We will need hundreds of GW-scale ammonia synthesis plants. Thousands, maybe. Fortunately, there are no impediments to operating them at any required scale. You just add on more units.

Nuclear reactors have very difficult engineering problems unknown in most other technologies. For a nuke, you might actually need to build a GW-scale pilot plant to discover the failure modes that show up there. Not so, most things. A bigger dam just needs more turbines. A bigger wind farm just needs more wind turbines. A bigger solar farm just needs more panels. A bigger ammonia plant just needs more catalyzer units. You can start it running after the first one, and add more at leisure.

That is a thing that makes renewables + storage so much more attractive than nukes: You are guaranteed no unpleasant surprises, and no existential disasters. That it is also radically cheaper, and starts working immediately, is icing on a very nice cake.