North Korea is thought to have enough plutonium-based fissile material for as many as a dozen small bombs.
WSJ: North Korea to Restart Yongbyon Nuclear Plant
2.
Japan's reactors are almost all fueled by enriched uranium, not plutonium-based fuel.
WSJ: U.S. Opposes Japan's Nuclear Plan
3.
Unlike the plutonium-based 2006 and 2009 tests, a uranium-based test would be a step forward in the sophistication of the North's nuclear capabilities.
BBC: Analysis: What is driving North Korea's nuclear test plan?