The Research On The Irradiation And Thermal Treatment Performance Of Reactor Pressure Vessel Steels Employed In HTGR

The Reactor Pressure Vessel(RPV)is the key component in the nuclear power plant,which contains the nuclear core,the core shroud,and the reactor coolant.It is considered irreplaceable,thus being the life-limiting feature of nuclear power plant if its mechanical properties degrade sufficiently.As a Generation IV reactor concept,the High Temperature Gas-cooled Reactor(HTGR)has perfect inherent safety.The HTGR RPV has different operation temperature with the Pressurized Water Reactor(PWR)RPV.So the irradiation and thermal behaviors of the new HTGR RPV are investigated in this study to support the HTGR life management.The studied material was the Chinese low Cu RPV steel A508-3 which is one of the RPV materials used in Shandong Shidaowan HTR-PM.Three experimental methods,ion irradiation,thermal ageing,and post-irradiation annealing,were used: 3 MeV Fe-ion irradiation experiments were performed under both high temperature and room temperature,thermal ageing experiments were conducted at 405 oC,and post-irradiation annealing experiments were done at different temperatures.Positron annihilation technique,3D atom probe tomography,nano-indentation hardness test and other techniques were used to characterize the materials.For the study of vacancy-type defects,the results showed that irradiation produced large amounts of vacancy-type defects: under room temperature irradiation the defect density first increased with the dose and then saturated;under high temperature irradiation the defect density first increased with the dose and then decreased,because the vacancy-type defects could be annealed at high temperature.For the study of cluster-type defects,the results showed they are Mn-Ni-Si-enriched clusters with few Cu atoms.The number density and volume fraction of the clusters both increased with the dose.In addition,the size,number density and volume fraction of the clusters in high temperature irradiated material were larger than those in room temperature irradiated material.However,clusters were not detected after thermal ageing at 405 oC up to 1000 h.For the study of mechanical property and morphology,the results showed the irradiation hardening and it is concluded that the cluster-type defects have a larger influence on the RPV embrittlement than the vacancy-type defects.The results also showed no significant change of structure and morphology after irradiation.Finally,for the study of defects and mechanical property using post-irradiation annealing,the results indicated that post-irradiation annealing can be an efficient method for the mitigation of HTGR RPV embrittlement: the vacancy-type defects almost totally recovered at 450 oC and mechanical property can recover at 750 oC.The behaviors of Chinese HTGR RPV steels at 250 oC were investigated for the first time in this study.It was confirmed that the Mn-Ni-Si solute clusters were the main cluster-type defects of low Cu RPV steels.And the mechanism of irradiation embrittlement of HTGR RPV steels was similar with RPV steels of PWR.