Invisible and visible point defect clusters in neutron irradiated iron

Abstract

Microstructure evolution in a low-dose neutron-irradiated iron was examined with a transmission electron microscope (TEM). The characteristics of the temperature dependence of defect structures in irradiated iron were as follows, (a) rather lower number density of defect clusters at 473 K than at 573 K, (b) development of dislocation loops and voids at an intermediate temperature of 623 K and (c) formation of irregularly shaped dislocation loops at 673 K. Comparing the defect structures produced by the irradiation with a conventional temperature control and that with an improved temperature control, nucleation of defect clusters was suppressed under neutron irradiation at 473 K. From the defect structures introduced by irradiations in which the irradiation temperature was cyclically changed between two temperatures (T-cycle irradiation), the accumulation of a large number of invisible vacancy type defect clusters by irradiation at 473 K was strongly suggested.