel were carried out. There were three sets of proton irradiated specimens. Namely,(1) A508-3steel specimens were irradiated to0.54-0.271dpa at room temperature, which denoted as A1, B1, C1, D1and E1specimens, respectively;(2) A508-3steel specimen was irradiated to0.163dpa at250℃, which was denoted as F2specimen and (3) A508-steel specimens were irradiated to0.55-0.273dpa at290℃, which denoted as A2, B2, C2, D2and E2specimens, respectively. The evolution of the microstructure features such as phase, vacancy-type defects and dislocation loops with the dose and irradiation temperature were systematically investigated by using grazing incidence X-ray diffraction technique (GI-XRD), slow positron annihilation technique (SPA) and transmission electron microscope (TEM). And the evolution of the mechanical properties with the dose and irradiation temperature was investigated by using the nano-indenter. The focal discussion point has been put on the relationship between the hardening component of the microstructure (loops and vacancy-type defects) and the total hardening converted from the nano-hardness, in order to reveal the microscopic mechanism of irradiation embrittlement. Secondly, based on the mean rate field theory, the cluster kinetics model was developed to predict the evolution of RPV microstructure. Finally, on the basis of the understanding of the physical mechanisms, the neutron irradiation embrittlement prediction model of RPV steels was newly created.The experimental study of domestic A508-3steel under the proton irradiation showed that proton irradiation neither induced the preicipitate of a new phase precipitates, nor induced the grain refinement and amorphization within the studied dose range. Vacancy-type defects and dislocation loops in the A508-3steel were produced by proton irradiation. The vacancy-type defects belongs to a single type defects, which may be single vacancy, vacancy-solute atom complex or small vacancy cluster with few vacancies. Burgers vector of the loops are mainly b=<100>. Some loops had also Bergers vector of b=1/2<111>. According to the inside and outside contrast technique and literature data, the majority of dislocation loops was inferred to be interstitial dislocation loops. As the dose increased, the concentration of vacancy-type defects rapidly increased in the beginning and then saturated at approximately0.15dpa. As the dose increased, the size distribution of the dislocation loops broadened, the average diameter of the loops increased and the number density of the loops increased slightly in the order of1022m-3. As the irradiation temperature increased, the average diameter of the loops increased and the number density of the loops decreased. The evolution equations of the concentration of the vacancy-type defects and the number density, size of the dislocation loops were obtained. Based on the Orowan hardening model, the evolution equations of the hardening components of both the vacancy-type defects and the dislocation loops were established. The total hardening evolution equation was obtained from the nanohardness of A508-3steel before and after the proton irradiation. Grazing incidence X-ray diffraction (GIXRD) was applied to measure the residual stress of A508-3steel before and after proton irradiation. Within the studied dose range for the proton irradiated A508-3steel, the hardening component of the dislocation loops was higher than that of the vacancy-type defects. If the dose exceeds a critic dose (at around0.05-0.1dpa), the hardening contribution of dislocation loops plays a dominant role. In addition to the hardening components of both the vacancy type defects and the dislocation loops, there are other hardening contributions from some unexplored irradiation-induced defects, which may be Cu-rich clusters. Because the irradiation embrittlement is of the hardening-type, the trend of irradiation embrittlement in the proton irradiated A508-3steel follows the similar law of irradiation hardening.A new cluster dynamics model named CLV model was developed based on the mean rate field theory. This model takes both the homogeneous nucleation and heterogeneous nucleation mechanism of the Cu-rich phase into consideration for the first time. This model can simulate the evolution of the vacancy clusters, interstitial clusters and Cu-rich phase. The CLV model was used to simulate several typical cases. The results can be described as follows. The forecasts of CLV model could be basically consistent with the proton irradiation-induced microstructure evolution and hardening of the A508-3steel. Compared with neutron irradiation, the proton irradiation accelerates the nucleation of point defect clusters but delays the precipitate of the Cu-rich phase. From the standpoint of the overall irradiation hardening and embrittlement, proton irradiation can successfully simulate neutron irradiation process, especially in the range of0.01-0.2dpa. Without consideration of Cu content effect on the diffusion of point defects, as the Cu content of RPV steel increases, the formation of point defect clusters is weakly affected, but the precipitation of Cu-rich phase is promoted and the saturated amount of this precipitation increases. As far as the RPV steels of0.06Cu which is neutron irradiated at290℃, there are no notable dose rate effect between the dose rate of10-8dpa/s and10-10dpa/s, which is consistent with the results of the neutron irradiated A508-3steels studied by SCK-CEN. When the dose rate increases to10-5dpa/s, the dose rate effect emerges and the total irradiation hardening reduces.Based on the evolution mechanism of matrix damage and Cu-rich phase, a new neutron irradiation embrittlement prediction model of RPV steels was created, which is named CSW model. The CSW model includes three sub-models, namely CSW-T, CSW-E and CSW-σ, which predicts the shift of the ductile-brittle transition temperature (ADBTT), the upper shelf energy (USE) and the increment of flow strength, respectively, the three sub-models are correlative, with a universal form. The model is applicable to a wide range of materials, including base metal, weld metal and the heat affected zone from China and France, Japan and the USA. The reliability of the prediction of CSW model is relatively high. Base on the CSW model, a synthetic lifetime prediction method is proposed using the three parameters of the reference temperature, the upper shelf energy (USE) and yield ratio. |
PDF Full Text Request