APPLICATION OF ION IRRADIATION FOR MECHANISTIC STUDY ON NEUTRON IRRADIATION EMBRITTLEMENT IN STEELS

轻水反应堆压力容器钢的中子辐照脆化是了解元件脆化机理和寿命预测的关键问题之一。本研究利用离子辐照实验对温度和离子通量等辐照条件具有良好的可控性，建立了钢的辐照脆化物理模型。在东京大学的HIT设施中设计并安装了用于离子辐照的样品室。该辐照室在技术上需要在液体N2温度和573K之间进行温度控制，电阻率能力和离子束剖面测量。这些都是通过辐照室和试样尺寸的详细设计来完成的。离子辐照实验分别在液态N2温度和室温下进行，质子能量为1mev和更高。在离子辐照过程中，成功地使离子束对准试样和法拉第杯的位置。用质子辐照的铁铜模型合金具有放射性，辐照后处理辐照试样存在困难。由于辐照过程中试样会产生噪声信号，因此束流上电阻率的测量是困难的，但可以通过打断离子束来测量低温下的电阻率。分析了离子辐照后铁试样中缺陷团簇的退火过程，获得了钢中缺陷形成和硬化行为的基本信息。

Neutron irradiation embrittlement in pressure vessel steels in light water reactors is one of the critical issues to understand mechanisms of embrittlements and prediction of lifetime of the component. In this study, ion irradiation experiments which have excellent controllability of irradiation conditions such as temperature and ion flux are applied to establish physical models of irradiation embrittlement in steels. Specimen chamber for ion irradiation is designed and installed in the HIT facility of the University of Tokyo. This irradiation chamber technically requires temperature control between liquid N2 temperature and 573K,electric resistivity capability and ion beam profile measurements. These are completed by detailed design of the irradiation chamber and specimen size. Ion irradiation experiments are performed at liquid N2 temperature and room temperature with 1 MeV and higher energy of protons. The alignments of ion beams to the position of specimens and Faraday cups are successfully made during ion irradiation. An iron-copper model alloy irradiated with protons has radio-activity which causes difficulty to handle the irradiated specimen after irradiation. On-beam electric resistivity measurements is found to be difficult because of the noise signals from the specimen during irradiation, but electric resistivity at low temperatures can be measured by interrupting ion beam. The annealing processes of defect clusters in irradiated iron specimens are analyzed after ion irradiation, and fundamental information on defect formation and hardening behavior in steels are obtained.