Development of controlled temperature-cycle irradiation technique in JMTR

To investigate the effects of cyclic temperature changes during neutron irradiation upon radiation induced microstructure evolution and resulting property changes of materials is very important from both fundamental and engineering viewpoints. Therefore, a technique that allows us to do the controlled temperature-cycle irradiation was developed in the Japan Materials Testing Reactor (JMTR). The technique meets the following requirements: (1) the temperature-cycle irradiation is to be performed under three different conditions by changing lower and upper temperatures; 200Leftrightarrow400 C, 300Leftrightarrow400 C and 300Leftrightarrow450 C; (2) the number and period of the temperature-cycles are to be six for 24-day full irradiation and approximately 44 h/44 h at the lower/upper temperatures; (3) the temperatures of each specimen assembly are to be maintained at the lower temperatures before start-up of the reactor and at the upper temperatures during shutdown until the complete absence of reactor power. In this paper, the details of the irradiation rig, successful results and several problems to be overcome for future improvement are presented. ((orig.))