Radiation Damage Studies in CTR Materials Using Dual Beam Irradiation

Radiation damage to first wall materials during CTR operation is being evaluated using a dual beam ion bombardment technique. The dual beams consist of a heavy ion beam, e. g., Ni+++ which produces damage similar to that from high energy neutrons and light ions, e.g., He+ which simulates the η,α production during neutron irradiation. A 2 MeV tandem accelerator with a sputter ion source produces the heavy ions. A 2 MeV Van der Graff produces the helium ions. A degrader foil in conjenction with a detector is used to obtain the proper helium energy to match the damage range of the heavy ions. The radiation induced microstructural changes are subsequently evaluated using transmission electron microscopy. Results have shown that in molybdenum at temperatures up to 1475 K, simultaneous injection of helium with the heavy ion had a small effect on the microstructure but no effect on the void swelling. In a Nb-lZr alloy, radiation did enhance internal oxide nucleation at elevated temperature. If the alloy was internally oxidized prior to irradiation, the resulting microstructural damage from the irradiation revealed much less void swelling.