Influence of neutron irradiation temperature on the void characteristics of niobium and niobium--1% zirconium alloy

Voids in Nb and Nb-1 wt. percent Zr alloy irradiated to a fast neutron fluence of approximately 1 x 1022 n cm-2 (E greater than 1 MeV) at six different temperatures between 430 and 10500C have been investigated. Transmission electron microscopy observations revealed the presence of voids in both Nb and Nb-1 Zr at all six irradiation temperatures. The void number density and size of the niobium specimens appeared unaffected by irradiation temperatures between 430 and 7000C, but the void number density decreased and the size increased at the higher temperatures. Other observations regarding Nb were that ordered voids were observed at 8000C with the lattice parameter of 685 A, and the maximum void swelling was approximately 0.5 percent which occurred at 10500C. In contrast, the Nb-1 percent Zr alloy specimens showed larger voids and lower number density than the corresponding Nb specimens. The void swelling of Nb-1 Zr reached the maximum of approximately 2 percent at 8000C. At the irradiation temperatures of 430, 580, and 10500C the voids were observed only in small localized areas resulting in negligible void swelling