Most heavy water for reactors was made by the Girdler sulfide process. This is what Canada used for CANDU reactors. Since then, they developed a better technology using catalytic exchange columns allowing equilibrium of hydrogen isotopes between hydrogen gas and water. By passing water down such a column counterflowed against hydrogen coming back up, the deuterium is stripped into the downflowing water. If the water is then electrolyzed to make the hydrogen then it becomes enriched in deuterium, with the hydrogen leaving the column depleted.

If Canada ever sells many more CANDU reactors they'll use this sort of technology to make their moderator.

I recall someone found that treating silicon chips with deuterium reduced the rate of electromigration in narrow channels, extending chip life.