Hollow North Korean Nuclear Warhead Pits?

Jeffrey Lewis has an interesting article exploring some of the possible technical advances represented by North Korea’s fifth nuclear weapons test.

He reminds us of the boast earlier this year, from Kim Jong-un, that North Korea had developed a nuclear warhead capable of delivery by ballistic missile

North Korea’s propaganda apparatus is pretty proud. In March, Kim Jong Un, the country’s leader, posed with a mock-up of one of the bombs, the same design that North Korea now claims to have tested and intends to deploy on its arsenal of long-range ballistic missiles. “It is very gratifying to see the nuclear warheads with the structure of mixed charge adequate for prompt thermonuclear reaction,” he said then

We, of course, don’t really know for certain, in the public domain, what North Korea’s nuclear warhead design capabilities are. Lewis adopts the interesting technique, as good as any other given the paucity of information, of looking at how far the established nuclear powers got after their fifth nuclear weapons test and then arguing by analogy

These five fifth tests are a fairly telling set. By their fifth tests, all five countries had demonstrated the technologies to reduce the size of first-generation weapons, and were well on their way to building thermonuclear weapons.

I’m tempted at this point to head off and grab my copy of Chuck Hanson, but seeing that I can’t be bothered here’s another quote from Lewis

The fifth U.S. nuclear test occurred in 1948, the second of a series of three nuclear explosions at Enewetak Atoll as part of Operation Sandstone. The test, known as “Yoke,” was a 49-kiloton explosion—the largest explosion to date, and a fairly fascinating bomb. Yoke’s implosion design was the first to use highly enriched uranium, something that is of interest to North Korea today. And it was one of the series of tests that confirmed the concept of the “levitated pit,” a design essential to reducing the size of U.S. nuclear weapons so they could fit atop ballistic missiles.

Arguing from analogy, it is possible to infer that North Korea has tested a composite core fission bomb based on a levitated pit, which opens up the prospect of developing a warhead for delivery by ballistic missile (this neglects reentry issues). North Korea’s first test was a fizzle, that of the established nuclear powers were not, so one might argue that the analogy does not hold however, as Lewis points out, the North Koreans know stuff, given the march of history, that the early weapons designers didn’t.

But I’m speculating;

What if North Korea has tested a hollow, composite, fissile pit, not a levitating one, and one which injects H2 and H3 just prior to implosion? This would be consistent with Kim Jong-un’s boast above. I am especially referring to the “charge adequate for prompt thermonuclear reaction.” Naturally, we are not speaking here of a true thermonuclear or hydrogen bomb, but rather one which uses thermonuclear reactions to boost the fission process.

Radionuclide data would be nice here. The South Koreans report that they have not been able to acquire any, however the CTBTO Radionuclide Monitoring Network might. Should radionuclides be detected, they would tell us plenty.

I look forward to reading Sig Hecker’s analysis of all this. He’s the undisputed heavyweight champion of the world when it comes to the North Korean nuclear programme.