The plutonium inventory of the United States stood at 95.4 metric tons in 2009, 4.1 MT lower than in 1994, according to a new report from the National Nuclear Security Administration (NNSA).

The 95.4 MT, held mainly at seven sites, was composed of 81.3 MT weapons grade, 12.7 MT fuel grade, and 1.4 MT power reactor grade plutonium, according to “The United States Plutonium Balance, 1944-2009,” which was released in June 2012.

The report provides the U.S. inventory of plutonium owned by the Department of Energy (DOE) and includes material in the possession of the Department of Defense (DoD) as of 30 September 2009.

The four most significant changes since the last inventory report some 15 years ago include: the completion of clean-up activities at the Rocky Flats Plant in Colorado in 2005; material consolidation and disposition activities; 2007 declaration of an additional 9.0 MT of surplus weapons-grade plutonium; and the opening of the Waste Isolation Pilot Plant (WIPP) in New Mexico.

“The most important factor for the reduction in inventory was the reclassification of process residues originally set aside for plutonium recovery as waste. Of the 4.1 MT reduction, 3.5 MT (85 %) came from Rocky Flats residues sent to WIPP for disposition,” the report states.

The remainder came mostly from four other sites: Hanford (0.5 MT), Idaho (0.5 MT), Los Alamos National Laboratory (0.3 MT), and Savannah River (0.1 MT).

The plutonium estimated in waste is 9.7 MT, a 5.8 MT increase to the 1994 inventory of 3.9 MT. The increase is attributed to: 4.4 MT in new discards from the accountable inventory; 0.8 MT increase in Rocky Flats solid waste generated prior to 1970; 0.4 MT increase in Hanford high level waste tank estimates; 0.1 MT in solid waste at a commercial low-level radioactive disposal facility not included in the 1996 report, and 0.1 MT from other sites.

Plutonium surplus to defence needs is now 43.4 MT, a 5.2 MT increase to the 1994 declaration.

“The public release of the U.S. plutonium inventory is a demonstration of our commitment to transparency whenever possible,” said NNSA administrator Thomas D’Agostino. “As the United States moved into the 21st Century, our nuclear security footprint changed, and our nonproliferation goals evolved. The updated inventory is a reflection of that transition and an important gesture of openness to the international community.”