Nope. Nuclear isn't hot enough. Only about 315°C at the output end. Electricity, though, has no thermodynamic upper limit on what temperature can be generated.
Steelmaking takes place around 1650C. Getting up to molten steel temperatures is hard.
Yes, you could potentially use waste heat from a reactor to preheat the tundish, and maybe the scrap and ladle. Nucor preheats using natural gas to save on electricity. No need to bring everything up from room temperature on electric power. A nuclear reactor immediately adjacent to a steel caster is probably not a great idea.
