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

轻水堆压力容器用钢的中子辐照脆化是理解脆化机理和预测构件寿命的关键问题之一。在这项研究中，离子辐照实验，具有良好的可控性的辐照条件，如温度和离子流量被应用于建立在钢中的辐照脆化的物理模型。在东京大学HIT装置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液氮温度和573 K之间的温度控制、电阻率能力和离子束轮廓测量。这些都是通过详细设计的辐照室和试样的大小。在液氮温度和室温下进行了1 MeV和更高能量质子的离子辐照实验。在离子辐照过程中，成功地实现了离子束与样品和法拉第杯位置的对准。用质子辐照的铁-铜模型合金具有放射性，这导致辐照后处理辐照样品的困难。在束电阻率测量被认为是困难的，因为在辐照过程中的样品的噪声信号，但在低温下的电阻率可以通过中断离子束测量。分析了离子辐照后铁中缺陷团的退火过程，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.