The Other Dangers From That North Korean Nuke Test
Scoffing at Pyongyang’s hydrogen-weapons claims ignored new, dangerous potential developments.
By Victor Gilinsky and Henry Sokolski
The first thing to say about North Korea’s Jan. 6 nuclear test is that, despite the pronouncements of instant experts, we know almost nothing about its technical characteristics. Even the relation of the seismic signal to the actual size of the explosion is uncertain. But there are some hints about the test’s significance for proliferation that the press, in its eagerness to dismiss North Korea’s claim that it detonated a hydrogen weapon, seems to have missed.
The estimated small size of the explosion—roughly six to nine kilotons according to South Korean officials—has been taken as a sign that it did not involve a two-stage thermonuclear device (thermonuclear being synonymous with “hydrogen weapon” in the bomb business). That is likely correct, but not necessarily for the reason stated. The purpose of a low-yield experimental explosion might have been to check thermonuclear design parameters. But a two-stage design is indeed a big step from a fission bomb, so we can reasonably set this possibility aside.
Unless the North Koreans were lying through their teeth when they claimed it was a hydrogen explosion, there is another possibility—one with lower technological demands, but still potent implications. A small amount of thermonuclear fuel, say a tenth of an ounce, inserted into a so-to-speak standard fission warhead can markedly improve its performance while allowing a very substantial reduction in weight. Known as a “boosted” fission weapon, it was invented in the late 1940s at the Los Alamos National Laboratory in the U.S., so the technology is nearly 70 years old.
Boosted fission technology results in lighter warheads, which means they can fit on missiles. It also—and most concerning for those of us in the nonproliferation business—permits a fission bomb to use any type of plutonium, including so-called reactor-grade, without degradation in performance.
Here’s how it works: When about 1% of the fission reaction has taken place, the thermonuclear fuel—deuterium and tritium (doubly and triply heavy hydrogen)—reacts and floods the remaining nuclear explosive with neutrons. Thus, the weapon needs less conventional explosive to trigger the nuclear reaction, and less heavy material surrounding it to keep it together long enough for the fission to take place. With a boosted weapon there is no concern about stray neutrons starting the fission chain reaction too early and having the bomb blow apart before attaining full yield.
Today’s missiles are highly accurate, so there is no need for the huge thermonuclear yields—up to megatons—sought years ago to compensate for missing a target by miles. And boosted fission technology puts plutonium stockpiled from the operation of nuclear power plants essentially on a par with so-called “weapons-grade plutonium.” We say “essentially” because some adjustment in design is needed to compensate for the greater heat generation in power-plant material, though engineers know how to do that.
Boosting is still pretty sophisticated technology, but not beyond countries with nuclear facilities and highly qualified scientists and engineers. The significance of North Korea’s boosting test—if that is what occurred—goes far beyond the region. Pyongyang is known for selling weapons technology and may sell this one, a worrying prospect. Equally concerning is that North Korea may have received the boosting technology from a more experienced state.
We may be witnessing a new, more virulent form of nuclear proliferation. If additional countries opt for nuclear weapons—the worry list includes several Middle Eastern nations, from Iran to Turkey, and Far Eastern states, including South Korea and Japan—they should not be expected to content themselves with 1945-era designs, even as a starting point. The tremendously greater availability of more-advanced designs, the rapidly growing increases in technical capabilities like computing and materials science, and improved methods for shaping materials assures that this will be so. Several of these countries have nuclear-power reactors. Others plan to get them. Some have stockpiled reactor-grade plutonium.
There is no question now, if there ever was, that the plutonium produced in nuclear-power reactors—whether in Russia, Iran, Japan, France, Pakistan or the U.S.—is weapons material. Unfortunately, many in the national security and arms-control communities have not caught up with these developments.
To return to whether North Korea has progressed toward hydrogen weapons: Although we agree with the general view that this is unlikely, it may be unwise to dismiss the possibility. North Korea’s technical personnel have been especially ingenious in their ability to perform with very limited resources. A former chief inspector for the International Atomic Energy Agency, who is familiar with North Korean capabilities, made the point by telling us that if he were on a desert island and could choose one person to help him survive, he would choose a North Korean engineer.