Compositional and temperature dependence of void swelling in model Fe-Cr base alloys irradiated in the EBR-II fast reactor

A series of annealed and aged Fe-xCr, Fe-12Cr-yC and Fe-12Cr-0.1C-zMo model alloys were irradiated in EBR-II at eight temperatures between 400 degrees C and 650 degreesC and dose levels ranging from 35 to 131 dpa. Swelling-ind uced density changes observed in the binary alloys generally peaked at mid- chromium levels, with the chromium and temperature dependence expressed pri marily in the duration of the transient regime. The steady-state swelling r ate at the lower irradiation temperatures was much higher than previous est imates, reaching similar to0.2%/dpa and possibly still climbing at higher n eutron exposures. The dependence of swelling on molybdenum and carbon was m ore complex, depending on whether the temperature was relatively low or hig h. At temperatures of 482 degreesC and above, the effect of carbon addition s was very pronounced with swelling of Fe-12Cr jumping dramatically from ne ar zero at 0.002% C to 6-10% at 0.1% C. This indicates that the major deter minant of the composition and temperature dependence probably lies in the d uration of the nucleation-dominated transient regime of swelling and not pr imarily in the steady-state swelling rate as previously envisioned. This ra ises the possibility that significant swelling may occur earlier in fusion and spallation neutron spectra where high gas generation rates may assist v oid nucleation. (C) 2000 Elsevier Science B.V. All rights reserved.