North Korea tried to sell nuclear weapons material to make miniaturized warhead: U.N. inspectors
Experts believe the fact that North Korea is producing Lithium-6 is proof they are attempting to miniaturize nuclear warheads to place on the ICBMs they have been testing repeatedly over recent months.
“Lithium-6 is ideal, not only for making tritium for boosting fission devices, but also for directly fueling advanced weapons—including thermonuclear bombs,” said Henry Sokolski, a former Pentagon official who heads the Nonproliferation Policy Education Center, a Washington think tank, reported Fox News.
WE can hope he miss calculates and sets off a 12,000 KT bomb in his backyard.
According to World Nuclear Association (updated FEB2017):
Lithium has two stable isotopes Li-6 and Li-7, the latter being 92.5% in nature (hence relative atomic mass of natural lithium of 6.94).
Lithium-7 has two important uses in nuclear power today and tomorrow due to its relative transparency to neutrons. As hydroxide it is necessary in small quantities for safe operation in pressurised water reactor (PWR) cooling systems as a pH stabilizer, to reduce corrosion in the primary circuit. As a fluoride, it is also expected to come into much greater demand for molten salt reactors (MSRs). However, for both purposes it must be very pure Li-7, otherwise tritium is formed by neutron capture
Production of lithium-7 had ceased in the USA in 1963, partly because of environmental and OHS concerns with mercury which was used in its enrichment.
Today the only sources of Li-7 (enriched from natural lithium) are Russia and China, though the latter is reported to be buying from Russia now. Production of lithium-7 at least in Russia and possibly China is as a by-product of enriching lithium-6 to produce tritium for thermonuclear weapons.
http://www.world-nuclear.org/information-library/current-and-future-generation/lithium.aspx
In addition there is a Japanese method http://jolisfukyu.tokai-sc.jaea.go.jp/fukyu/mirai-en/2012/4_10.html
It is really important if NK is selling Li-7, this is a strong indication that 1) they are separating Li-6/Li-7 and b) that they are interested in Li-6 for their own use, i.e. to produce tritium.
Probably best to take them out before they cause big damage.