Since Orion has already been mentioned, I’ll toss out the NERVA style rockets, for a less-crazy option for nuclear assisted heavy lift capacity.
Which isn’t a completely dead technology (well, more modern derivatives of nuclear thrust rockets are still being researched at least) - from the link above.
An engine for interplanetary travel from Earth orbit to Mars orbit, and back, was studied in 2013 at the MSFC with a focus on nuclear thermal rocket (NTR) engines.[116] Since NTRs are at least twice as efficient as the most advanced chemical engines, they allow quicker transfer times and increased cargo capacity. The shorter flight duration, estimated at 3–4 months with NTR engines,[117] compared to 8–9 months using chemical engines,[118] would reduce crew exposure to potentially harmful and difficult to shield cosmic rays.[119] NTR engines, like the Pewee of Project Rover, were selected in the Mars Design Reference Architecture (DRA).[120]
Congress approved $125 million in funding for the development of nuclear thermal propulsion rockets on 22 May 2019.[121][122] On 19 October 2020, the Seattle-based firm Ultra Safe Nuclear Technologies delivered a NTR design concept to NASA employing high-assay low-enriched Uranium (HALEU) ZrC-encapsulated fuel particles as part of a NASA-sponsored NTR study managed by Analytical Mechanics Associates (AMA).[123][124]