All references I have browsed for this Norsk Hydro plant mention very little on the actual heavy water production process used. I understand that this plant was adjacent to a power station that had a high electrical power output by exploiting a 138 meter water drop of dammed river. My guess is that therefore some kind of electrolysis was used. Other references mentioned heavy water as side product of ammonia production.
closed as off-topic by Kyle Kanos, John Rennie, Qmechanic♦ Aug 17 '17 at 18:16
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