North Korean media’s claims they they tested a hydrogen bomb on Wednesday have caused widespread speculation about the current status on the DPRK’s nuclear weapons technologies.
Thermonuclear explosions – such as the pictured Ivy Mike nuclear test.– are orders of magnitude more powerful than their atomic predecessors, potentially indicating the DPRK has advanced through numerous technological barriers since its first nuclear test of October 2006.
Experts, however, have expressed scepticism at the news, citing a much weaker seismic event than could be expected as evidence for either a failed test, or an exaggeration of the North’s evolving capabilities.
Bruce Bennett, a senior defense analyst at the RAND Corporation, spoke to NK News early on Wednesday about the technical differences between atomic and hydrogen bombs and their testing, saying that current lines of evidence do not point to a successful test.
But notably, even if North Korea did not detonate a fully fledged hydrogen bomb, Bennett adds, the device could have been a “boosted weapon”. And the DPRK’s claims that it was miniaturized should also be of great concern to North Korea’s neighbors.
NK News: What is your opinion of North Korea’s hydrogen bomb claim?
I am skeptical. To understand this, it is important to understand the nature of nuclear weapons. The first generation of nuclear weapons developed by the United States and also by North Korea are referred to as fission weapons. These weapons take very large atoms like uranium or plutonium and split them into smaller parts, creating a significant amount of energy. The nuclear weapons that the United States detonated on Hiroshima and Nagasaki were fission weapons, and had weapon yields (explosive power) in the range of 10 to 20 kilotons (the equivalent of 10,000 to 20,000 tons of TNT).
The US nuclear weapon developers then pursued fusion bombs that are often referred to as hydrogen bombs because they typically use small atoms like hydrogen to combine together and produce vastly more energy. The US designers anticipated that hydrogen bombs would have far bigger effects—these weapons can have weapon yields in the range of 1 to 10 Mt (the equivalent of 1 to 10 million tons of TNT), or 100 to 1,000 times the yield of basic fission weapons. These hydrogen bombs are far more complex to develop.
The yield of nuclear weapons is often measured by the size of the earth tremor that they cause during an underground nuclear test. The North Korean third nuclear test in 2013 had a Richter scale tremor reading of about 4.9, or roughly a yield in the range of 6 to 10 kilotons (kt) — smaller than the U.S. Hiroshima weapon. The North Korean fourth nuclear test appears to have had a Richter scale reading of 5.1 (which might still get adjusted a bit).
Because this scale is logarithmic, the fourth test was about 1.5 times as powerful as the 2013 test, or perhaps 10 to 15 kt. Thus even this fourth test has just barely reached the yield of the US Hiroshima weapon, more than 70 years later. It is not clear whether North Korea has chosen to suppress the yields of its nuclear tests in order to limit international reaction to those tests, or whether North Korea simply has had difficulty mastering the basic technology of nuclear weapons.
NK News: What are the consequences for the North’s technical capabilities?
Since the yield of this fourth test was comparable to the yield of the Hiroshima weapon, the North Korean weapon either did not involve fusion (that is, it really was not a hydrogen bomb) or the fusion component of the bomb failed seriously. If North Korea really did test a hydrogen bomb, its yield should have been about 100 times as large has the yield of this test. Thus the North’s nuclear weapon designs appear to still be very primitive.
Still, to be clear, if this fourth nuclear test was of a weapon that North Korea could put on one of its ballistic missiles, that weapon still might be able to cause hundreds of thousands of fatalities and serious casualties if delivered against a major city in one of the countries surrounding North Korea.
There is, of course, another possibility. As I noted in my recent CNN commentary, there is also a nuclear weapon design referred to as a boosted weapon. A boosted weapon is a largely fission weapon which has a small amount of fusion intended to improve the efficiency of the fission reaction. While not really a hydrogen bomb, a boosted weapon might still be called such because it has a small fusion component. But boosted weapons should have a weapon yield about 5 to 10 times the size of the fourth test, so even if this weapon was only boosted, it did not achieve the designed intent.
NK News: Is it more complex to test H-bombs?
Absolutely. North Korean Nuclear weapons tested underground must be buried sufficiently deeply and sealed underground to prevent some of the radiation from breaking through to the surface (so-called “venting”). The bigger the weapon, the more likely that any given underground design will not be adequate to prevent venting.
That venting could spread radiation to areas dozens to hundreds of kilometers downwind of the test site. In addition, large weapons appear more likely to cause earthquakes in adjoining areas. The North Korean government’s decision to test weapons which may have much larger yields demonstrates its lack of compassion for the safety of its citizens and the people in surrounding areas, to include China, Japan, South Korea, and Russia. In short, the North Korean behavior is irresponsible.
NK News: So what happened?
We don’t know, and may never know. Note that North Korea also announced that this weapon was miniaturized, meaning that it was designed to be placed on top of a ballistic missile. The miniaturization process, making it smaller than previous weapons, may not have worked properly, causing a yield that was lower than desired.
NK News: What is North Korea’s next step?
Kim Jong-un appears intent to demonstrate his empowerment. He wants to show his people and especially his elites that he has accomplished amazing technical achievements. He claims to have developed a hydrogen bomb, and with this claim appears to be positioning himself to argue that North Korea is a peer of the United States, China, and Russia.
But the failure of this test to demonstrate anything close to the yield of a hydrogen bomb will frustrate Kim Jong-un’s objective. With his important 7th Party Congress coming up in May, he may feel compelled to order another nuclear weapon test before then, hoping to demonstrate weapon yields consistent with a hydrogen bomb. That is not good news for North Korea’s neighbors.
Thus a key question is: What will China, Japan, Russia, South Korea, and the United States each do about this nuclear test, a test that was prohibited by prior UN Security Council resolutions? China in particular appears to have had a major role in deterring the further nuclear weapon testing that North Korea threatened in 2013. Will China take further action now in the aftermath of North Korea showing total disrespect for Chinese wishes and interests?
(Leo Byrne is the Data and Analytic Director at NK News and is based in Seoul, South Korea.Follow him on twitter @LeoPByrne)