Armacost has served on numerous corporate and nonprofit boards, including TRW, AFLAC, Applied Materials, USEC, Inc., Cargill, Inc, Carleton College, and The Asia Foundation.
USEC ceased enrichment operations at the Portsmouth Gaseous Diffusion Plant in May 2001 after it consolidated operations at the Paducah Gaseous Diffusion Plant in Kentucky.
In November 1996 Silex Systems Limited licensed its technology exclusively to United States Enrichment Corporation (USEC) for uranium enrichment.
USEC was the executive agent in the U.S./Russia Highly Enriched Uranium Purchase Agreement, implemented under the Megatons to Megawatts Program.