Improvement of Validation Technique for Long Term Soundness of In-core Component Materials of Light Water Reactor Plant after Repair and Maintenance

本研究的目的是研究损伤的微观结构的发展，包括He气泡的形成，在奥氏体不锈钢的核心组件，包括由于热处理过程中的再焊接和中子辐照后，通过模拟实验，使用轻离子注入/辐照，使用加速器。利用He离子注入模拟了He原子的形成。采用炉内静态热处理模拟了再焊接过程中的热处理过程。热处理对固溶退火态316L奥氏体不锈钢损伤组织的影响（850和1050_oC，5-500 min）（10-1000 appm）和氢（H）离子辐照研究了热处理后在300 ℃温度下（0-0.5 dpa）的拉伸强度，以评估热影响区（HAZ）区域的显微组织退化 ...更多信息 裂变反应堆堆芯组件在重新焊接和焊后中子辐照期间的辐射。氦泡的长大与氦浓度、热处理时间和热处理温度的增加以及氢辐照引起的位移损伤有关。在热处理过程中和H离子辐照后形成的He气泡分布在晶界和基体中。实验结果表明，当辐照强度达到0.5dpa时，He气泡在晶界处明显长大，这与He浓度、退火时间和热处理温度的增加以及He离子注入和热处理后的位移损伤有关。众所周知，晶界中气泡的形成会导致脆化、焊缝金属开裂和可焊性降低。因此，为了保证核电站的高可靠性运行，确定补焊前的He浓度、在精确控制的条件下补焊、补焊后的运行周期和检查周期就显得尤为重要。此外，热应力及其循环发生由于重新焊接也被认为是导致氦泡的增长。因此，热应力水平和循环对氦泡形成和生长行为的影响必须在未来的工作中进行研究。少

The objective of this study is to investigate damage microstructure development including He bubble formation in the austenitic stainless steel for in-core components including transmutant He atoms due to heat treatment during re-welding and neutron irradiation after rewelding by means of the simulation experiments using light ion implantation/irradiation by using an accelerator. The formation of He atoms was simulated using He ion implantation. The heat treatment during re-welding was simulated using a static heat treatment in a furnace.Damage microstructure development including helium (He) bubble formation in solution annealed type 316L austenitic stainless steel due to heat treatment (850 and 1050_oC for 5-500 min) after He ion pre-implantation (10-1000 appm) at room temperature and hydrogen (H) ion irradiation (0-0.5 dpa) at the temperature of 300_oC after the heat treatment was investigated in order to evaluate the microstructural degradation in a HAZ (heat affected zone) region … More of in-core components of fission reactors during re-welding and post welding neutron irradiation. The growth of He bubbles was observed due to the increment of He concentration, annealing time and annealing temperature of heat treatment, and displacement damage by H irradiation. He bubbles formed during the heat treatment and after H ion irradiation were distributed both in the grain boundary and in the matrix. The significant growth of He bubbles in the grain boundary after H irradiation up to 0.5 dpa was observed.It was clarified by this study that the growth of He bubbles significantly occurred due to the increment of He-concentration, annealing time and temperature of heat treatment, and displacement damage followed by He-ion implantation and heat treatment. He bubble formation in the grain boundary is well known to cause an embrittlement, weld metal cracking and degradation of weldability. Thus, in order to keep the highly reliable operation of fission reactor plants, the identifying the He concentration before re-welding repair, re-welding under the precisely controlled conditions, and the operation term and inspection periods after re-welding repair would be significantly important. Moreover, thermal stress and its cycling occurring due to the re-welding are also considered to cause the growth of He bubble. Therefore, the effect of thermal stress level and cycling on the He bubble formation and growth behavior must be investigated in future work. Less