A refinement facility for nuclear material isn’t quite the same thing
It's definitely part of the infrastructure of nuclear weapons. That's why it was hacked in the first place. They were making weapons grade nuclear material.
So is a steel plant though. Keeping a missile from being hacked is much different than something in the supply chain.
Considering the number of steel plants and the relative cost of the material, that’s not a very good comparison. The whole point of Stuxnet was that the facility was a critical single failure point in the supply chain. When it went down, it disrupted the project for years. I don’t think the same dynamic holds for steel manufacturing. If you think they’re comparable, try getting into Oak Ridge or similar; I suspect you’ll find it very well guarded compared to a steel plant.