(But it had better be unmanned, because it ain't going to be stable)
As stated in @jdunlop 's answer, steel melts at around 1400-1550°C, while uranium melts at 1132°C. However, most reactors don't use pure uranium metal, they use uranium dioxide. This is a ceramic, rather than a metal, and melts at an astounding 2865°C instead of 1132. This is promising, although taking the fuel itself up to those temperatures is difficult. There are a couple main concerns:
1) Moving / using the heat
Sure, you could potentially get this fuel up to steel-melting temperatures, but how are you going to use that heat? Power reactors generally use pressurized water, which doesn't like to be above 315°C. No good. You could try using a molten salt to transfer the energy, but those reactors usually operate at around 600-800°C. One commonly considered salt, FLiNaK, could potentially work, although not that well, since it boils at 1570°C. You might be able to find another salt that wouldn't boil until a higher temperature, but beware of anything with chlorides, and actually good luck finding anything that will hold a superheated molten corrosive substance at that temperature. Some liquid metals could work (sodium has been used, although it wouldn't work here), but be aware that as it passes through the reactor, the neutron bombardment can transmute your metal: Copper, for instance, could become Nickel in a matter of days, severely changing your metal properties).
2) Keeping everything stable
One problem with running nuclear reactors is that the reactivity (sort of the balancing point) depends on the temperature of the fuel. Letting the reactivity tip even slightly towards positive or negative can result in a power surge that could melt your reactor. As your fuel heats up to operating temperature, you have to carefully position your control method to keep it from running away. If you're using a ceramic, you also have to be careful that the temperature change from room-temperature to operating temperature doesn't fracture your fuel, altering the shape and messing with your reactivity.
Your best bet is something like a TRISO fuel, which is like little pellets encased in a durable ceramic. You could run your heating fluid through these, and then use the fluid to heat your crucible. Or, if you're willing to throw some nuclear physics out the window, you could put these beads directly into the crucible, and use it as the reactor. The problem with this is that as the pellets move around, that will mess wildly with your reactivity. If you want a realistic scenario, though, your best bet is probably to use nuclear power to generate electricity somehow, and then use arc furnaces to melt your metal. Electricity is much more easily stored and controlled than raw nuclear energy.