After reports of a small, magnitude 5.1 seismic event in the vicinity of North Korea’s Punggye-ri nuclear test site on Tuesday, the state-controlled North Korean news service announced a successful test of a miniaturized hydrogen bomb — which it called a “hydrogen bomb for justice.” A North Korean television anchor said the test elevated North Korea’s “nuclear might to the next level.”
It is very unlikely that this was a test of a true H-bomb, a thermonuclear device in which a primary fission reaction ignites a much larger secondary fusion/fission reaction. The technical challenges of constructing a true H-bomb, which could be over 1000 times more powerful than North Korea’s previous three nuclear tests, are far beyond North Korean capabilities. The real meaning of this nuclear test, regardless of its type, may be an attempt by North Korea to get a nuclear deal similar to Iran’s before President Obama leaves office.
It is possible this was a test of a “boosted-fission” nuclear weapon. In such a device, a small fusion reaction of two hydrogen isotopes, deuterium and tritium, is initiated in the core. This reaction releases a flood of high-energy neutrons that causes a more efficient fission reaction by the weapon’s enriched uranium or plutonium fuel resulting in an explosive yield several times higher. Boosted fission enables states to construct smaller and lighter nuclear weapons and to make more efficient use of scarce nuclear fuel.
North Korea has been claiming for several years that it was engaged in nuclear-fusion research. In 2010, North Korean officials even said that their nation had mastered nuclear fusion. In January 2013, the Japanese newspaper Asahi Shimbun reported that a “new higher level nuclear device” that North Korea was threatening to test might be a boosted-fission nuclear device. Last month, North Korean leader Kim Jong-Un said his country had developed a hydrogen bomb.
Although most experts dismissed North Korea’s nuclear fusion claims as bravado, a boosted-fission nuclear test would be the next step in the development of a North Korean nuclear-weapons program. Building such a device would be technically challenging. India, which has a more advanced nuclear-weapons program than North Korea, reportedly conducted a failed test of a booted-fission nuclear device in 1998.