Monday, October 23, 2006

The Big Fizzle

Much was made last week of Kim Jong-il's apparent "apology" to China over North Korea's recent nuclear test. And, if regional media accounts are accurate, the DPRK's nut-job leader also promised to conduct additional tests, which Pyongyang had threatened in reaction to new U.N. sanctions against his regime.

At the time, Kim's mea culpa was viewed as an effort to curry favor with Beijing (which was angered by North Korea's nuclear test) and attempt to pressure the U.S. into direct talks. It is worth noting that Beijing has never confirmed the apology, and the U.S.--correctly--is continuing the six-party process as the "only" means for engaging Pyongyang.

But there's another reason that North Korea is suddenly acting a bit more conciliatory on the nuclear issue: its first test was a gigantic flop, at least from a technical perspective. U.S. experts now estimate that the DPRK blast had a yield of roughly 200-400 tons of TNT, or only 5-10% of what they hope to achieve with the weapon.

As we described it last week, the North Korean device was a veritable pop-gun by any standard; the first U.S. nuclear devices (used against Hiroshima and Nagasaki) produced yields of 10-20 kt; Indian and Pakistani bombs detonated in the late 1990s produced only slightly smaller yields. Current U.S., Russian, British, Chinese and French thermo-nuclear devices are gargantuan by comparison, with yields often measured in the hundreds of kilotons, or even in megatons (one megaton is an explosive force equivalent to one million tons of TNT).

North Korea's low-yield device suggests serious design flaws, and indicates that much of planned fissile reaction was a abject failure. And that brings us to Mr. Kim's sudden desire for dialogue. Unable--and unwilling--to risk another fizzle, North Korea now prefers diplomacy instead, giving them a chance to push for sanctions relief, while giving their engineers more time to figure out what went wrong.

If recent DPRK missile flops are any indication, the diplomatic push on the nuclear front will last for an extended period, with periodic spells of saber-rattling for added effect. Almost eight years passed between 1998's partially-successful TD-2 test and July's TD-2 test failure, allowing NK scientists to figure out what went wrong the first time, and incorporate lessons learned into the longer-range TD-2. With the TD-2 launch a colossal failure, it seems likely that North Korea won't try another long-range missile test for several years, if it doesn't abandon that program altogether, in favor of the recently acquired SS-N-6/Musudan IRBM, which can be "stretched" into an ICBM.

With countries like Iran and Venezuela eagerly watching the North Korean nuclear show (and probably providing some funding for the program), Kim Jong-il cannot afford another nuclear flop. Until his nuclear scientists can get it right, Mr. Kim will find the diplomatic track more practical, and he will actively pursue it. Having decided on a nuclear test long ago, Pyongyang likely had a contingency plan for all outcomes, including a detonation that was largely a failure.

5 comments:

John said...

It seems you have concluded the test was not designed to have low yield. I have read some speculation that they were testing the trigger device for an H-bomb and that the last, low yield, 1998 Pak test may have been for the North Koreans and that, therefore, we should not be too quick to conclude there was a fizzle.

jd watson said...

John: There was another rumor that the Norks told China they were aiming for a 4 KT yield. If so, it was then still a fizzle. I'm not sure a 200-400 ton yield would be sufficient for a trigger. It would be really arrogant to try to develop an H-bomb trigger without first demonstrating a working fission bomb.

IMHO the best explanation is that it was a plutonium implosion weapon made from reprocessed fuel rods from a commercial power reactor rather than a breeder. This resulted in too much plutonium 240, which fissions so readily that it prevents assembly of a critical mass for sufficient time to produce a significant yield.

Zorfwaddle said...

What if the 200-400 ton was their aim and they lied (hah!) to the Chinese? How big would an assembly have to be to produce what the US saw? Could they be going for a backpack nuke vice a missile portable warhead? The world wonders....

George

Glenmore said...

To achieve a small yield from a reasonably efficient (ie. non 'fizzle') fission reaction is a whole lot harder than the classic 10-20 KT yield. While it's not impossible NK intended a small yield, it strikes me as unlikely.
An accidental 4 KT yield could come from a large mass of fuel that doesn't get held together long enough for more than a few 'links' of the chain reaction - because of weak metal alloys, or poor conventional shaped charge design or manufacture, or poor fuse design or manufacture. Or even if the bomb design & manufacture were good, the fuel could be contaminated such that neutrons are either absorbed too frequently by an impurity, or released too frequently by a fuel 'hotter' than the design. NONE of these are trivial problems to solve. And the smaller the fuel mass employed, the more sensitive the whole process becomes. Big bombs (20 KT) are hard; huge bombs (200 KT) are harder; small bombs (2 KT) are really, really hard to make.

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