[lenerdenator]

The problem with launching anything into orbit using current rocket motor technologies is that heavier stuff costs more to put into orbit.

The elements that are used in nuclear reactors (particularly Uranium and Plutonium) are pretty dense, and thus heavy.

[pfdietz]

That's true, but the cost of reprocessing is also very high, per kg. And aren't the nuclear bros always telling us how little nuclear waste is actually produced? There's about 30 tons of spent fuel per GW(e)-year from today's burner reactors. At $10/kg to space that would be just $300,000 (yes, ignoring lots of costs there, at $10/kg is aggressive, but this is for comparison), a pittance compared to the value of energy produced from the power plant: at $0.05/kWh it produces > $300 M in electrical energy, three orders of magnitude higher.