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Lithium Production

     Lithium [Li] is a critical material for the manufacture of the
     secondaries of so-called dry thermonuclear devices, which do not
     require the use of liquid deuterium and tritium. The largest
     nuclear device ever detonated was a multi-stage Soviet product
     with a yield of nearly 60 megatons. It was exploded at only half
     of its design maximum yield of about 100 megatons.

     Lithium enriched in the isotope 6 Li remains a controlled material
     because of its utility in the production of compact and highly
     efficient thermonuclear secondaries. Two-stage nuclear weapons
     incorporating a lithium-deuteride-fueled component can deliver
     greater nuclear yield from a smaller and lighter package than if a
     pure fission device were used. The tradeoff is that the design and
     construction of reliable two-stage “dry” weapons may require
     significant knowledge of nuclear weapons physics and technology,
     knowledge which is hard to acquire without a program involving
     full-yield testing of the fission primary to be used and
     measurement of its production of x-rays and their transport
     through a case surrounding both primary and secondary stages.
     Therefore, 6Li is more likely to be of interest to a state with
     nuclear weapons experience than it is to a beginning nuclear
     state.

     Lithium is a very low-density silvery metal, prone to spontaneous
     combustion. On the periodic table of the elements it lies directly
     beneath hydrogen and has but three protons. It is the lightest
     solid element. The most common stable isotope is 7Li, consisting
     of three protons and four neutrons; less common, comprising 7.4
     percent of normal lithium, is 6Li, which has three protons and
     three neutrons in its nucleus.

     Lithium-6 is most often separated from natural lithium by the
     COLEX (Column exchange) electrochemical process, which exploits
     the fact that 6Li has a greater affinity for mercury than does
     7Li. A lithium-mercury amalgam is first prepared using the natural
     material. The amalgam is then agitated with a lithium hydroxide
     solution, also prepared from natural lithium. The desired 6Li
     concentrates in the amalgam, and the more common 7Li migrates to
     the hydroxide. A counter flow of amalgam and hydroxide passes
     through a cascade of stages until the desired enrichment in 6Li is
     reached. The 6Li product can be separated from the amalgam, and
     the “tails” fraction of 7Li electrolyzed from the aqueous lithium
     hydroxide solution. The mercury is recovered and can be reused
     with fresh feedstock.

     Russia, the UK, France, and China are all believed to be capable
     of making 6Li in the quantities needed for the manufacture of
     large nuclear stockpiles. Russia exploded a device making use of
     6Li before the United States did; however, the Soviet device was
     not a “true” thermonuclear weapon capable of being scaled to any
     desired yield. United States production of 6Li ceased in 1963.

Sources and Methods

   * Adapted from - Nuclear Weapons Technology Militarily Critical
     Technologies List (MCTL) Part II: Weapons of Mass Destruction
     Technologies

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Updated Wednesday, October 21, 1998 4:35:26 PM