The U.S. administration published an update on the status of the U.S. stock of highly-enriched uranium:

• As of September 30, 2013, the total U.S. HEU inventory was 585.6 metric tons.
• Of this amount, 499.4 metric tons was for national security or non-national security programs including nuclear weapons, naval propulsion, nuclear energy, and science.
• Of the remaining 86.2 metric tons, 41.6 metric tons was available for potential down-blend to low enriched uranium or, if not possible, disposal as low-level waste, and 44.6 metric tons was in spent reactor fuel.

According to the press-release, the inventory in 1996 was 740.7 metric tons (as reported by DoE in 2001). Also, the ongoing HEU disposition program down-blended additional 7.1 MT of HEU since 30 September 2013, suggesting that the current inventory is 578.5 MT of HEU, of which 34.5 MT is marked for down-blending or disposal.

In another release issued today, the administration reported that "the United States has down-blended 148 MT of this HEU to low-enriched uranium so it can no longer be used for nuclear weapons."