Kim Jong Un Preparing a Birthday Cake for Kim Il Sung: North Korea’s Prospective Sixth Nuclear Test a Sloika or Layer Cake?

One of the most read popular accounts of nuclear weapons is Robert Jungk’s “brighter than a thousand suns” and the image of the sun still resonates when we think of nuclear weapons especially those that incorporate thermonuclear reactions.

Kim Il Sung’s birthday, on April 15, in North Korea is known as “the day of the sun.”

38North reports on continued activity at North Korea’s nuclear test site at Punggye-ri, suggesting that Pyongyang is preparing for a sixth nuclear test

Commercial satellite imagery of North Korea’s Punggye-ri Nuclear Test Site from April 12 shows continued activity around the North Portal, new activity in the Main Administrative Area, and a few personnel around the site’s Command Center

Now an intriguing little matter involving lithium-6 has caught the attention of nuclear analysts

The online ad reads like something only a metallurgist could love: an offer to sell 22 pounds of highly pure lithium 6 every month, set for delivery from the port of Dandong, China.
But it caught the attention of intelligence agencies around the world for a simple reason: Lithium 6 offers a fast way to turn an ordinary atom bomb into a hydrogen bomb, magnifying its destructive power by up to 1,000 times. The seller listed in the ad — who even provided his cellphone number — was identified in a recent United Nations report as the third secretary in the North Korean Embassy in Beijing…
…But experts say the offer to sell excess lithium is evidence that North Korea has produced so much of the precious material that it is too late to prevent the nation from becoming an advanced nuclear power

North Korea has tested a nuclear device five times, and the consensus is that North Korea has achieved a nominal yield for a first generation device and has the capability to develop boosted fission weapons.

Historically, in between the development of boosted fission devices and a true thermonuclear weapon, or hydrogen bomb, the nuclear powers developed what Andrei Sakharov called a “sloika” which is Russian for layer cake, nuclear device which we might call “Bohr’s model of the bomb” as it incorporates distinct shells of nuclear materials around the fissile core.

This system was dubbed “Layer Cake” by the Soviets because it uses a spherical assembly of concentric shells. In the center is a fission primary made of U-235/Pu-239, surrounding it is an (optional) layer of U-238 for the fission tamper, then a layer of lithium-6 deuteride/tritide, a U-238 fusion tamper, and finally the high explosive implosion system. The process begins like an ordinary implosion bomb. After the primary in the center completes its reaction, the energy it releases compresses and heats the fusion layer to thermonuclear temperatures. The burst of fission neutrons then initiates a coupled fission-fusion-fission chain reaction. Slower fission neutrons generate tritium from the lithium, which then fuses with deuterium to produce very fast neutrons, that in turn cause fast fission in the fusion tamper, which breed more tritium. In effect the fusion fuel acted as a neutron accelerator allowing a fission chain reaction to occur with a large normally non-fissionable U-238 mass. While spiking the fusion layer with an initial dose of tritium is not strictly necessary for this approach, it helps boost the yield

The use of lithium-6 in the Soviet design was a modification to Sakharov’s initial design at the suggestion of Vitaly Ginzburg. Ginzburg played an important role in the renaissance of general relativity after World War Two

Later that year, Russian physicist V.L. Ginzburg thought of using lithium-6 deuteride instead of liquid deuterium. The combination of lithium-6 with neutrons produces tritium, helium-4 and energy, and this idea was incorporated into Sakharov’s Layer Cake design in 1949

When the Soviet’s tested the sloika Hans Bethe, through an analysis of radionuclides produced by the explosion, correctly inferred the nature of its design, shells and all, in a brilliant act of deduction.

North Korea, on its way to developing a true hydrogen bomb, might well follow the historical pattern, as they thus far have, and first test the intermediate stage sloika or layer cake bomb. The matter of the lithium-6 does not necessarily mean that North Korea will test a hydrogen bomb.

Should North Korea indeed proceed with a sixth nuclear test a sloika or layer cake device might well be on the cards. The Soviet sloika had a yield of 400kt, so the North Korean layer cake wouldn’t have that yield as the deepest tunnel under the North portal at Punggye-ri can contain an explosion of approximately 282kt.

Let us see whether on the day of the sun Kim Jong Un provides Kim Il Sung with a birthday cake to fit the occasion.

The Korean’s have a rainbow coloured layered rice cake called the mujigae tteok.