Thermal stability of point defect clusters in neutron irradiated Fe-16Ni-15Cr

Annealing behavior of point defect clusters in neutron irradiated Fe-16Ni-15Cr alloy with a fission reactor was examined. From the comparison of the variation of the size distribution of vacancy (V)-type clusters during annealing with the change of their size distribution by irradiation temperature, it was deduced that at higher irradiation temperature the nuclei of clusters formed directly from collision cascades do not annihilate after their formation but they do not form from the beginning. From the results of the thermal stability of defect clusters, the process of defect structure formation in temperature-cycle neutron irradiation, in which irradiation temperature was changed cyclically between two temperatures In a fission reactor (T-cycle irradiation), was discussed. Characteristic microstructure of T-cycle irradiation, the suppression of I-type cluster formation, was found to depend on the decomposition rate of V-type clusters accumulated at the low temperature of T-cycle irradiation after the shift to high temperature of T-cycle irradiation. When the low temperature of T-cycle irradiation is lower and its high temperature is higher, the characteristic of T-cycle irradiation is enhanced.