Since North Korea tested a nuclear bomb for a third time on Feb. 12, it has said repeatedly it now has a "smaller, lighter and diversified" nuclear weapons capability. The intended message: we can now make nuclear bombs from highly enriched uranium as well as plutonium, and they're small enough to put on a warhead.

Experts and scientists doubt the latter claim but aren't sure about the former. In 2010 North Korea revealed a facility for enriching uranium, which it said was for creating fuel for its nuclear reactor...