The security summit that begins in Washington Monday aims to ensure that nuclear weapons and weapons-grade materials are put under lock and key to prevent terrorists from getting them.
The May 25 test provided the world with a host of data about North Korea's bomb-making abilities. But only Pyongyang knows if the test was a success.
New process could replace centrifuges but renew threat of nuclear proliferation.
Some US experts worry that a smuggling ring gave rogue states plans for a light warhead, apparently from Pakistan.