The U. S. Atomic Energy Commission is conducting an extensive program directed toward the development of thin-wall small diameter tubing that can remain in the fast reactor environment for periods up to three years at temperatures to 800 C, strains to 3 percent, and a total fluence of 3 × 10 ²³ nvt. Austenitic stainless steels have been selected as the reference material with vanadium alloys as the primary backup material. Emphasis has been placed upon quality assurance for commercially produced stainless tubing. The experimental program also includes extensive work on sodium corrosion and radiation damage.