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.

Organic chemists use Nuclear Magnetic Resonance spectroscopy as a standard tool for monitoring what they have made in various reactions, and for determining the structure of the molecules more generally. Since ordinary hydrogen gives a huge signal, it is often useful to be able to turn it off, and that's why all organic chemists have a bottle of heavy water sitting around. One can also easily buy various deuterated organic solvents for the same purpose. The D2O itself is not even very expensive, compared to a lot of other chemicals.

When people talk about the WWII atomic bomb projects, heavy water is usually mentioned only due to the dramatic sabotage operation in Norway. The heavy water projects in the USA are mostly left out, as not a very interesting part of the Manhattan Project.

But before it became certain that very high purity graphite could me mass produced for the reactors, there was a big push to set up an industrial production of heavy water. Several large factories were set up in the USA in 1943. Then they were very quickly shut down and the produced heavy water was given to Canada. The USA focused on the graphite. The heavy water production was later restarted for other needs. It is not a secret [1], but this is simply seldom emphasized.

[1] https://en.wikipedia.org/wiki/P-9_Project

Same, I just started reading "D: Heavy water", Neal Stephenson's new novel which then got me reading about Deuterium and heavy water.

It's also used to significantly increase the efficiency of nuclear weapons, without the need for developing an outright thermonuclear/hydrogen bomb [0].

[0] https://en.wikipedia.org/wiki/Boosted_fission_weapon

If you are going to fall down that rabbit hole make sure you fall down the part about the history of Deuterium in Norway during World War II.

During the Nazi occupation they were trying to produce Deuterium for their nuclear weapons program in Norway and the Norwegian resistance staged an incredible series of sabotage events to stop them.

"The Winter Fortress" by Neil Bascomb is a really great read about this. The Nazis probably still wouldn't have gotten their first but we all owe something to the Norwegians for their role in making sure they didn't get there at all.

HN front page is rife with SEO slop today. Problem is not everyone can feedback this to the algo.

Gold plated connectors make everything faster too!!1!

Indeed, bless his soul!