Thursday, January 07, 2016

The North Korean "H-Bomb" tests

The DPRK leadership has claimed that it has the ability to make an "H-bomb", When people think about this - they usually assume a high yield 100kT-1MT device, this is the wrong way to think about it.

MT yield devices were valid in the US-USSR context only because the two nations were in a weapons race. They were trying to show each other up (that is why impractical devices like Tsar Bomba was made). Also neither nation had very good missile guidance technology. So there was very poor CEP and the push towards high yields came about because of that factor. Once the high yields were specified by the end user the AECs on both sides were on the hook for testing such devices (all practically considerations non-withstanding).

That kind of high yield device is meaningless in the Korean context. Even if DPRK could make such a device, there would be of no deterrent value as they would have no place to test such a device and no means of delivering such a complex device to any target. No one would believe them if they claimed that they had one of those.

Internally - as you are all aware - the grasp of the Kim family on the DPRK leadership is always contested at some level. If they assemble a device of MT capability (even theoretically) the possibility of it falling into the hands of someone who wants to depose the Kim dynasty will be too scary to Kim Jong Un. So such a high yield device will most likely never be assembled inside DPRK.

A more rational approach from their perspective is to seek the know-how to make such a device and then leverage their control over the proliferation of such knowledge to blackmail the world. Essentially global nuclear security regimes rely on keeping the exact "recipe" (in as much as one exists) for high yield thermonuclear weapon secret. Demonstrating knowledge of even a part of the recipe provides a lucrative option for a cash starved entity.

If the objective is knowledge building, then a much smaller test is sufficient - there is no need to demonstrate a high yield.

This kind of thing was attempted on fission devices early on in Los Alamos. It was called "tickling the dragon's tail" - a very dangerous set of experiments that tried to push certain nuclear fission reaction rates in a controlled fashion. This is more difficult to do in a fusion context because you have to use a fission reaction to kick-start a fusion reaction. Fusion reactions typically happen when nuclei collide at extremely high speeds. Those conditions are not easy to produce in a highly controlled fashion.  Perhaps the DPRK scientists have figured out a way to do this - that prospect is very disconcerting.

That sort of thing IMO is an explanation for the Lars Erik De Geer analysis of the 2010 data set that showed fluctuations in the ratio short lived isotopes and long lived isotopes. Lars' work was greeted with skepticism because there was no seismic signature.

The relevant questions then become the following:

1) Can DPRK access enough Deuterium or Tritium to produce a technology demonstrator?

This part is hotly debated,

It could be imported from Pakistan (as Jeffrey Lewis hints). Or it could be made at the Yongbyon facility - from Li-6 irradiated at the 5MWth reactor, and then refined in the new hot cell facility (as David Albright pointed out).

Deuterium is relatively easier to get one's hand on. Let us assume that DPRK picked that up from somewhere. With their underworld channels, it should not be impossible to get a hold of. The Tritium is another matter.

2) How much Tritium can DPRK get its hands on?

As the amounts needed for demonstrating a boosting effect is a few grams and a best case scenario for a 20 MWth reactor is ~ 30 grams of tritium per year (per J. Wilson at SRNL). Even if we assume that the Yongbyon reactor is up and running for about 10% of the time a normal reactor is running for, the DPRK people would be able to pull together enough Tritium in a few years.

The amount needed for a boosting experiment is not out of reach of the DPRK people - though this is likely to be the rate limiter in carrying out too many experiments.

3) So what sort of experiments could DPRK carry out? 

This part is a little difficult to answer publicly for obvious reasons, but without getting into any details, the DPRK might want to show that

a) it can actually achieve a nominal fusion yield from heating by a fission primary - specifically show that they are getting fast neutron production.

b) that they can demonstrate the achievement of large amounts of x-ray production and significant quantities of ablation induced pressure.

If they do either of those - their claims to "thermonuclear know-how" will be pretty hard to debate.

4) How does one know that they have really done either?

If the North Koreans decide to publish the data on local radio-isotope abundance shifts then we have a way to examining their claims.

There is a precedent to this - India did that in 1998. India was keen to have people take its claims seriously - so Sikka, Falguni et. al. published the radio-chem analysis. If DPRK leadership wants to be taken seriously - they will need to do likewise.

There may be remotely monitored signals (NOT seismic - think Neutrino or Xe or Ba isotope shifts) that show enough signal to noise to be considered viable as potential supporting evidence.

For example, given the rarity of detecting neutrinos, if there was a sudden increase in the number of neutrinos detected at the exact same time as the DPRK claims of testing - then that is a signature that could be interpreted independently of anything the DPRK leadership might want to claim.

5) What about the IMS and Seismology?

That is useful only for relative magnitude estimation. So far within the error of the data, all the tests have been comparable in yield.

Seismology absent detailed local geophysical knowledge lacks the ability to produce absolute numbers.

6) What does this mean for the regional stability?

If the North Koreans are able to present evidence of achieving either 3a) or 3b) - then the will be able to leverage keeping their mouth shut for concessions. It may be that the concession they seek is a readjustment of the NLL - either in the form of transit rights to Chinese ports from Haeju or in the form of a complete re-alignment of the NLL with their proposed MDL.

In a very unanticipated way - these claims (if proven accurate) will stabilize the region. They will shore up the DPRK leadership and increase the economic stability of DPRK.

With greater stability DPRK will have more to lose by going balls-out-insane.

Therein lies the paradox of nuclear weapons - you can have that knowledge and claim the ability to kill millions of people but you can't behave badly with anyone after that. 

Added on the 11th...

Alex Wellerstein, who runs the RestrictedData blog has similar views. Note the reference to the DPRK press release.

"Through the test conducted with indigenous wisdom, technology and efforts the DPRK fully proved that the technological specifications of the newly developed H-bomb for the purpose of test were accurate and scientifically verified the power of smaller H-bomb."