Friday, March 25, 2016

Dissecting the DPRK Miniaturized Bomb Mockup

Ara Barsamian
Nuclear Non-Proliferation Institute

As part of the “tit-for-tat” war of words between the West and DPRK regarding the nuclear development and testing in the Korean peninsula, Kim Jong Un felt compelled to show the world a display of a mock-up of a miniaturized nuclear warhead.

What do we see?
The mockup seems to be about 65 cm in diameter, encased in plexiglass. Its maximum weight, assuming it is a sphere of all PBX HE is about 226 kg. Of course, the “pit” will occupy some of the space, and depending whether it is hollow or solid, could weigh significantly less than 226 kg, possibly less than 50 to 80 kg. 
The “rumor-mill” speculates that DPRK uses either a 2 kg or 4.4 kg Israeli-type hollow Plutonium pit, about 15 cm in diameter, and about 2 to 3 mm thick. There is no credible open-source data about this.

It has 84 visible explosive lenses, some hexagonal, some pentagonal, (classical soccer ball pattern), clearly visible. Each lens seems to have two initiating points.

There are three feed-through “nipples” visible at the top of the hemisphere, each with 2 multi-pair cables (6 total), and if we assume spherical symmetry, there could be another mirror image on the opposite side, for a total of 12 pretty hefty-looking, high current carrying  cables, seeming to end in a black flat ribbon multi-pair cable.
There is no externally visible detonator cable assembly harness emanating from each individual lens a la Fat Man. We know, however, that the power required to initiate 168 (84 X 2) bridgewires or slappers is quite high, so if it is a printed wiring harness, it must be quite hefty. Another possibility is using the printed “explosive channel initiating train” a la Iran, courtesy of V. Danilenko, formerly of VNIITF, Chelyabinsk, USSR weapons lab.
At the lower right side seems to be a solid machined “Tritium boost gas bottle” with a thin gas transfer tubing going up to the bomb sphere.

Oh, God…Isn’t my bomb beautiful?

The solid machined tube at upper left corner has about 12 cm internal diameter, but what is its function? Is it a pit trap door or pit diagnostics? In any case, it cannot interfere with the lenses or it will ruin the implosion symmetry.
All other items like power cable assembly, diagnostics sensors, and the boost gas transfer tube seem to be external to the spherical assembly..

A Note of Caution

The external visible details look pretty impressive, but then it is a mock-up, part of a propaganda war, and with DPRK masters of deception, it’s hard to say what the actual tested design is.

  • ·       Does DPRK have enough Tritium for boost gas (anywhere from 2 to 4 grams per shot)?
  • ·       Is the implosion system lensed or just multi-point? This significantly affects implosion symmetry, compression, and obviously yield.
  • ·       Did DPRK master the symmetric implosion of very thin millimeter shell hollow pits? If so, you get very high compression and very good yields even from 1 or 2kg of Plutonium.
  • ·       Do they have external initiators like neutron tubes?

We don’t really expect answers to these questions, but certainly things are getting “ratcheted up”.

Is it a bluff? All tests so far have been less than 7kt, some say, far less…in which case the answer to the above questions is NO.

The thing to worry about is the goading DPRK is doing to its neighbors. If they go too far, psychological/political push for S. Korea, Japan, and Taiwan to go nuclear will become unstoppable. And…they have the material, know-how, and the infrastructure to go at it FAAAST!.