Mechanical property changes and defect structures of Ni and Fe irradiated with fission and fusion neutrons

The correlation between the fission and 14-MeV D-T fusion neutron irradiation effects on the mechanical property changes is discussed for Ni and Fe with reference to the defect structures induced by the irradiation. In Ni irradiated with fission and fusion neutrons at 470 K, no significant difference in size distribution was found in the defect structures of small SFTs (stacking fault tetrahedra) and dislocation loops except for the absolute value of their number density and the dependence of the change in the yield stress on the defect number density is the same. In irradiations at higher temperatures, 720 K in RTNS-II and 670 and 770 K in Joyo, the dominant defect clusters are SFTs in RTNS-II and voids in Joyo irradiation. The difference in the amount of the yield stress increase for the same defect number density is understood from the difference in the defect cluster species. The dependence of the yield stress on the fluence in Fe was discussed on the basis of the results of Ni.