> Nuclear requires a lot of concrete and steel, both sources of carbon emissions

Alternative sources of energy also require materials to produce them. Natural gas plants require similar amounts of concrete and steel but have lower energy yields. Renewable sources like wind and solar require immense amounts of materials, including heavy metals and other toxic, non-recyclable materials. Because they are far less dense (~50 watts per sq. meter versus 2000-6000 watts per sq. meter from nuclear), they have a substantially greater environmental impact.

> As for the "efficiency" of hydrogen, the only efficiency that matters is economic efficiency, and all indications point to hydrogen storage of wind/solar to be more economically efficient than nuclear.

Solar and wind are heavily subsidized, at least in the United States, while nuclear is subject to expensive and arbitrary regulatory burdens. There’s not a level playing field to support the argument that nuclear energy is not economically competitive.

From the perspective of physics, hydrogen is necessarily less efficient than other energy sources. Generating the initial source of electricity to produce the hydrogen has a given level of inefficiency. Then actually producing the hydrogen compounds the amount of energy wasted. Finally, utilizing the hydrogen as an energy source also loses some energy. There’s no scenario where it’s more efficient to use hydrogen as an intermediary than it is to use the original source.