Thwarting nuclear terrorism

Civilian research reactors contain highly enriched uranium (HEU) that could be used by the terrorists to build nuclear bombs. HEU is a uranium in which uranium 235, the isotope capable of sustaining a nuclear chain reaction, has been concentrated to levels of 20 percent or more by weight. People have raised credible concerns that suicidal malefactors could penetrate an HEU storage facility, construct a so-called improvised nuclear device and detonate it before security guards could respond. The US and its allies have established programs to bolster security measures, convert reactors to use low-enriched uranium and retrieve HEU from research- reactor sites around the world.