DEVELOPMENT OF CONTROLLED TEMPERATURE-CYCLE IRRADIATION TECHNIQUE IN JMTR

The effects of cyclic temperature changes during neutron irradiation u pon radiation induced microstructure evolution and resulting property changes of materials is very important from both fundamental and engin eering viewpoints. Therefore, a technique that allows us to do the con trolled temperature-cycle irradiation was developed in the Japan Mater ials Testing Reactor(JMTR). The technique meets the following requirem ents: (1) the temperature-cycle irradiation is to be performed under t hree different conditions by changing lower and upper temperatures; 20 0 --- 400 degrees C, 300 --- 400 degrees C and 300 --- 450 degrees 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 b e maintained at the lower temperatures before start-up of the reactor and at the upper temperatures during shut-down until the complete abse nce of reactor power. In this paper, the details of the irradiation ri g, successful results and several problems to be overcome for future i mprovement are presented.