FISSION REACTOR IRRADIATION OF MATERIALS WITH IMPROVED CONTROL OF NEUTRON FLUX-TEMPERATURE HISTORY

Eliminating the deficiency in the conventional temperature control, irradiation of materials with the Japan Material Testing Reactor is performed with an newly-designed in-core irradiation ring with which the sample temperature can be maintained regardless of the reactor power. The defect microstructures in various materials are compared with those introduced by irradiation with conventional control. The strong influence of the transient lower temperature irradiation during the start-up of the reactor is obvious for the samples irradiated with conventional control. The influence is fully understood from the temperature dependence of the microstructure evolution mechanism. The necessity of improved control is reconfirmed.