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Plutonium generated by nuclear plants is often contaminated with highly
radioactive americium and lanthanides. The material is usually purified with
potassium chloride, but this process is slow and even when repeated, it strips
out only 90 per cent of the americium. A better way, according to Britain’s
Ministry of Defence, is to mix molten plutonium with molten calcium chloride and
magnesium chloride in an inert argon atmosphere (GB 2355107). The contaminants
are drawn out of the plutonium into the chloride mixture, which is then cooled
and processed to extract the americium. The whole extraction process takes less
than 2 hours.