The Study of Fusion Reactor Materials Behavior Using Dual-Ion Irradiation

Small concentrations of transmutant helium (e.g., 10-7 He·disp-1 in Type 316 stainless steel) are produced by neutrons during irradiation in fast-reactors and have been simulated in charged-particle irradiations by He preinjection. In a D-T magnetic fusion reactor (MFR), the 14-MeV plasma neutrons produce higher and more significant concentrations of transmutant helium (e.g., 1.5 × 10-5 He·disp-1 in Type 316 stainless steel). These levels of helium are sufficient to impact heavily on the irradiation microstructure development, and hence, on the mechanical properties of candidate MFR structural materials. We have used simultaneous dual-ion (heavy ions + 3He+) irradiations to simulate the radiation environment in an MFR for our studies of microstructural evolution during irradiation of candidate MFR alloys. Single and dual-ion irradiations of an Fe-20Ni-15Cr alloy, a V-15Cr binary alloy, and selected Ti alloys (Ti-64, Ti-811, and Ti 15333) have been performed over a range of doses, helium to dpa ratios, and temperatures. For the Fe-20Ni-15Cr alloys, a dose dependence study at 700°C revealed that swelling decreased as the rate of helium injection was increased from 2.3:1 to 21:1 (appm He:dpa). Furthermore, the simultaneous injection of helium did not cause a signficant change in the peak swelling temperature of this alloy but did tend to inhibit cavity growth at higher temperatures. A dose dependence study (5-55 dpa) on the V-15Cr alloy at 650° revealed ~20% void swelling at 55 dpa with void diameters approaching 900 Å.