Today, the United States and Japan announced that Japan would eliminate all the plutonium and highly-enriched uranium at its Fast Critical Assembly (FCA) at Tokai-mura. This is a tremendous step forward for nuclear security; for terrorists, this would be some of the best material that exists in any non-nuclear-weapon state. The material includes 331 kilograms of plutonium, most of it weapons-grade, and 214.5 kilograms of weapons-grade HEU. (The FCA also includes over a ton of material just at the 20 percent U-235 mark that defines HEU.) The weapons-grade HEU is enough for four simple terrorist “gun-type” bombs or a larger number of trickier-to-build implosion bombs. The plutonium amounts to more than 40 bombs worth of material.