Heavy water is necessary to produce plutonium in a nuclear reactor.
Plutonium is far more potent than uranium. Until now, it was commonly believed Pakistan got heavy water from China and was not able to produce it indigenously, FAS senior analyst John Pike said. It was publicly unknown until now where that heavy water facility was located. These are unsafeguarded facilities, not controlled by any international authority. Plutonium can be packed into M-11 missile casings and launched independent of aircraft, and Pakistan has built the Sargodha missile base for a slew of just such weapons, according to Pike.