DEVELOPMENT AND TESTING OF VANADIUM ALLOYS FOR FUSION APPLICATIONS

Vanadium-base alloys are promising candidate materials for application in fusion reactor first-wall and blanket structure because of several important advantages, i.e., inherently low irradiation-induced activi ty, good mechanical properties, good compatibility with lithium, high thermal conductivity, and good resistance to irradiation-induced swell ing and damage. To screen candidate alloys and develop an optimized va nadium-base alloy, extensive investigations of physical and mechanical properties of various V-Ti, V-Cr-Ti, and V-Ti-Si alloys have been con ducted before and after irradiation in lithium environment in fast fis sion reactors. From these investigations, a V-4Cr-4Ti alloy containing 500-1000 wppm Si and < 1000 wppm O + N + C has been identified as the most promising alloy, end more comprehensive testing on the performan ce of this alloy is being conducted for fusion-relevant conditions. Ma jor results of the comprehensive work to develop the optimal alloy and test the irradiation performance are presented in this paper. The ref erence alloy V-4Cr-4Ti exhibited the most attractive combination of th e mechanical and physical properties that are prerequisite for first-w all and blanket structures, i.e., good thermal creep behavior, good te nsile strength and ductility, high impact energy, excellent resistance to swelling, and very low ductile-brittle transition temperature befo re and after irradiation. The alloy was highly resistant to irradiatio n-induced embrittlement in Li at 420-600 degrees C, and the effects of dynamically charged helium on swelling and mechanical properties were insignificant. However, several important issues remain unresolved, e .g., welding, low-temperature irradiation properties, helium effect at high dose and high helium concentration, irradiation creep, and irrad iation performance in air or helium environment. Initial results of in vestigation of some of these issues are also given.