After Humans 1.12.2 updated to version 1.12.1a
bug in ae2 stuff fixed
nuclear craft added
Type in the modpack name (After Humans 1.12.2) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select After Humans 1.12.2 from the list on the left. The launcher will handle everything else!