DEVELOPMENT OF VANADIUM-BASE ALLOYS FOR FUSION FIRST-WALL BLANKET APPLICATIONS

Vanadium alloys have been identified as a leading candidate material for fusion first-wall-blanket applications. Certain vanadium alloys exhibit favorable safety and environmental characteristics, good fabricability, high temperature and heat load capability, good compatibility with liquid metals and resistance to irradiation damage effects. The current focus is on vanadium alloys with (3-5)% Cr and (3-5)% Ti, with a V-4Cr-4Ti alloy as the leading candidate. The available database indicates that the V-Cr-Ti alloys provide the following advantages: (1) These alloys are readily formable and weldable; however, atmospheric contamination must be avoided during welding and high temperature processing. (2) The relatively high thermal conductivity and low thermal expansion provide for a high heat: load capability. (3) These alloys exhibit good high temperature tensile and creep properties which permit high temperature operation. (4) V-Cr-Ti alloys exhibit low long-term activation and low radioactive decay heat which provide safety and environmental advantages. (5) These alloys are characteristically resistant to liquid metal corrosion. (6) Alloys with a few per cent titanium are highly resistant to irradiation-induced swelling, which provides for the possibility of long lifetime. (7) Results obtained to date indicate that the V-4Cr-4Ti alloy is highly resistant to irradiation-induced degradation of the mechanical properties. Substantial progress has been made in the development of these alloys for fusion application. Larger heats of the V-4Cr-4Ti alloy have been prepared in the USA and Russia. The baseline property database has been expanded. Recent results indicate that these alloys are resistant to irradiation damage. The irradiation-induced swelling is low, the uniform elongation of alloys irradiated at 400-600 degrees C remains above 8% and the ductile-brittle transition temperature of the V-4Cr-4Ti alloy after irradiation remains well below room temperature. Preliminary results indicate that the crack growth rates of certain alloys are not highly sensitive to irradiation. Results from the dynamic helium charging experiment (DHCE) which simulates fusion relevant helium/dpa ratios are similar to results from neutron-irradiated material. This paper presents an overview of recent results on the development of vanadium alloys for fusion first-wall-blanket applications.