Heavy water production
Heavy-water production is a byproduct of ammonia fertilizer production. Hydrogen was, at the time, mainly produced by electrolysis of water.[2] The Haber Process is then used, reacting the hydrogen with nitrogen from air to produce ammonia. At the time, Europe's major supply of ammonia came from the Norwegian Vemork hydroelectric plant, run by Norsk Hydro, near Rjukan in the Telemark region.
The technology is straightforward. Heavy water (D2O) is separated from regular water by electrolysis because the difference in mass between the two hydrogen isotopes translates into a slight difference in the speed at which the reaction proceeds. To produce pure heavy water by electrolysis requires a large cascade of electrolysis chambers, and consumes large amounts of power. Since the production of hydrogen relied on electrolysis at Vemork, heavy water was a routine byproduct.
Hans Suess was a German advisor to the production of heavy water. Suess had assessed the Rjukan plant as being incapable of producing militarily useful quantities of heavy water in less than five years at its then current capacity.