A North Korean Hydrogen Bomb

On September 2, 2017 Kim’s regime revealed what appears to be a 2-stage thermonuclear device. Shaped roughly like a peanut the device was shown next to Kim Jong Un being loaded into a HS-14. In the following hours the North Korean’s detonated the device with of roughly 1 Megaton.

DIwO-DEUIAAqCO1
North Korea’s Hydrogen Bomb.

Why the DPRK build such a weapon?

A hydrogen bomb provides a number advantages to a fledgling nuclear power. It opens up the path to more advanced and powerful bombs with greater military and deterrence capabilities. There is also a prestige factor involved. Even though many thinks have changed since the 1950s, the hydrogen bomb still represents unique technical prowess and skill that would grant the DPRK substantial stature.

Technical Specifications

On the technical side there are a few clues as to what kind of weapon this is. Given the power of their current ICBM and the power and size of their current warhead and pictures provided we can make some assumptions regarding the physical characteristics and yield of such a weapon.

First of all, it is clearly a two-stage Teller-Ulam style device. This is a full-scale thermonuclear bomb, not a boosted weapon like the last test.The two orbs on either side house the primary and secondary components and the case sitting behind the bomb likely houses a neutron generator and /or detonation controls. In concept it very much resembles the American W87 warhead designed for the Peacekeeper missile in the 1980s although it appears to be about 3 times the weight and volume.

While some claim that this is simply a larger boosted device I find that unlikely. North Korea would be unlikely to waste fissile material on a device that doesn’t give them any more technical knowledge. This is especially true given the size of the weapon and the amount of fissile material needed to produce them. From an economics perspective another boosted weapon simply doesn’t make sense.

W87Schematic781
An illustration of the W87 warhead. Note the Peanut shape of the physics package and positioning.

 

Yield

When discussing yield it’s important to remember that the DPRK is constrained in terms of testing facilities. Unlike the American program which used the vast expanse of the Pacific to test weapons up to 15 Megatons (by accident but still), the political environment and geography of the DPRK are not conducive to open air testing. Ergo, they confined to underground testing. This limits the maximum yield of their test to between 282 and 350 kilotons, that of their largest testing chamber at Punggye-ri. A megaton device could probably be ruled out on that basis.

The seismic readings are all over the place with some measuring the device at a Megaton and some as low as 100 kilotons. South Korea even claimed 50 kilotons, although this is an extreme outlier. Most are now centering around estimates from 100 kt to 300 kt with a lot in the middle. This is reasonable given that the yield would have needed to be low enough to test at full yield inside Punggye-ri while maximizing the capacity of the test chamber. It is also consistent with the KCNA statement claiming that device has a variable yield “which is adjustable from tens kiloton to hundreds kilotons(sic).”

Deliverability

North Korea  has already shown that they can fit this device inside an ICBM. The real question is whether this weapon can currently reach the continental United States. For this there are two possibilities:

The first possibility assumes that the HS-14 ICBM is capable of delivering a 500 kg payload up to 10400 kilometers. Because the range decreases significantly with added weight, the warhead and reentry vehicle will have to be around 600 kg kilograms or less so the missile can still retain its ability to threaten targets in the continental U.S. I still haven’t seen mass estimates for this device and given that the volume of the secondary is mostly foam and lithium-deuteride it might be close to that mark, meaning that it could hit parts of Alaska or even California.

The second possibility is that the North Korean’s have already tested a mock-up of this device in flight. Meaning that the “heavy warhead” on the HS-14 tests was not the 500 kilograms assumed in the models but a mock-up meant to approximate a thermonuclear weapon. In which case it is probable that they can reach somewhat deeper into the continental U.S.

There are some skeptics who contend that this design could not reliably fit on a missile, that North Korea could not miniaturize a hydrogen device so fast. I believe that they can because the device shown is not actually miniaturized in the sense that American warheads are.

When you look at the device it is still fairly large. It likely weighs around 350 kilograms (+/- 50 kg) and produces a yield of between to 150 and 300 kilotons, giving it a 0.5 to 1 kiloton to kilogram ratio. This is consistent with early American thermonuclear weapons that were not “miniaturized”.

yield-to-weight-trends
Yield to Weight ratio or time. From nuclearsecrecy.com

 

I’m not a physicist but my guess at the time is that the device is not miniaturized, it simply sacrifices efficiency and yield for reductions in weight and volume. America’s early thermonuclear weapons were heavy because they were intended to be dropped from bombers that could carry weapons that weighed as much as a city bus. There was also a much heavier emphasis on yield and volume was not as much of a concern.

It’s also important to remember that they North Koreans started out with much more knowledge then the United States did in 1950. They didn’t have to spend years messing around with cryogenically frozen fuels or figuring out the basic Teller-Ulam concept. A successful test means they are closer to 1955 then 1952 in terms of design.

When could they have this thing operational?

The North Koreans have attempted to telescope the process to the degree that is possible. They are not moving incrementally like the U.S or Soviet Union did in the 1950s. I would assume that this device may already be on some missiles or close to being fitted. From a deterrence perspective getting this thing ready as soon as possible is a priority. Deterrence of course is what this weapon is for.

Kim Thermonuclear
Kim Jong Un demonstrating to the world that the warhead fits in the HS-14 shroud. In back a poster shows how the actual reentry vehicle would be configured.

How does it help them?

North Korea’s missiles are relatively inaccurate and therefore are less capable of holding certain targets at risk. Their threat against Guam implied that their HS-12 IRBMs might have a CEP as big as 5 kilometers. With a 100 kiloton  weapon the accuracy of the missile becomes less important. The fireball and blast are so massive that they can hollow out a city even if it lands a few kilometers off target.

From a deterrence perspective, a thermonuclear weapon has a clear advantage over a fission bomb owing to its significantly higher destructive capabilities. Civil defense will not work against a warhead that can blast apart an entire metro area and literally excavate an underground shelter.

Militarily, a thermonuclear weapons is much more effective at holding certain hardened targets at risk, especially when the accuracy of their delivery systems are low. Naval bases for example house warships that may be more difficult to destroy with lower yield weapons. This is especially true if the ships are dispersed or the weapon is inaccurate.

Future of DPRK Nukes.

Expect further advancements as the months and years ahead. The DRPK won’t get thermonuclear weapons perfect on their first try. The science behind a hydrogen bomb is complicated and can take decades to perfect and miniaturize them to the degree that the U.S and Russia have.

In the future I would expect further refinement of their nuclear arsenal. The KNCA statement regarding variable yield points to the development of a much broader spectrum of nuclear capabilities likely including tactical weapons.

Such capabilities would allow Kim’s regime the ability to more convincingly threaten the United States by lowering the threshold for nuclear use.

What does mean for us?

With the Kim Regime preparing to produce such a weapon we will be firmly within the realm of mutual deterrence. With the only realistic military option in the event of a general war being a preemptive nuclear strike. Meaning that unless Trump is truly out of his mind, a general war is off the table.

Because of this we must come to a modus vivendi with Kim. This situation is not tenable over the long-term the risks of miscalculation and war are too high. What this will look like I do not know but it is not likely with our current leadership. Expect more tests and more advanced missiles. Also expect the regime to diversify their stockpile as it grows. Barring a war this isn’t ending anytime soon.

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