Dislocation-loop formation and development in an Fe-10%Cr alloy and in a low-activation ferritic alloy (JLF-5), during 1MeV electron irradiation, were investigated at various temperatures. The type of loop which formed was found to be sensitive to the irradiation temperature. In the case of low-temperature irradiation, followed by high-temperature irradiation, the type of loop was similar to that produced by irradiation at the lower temperature alone. In the case of Fe-10%Cr, this rule was obeyed even when the period of low-temperature irradiation was very short (15s, 0.003dpa). In the case of JLF-5, longer irradiation times at the lower temperature were required in order to affect the loop type. It was shown that, in ferritic alloys, the Burgers vectors of dislocations and void swelling at high fluences would be strongly affected by short-term negative temperature excursions in the initial period of the irradiation.

T.Muroga, Y.Nonaka, N.Yoshida: Journal of Nuclear Materials, 1996, 233-237B, 1035-9