Joseph De Trani, former head of the National Counterproliferation Center, predicted U.S. intelligence would determine the size and composition of the nuclear device in one to three days based partly on radioactive elements released into the environment.

NPR: NKorean Nuclear Test May Be Intelligence Windfall

"We can and will change the size, the composition, the character of our nuclear forces in a way that reflects the reality that the Cold War is over, " Bush said.

CNN: Bush suggests junking missile treaty with Russia

The size and composition of the current U.S. nuclear weapons stockpile have been determined by a number of relevant factors over time.

CENTERFORSECURITYPOLICY: US Nuclear Stockpile